NOAA's Estuarine Living Marine Resources Program 


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Distribution and Abundance of Fishes and 

Invertebrates in Gulf of Mexico Estuaries 

Volume II: Species Life History Summaries 


August 1997 


U.S. Department of Commerce 

National Oceanic and Atmospheric Administration 

National Ocean Service 


NOAA's Estuarine Living Marine Resources Program 


The Strategic Environmental Assessments (SEA) Division of NOAA's Office of Ocean Resources Conservation and 
Assessment (ORCA) was created in response to the need for comprehensive information on the effects of human activities 
on the nation's coastal ocean. The SEA Division performs assessments of the estuarine and coastal environments and of the 
resources of the U.S. Exclusive Economic Zone (EEZ). SEA Divison's Biogeographic Characterization Branch develops and 
disseminates information on the distribution and ecology of living marine resources throughout the Nation's estuarine and 
coastal environments (Monaco and Christensen 1997). 

In June 1985, NOAA began a program to develop a comprehensive information base on the life history, relative abundance, 
and distribution of fishes and invertebrates in estuaries throughout the nation. The Estuarine Living Marine Resources (ELMR) 
program has been conducted jointly by the SEA Division, the National Marine Fisheries Service (NMFS), and other agencies 
and institutions. The nationwide ELMR data base was completed in 1994, and includes data for 153 species found in 122 
estuaries and coastal embayments. Ten reports and reprints are now available free upon request. This report, Distribution 
and Abundance of Fishes and Invertebrates in Gulf of Mexico Estuaries, Volume II: Species Life History Summaries, 
summarizes information on the estuarine life history characteristics of 44 fish and invertebrate species of the Gulf of Mexico. 
It complements distribution and abundance information presented in Volume I: Data Summaries (Nelson et al. 1 992). A national 
report summarizing the data and results from the ELMR program is planned for publication in late 1997. 

Three to five salinity zones, as defined in NOAA's National Estuarine Inventory Program (NOAA 1985) provided the spatial 
framework for organizing information on species distribution and abundance within each estuary. The primary data developed 
for each species include spatial distribution by salinity zone, temporal distribution by month, and relative abundance by life 
stage, e.g., adult, spawning, juvenile, larva, and egg. In addition, life history summaries and tables are developed for each 
species. 

Additional information on this or other programs of NOAA's SEA Division is available from: 

NOAA/NOS SEA Division, N/ORCA1 

1305 East-West Hwy., 9th Floor 

Silver Spring, Maryland 20910 

Phone (301) 713-3000, Fax (301) 713-4384 


Selected reports and reprints available from NOAA's Estuarine Living Marine Resources program include: 

Monaco, M.E., et al. 1990. Distribution and abundance of fishes and invertebrates in west coast estuaries, Vol. I: Data 
summaries. ELMR Rep. No. 4. NOAA/NOS Strategic Assessment Branch, Rockville, MD. 232 p. 

Emmett, R.L., et al. 1 991 . Distribution and abundance of fishes and invertebrates in west coast estuaries, Vol. II: Species life 
history summaries. ELMR Rep. No. 8. NOAA/NOS SEA Division, Rockville, MD. 329 p. 

Nelson, D.M., et al. 1991 . Distribution and abundance of fishes and invertebrates in southeast estuaries. ELMR Rep. No. 
9. NOAA/NOS SEA Division, Rockville, MD. 167 p. 

Monaco, M.E., et al. 1992. Assemblages of U.S. west coast estuaries based on the distribution of fishes. Journal of 
Biogeography 19: 251-267. 


Nelson, D.M. (editor), et al. 1992. Distribution and abundance of fishes and invertebrates in Gulf of Mexico estuaries, Vol. 
I: Data summaries. ELMR Rep. No. 10. NOAA/NOS SEA Division, Rockville, MD. 273 p. 

Bulger, A. J., et al. 1993. Biologically-based salinity zones derived from a multivariate analysis. Estuaries 16: 31 1-322. 

Stone, S.L., et al. 1994. Distribution and abundance of fishes and invertebrates in Mid-Atlantic estuaries. ELMR Rep. No. 

12. NOAA/NOS SEA Division, Silver Spring, MD. 280 p. 

Jury, S.H., et al. 1994. Distribution and abundance of fishes and invertebrates in North Atlantic estuaries. ELMR Rep. No. 

13. NOAA/NOS SEA Division, Silver Spring, MD. 221 p. 

Christensen, J.D., et al. 1997. An index to assess the sensitivity of Gulf of Mexico species to changes in estuarine salinity 
regimes. Gulf Res. Rep. 9(4):21 9-229. 

Pattillo, M.E., et al. 1997. Distribution and abundance of fishes and invertebrates in Gulf of Mexico estuaries, Vol. II: Species 
life history summaries. ELMR Rep. No. 11. NOAA/NOS SEA Division, Silver Spring, MD. 377 p. 


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Distribution and Abundance of Fishes and 

Invertebrates in Gulf of Mexico Estuaries 

Volume II: Species Life History Summaries 


Project Team 

Mark E. Pattillo and Thomas E. Czapla 

Galveston Laboratory 

Southeast Fisheries Science Center 

NOAA National Marine Fisheries Service 

Galveston, TX 77551 

David M. Nelson 3 and Mark E. Monaco 

Biogeographic Characterization Branch 

Strategic Environmental Assessments Division 

Office of Ocean Resources Conservation and Assessment 

NOAA National Ocean Service 

Silver Spring, MD 20910 


ELMR Report Number 11 
August 1997 


T MfWTOf 


'Current address: U.S. Army Corps of Engineers, Galveston TX 77553. 
2 Current address: U.S. Fish and Wildlife Service, Denver CO 80225. 
Correspondence to: D.M. Nelson, NOAA N/ORCA1, Silver Spring MD 20910. 


This report should be cited as: 

Pattillo, M.E., T.E. Czapla, D.M. Nelson, and M.E. Monaco. 1997. Distribution and abundance of fishes and 
invertebrates in Gulf of Mexico estuaries, Volume II: Species life history summaries. ELMR Rep. No. 1 1 . NOAA/ 
NOS Strategic Environmental Assessments Division, Silver Spring, MD. 377 p. 


Contents 


Introduction 1 

Rationale 1 

Data Collection and Organization 2 

Selection of Estuaries 2 

Selection of Species 4 

Data Sheets 5 

Data Verification 6 

Data Content and Quality 6 

Life History Summaries and Tables 6 

Life History Summaries 6 

Life History Tables 11 

Concluding Comments 11 

Acknowledgements 11 

Literature Cited 11 

Species Life History Summaries 

Bay scallop 13 

American oyster 21 

Atlantic rangia 32 

Hard clam 38 

Bay squid 49 

Brown shrimp 55 

Pink shrimp 64 

White shrimp 73 

Grass shrimp 81 

Spiny lobster 88 

Blue crab 97 

Stone crab 1° 8 

Bull shark 118 

Tarpon 122 

Alabama shad 130 

Gulf menhaden 134 

Yellowfin menhaden 144 

Gizzard shad 148 

Bay anchovy 153 

Hardhead catfish ." 161 

Sheepshead minnow 169 

Gulf killifish 176 

Silversides 163 

Common snook 193 

Bluefish 203 

Blue runner 211 

Crevalle jack 216 

Florida pompano 222 

Gray snapper 228 


Sheepshead 235 

Pinfish 241 

Silver perch 247 

Sand seatrout 252 

Spotted seatrout 259 

Spot 269 

Atlantic croaker 277 

Black drum 284 

Red drum 291 

Striped mullet 305 

Code goby 315 

Spanish mackerel 320 

Gulf flounder 329 

Southern flounder 334 

Glossary 341 

Life History Tables 

Table 6. Habitat associations 355 

Table 7. Biological attributes 365 

Table 8. Reproduction 375 


Distribution and Abundance of Fishes and Invertebrates in Gulf of Mexico Estuaries 

Volume II: Species Life History Summaries 


Introduction 


This is the second of two volumes that present informa- 
tion on the spatial and temporal distributions, relative 
abundance, and life history characteristics of 44 fish 
and invertebrate species in 31 Gulf of Mexico estuar- 
ies. This volume contains life history summaries for 
each species. Each summary identifies the life history 
characteristics that describe a species' occurrence in 
these estuaries. These summaries were developed to 
complement data presented in Distribution and Abun- 
dance of Fishes and Invertebrates in Gulf of Mexico 
Estuaries, Volume I: Data Summaries (Nelson et 
al.1992), hereafter referred to as Volume I. 

The summaries presented here are not a complete 
treatise on all aspects of each species' biology, but they 
provide a concise account of the most important physi- 
cal and biological factors known to affect a species' 
occurrence within estuaries. As a supplement to the 
life history summaries, their content was augmented 
with additional physical and biological criteria and 
condensed into three life history tables. These tables 
present life history characteristics for each species 
along with behavioral traits and preferred habitats. 

This report is a product of the National Oceanic and 
Atmospheric Administration's (NOAA) Estuarine Liv- 
ing Marine Resources (ELMR) Program (see inside 
front cover), a cooperative study of the National Ocean 


Service (NOS), the National Marine Fisheries Service 
(NMFS), and other research institutions. The objective 
of the ELMR program is to develop a consistent data 
base on the distribution, abundance, and life history 
characteristics of important fishes and invertebrates in 
the Nation's estuaries. This data base contains the 
relative abundance and monthly occurrence of each 
species' life stage by estuary for three to five salinity 
zones identified in NOAA's National Estuarine Inven- 
tory (NEI) Program (NOAA 1985b). The nationwide 
data base is divided into five study regions (Figure 1), 
and contains information for 153 fish and invertebrate 
species found in 122 U.S. estuaries. 


Rationale 


Estuaries are among the Earth's most productive natu- 
ral systems and are important nursery areas that 
provide food, refuge from predation, and valuable 
habitat for many species (Gunter 1 967, Joseph 1 973, 
Weinstein 1979, Mann 1982). Estuarine-dependent 
organisms that support important commercial and rec- 
reational fisheries include sciaenids.clupeids, shrimps, 
and crabs. In spite of the well-documented importance 
of estuaries to fishes and invertebrates, few consistent 
and comprehensive data bases exist which allow ex- 
aminations of the relationships between estuarine spe- 
cies found in or among groups of estuaries. Further- 
more, much of the distribution and abundance informa- 
tion for estuarine-dependent species (i.e., species that 


NOAA NMFS, 
Hammond, OR 

West Coast 

32 estuaries, 
47 species 


North Atlantic 

17 estuaries, 
58 species 

Maine DMR, 
Boothbay Harbor, ME 
UNH, Durham, NH 
Mid-Atlantic 
22 estuaries, 
61 species 
NOAA SEA Division, 
Silver Spring, MD 


VIMS, Gloucester Point, VA 


NOAA NMFS, Beaufort, NC 


Southeast 

20 estuaries, 
40 species 


Gulf of Mexico 

31 estuaries, 
44 species 


Figure 1. ELMR study regions and regional research institutions. 


require estuaries during their life cycle) is for offshore 
life stages and does not adequately describe estuarine 
distributions (Darnell et al. 1983, NOAA 1985a). 

Only a few comprehensive sampling programs collect 
fishes and invertebrates with identical methods across 
groups of estuaries within a region (Hammerschmidt 
and McEachron 1986). Therefore, most existing es- 
tuarine fisheries data cannot be compared among 
estuaries because of the variable sampling strategies. 
In addition, existing research programs do not focus on 
how groups of estuaries may be important for regional 
fishery management, and few compile information for 
species having little or no economic value. 

Because life stages of many species use both estua- 
rine and marine habitats, information on distribution, 
abundance, temporal utilization, and life history char- 
acteristics is needed to understand the coupling of 
estuarine, nearshore, and offshore areas. To date, a 
national, comprehensive, and consistent data base of 
this type does not exist. Consequently, there is a need 
to develop a program which integrates fragments of 
information on marine and estuarine species and their 
associated habitats into a useful, comprehensive, and 
consistent format. The ELMR program was designed 
to help fulfill this need by developing a uniform nation- 
wide data base on selected estuarine species. Results 
complement NOAA efforts to develop a national estua- 
rine assessment capability (NOAA 1985b), identify 
information gaps, and assess the content and quality of 
existing estuarine fisheries data. 


Data Collection and Organization 


Volume /contains detailed distribution and abundance 
data for 44 fish and invertebrate species in 31 Gulf of 
Mexico estuaries, and a complete discussion of the 
methods used to compile these data. However, a brief 
description of methods from Volume I is presented 
here to aid interpretation of distribution and relative 
abundance tables included in the species life history 
summaries presented in this report. Figure 2 summa- 
rizes the major steps taken to collect and organize 
information on the distribution and abundance of fishes 
and invertebrates in Gulf of Mexico estuaries. The 
following sections provide an overview of the estuary/ 
species selection process, and development of the 
ELMR data base. 

Selection of Estuaries. Thirty estuaries of the Gulf of 
Mexico (Table 1 , Figure 3) were initially selected from 
the National Estuarine Inventory (NEI) Data Atlas: 
Volume I (NOAA 1985b). However, Florida Bay was 
added to the NEI, and to the ELMR program, because 
of its importance as habitat for Gulf of Mexico fishes 
and invertebrates. Data on the spatial and temporal 
distributions of species were initially compiled and 
organized based on three salinity zones delineated for 
each estuary in the NEI; tidal fresh (0.0 to 0.5 parts per 
thousand (%o)), mixing (0.5 to 25.0% o ), and seawater 
(>25.0%o). The ELMR Gulf of Mexico data base is now 
being revised and updated for five biologically relevant 
salinity zones (Bulger et al. 1993, Christensen et al. 
1997, NOAA 1997). While some Gulf of Mexico 
estuaries do not contain all salinity zones (e.g., Laguna 
Madre has no mixing or tidal fresh zone), they were 


Outputs 


National 

Estuarine 

Inventory 

Data 


— ^- 


31 
Estuaries 


Compile 

Estuary 

Information 


Prepare 

Species/Estuary 

Data Sheets . 


Select 
Species 


— »- 


44 
Species 


Develop 
Life History 
Summaries 


Peer Review: 
Data Verification 


Spatial 
Distribution 


Temporal 
Distribution 


Microcomputer 
Data Base 


Relative 
Abundance 


Data 

Reliability 


Figure 2. Major steps to complete the Gulf of Mexico ELMR study. 


Table 1. ELMR Gulf of Mexico estuaries (n=31) and 
associated salinity zones. 


Table 2. ELMR Gulf of Mexico species (n=44). 


Estuary, State 


Zones present 


Florida Bay, FL 


T M 


S 


Ten Thousand Islands, FL 


T M 


S 


Caloosahatchee River, FL 


T M 


* 


Charlotte Harbor, FL 


T M 


s 


Tampa Bay, FL 


T M 


s 


Suwannee River, FL 


T M 


s 


Apalachee Bay, FL 


T M 


s 


Apalachicola Bay, FL 


T M 


s 


St. Andrew Bay, FL 


T M 


s 


Choctawhatchee Bay, FL 


T M 


s 


Pensacola Bay, FL 


T M 


s 


Perdido Bay, FL/AL 


T M 


s 


Mobile Bay, AL 


T M 


s 


Mississippi Sound, MS/AL/LA 


T M 


s 


Lake Borgne, LA 


T M 


* 


Lake Pontchartrain, LA 


* M 


* 


Breton/Chandeleur Sounds, LA 


* M 


s 


Mississippi River, LA 


T M 


* 


Barataria Bay, LA 


T M 


s 


Terrebonne/Timbalier Bays, LA 


T M 


s 


Atchafalaya/Vermilion Bays, LA 


T M 


* 


Calcasieu Lake, LA 


T M 


* 


Sabine Lake, LA/TX 


T M 


* 


Galveston Bay, TX 


T M 


s 


Brazos River, TX 


T M 


* 


Matagorda Bay, TX 


T M 


s 


San Antonio Bay, TX 


* M 


s 


Aransas Bay, TX 


* M 


s 


Corpus Christi Bay, TX 


* M 


s 


Laguna Madre, TX 


* * 


s 


Baffin Bay, TX 


* * 


s 


T - Tidal fresh zone 

M - Mixing zone 

S - Seawater zone 

* - salinity zone not present 


Common Name 


Scientific Name 


Bay scallop 
American oyster 
Common rangia 
Hard clam 
Bay squid 
Brown shrimp 
Pink shrimp 
White shrimp 
Grass shrimp 
Spiny lobster 
Blue crab 
Gulf stone crab 
Florida stone crab 
Bull shark 
Tarpon 

Alabama shad 
Gulf menhaden 
Yellowfin menhaden 
Gizzard shad 
Bay anchovy 
Hardhead catfish 
Sheepshead minnow 
Gulf killifish 
Silversides 
Snook 
Bluefish 
Blue runner 
Crevalle jack 
Florida pompano 
Gray snapper 
Sheepshead 
Pinfish 
Silver perch 
Sand seatrout 
Spotted seatrout 
Spot 

Atlantic croaker 
Black drum 
Red drum 
Striped mullet 
Code goby 
Spanish mackerel 
Gulf flounder 
Southern flounder 


Argopecten irradians 
Crassostrea virginica 
Rangia cuneata 
Mercenaria species 
Lolliguncula brevis 
Penaeus aztecus 
Penaeus duorarum 
Penaeus setiferus 
Palaemonetes pugio 
Panulirus argus 
Callinectes sapidus 
Menippe adina 
Menippe mercenaria 
Carcharhinus leucas 
Megalops atlanticus 
Alosa alabamae 
Brevoortia patronus 
Brevoortia smith i 
Dorosoma cepedianum 
Anchoa mitchilli 
Arius felis 

Cyprinodon variegatus 
Fundulus grandis 
Menidia species 
Centropomus undecimalis 
Pomatomus saltatrix 
Caranx crysos 
Caranx hippos 
Trachinotus carolinus 
Lutjanus griseus 
A rchosargus proba tocephalus 
Lagodon rhomboides 
Bairdiella chrysoura 
Cynoscion arenarius 
Cynoscion nebulosus 
Leiostomus xanthurus 
Micropogonias undulatus 
Pogonias cromis 
Sciaenops ocellatus 
Mugil cephalus 
Gobiosoma robustum 
Scomberomorus maculatus 
Paralichthys albigutta 
Paralichthys lethostigma 


Estuary names are primarily from NOAA 1985b. 


Common and scientific names are primarily from Rob- 
ins et al. 1980, Turgeon et al. 1988, Williams et al. 
1989, and Robins et al. 1991. 


included because they provide important habitat for 
many euryhaline species. 

Selection of Species. To ensure that important Gulf 
of Mexico estuarine species were included in the 
ELMR study, a species list was developed (Table 2) 
and reviewed by regional experts. Four criteria were 
used to identify the 44 species entered into the data 
base: 

1) Commercial value - a species that commercial 
fishermen specifically try to catch (e.g., gulf menha- 
den, Brevoortia patronus, and blue crab, Callinectes 
sapidus), as determined from catch and value statistics 
of the NMFS and state agencies. 


2) Recreational value - a species that recreational 
fishermen specifically try to catch that may or may not 
be of commercial importance. Recreational species 
(e.g., red drum, Sciaenops ocellatus, and common 
snook, Centropomus undecimali$ were determined 
by consulting regional experts and NMFS reports. 

3) Indicator species of environmental stress -identified 
from the literature, discussions with fisheries experts, 
and from monitoring programs such as NOAA's Na- 
tional Status and Trends Program (O'Connor 1990). 
These species (e.g., American oyster, Crassostrea 
virginica, and Atlantic croaker, Micropogonias 
undulatus) are molluscs or bottom fishes that consume 
benthic invertebrates or have a strong association with 
bottom sediments. Their physiological disorders, mor- 


Central Gulf of Mexico 

14. Mississippi Sound 

15. Lake Borgne 

16. Lake Pontchartrain 

17. Breton/Chandeleur Sound 

18. Mississippi River 

1 9. Barataria Bay 

20. Terrebonne/Timbalier Bay 

21. Atchafalaya/Vermilion Bay 

22. Calcasieu Lake 


Western Gulf of Mexico 

23. Sabine Lake 

24. Galveston Bay 

25. Brazos River 

26. Matagorda Bay 

27. San Antonio Bay 

28. Aransas Bay 

29. Corpus Christi Bay 

30. Laguna Madre 

31 . Baffin Bay 


Eastern Gulf of Mexico 

1 . Florida Bay 

2. Ten Thousand Islands 

3. Caloosahatchee River 

4. Charlotte Harbor 

5. Tampa Bay 

6. Suwannee River 

7. Apalachee Bay 

8. Apalachicola Bay 

9. St. Andrew Bay 

10. Choctawhatchee Bay 

1 1 . Pensacola Bay 

12. Perdido Bay 

13. Mobile Bay 


V 


Figure 3. ELMR Gulf of Mexico estuaries. 


phological abnormalities, and ability to bioaccumulate 
contaminants indicate environmental pollution orstress. 

4) Ecological value - based on several species at- 
tributes, including trophic level, relative abundance, 
and importance of species as a key predator or prey 
organism (e.g., grass shrimp, Palaemonetes pugio, 
and bay anchovy, Anchoa mitchilli). 

Data Sheets. A data sheet was developed for each 
species in each estuary to enable quick compilation 
and data presentation. For example, Figure 4 depicts 
the data sheet for red drum in Galveston Bay. Data 
sheets were developed by project staff and reviewed 
by local experts. Data compiled for each species' life 
stage included: 1) the salinity zones it occupies, 2) its 
monthly occurrence in the zones, and 3) its relative 
abundance in the zones. 

The relative abundance of a species was defined using 
one of the following categories: 


• Highly abundant - species is numerically dominant 
relative to other species 

• Abundant - species is often encountered in substan- 
tial numbers relative to other species. 

• Common - species is generally encountered but not 
in large numbers; does not imply an even distribution 
over a specific salinity zone. 

• Rare - species is present but not frequently encoun- 
tered. 

• Not present - species or life stage not found, question- 
able data as to identification of the species, or recent 
loss of habitat or environmental degradation suggests 
absence. 

• No information available - no data available, and after 
expert review it was determined that even an educated 
guess would not be appropriate. 


Sciaenops ocellatus 
Red drum 


Galveston Bay 
Texas 


Salinity 
zone 


Life stage 


Relative abundance by month 

jfmamjja|son|d 


R 


Tidal fresh 
0.0 - 0.5 ppt 


Adults 


2 


Spawning 


1 


Juveniles 


2 


Larvae 


1 


Eggs 


1 


Mixing 
0.5 - 25.0 ppt 


Adults 


2 


Spawning 


1 


Juveniles 


2 


Larvae 


1 


Eggs 


1 


Seawater 
>25.0 ppt 


Adults 


2 


Spawning 


3 


Juveniles 


2 


Larvae 


I 


2 


Eggs 


3 


Legend: Relative Abundance: 

= Not Present 
= Rare 
= Common 
= Abundant 
= Highly Abundant 


Data Reliability (R): 

1 = Highly Certain 

2 = Moderately Certain 

3 = Reasonable Inference 


Figure 4. Example of a species/estuary data sheet: red drum in Galveston Bay. 


Information was compiled for each of five life stages. 
Adults were defined as sexually mature individuals, 
juveniles as immature but otherwise similar to adults, 
and spawning adults as those releasing eggs or sperm. 
A few exceptions existed to these defined life stages, 
such as mating of crabs and spiny lobster, and partu- 
rition (live birth) of the viviparous bull shark. 

For well-studied species such as shrimp, quantitative 
data were used to estimate abundance levels. For 
many species, however, reliable quantitative data were 
limited. Therefore, regional and local experts were 
consulted to estimate relative abundances based on 
the above criteria. Several reference or "guide" spe- 
cies with abundance levels corresponding to the above 
criteria were identified for each estuary. These guide 
species typified fishes and invertebrates belonging to 
a particular life mode (e.g., pelagic, demersal) or 
occupying similar habitats. Once guide species were 
selected, other species were then placed into the 
appropriate abundance categories relative to them. 
These data represent relative abundance levels within 
a specific estuary only; relative abundance levels across 
Gulf of Mexico estuaries could not be determined. 

Information was compiled for each species and estu- 
ary combination, and organized into four data summa- 
ries in Volume I : 

• Presence/absence 

• Spatial distribution and relative abundance 

• Temporal distribution 

• Data reliability 

The presence/absence information is also presented 
here in Volume II, with some minor revisions based on 
peer review. Table 4 (p. 8-9) was developed to readily 
convey the occurrence of each of the 44 ELMR species 
in each of the 31 Gulf of Mexico estuaries. This table 
depicts the highest relative abundance of the adult or 
juvenile life stage of each species, in any month, in any 
salinity zone within each estuary. The spawning, egg, 
and larval life stages are not considered. This table 
also suggests the zoogeographic distribution of spe- 
cies among Gulf of Mexico estuaries. 

Data Verification. Several years were required to 
develop the 1,364 data sheets and consult with re- 
gional and local experts. Each data sheet was carefully 
reviewed during consultations or by mail. These con- 
sultations complemented the published and unpub- 
lished literature and data sets compiled by NOAA. 
Over 100 scientists at approximately 50 institutions or 
agencies were consulted. Local experts were particu- 
larly helpful in providing estuary/species-specific infor- 
mation. They also provided additional references and 
contacts and identified additional species to be in- 
cluded in the ELMR data base. 


Life History Summaries and Tables 


Life History Summaries. A concise life history sum- 
mary was written for each species to provide an over- 
view of how and when a species uses estuaries and 
what specific habitats it uses. The summaries empha- 
size species-specific life history characteristics that 
relate directly to estuarine spatial and temporal distri- 
bution and abundance (e.g., many molluscs have 
particular salinity and substrate preferences). Informa- 
tion for the species life history summaries was gath- 
ered primarily from published and unpublished litera- 
ture, and experts with species-specific knowledge were 
also consulted. Summaries were written using the 
format shown in Table 3, p. 7. A glossary of scientific 
terms used is provided on pages 341-353. 

Included with each summary is a relative abundance 
table based on ELMR data from Volume I, with minor 
revisions based on review. These tables (Tables 5.01 - 
5.44) provide a synopsis of the species' occurrence in 
the 31 ELMR Gulf of Mexico estuaries. Information for 
each table was obtained by summarizing the ELMR 
data for each month of the year and across all salinity 
zones to obtain the highest level of abundance for each 
life stage. Hence, these tables depict a species' 
highest abundance within an estuary, but lack the 
temporal and spatial resolution provided in Volume I. 

Life History Tables. While the species life history 
summaries provide brief accounts of important life 
history attributes, they do not permit a direct and simple 
assessment of characteristics that a species shares 
with others. Furthermore, many life history attributes 
are categorical (e.g., feeding types can be classified as 
carnivore, herbivore, detritivore, etc.) and more easily 
viewed in a tabular format. Therefore, information 
found in the species life history summaries was aug- 
mented with additional physical and biological criteria 
and condensed into three life history tables: Table 6, 
Habitat Associations, p. 355-363; Table 7, Biological 
Attributes, p. 365-373; and Table 8, Reproduction, p. 
375-377. Column headers for these three tables are 
depicted in Figure 5. These tables present life history 
characteristics for each species along with behavior 
traits and preferred habitats. They reflect the most 
current information about a species as gathered from 
published and unpublished literature and can be used 
to quickly identify species with similar traits. For 
example, a reader interested in only benthic species 
can use Table 6, Habitat Associations, to identify 
relevant species. Terms used in the life history tables 
are defined at the beginning of each table, and in the 
Glossary, p. 341-353. 


Table 3. Format of species life history summaries. 


Common Name: the most often used common name. 

Scientific Name: the most recent taxonomic genus and species name. 

Other Common Names: other names that are sometimes used for a species. 

Classification: the most recent taxonomic classification (Phylum, Class, Order, and Family). 

Value 

Commercial : information on commercial harvest. 

Recreational : information on recreational fisheries. 

Indicator of Environmental Stress : identifies if a species is an indicator of environmental degradation. 

Ecological : the role (e.g., key predator or prey) a species plays in marine/estuarine ecosystems. 

Range 

Overall : the complete range of a species. 

Within Study Area : the range of a species within Gulf of Mexico estuaries. In addition, each summary 

contains a relative abundance table (derived from information in Volume I) for the 31 ELMR Gulf of 

Mexico estuaries. 

Life Mode: the life history strategy of a species and its life stages (e.g., anadromous, estuarine resident). 

Habitat 

Ty pe: the habitats used by specific life stages (e.g., riverine, neritic, epipelagic). 

Substrate : the substrate preferences of specific life stages. 

Physical/Chemical Characteristics : the physical and water chemistry preferences of specific life stages 

(e.g., temperature and salinity). 
Migrations and Movements : the movements and migratory behavior of a species/life stage between or 

within habitats. 

Reproduction 

Mode : type of reproductive strategy (e.g., oviparous, viviparous) and fertilization (e.g., external, internal). 
Mating/Spawning : timing of spawning and description of mating or spawning behavior. 
Fecundity : the number of eggs or young produced by an individual. 

Growth and Development 

Egg Size and Embryonic Development : the size of an egg and length of time for embryonic development. 

Age and Size of Larvae : the age and size range of larvae. 

Juveniles Size Range : the size range of juveniles. 

Age and Size of Adults : the age and size range of adults. 

Food and Feeding 

Trophic mode : type of feeder (e.g., carnivorous, herbivorous). 

Food Items : the types of prey eaten (e.g., copepods, amphipods, larval fish). 

Biological Interactions 

Predation : predators known to consume a species. 

Factors Influencing Populations : biological and physical parameters that are known to influence a 
species' population abundance (e.g., overfishing, ocean productivity, spawning habitat, parasites). 

Personal communications: individuals that provided relevant information. 

References: alphabetical listing of literature cited. 


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10 


Concluding Comments 


Literature Cited 


As it becomes apparent that the cumulative effects of 
small alterations in many estuaries have a total sys- 
temic impact on coastal ocean resources, it is more 
important than ever to compile consistent information 
on the Nation's estuarine fishes and invertebrates. 
Although the knowledge available to effectively pre- 
serve and manage estuarine resources is limited, the 
ELMR data base provides an important tool for assess- 
ing the status of estuarine fauna and examining their 
relationships with other species and their environment. 
These life history summaries and life history tables 
highlight many of the biological and environmental 
factors that play a role in determining each species' 
distribution and abundance. Together, the ELMR data 
base and life history information will provide valuable 
baseline information on the biogeography and ecology 
of estuarine fishes and invertebrates, and identify gaps 
in our knowledge of these valuable natural resources. 


Acknowledgments 


The authors thank the many individuals who provided 
information for this report, and the many other scien- 
tists and managers who provided contacts and refer- 
ences. We thank the following individuals for their 
review of this document and their comments: Dean 
Ahrenholz, Bill Arnold, Theresa Bert, Mark Butler, 
David Camp, Marie Castiglione, Alan Collins, Bruce 
Comyns, Roy Crabtree, Ned Cyr, Doug DeVries, Rob 
Dillon, Jim Ditty, Gary Fitzhugh, Chris Friel, Churchill 
Grimes, Richard Harrel, Peter Hood, John Hunt, Terry 
Jordan, Steve Jury, Stu Kennedy, Tony Lowery, Bill 
Lyons, Dan Marelli, Tom Matthews, Rich McBride, 
Scott Mettee, Harriet Perry, Mark Peterson, Duane 
Phillips, Allyn Powell, Steve Ross, Peter Rubec, Pam 
Rubin, Tom Schmidt, Rosalie Shaffer, Pete Sheridan, 
Joe Smith, Phil Steele, Ken Stuck, Ron Taylor, Mark 
VanHoose, Mike Vecchione, Mary Ellen Vega, Robert 
Vega, Jean Williams, and Brent Winner. We also thank 
the authors and publishers that granted permission to 
use the species illustrations included with each sum- 
mary. The illustrations of black drum on the front cover 
are from Goode (1884) and Johnson (1978). 


Bulger, A.J., B.P. Hayden, M.E. Monaco, D.M. Nelson, 
and M.G. McCormick-Ray. 1993. Biologically-based 
salinity zones derived from a multivariate analysis. 
Estuaries 16(2):31 1-322. 

Christensen, J.D., M.E. Monaco, and T.A. Lowery. 
1997. An index to assess the sensitivity of Gulf of 
Mexico species to changes in estuarine salinity re- 
gimes. Gulf Res. Rep. 9(4):21 9-229. 

Darnell, R.M., R.E. Defenbaugh, and D. Moore. 1983. 
Northwestern Gulf shelf bio-atlas. Open File Rep. No. 
82-04. U.S. Min. Manag. Serv., Gulf of Mexico OCS 
Regional Office, Metairie, LA, 438 p. 

Goode, G.B. 1884. The fisheries and fishing industry 
of the United States. Sec. I, Natural history of useful 
aquatic animals. U.S. Comm. Fish, Washington, DC, 
895 p., 277 pi. 

Gunter, G. 1967. Some relationships of estuaries to 
the fisheries of the Gulf of Mexico. In Lauff, G.H. (ed.), 
Estuaries, p. 621-638. AAAS Spec. Pub. No. 83. Am. 
Assoc. Adv. Sci., Washington, DC. 

Hammerschmidt, P.C., and L.W. McEachron. 1986. 
Trends in relative abundance of selected shellfishes 
along the Texas coast: January 1977 - March 1986. 
Texas Parks Wildl. Dept., Coast. Fish. Branch, Manag. 
DataSer. No. 108, 149 p. 

Johnson, G.D. 1978. Development of Fishes of the 
Mid-Atlantic Bight; An Atlas of Egg, Larval and Juvenile 
Stages, Volume IV, Carangidae through Ephippidae. 
U.S. Fish Wildl. Serv., Biol. Rep. FWS/OBS-78/12, 314 
P- 

Joseph, E.B. 1973. Analysis of a nursery ground. In 
Pacheco, A.L. (ed.), Proceedings of a workshop on 
egg, larval, and juvenile stages of fish in Atlantic Coast 
estuaries, p. 1 1 8-1 21 . Tech. Pub. No. 1 , NOAA NMFS 
Mid. Atlantic Coast. Fish. Cent., Highlands, NJ, 338 p. 


Mann, K.H. 1982. Ecology of coastal waters. 
Calif. Press, Los Angeles, CA, 322 p. 


Univ. 


National Oceanic and Atmospheric Administration 
(NOAA). 1985a. Gulf of Mexico Coastal and Ocean 
Zones Strategic Assessment: Data Atlas. NOAA/NOS 
Strategic Assessment Branch, Rockville, MD, 161 p. 


11 


National Oceanic and Atmospheric Administration 
(NOAA). 1985b. National Estuarine Inventory: Data 
atlas. Volume 1 . Physical and Hydrologic Character- 
istics. NOAA/NOS Strategic Assessment Branch, 
Rockville, MD, 103 p. 

National Oceanic and Atmospheric Administration 
(NOAA). 1997. Gulf Wide Information System: ORCA 
Component. Prospectus: February 1997. NOAA/NOS 
SEA Division, Silver Spring, MD, 29 p. 

Nelson, D.M., M.E. Monaco, CD. Williams, T.E. Czapla, 
M.E. Pattillo, L. Coston-Clements, L.R. Settle, and E.A. 
Irlandi. 1992. Distribution and abundance of fishes 
and invertebrates in Gulf of Mexico estuaries, Vol. I: 
Data summaries. ELMR Rep. No. 10. NOAA/NOS 
Strategic Environmental Assessments Division, 
Rockville, MD, 273 p. 

O'Connor, T. P. 1990. Coastal Environmental Quality 
in the United States, 1 990: Chemical Contamination in 
Sediment and Tissues. NOAA/NOS Ocean Assess- 
ments Division, Rockville, MD, 34 p. 

Robins, OR., R.M. Bailey, C.E. Bond, J.R. Brooker, 
E.A. Lachner, R.N. Lea, and W.B. Scott. 1 980. A list of 
common and scientific names of fishes from the United 
States and Canada, Fourth Edition. Am. Fish. Soc. 
Spec. Pub. No. 12. American Fisheries Society, 
Bethesda, MD, 174 p. 

Robins, OR., R.M. Bailey, C.E. Bond, J.R. Brooker, 
E.A. Lachner, R.N. Lea, and W.B. Scott. 1 991 . A list of 
common and scientific names of fishes from the United 
States and Canada, Fifth Edition. Am. Fish. Soc. Spec. 
Pub. No. 20. American Fisheries Society, Bethesda, 
MD, 183 p. 

Turgeon, D.D., A.E. Bogan, E.V. Coan, W.K. Emerson, 
W.G. Lyons, W.L. Pratt, C.F.E. Roper, A. Scheltema, 
F.G. Thompson, and J. D. Williams. 1988. Common 
and scientific names of aquatic invertebrates from the 
United States and Canada: Mollusks. Am. Fish. Soc. 
Spec. Pub. No. 16. American Fisheries Society, 
Bethesda, MD, 277 p. 

Weinstein, M. P. 1979. Shallow marsh habitats as 
primary nurseries for fishes and shellfish, Cape Fear 
River, North Carolina. Fish. Bull., U.S. 77:339-357. 

Williams, A.B., LG. Abele, D.L Felder, H.H. Hobbs, 
Jr., R.B. Manning, P. A. McLaughlin, and I. Perez 
Farfante. 1989. Common and scientific names of 
aquatic invertebrates from the United States and 
Canada: Decapod crustaceans. Am. Fish. Soc. Spec. 
Pub. No. 17. American Fisheries Society, Bethesda, 
MD, 77 p. 


12 


Bay scallop 


Argopecten irradians 
Adult 


2 cm 


(fromGoode 1884) 


Common Name: bay scallop 

Scientific Name: Argopecten irradians 

Other Common Names: Atlantic bay scallop, peigne 

baie de I'Atlantique (French), peine caletero atlantico 

(Spanish) (Fischer 1978). 

Classification (Turgeon et al. 1988) 

Phylum: Mollusca 

Class: Bivalvia 

Order: Ostreoida 

Family: Pectinidae 

Value 

Commercial : Bay scallops are harvested commer- 
cially by dredging, dip netting, raking, and hand picking 
(Peters 1978). Reported U.S. 1992 bay scallop land- 
ings werel 61 .5 metric tons (mt), with a dollar value of 
$2.1 million (NMFS 1993). This an important commer- 
cial species along the U.S. Atlantic coast, with fisheries 
in Massachusetts, Rhode Island, New York, North 
Carolina, and the Gulf coast of Florida (Heffernan et al. 
1988, MacKenzie 1989, Rhodes 1991). Landings for 
1992 totaled 58.5 mt in the Gulf of Mexico (Newlin 
1993). However, the commercial scallop fishery in 
Florida has been closed since 1995 (Arnold pers. 
comm.). There is no apparent commercial fishery for 
this species in the remaining Gulf coastal states be- 
cause of their relatively low abundance, but their high 
value and the available market has sparked consider- 
able interest in maricultural production (Hall 1984, 
Rhodes 1991). There are few commercial scallop 
mariculture ventures currently in operation, but hatch- 
ery technology is well developed and research is in 
progress (Hall 1984, Crenshaw et al. 1991, Rhodes 
1991, Walker et al. 1991). 


Recreational : Bay scallops are sometimes collected 
by hand picking while wading in seagrass beds. In 
Florida waters of the Gulf of Mexico, recreational 
harvest is common from Steinhatchee north and west 
to Panama City (Arnold pers. comm.). However, 
recreational harvest elsewhere in the Gulf of Mexico is 
not especially common because of the bay scallop's 
relatively low abundance. In Florida, the recreational 
seasons extends from July 1 to September 10, from 
Suwannee River southward (Arnold pers. comm.). 
The bag limit is two gallons of whole bay scallops in the 
shell, or one pint of meat, per day per person, or ten 
gallons of whole scallops per day per boat (Arnold pers. 
comm.). In Texas, they may be taken year-round in 
waters approved by the Texas Department of Health. 

Indicator of Environmental Stress : Filter feeders such 
as bay scallops often ingest and accumulate resus- 
pended detritus and organic matter from polluted ar- 
eas. This species has been used to test the effects of 
pollutants from the petroleum industry (Hamilton et al. 
1981). Mortality of juvenile bay scallops has been 
demonstrated in the laboratory in the presence of 
heavy metals (Nelson et al. 1976). 

Ecological : The bay scallop is an important part of the 
estuarine food web through its conversion of phy- 
toplankton and detritus into available biomass for sec- 
ond order consumers. 

Range 

Overall : The range of this species extends along the 
western Atlantic from Cape Cod into the Gulf of Mexico, 
and down to Colombia (Turnerand Hanks 1 960, Sastry 
1 962, Fischer 1 978, Peters 1 978, Robert 1 978, Fay et 
al. 1983). Areas of abundance as determined from 


13 


Bay scallop, continued 


Table 5.01 . Relative abundance of bay scallop in 
Gulf of Mexico estuaries (from Volume 1). 

Life stage 


31 


Estuary 


A S J L E 


Florida Bay 


V 


V 


V 


V 


V 


Ten Thousand Islands 


V 


V 


V 


V 


V 


Caloosahatchee River 


V 


V 


V 


V 


V 


Charlotte Harbor 


V 


V 


V 


V 


V 


Tampa Bay 


V 


V 


V 


V 


V 


Suwannee River 


Apalachee Bay 


o 


o 


o 


o 


o 


Apalachicola Bay 


V 


V 


V 


V 


V 


St. Andrew Bay 


o 


o 


o 


o 


o 


Choctawhatchee Bay 


Pensacola Bay 


V 


V 


V 


V 


V 


Perdido Bay 


Mobile Bay 


Mississippi Sound 


o 


o 


o 


o 


Lake Borgne 


Lake Pontchartrain 


Breton/Chandeleur Sounds 


V 


V 


V 


V 


V 


Mississippi River 


Barataria Bay 


Terrebonne/Timbalier Bays 


Atchafalaya/Vermilion Bays 


Calcasieu Lake 


Sabine Lake 


Galveston Bay 


V 


V 


V 


V 


V 


Brazos River 


Matagorda Bay 


V 


V 


V 


V 


V 


San Antonio Bay 


V 


V 


V 


V 


V 


Aransas Bay 


V 


V 


V 


V 


V 


Corpus Christi Bay 


V 


V 


V 


V 


V 


Laguna Madre 


V 


V 


V 


V 


V 


Baffin Bay 


A S J L E 


Relative abundance: 

# Highly abundant 

® Abundant 

O Common 

V Rare 
Dlank Not present 


Life stage: 

A - Adults 

S - Spawning adults 

J - Juveniles 

L - Larvae 

E - Eggs 


commercial landings are coastal areas of Massachu- 
setts, Rhode Island, New York, North Carolina, and the 
gulf coast of Florida (Heffernan et al. 1988, Rhodes 
1991). 

In the United States, Argopecten irradians is consid- 
ered to include three subspecies: A. i. irradians, rang- 
ing from Cape Cod to New Jersey; A. i. concentricus, 
New Jersey to the Chandeleur Islands, east of the 
Mississippi River; and A. i. amplicostatus, Galveston 
Bay to Tuxapan, Veracruz, Mexico (Andrews 1981, 
Fay etal. 1983). 

Within Study Area : Along the Florida Gulf coast, bay 
scallops are most abundant from Pepperfish Keys, 
south of Steinhatchee, north and westward to St. 
Andrew Bay (Arnold pers. comm.). Populations are 
scattered in the northwestern Gulf, but become more 
common in the western Gulf. In Texas, the bay scallop 
is most abundant in bays of the southern coast where 
the salinities are generally higher and seagrass mead- 
ows are extensive. The subspecies Argopecten 
irradians concentricus ranges from Key West, Florida 
to the Chandeleur Islands of Louisiana (Broom 1 976). 
Argopecten irradians amplicostatus ranges from 
Galveston, Texas to the Laguna Madre (Broom 1976, 
Andrews 1981) (Table 5.01). 

Life Mode 

Fertilized eggs are demersal (Belding 1910). Early 
larval stages are pelagic and planktonic. Late larval 
stages are epibenthic. Juveniles up to 20-30 mm in 
length attach to a surface suspended off the bottom by 
byssal threads (Sastry 1 965). Adults and juveniles >30 
mm in length are epibenthic, sometimes motile, and 
gregarious (Belding 1910, Gutsell 1 930, Marshall 1 947, 
Sastry 1 962, Robert 1 978, Peters 1 978, Fonseca et al. 
1984). 

Habitat 

Type : All life stages are estuarine, and marine in 
nearshore waters, occurring in high salinity (euhaline 
to polyhaline) waters. Bay scallops are typically sub- 
tidal, but may be exposed during especially low tides 
(Rhodes 1991). Collections have been recorded at 
depths from to 10 m and a maximum of 18 m. They 
are most abundant in waters from 0.3 to 0.6 m at low 
tide (Marshall 1960, Sastry 1962, Thayer and Stuart 
1974, Peters 1978, Robert 1978, Fay et al. 1983, 
Fonseca etal. 1984). Larvae inhabit the water column 
while searching for a settlement site (Sastry 1 965). At 
settlement the young scallop attaches epifaunally to a 
surface suspended off the bottom (rock, seagrass, 
algae, rope) by means of byssal threads (Belding 
1910). At 20 to 30 mm in length the juvenile scallop 
settles to the bottom, beginning a demersal existence 
that continues through the adult stage (Castagna 1 975). 


14 


Bay scallop, continued 


Substrate : Late larval/early juvenile stages use vari- 
ous substrates for attachment, including oyster shells, 
rope, algae, seagrass, and submerged macrophytes 
(Gutsell 1930, Marshall 1947, Marshall 1960, Thayer 
and Stuart 1974, Fay et al. 1983). Seagrasses, such 
as eel grass (Zostera marina) and shoal grass (Halodule 
wrightii), appear to be the preferred settling site given 
the abundance that is often associated with seagrass 
habitats (Belding 1910, Gutsell 1930, Sastry 1962, 
Thayer and Stuart 1974, Castiglione pers. comm.). 
However, if seagrass density is too great, current 
velocity is reduced and bay scallop abundance may 
decline (MacKenzie 1989). Scallops can settle and 
survive in areas lacking seagrass (Marshall 1947, 
Marshall 1960), but individuals <10 mm generally 
cannot tolerate silty substrates (Castagna 1975), and 
burial can occur in muddy substrates (Tettelbach et al. 
1990). Smith et al. (1988) have demonstrated that 
transplanted seagrass does not serve as a highest 
quality habitat, due to greater losses from predation 
and/or transport as compared to a natural seagrass 
site. 

Physical/Chemical Characteristics : 
Temperature: Eggs and larvae are stenothermal, with 
15 to 20°C required for early development. Optimal 
embryonic development occurs from 20 to 25° and 
best larval growth from 25 to 30°C (Tettlebach and 
Rhodes 1 981 ). Wright et al. (1 983, 1 984) found larvae 
subjected to temperatures below the spawning tem- 
perature experienced a cold-shock which resulted in 
higher mortalities. Juveniles and adults are euryther- 
mal, and Connecticut bay scallops are reportedly able 
to tolerate temperatures as low as -6.6°C for short 
periods (Marshall 1 960). Throughout their range they 
occur in areas where summer maximum water tem- 
peratures do not exceed 32°C (Sastry 1965, Barber 
and Blake 1983). 


salinities on scallop behavior indicated that at salinities 
of 16%o and temperatures of 10° to 15°C the animals 
became inactive, and at 20° to 25°C reduced activity 
occurred at 22%, and 1 8%o (Duggan 1 973). Mortality of 
scallops has been demonstrated in the laboratory at 
salinities of 10% o and less over a range of temperatures 
(Mercaldo and Rhodes 1982). 

Dissolved Oxygen: Oxygen resting requirements of 70 
ml/kg/hour at 20° have been reported (Van Dam 1 954). 
Critical dissolved oxygen (DO) concentrations for this 
species may be related to individual size and ambient 
water temperature (Voyer 1992). 

Other: Turbidities greater than 500 ppm may interfere 
with normal growth and reproduction (Fay et al. 1 983). 
Water currents can displace scallops from their "home" 
habitat, and current velocity can have effects on growth 
related to food availability (Moore and Marshall 1967, 
Kirby-Smith 1972, Rhodes 1991). An optimal amount 
of current is necessary to maintain high concentrations 
of suspended food and remove waste materials rapidly 
(Kirby-Smith 1972). 

Movements and Migrations : Egg and early larval 
stages may be transported by tidal currents. Late larval 
stages are capable of swimming by use of the ciliated 
velum and crawling with the foot (Gutsell 1 930, Sastry 
1965, Hall 1984). Juvenile and adult scallops are 
capable of swimming via propulsion created by the 
clapping of the two valves (Belding 1910, Gutsell 1 930, 
Moore and Marshall 1967). This ability apparently 
serves to maintain position in grassbeds and avoid 
competitors and predators (Peterson et al. 1 982, Win- 
ter and Hamilton 1985). The extent of late juvenile and 
adult movements is unclear. There are, however, 
some reports of scallops migrating in mass (Roessler 
and Tabb 1 974). 


Salinity: Eggs and larval stages are generally found in 
polyhaline salinities (18 to 30%o), and egg and larval 
development are most successful within that range. In 
laboratory studies, normal embryo development oc- 
curs over a narrow range of salinities. Egg develop- 
ment was successful at 25%o, but no embryo develop- 
ment occurred at 1 or 1 5%° (Castagna 1 975, Tettlebach 
and Rhodes 1981). Larvae develop at salinities from 
20 to 35%o with optimal development at 25%o (Tettlebach 
and Rhodes 1981), and are not found below 22%o. 
Although they tend to occur in higher estuarine salini- 
ties (15-30%o), juveniles and adults are considered 
euryhaline and can tolerate moderate salinities. How- 
ever, symptoms of stress appear when salinities drop 
below 16%o (Sastry 1966, Duggan 1973). The mini- 
mum salinity determining overall distributions is ap- 
proximately 14%o (Belding 1910, Gutsell 1930). Labo- 
ratory experiments examining the influence of reduced 


Reproduction 

Mode : Bay scallops are hermaphroditic, usually 
protandrous (Peters 1978), and semelparous (Bricelj 
et al. 1987). Fertilization is external, in the water 
column or on the bottom. Male gametes are generally 
(but not always) released before female gametes, 
reducing the chance of self-fertilization (Belding 1910, 
Gutsell 1930, Loosanoff and Davis 1963, Hall 1984). 

Spawning : Spawning is influenced by temperature, 
photoperiod, salinity and food abundance (Sastry 1 975). 
It occurs in estuaries and in nearshore areas at various 
times throughout the range. In the New England area, 
spawning is triggered by increasing temperatures 
(Belding 1910, Cooper and Marshall 1 963, Taylor and 
Capuzzo 1983), while spawning south from North 
Carolina is triggered by decreasing temperatures (Bar- 
berand Blake 1983). In Florida, spawning begins with 


15 


Bay scallop, continued 


the decline in summer temperatures, August to Octo- 
ber (Sastry 1962, Barber and Blake 1983). Scallops 
can be conditioned in the laboratory to spawn out of 
season by raising the temperature to 30°C followed by 
gradual cooling to 28-26°C (Castagna and Duggan 
1 971 , Castagna 1 975). Gametogenesis is triggered by 
food and temperature (Sastry 1975, Hall 1984). With 
adequate food supplies, a minimum temperature of 1 5- 
20°C is necessary for its initiation (Sastry 1968, Sastry 
and Blake 1971), with slightly higher temperatures 
required for complete maturation of gametes and spawn- 
ing (Sastry 1 966, Sastry 1 968). As the gonads mature, 
nutrients stored during the nonreproductive period are 
diverted to their development (Sastry 1975). Few 
studies have investigated salinity as a factor in spawn- 
ing. 

Fecundity : Kraeuter et al. (1 982) reported a fecundity 
estimate of 100,000 to 1,000,000 eggs per female. 
Bricelj et al. (1987) reported fecundities ten to twenty 
times greater. Some scallops may survive to spawn a 
second time, but most do not (Robert 1978). 

Growth and Development 

Egg Size and Embryonic Development : The unfertil- 
ized mature oocyte is 62-63 (j.m in diameter (Sastry 
1965, Sastry 1966). After fertilization, the first polar 
body occurs in 35 minutes with the second cleavage 
stage occurring in 105 minutes. By 5 hours and 15 
minutes the blastula has formed and rapidly develops 
to the ciliated gastrula stage by 9 to 10 hours and 
reaches the trochophore stage by about 24 hours 
(Gutsell 1930, Sastry 1965). 

Age and Size of Larvae : Larval development in bay 
scallops proceeds rapidly. The transition from tro- 
chophore to straight-hinged larval stage occurs in 
about 24 hours (Gutsell 1930, Sastry 1965, Rhodes 
1991). In laboratory studies at 24° C the veliger 
(shelled) larval stage develops within 48 hours at a size 
of approximately 101 u.m (Sastry 1965). By the tenth 
day of the veliger phase, the pediveliger begins to 
develop and is complete by day 12, beginning the 
settlement process at a size of approximately 184 |im 
(Sastry 1 965, Castagna and Duggan 1 971 , Hall 1 984). 
Attachment with byssal threads occurs between the 
10th and 19th day of the veliger stage with the devel- 
opment of the prodissoconch (=1 90 u.m) and metamor- 
phosis into the juvenile stage commences. The juve- 
nile stage is reached about 29 days from fertilization 
when larval development is complete (Sastry 1965). 
Loosanoff and Davis (1 963) reported larval growth rate 
to be greater than 10 urn/day. 

Juvenile Size Range : By day 35 the young scallop 
resembles the adult and is approximately 1.175 mm in 
length (Sastry 1965). Juveniles remain attached by 


byssal threads until 20-30 mm in size, but retain the 
ability to attach throughout their lives (Hall 1 984, Garcia- 
Esquivel and Bricelj 1993). Growth is dependent on 
temperature and food availability (Sastry 1 965). Growth 
rates are rapid during the warm months, and a market- 
able size of 50 mm is reportedly reached within 1 2 to 1 3 
months on the U.S. east coast (Castagna and Duggan 
1 971 , Spitsbergen 1 979, Rhodes 1 991 ), or within 6 to 
8 months in Florida (Arnold pers. comm.). Little growth 
occurs during winter, especially in the northern part of 
the bay scallop's range. When growth resumes in the 
spring, a raised shell check or color change occurs in 
the shells of these individuals. Growth rates of 3.8 to 
8.0 mm/month (umbo to ventral margin) have been 
determined. Optimal growth occurs in currents <1cm/ 
s and no growth occurs in currents >12 cm/second 
(Kirby-Smith 1972). 

Age and Size of Adults : Maturity is reached by the end 
of the first year, and is a function of age and not size 
(Gutsell 1 930, Sastry 1 963). Adult sizes range from 60 
to 70 mm with a reported maximum of 90 mm. Life 
expectancy is 12-30 months, and is usually less than 
two years (Belding 1910, Gutsell 1 930, Robert 1 978). 

Food and Feeding 

Trophic Mode : The bay scallop filter feeds at all 
development stages (Castagna 1 975). Veliger feed by 
means of cilia on their velum (Hall 1984). Chipman 
(1 954) determined that young scallops filter at a rate of 
3 l/hour, which increases as they grow reaching an 
average of 15 l/hour, and a maximum of 25.4 l/hour. 
Intensity of feeding increases with temperature. 

Food Items : The bay scallop feeds primarily on phy- 
toplankton, but it also consumes zooplankton, sus- 
pended benthic particles, bacteria, detritus, organic 
matter, gametes from other species and algae spores. 
In the laboratory larvae grow and develop well on a diet 
of unicellular algae and naked dinoflagellates (Castagna 
1975), although some algal species have low nutritive 
value and can result in poor growth and survival 
(Nelson and Siddall 1 988). Juveniles and adults ingest 
phytoplankton and detritus as well as benthic diatoms 
(Gutsell 1930, Davis and Marshall 1961, Broom 1976, 
Fay et al. 1 983), but what is actually assimilated has not 
been determined. 

Biological Interactions 

Predation : Known and suspected predators of the bay 
scallop include various gulls and wading birds, starfish, 
cow-nosed rays, pinfish, boxfish, toadfish, whelks, and 
various crabs (Thayer and Stuart 1974, Broom 1976, 
Peterson et al. 1989, Prescott 1990). Scallops in 
intertidal and/or bare bottom areas appear to be more 
vulnerable to predation than individuals in seagrass 
beds or covered by 1 -3 cm of water or more (Peterson 


16 


Bay scallop, continued 


etal. 1989, Prescott 1990). 


Personal communications 


Factors Influencing Populations : A probable limiting 
factor for distribution in the southern range of the bay 
scallop is its increased metabolic rate in this area 
associated with the higher temperatures of this region 
and a decreased food supply that causes a net loss of 
available energy for reproduction (Barber and Blake 
1 983). Excessive turbidities and current velocities can 
inhibit growth and reproduction (Kirby-Smith 1 972, Fay 
et al 1983). Bay scallops living on soft mud substrate 
are subject to burial during events that increase current 
velocity (Tettelbach et al. 1 990). Seagrass provides a 
substrate for attachment by bay scallop larvae, and the 
abundance of this species is influenced by its presence 
(Thayer and Stuary 1974, MacKenzie 1989). Destruc- 
tion of seagrass areas results in decreased abundance 
of this species. Smith et al. (1 988) have demonstrated 
that transplanted seagrass does not serve as a quality 
habitat with apparently greater loss due to predation 
and/or transport in the transplanted seagrass as com- 
pared to the natural seagrass. Blooms of red tide algae 
in sufficient concentrations can result in conditions 
toxic to adult and larval bay scallops (Summerson and 
Peterson 1 990). Nuisance blooms of algae can affect 
bay scallops by altering feeding rates. These species 
are often low in nutritive value causing poor recruitment 
and settlement of the bay scallop due to the algae's 
inability to suport adequate larval growth (Nelson and 
Siddal 1988, Summerson and Peterson 1990). Popu- 
lation sizes are subject to a large degree of variation 
within the year because of the bay scallop's short life 
span and semelparous reproductive cycle (Fay et al. 
1983, Nelson and Siddall 1988, MacKenzie 1989). 
Bay scallops generally spawn only once during their 
lives when they reach the end of their first year. 
Although two year old animals occur rarely, popula- 
tions are almost entirely composed of only one year 
class, upon which the following year class is com- 
pletely dependent. Unfavorable conditions that result 
in poor larval recruitment in any given year may there- 
fore lower abundance the following year. Low DO 
episodes may have long-term population effects due to 
the bay scallops semelparous reproductive cycle as 
well as effecting short-term mortality (Voyer 1992). 
Predation by visually oriented carnivores may be exert- 
ing selection pressures on populations of bay scallops 
resulting in shell color polymorphism (Elek and 
Adamkewicz 1990). Known parasites include the pea 
crab, Pinnotheres maculatus (Kruczynski 1972). Bay 
scallops parasitized by this organism display stunted 
growth rates and reduced weights. Another parasite is 
the polychaete Polydora which can penetrate bay 
scallop shells and sometimes produce blisters on the 
interior shell surfaces (Rhodes 1991). 


Arnold, William S. Florida Marine Research Inst., St. 
Petersburg, FL. 

Castiglione, Marie C. NOAA National Marine Fisheries 
Service, Galveston, TX. 

Shelfer, L.W. Florida Marine Patrol, Tallahassee, FL. 

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18 


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19 


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20 


American oyster 


Crassostrea virginica 
Adult 


2 cm 


(from Galtsoff 1964) 


Common Name: American oyster 

Scientific Name: Crassostrea virginica 

Other Common Names: Eastern oyster (Turgeon et 

al. 1988), huitre creuse americaine (French), ostion 

americano (Spanish) (Fischer 1978). 

Classification (Turgeon et al. 1988) 

Phylum: Mollusca 

Class: Bivalvia 

Order: Ostreoida 

Family: Ostreidae 

Value 

Commercial : The American oyster has historically sup- 
ported a valuable fishery throughout the Gulf of Mexico 
(Stanley and Sellers 1986). In 1993, 15,241 metric 
tons (mt) of oyster meat valued at $86.7 million were 
landed in the United States, and the Gulf region led in 
production with 9,072 mt of meats (O'Bannon 1994). 
Led by Louisiana, the Gulf region produced about 
8,390 mt and nearly 41% of the national total during 
that year. Individual state harvests for the Gulf during 
1 992 have been compiled by Newlin (1 993). The west 
coast of Florida ranked second in Gulf production with 
1,571 mt harvested during that season. Alabama and 
Mississippi landings are typically small, but landings 
during 1992 were much higher than usual totaling 543 
and 321 mt respectively. Louisiana led the Gulf states 
in production during that year with 5,015 mt of meats. 
In Texas, the harvest was about 936.7 mt. Harvest 
methods include hand picking, tonging from boats, and 
dragging or dredging from boats (Stanley and Sellers 
1986). Most of the Gulf landings are from publically- 
owned oyster beds, but an estimated 30% of the 
harvest isf rom privately-leased beds (MacKenzie 1 989). 
Oysters from restricted waters are sometimes moved 
to approved waters for depuration or further growth. 


Broken oyster shell, rangia shell, or limestone are 
sometimes used as substrate to enhance oyster settle- 
ment and growth in Florida and Louisiana (MacKenzie 
1996). Commercial fishery regulations vary among the 
Gulf coast states, but all oysters harvested must mea- 
sure at least three inches from hinge to mouth (GSMFC 
1 993, TPWD 1 993a). A regional fishery management 
plan has been developed for this species (Berrigan et 
al. 1991). 

Recreational : Oysters are often collected from ap- 
proved areas for personal use by hand (cooning), 
tongs, or sport dredges. Recreational fishery regula- 
tions vary among the Gulf coast states, but a three inch 
minimum size limit generally applies, along with bag 
limits and closed seasons (GSMFC 1993, TPWD 
1993b). 

Indicator of Environmental Stress Oysters are ideal for 
use as indicators of pollution due to their sessile, filter 
feeding life mode (NOAA 1 989). Broutman and Leonard 
(1 988) review the methodology and problems of water 
classification, predominantly based on fecal coliform 
bacteria, for shellfish throughout the Gulf of Mexico. 
The American oyster is often used for pesticide and 
petroleum by-product LD-50 analyses. It is used by 
NOAA's Status and Trends program and other state 
and federal agencies to monitor concentrations and 
accumulation of organic and metallic contaminants in 
the marine environment (Lytle and Lytle 1982, Mo- 
rales-Alamo and Haven 1982, NOAA 1989, Wade 
1 989, Sericano et al. 1 990, Alvarez et al. 1 991 , Palmer 
et al. 1 993). In addition, shell thickness and condition 
is used to detect heavy metal pollution (Marcus et al. 
1989). This species has also been used by the U.S. 
Environmental Protection Agency (EPA) to study the 


21 


American oyster, continued 


Table 5.02. Relative abundance of American oyster 

in 31 Gulf of Mexico estuaries (Nelson et al. 1992, 

Van Hoose pers. comm.). 

Life stage 


Estuary 


A S J L E 


Florida Bay 


Ten Thousand Islands 


O 


O 


o 


o 


o 


Caloosahatchee River 


® 


O 


o 


o 


o 


Charlotte Harbor 


o 


O 


o 


o 


o 


Tampa Bay 


o 


O 


o 


o 


o 


Suwannee River 


® 


® 


lit 


® 


® 


Apalachee Bay 


® 


® 


® 


® 


® 


Apalachicola Bay 


® 


® 


® 


® 


® 


St. Andrew Bay 


o 


o 


o 


o 


Choctawhatchee Bay 


_Qj 


o 


o 


o 


o 


Pensacola Bay 


o 


o 


o 


o 


o 


Perdido Bay 


V 


V 


V 


V 


V 


Mobile Bay 


® 


® 


® 


® 


® 


Mississippi Sound 


o 


• 


o 


• 


• 


Lake Borgne 


o 


o 


o 


o 


o 


Lake Pontchartrain 


o 


o 


o 


o 


o 


Breton/Chandeleur Sounds 


® 


® 


® 


® 


® 


Mississippi River 


V 


V 


V 


V 


V 


Barataria Bay 


® 


® 


® 


® 


® 


Terrebonne/Timbalier Bays 


® 


® 


® 


® 


® 


Atchafalaya/Vermilion Bays 


® 


® 


® 


• 


® 


Calcasieu Lake 


o 


o 


o 


o 


o 


Sabine Lake 


o 


o 


o 


o 


o 


Galveston Bay 


® 


® 


• 


® 


® 


Brazos River 


na 


na 


na 


na 


na 


Matagorda Bay 


o 


o 


o 


o 


o 


San Antonio Bay 


® 


® 


® 


® 


® 


Aransas Bay 


o 


o 


o 


o 


Corpus Christi Bay 


o 


o 


o 


o 


o 


Laguna Madre 


V 


V 


V 


V 


V 


Baffin Bay 


A S J L E 


Relative abundance: 

9 Highly abundant 
® Abundant 
O Common 
V Rare 
blank Not present 
na No data available 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


effects of bioaccumulation of toxic substances from 
dredge materials (Parrish et al. 1989). Rates of accu- 
mulation and depuration of mercury from the environ- 
ment by this species have also been studied (Palmer et 
al. 1993). 

Ecological : This species is important in providing reef 
habitats that serve as areas of concentration for many 
other organisms (Wells 1 961 , Bahr and Lanier 1 981 ), 
as well as a food source for a variety of estuarine fish 
and invertebrates (Burrell 1986). Oysters form an 
important link between pelagic and benthic food webs 
by making available a portion of the organic material 
they filter as dense, mucus-bound biodeposits that can 
provide a food resource for benthic organisms (Newell 
1 988). Oysters and other molluscan suspension feed- 
ers may also act as a natural control against the 
adverse effects of eutrophication in estuaries by filter- 
ing out both inorganic and organic particles and limit- 
ing turbidity and phytoplankton blooms. This could 
enable greater light penetration through the water 
column, and benefit submerged aquatic vegetation. 
Thus, oysters can affect many aspects of an estuarine 
ecosystem (Kennedy 1991). 

Range 

Overall : The American oyster occurs from the Gulf of 
St. Lawrence to the Yucatan Peninsula of Mexico and 
to Venezuela. It is abundant in the estuaries along the 
coast of the Gulf of Mexico. Along the Atlantic coast, it 
is historically abundant in Chesapeake Bay and Long 
Island Sound (Burrell 1 986, Stanley and Sellers 1 986). 
Results of biochemical analyses suggest that four 
distinct races occur: Canadian, U.S. Atlantic, U.S. Gulf 
of Mexico, and Bay of Campeche (King and Gray 
1989). 

Within Study Area : Along the U.S. Gulf coast, this 
species occurs from Texas to Florida (Table 5.02). 
The estuaries of Louisiana and Texas east of Corpus 
Christi generally have the highest abundances. Re- 
cent evidence indicates two races occupying the Texas 
coast, with the upper Laguna Madre being the location 
of the transition zone (King and Gray 1 989). It is not yet 
known if this is a race unique to the Texas coast, or the 
northernmost population of the Bay of Campeche race. 

Life Mode 

Eggs are planktonic. Larvae are meroplanktonic to 
benthic. Larvae are gregarious, enabling oysters to 
form extensive reefs over long periods of time. Juve- 
niles (spat) and adults are sessile and benthic (Burrell 
1986, Stanley and Sellers 1986). 

Habitat 

Ty pe: All oyster life stages are estuarine, and can occur 
in coastal sounds, bays, and estuaries of the coastal 


22 


American oyster, continued 


U.S. Egg, larval, juvenile, and adult stages all occur in 
mesohaline to euhaline environments in depths up to 
10 m (Galtsoff 1964, Bahr and Lanier 1981, Burrell 
1986). Price (1954) discusses the various develop- 
ment, shapes and location of oyster reefs with respect 
to shoreline, channels and distance from the Gulf. 
Reefs grow from the shoreline out; as a current is 
encountered the reef turns to a right angle and parallels 
the current, eventually turning back on itself. Other 
reefs grow parallel to channels. Oysters can grow and 
survive over a wide range of environmental conditions, 
but they are most successful when attached to firm 
substrate in areas where water circulation provides 
sufficient food (Berrigan et al. 1991). The preferred 
habitats are estuarine intertidal areas, shallow bays, 
other oyster shell and hard surfaces, mud flats and 
offshore sand bars (Butler 1954, Marshall 1954, 
Copeland and Hoese 1966, Menzel et al. 1966). The 
intertidal zone affords oysters some protection from 
predation by carnivorous gastropods and other com- 
mon oyster predators (Marshall 1954). Wild popula- 
tions of oysters need to be in the vicinity of freshwater 
discharges such as rivers, creeks, and bayous (Berrigan 
et al. 1 991 ). These discharges provide food and dilute 
the higher salinity waters of the Gulf of Mexico. The 
resulting moderate salinity habitats that are created 
are necessary forsuccessful oyster settling and growth, 
and provide protection from high salinity predators and 
disease. 

Substrate : Hard, elevated substrates provide increased 
surface area on the bottom to help support oysters as 
they grow and prevent them from sinking into the 
sediment and smothering (Marshall 1954, Berrigan et 
al. 1991). Any type of hard substrate such as glass, 
rock, concrete, metal, wood, rubber, or shell is suitable 
for settlement of oyster spat (Burrell 1 986, Berrigan et 
al. 1991). Oyster reefs are typically on hard bottoms, 
but individuals are also abundant on surrounding mud 
bottoms. Maximum setting occurs on horizontal sur- 
faces (Clime 1 976). Larvae do, however, show prefer- 
ence for established oyster beds, responding perhaps 
to pheromones, ammonia, or other metabolites re- 
leased by adult oysters or to proteins on the surface of 
oyster shells (Hidu and Haskin 1 971 , Bahr and Lanier 
1 981 , Fitt and Coon 1 992). Harry (1 976) demonstrated 
that the American oyster can thrive on bottoms consist- 
ing of 17 to 100% sand. 

Physical/Chemical Characteristics : The American oys- 
ter is typically exposed to wide variation in environmen- 
tal parameters (salinity, temperature, dissolved oxy- 
gen, etc.) in its estuarine habitat (Killam et al. 1992). 
Because of the oyster's tolerance of these fluctuations, 
the environmental requirements of this species are not 
readily defined with precision. 


Temperature - Eggs and Larvae: Normal egg develop- 
ment occurs between approximately 18° and 30°C 
(Loosanoff 1965). Larval development occurs gener- 
ally at >20°C (Burrell 1 986) with maximal growth occur- 
ring between 30° to 32.5°C at salinities ranging from 
7.5 to 27%o (Davis and Calabrese 1964, Loosanoff 
1965). 

Temperature - Juveniles and Adults: Adults exist 
within the range of -2°C in New England to 36°C in the 
Gulf of Mexico. During low tide, the American oyster 
can withstand temperatures below freezing and above 
49°C, but it typically stops feeding at 6°-7°C, and at 
42°C most bodily functions cease or are greatly re- 
duced (Galtsoff 1964). Normal growth occurs at tem- 
peratures ranging from 10° to 30°C or greater (Burrell 
1986). There may be as many as three races of 
American oyster based on temperature regimes (Ahmed 
1975). Buroker et al. (1979) found all oysters to be 
genetically equivalent, and Groue and Lester (1982) 
found the Laguna Madre oysters to be genetically 
distinct from four other Gulf populations. These racial 
distinctions may be reflected in spawning tempera- 
tures determined by Stauber (1950): Gulf of Mexico 
oysters spawn around 25°C (water temperatures must 
be consistently over 20°C and above 25°C for mass 
spawnings); there are two races on the East Coast that 
spawn at 16 and 20°C. Cake (1983) reports that Gulf 
oysters are not as tolerant of freezing as the East Coast 
race. 

Salinity - Eggs and Larvae: Normal egg cleavage in 
Virginia waters occurs between 7.5 and 34%o (meso- 
euhaline) with optimum development between 10 and 
22%o (Castagna and Chanley 1973). The optimum 
salinity for proper egg and larval development may be 
related to the salinity at which the adult gonads com- 
plete gametogenesis (Davis 1958, Loosanoff 1965). 
Egg and larval development from mesohaline adult 
populations (9-1 0%>) are optimum at approximately 10 
to 1 5%o (Davis 1 958), with an upper limit of about 22%o 
(Loosanoff 1965). Development of spawn from adults 
in polyhaline areas (26-27%o) is best at 23%o for the 
eggs and 18%o for the larvae (Davis 1958) with a 
tolerance of 15 to 35%o. In general, larvae are meso- 
to euhaline tolerating salinities between 5 and 39%o 
(Castagna and Chanley 1973). Larval growth is usu- 
ally limited at lower salinities (10%o) (Chanley 1957) 
with optimums, in most cases, at higher salinities (25- 
29%o) (Castagna and Chanley 1973). Spat setting is 
usually less at low salinities, with consistent settling 
occurring from 16% to 22%o, and peaking at 20%o to 
22%o (Menzel etal.1 966, Chatryetal. 1983). Metamor- 
phosis occurs between 5.6%o and 35%o, with best spat 
growth between 13 to 30%o (Chanley 1957, Castagna 
and Chanley 1973). 


23 


American oyster, continued 


Salinity - Juveniles and Adults: The salinity require- 
ments of oysters vary depending on geographic loca- 
tion, life cycle stage, and environmental parameters 
(Killam et al. 1992). Adults are euryhaline, tolerating 
meso- to euhaline waters (Galtsoff 1 964, Burrell 1 986). 
In Gulf of Mexico estuaries, they normally occur at 
salinities from 10 to 30% o , tolerating a range from 2 to 
43.5%o (Gunter and Geyer 1 955, Copeland and Hoese 
1966). Low salinities (0%o) may be tolerated for short 
periods of time (Loosanoff 1965) with optimum adult 
growth occurring from 14 to 30%o (Castagna and 
Chanley 1973). Gunter (1953) reported high mortali- 
ties during spring floods in Mississippi Sound and 
Louisiana. This has also been reported for Mobile Bay 
(May 1972) and the Santee River, South Carolina 
(Burrell 1977). Oysters from the Laguna Madre of 
Texas tolerate higher salinities, growing and spawning 
in salinities greater than 40%o (Breuer 1 962). Eleuterius 
(1977) found salinities from 2 to 22%o from areas of 
productive reefs. Salinity tolerance is inversely corre- 
lated to the surrounding water temperature (Berrigan 
et al. 1991). Higher water temperatures generally 
result in reduced tolerance to salinity. At temperatures 
below 5° C, oysters are tolerant of low salinity condi- 
tions, but will die after only a few days at the same 
salinity when the temperature is 15° C. 

pH: pH can influence oyster reproduction and develop- 
ment (Berrigan et al. 1 991 ). Normal egg development 
and larval growth occur between a pH of 6.75 to 8.75, 
with an optimum pH for larval growth between 8.25 to 
8.50 (Calabrese and Davis 1966, Calabrese 1972). 
Optimum pH for spawning is 7.80, and the pH must be 
greater than 6.75 for successful recruitment to occur. 

Dissolved oxygen (DO): Information on the DO re- 
quirements for the American oyster is limited (Killam et 
al. 1 992). Oysters are facultative anaerobes, enabling 
them to withstand daily periods of low or no oxygen, but 
an oxygen debt builds up (Berrigan et al. 1991). In a 
laboratory experiment, the hourly oxygen consumption 
for six whole animals (including shell) was 39 ml/kg or 
303 ml/kg of wet tissue weight (Hammen 1969). Sur- 
vival for up to five days has been noted in oysters kept 
in water with <1 ppm DO content (Sparks et al. 1 958). 
Larvae appear able to cope well aerobically with most 
low oxygen conditions through simple diffusive. pro- 
cesses (Mann and Rainer 1990). The consumption 
rate of oxygen is a function of water salinity and 
temperature (Berrigan etal. 1991). In Mobile Bay, low 
oxygen conditions killed oysters and reduced the set- 
ting of spat in 1971 (May 1972). 

Migrations and Movements : Since adults are sessile, 
their distribution is determined by settlement of larvae 
and subsequent survival of the spat. The planktonic 
larval stages are transported by tides and migrate 


vertically through the water column. Larvae aggregate 
near the surface on rising tides and near the bottom on 
falling tides, thus ensuring their wide dispersion and 
diminishing their chances of being swept out to sea. 
Plantigrade larvae are capable of crawling on sub- 
strates to determine suitability (Burrell 1986, Stanley 
and Sellers 1986). Spat and adults from restricted 
waters are often moved to leased lots in approved 
waters for depuration and/or to increase the abun- 
dance in that area for future harvests. 

Reproduction 

Mode : Adults exhibit protandry and protogyny, but are 
gonochoristic (Andrews 1979). True functional her- 
maphrodites occur in less than 1% of a given popula- 
tion. Young oysters are predominantly male; subse- 
quent sex inversion with age increases the proportion 
of females (Loosanoff 1965, Bahr and Lanier 1981, 
Burrell 1 986). The male releases sperm and a phero- 
mone into the water column that can be detected by the 
females at the inhalent siphon, triggering the release of 
eggs for external fertilization (Andrews 1979). 

Spawning : The reproductive state is dependent upon 
a number of factors, the most important of which is 
water temperature. Water temperature triggers the 
time of spawning, and the critical temperature varies 
with geographical location (Burrell 1 986, Gauthier and 
Soniat 1989). In the Gulf of Mexico, the temperature 
must be constantly above 20°C for spawning, and 
above 25°C for mass spawning (Hopkins 1931, Ingle 
1 951 , Bahr and Lanier 1 981 , Burrell 1 986, Stanley and 
Sellers 1986, Gauthier and Soniat 1989). Along the 
lower part of Florida's west coast, spawning probably 
occur during all months except during periods of high 
orlowtemperatureextremes(Killametal. 1992). Peak 
spawning in this area probably occurs in the spring and 
fall months, with the fall being the more successful. In 
the northern Gulf of Mexico, spawning occurs from 
March to November (Butler 1954). Peaks occur in 
Louisiana in late May-early June and September- 
October (Pollard 1 973, Gauthier and Soniat 1 989). In 
Mississippi, spawning occurs from May to October with 
a peak in June (MacKenzie 1977). In south Texas, 
spawning occurs in all months except July and August 
because of high temperature (Copeland and Hoese 
1966). 

Fecundity : A single female can produce 15 to 114.8 
million eggs in a single spawn; fecundity is generally 
proportional to the size of the female. Females may 
spawn several times within a season (Davis and Chanley 
1955, Galtsoff 1964, Loosanoff 1965, Gauthier and 
Soniat 1989). 


24 


American oyster, continued 


Growth and Development 

Egg Size and Embryonic Development Egg develop- 
ment is oviparous. Fertilized eggs are pear shaped 
(55-75 u.m long and 35-55 ^m wide), and contain 
numerous oil droplets. These droplets are important 
for providing energy and nutrients to the developing 
embryo. The eggs hatch 6 hours after fertilization at a 
temperature of 24°C, and progress through blastula 
and gastrula stages, developing into a trochophore 
larvae in 6 to 9 hours (Galtsoff 1 964, Loosanoff 1 965, 
Bahr and Lanier 1 981 , Burrell 1 986, Lee and Heffernan 
1991). 

Age and Size of Larvae : Larvae remain in the water 
column 2 to 3 weeks after hatching, passing through 
several developmental stages (trochophore, 
prodissoconch I, prodissoconch II orpediveliger). The 
final larval stage, the eyed pediveliger, is approxi- 
mately 300 urn in length. At this stage the larval oyster 
uses its eyespot and foot to find a suitable substrate for 
settlement. In Galveston Bay, Texas, setting was first 
seen about 2 months after spawning when the larvae 
were approximately 0.2 mm in length (Hopkins 1931). 
Upon attachment, the larval foot and eyespot are lost 
and the newly settled, sessile juveniles are referred to 
as spat (Ritchie and Menzel 1 969, Palmer 1 976, Manzi 
et al. 1 977). Spat-fall on the Gulf coast typically occurs 
from March until mid-November (Hopkins 1931, Ingle 
1951, Hopkins 1955). 

Juvenile Size Range : Juveniles (spat) develop when 
larvae cement themselves to the substrate. Growth of 
spat varies with location of settlement site with an 
average monthly growth rate of approximately 1 to 4 
mm (Palmer 1 976, Manzi et al. 1 977). Fastest growth 
for juveniles occurs during the first 3 months, and 
decreases as they increase in size (Bahr 1 976). Func- 
tional gonads may be present at 2-3 months of age and 
a size of only 1 cm (Bahr and Lanier 1981). 

Age and Size of Adults : In the Gulf of Mexico, sexual 
maturity may be reached as soon as 4 weeks after 
attachment (Menzel 1951), but generally 18 to 24 
months is normal (Quast et al. 1988). Butler (1954) 
reports growth for the Gulf oysters to be approximately 
50 mm/year. Gunter (1 951 ) gives growth rates of 0.26- 
0.30 mm/day in the first 3 months, 60 mm in the first 
year, 90 mm in the second year, and 1 1 5 mm in the third 
year. Growth coefficients in Louisiana are highly 
variable, fluctuating from 0.42 to 0.86 mm/day (Gillmore 
1982). Growth is greatest in August and September, 
after spawning when glycogen reserves are restored 
(Loosanoff and Nomejko 1949, Price et al. 1975). 
Mortality rates for adult oysters generally increase with 
their size and age (Quast et al. 1 988). In the absence 
of predation and fishing, 98% of all individuals die 
before they reach 6 years of age with the lowest 


mortality occurring in salinities below 15%o and even 
10%o (Hopkins 1 955, Mackin 1961 , Quast et al. 1988). 
The maximum adult size is approximately 300 mm. 

Food and Feeding 

Trophic Mode : Larvae are planktivorous with large 
umbo stage larvae able to ingest particles from 0.2 to 
30 u.m (Davis 1953, Guillard 1957, Loosanoff 1965, 
Bahr and Lanier 1981, Burrell 1986, Baldwin et al. 
1989). Juveniles and adults are suspension filter 
feeders that filter large quantities of brackish water, 
and are particularly effective at removing particles 
around the 3-4 urn range (Haven and Morales-Alamo 
1970, Stanley and Sellers 1986). The rate of filtration 
varies with water temperature, with the volume filtered 
almost 1500 times the volume of the oyster's body 
(Stanley and Sellers 1986, Berrigan et al. 1991). 

Food Items : Food is obtained from suspended par- 
ticles entering through the ventral inhalent siphon and 
passed to the gills. The particles are sorted in the gills, 
and large particles are rejected. The rejected material 
is voided as pseudofeces through the inhalent siphon 
(Barnes 1 980). Larvae feed on microscopic algae and 
naked flagellates (Davis 1 953, Guillard 1 957, Loosanoff 
1 965, Bahr and Lanier 1 981 , Burrell 1 986, Stanley and 
Sellers 1986). Naked flagellates are preferred by 
adults. Bacteria are sometimes consumed, presum- 
ably because they are attached to detritus particles, 
but bacteria are generally a minor component of the 
diet. Oysters have variable uptake of carbon from 
Spartina altemiflora crude fiber ranging from less than 
1% in Chesapeake area to over 20% in the southeast 
region, primarily due to differences in crude fiber con- 
centrations in the seston (Crosby et al. 1989). 

Biological Interactions 

Predation : Larvae are susceptible prey to a variety of 
filterfeeders such as ctenophores, coelenterates, tuni- 
cates, barnacles, molluscs, and and fishes (Hofstetter 
1977, Berrigan et al. 1991). Ciliated protozoans also 
prey on larvae, and are able to ingest as many as six 
larvae at a time. Among sessile oysters, the predatory 
oyster drill, Thais haemastoma, is responsible for the 
majority of mortalities in Louisiana, Mississippi and 
Alabama (Chapman 1959, Gunter 1979). In Missis- 
sippi, rocksnails can destroy up to 50% of the oysters 
on a productive reef, and up to 1 00% of the oysters on 
a nonproductive reef. It is also a serious predator in 
high salinity areas of Texas bays (Hofstetter 1977, 
Soniat et al. 1989). All sizes of oysters are potential 
prey for the rocksnail, but spat are particularly vulner- 
able (Butler 1 954, Chapman 1 959). A single snail can 
consume up to 4 spat per hour, or up to one adult oyster 
every 8 days (Butler 1954, Gunter 1979). Rocksnails 
open oysters by a combination of chemical dissolution 
of the shell and drilling (radular rasping) (Stanley and 


25 


American oyster, continued 


Sellers 1986). Stone crabs are also major oyster 
predators in the Gulf of Mexico (Menzel and Hopkins 
1956, Berrigan et al. 1991). In Louisiana, it was 
estimated that one stone crab could kill up to 219 
oysters per year. In addition, the blue crab and smaller 
mud crabs (Xanthidae), prey on oyster spat and young 
thin-shelled oysters. The black drum is an important 
predator of oysters as well (Pearson 1 929, Cave 1 978, 
Cave and Cake 1980, Berrigan et al. 1991). Black 
drum will attempt to crush and consume any oyster that 
will fit in their pharyngeal apparatus. Large black drum 
(>900 mm TL) can consume oysters up to 1 12 mm in 
length, while smaller drum (<900 mm TL) consume 
oysters less than 75 mm. It has been estimated that 
black drum consume up to two oysters per day for 
every kilogram of body weight, and a single large drum 
can consume an average of up to 48 oysters per day. 
Other predators include the oyster leech (Stylochus 
frontalis), the lightning whelk (Busycon contrarium), 
the crown conch (Melongena corona), echinoderms, 
flat worms, cownose ray (Rhinoptera bonasus), south- 
ern eagle ray (Mylibatisgoodei), Atlantic croaker, spot, 
toad fish (Opsanus sp.), sheepshead, pinfish, and 
striped burrfish (Chilomycterus schoepfl) (Hopkins 
1 955, Menzel et al. 1 966, Hofstetter 1 977, Cake 1 983, 
Stanley and Sellers 1986, Berrigan et al. 1991). 

Factors Influencing Populations : Salinity is probably 
the single most important factor that influences the 
distribution and abundance of estuarine organisms 
(Copeland and Hoese 1 966, Berrigan et al. 1 991 ), and 
this is particularly important with respect to oysters. 
Droughts can increase salinities over oyster reefs and 
contribute to higher mortality due to increased num- 
bers of high salinity, stenohaline oyster predators 
'(Gunter 1 955, Cake 1 983, Lowery 1 992). High mortal- 
ity due to prolonged exposure to lowered salinities can 
occur during episodes of heavy flooding from storm 
events (Gunter 1 953, May 1 972, Burrell 1 977, Hofstetter 
1 977, Soniat et al. 1 989, Berrigan et al. 1 991 ). Some 
flooding is beneficial because it maintains low levels of 
Perkinsus marinus infection (Soniat et al. 1989), and 
excludes marine predators and parasites (Hofstetter 
1 977) by keeping salinities low. Increased salinities in 
estuaries due to a reduction of freshwater inflow have 
caused oysters beds to relocate toward the headwa- 
ters of estuarine basins to more favorable salinities 
(Berrigan et al. 1991). Since this shift in location has 
occurred over a relatively short period of time, these 
areas lack extensive reefs for larval settlement. Oys- 
ters are also more prone to mortalities from freshwater 
flooding events in these areas. Another problem is that 
these locations are closer to areas of human habitation 
where sanitary conditions can become compromised, 
and other pollutant-related diseases and mortality will 
occur. 


Hurricanes, tropical storms, and flooding can have 
both positive and negative effects on oyster popula- 
tions in Gulf of Mexico estuaries (Berrigan et al. 1991, 
Lowery 1992). Hurricanes impact oyster production 
through several mechanisms. They can destroy reef 
integrity, remove live oysters and shell cultch, cause 
sedimentation that buries reefs, increase current ve- 
locity causing scouring and abrasion, and bring fresh- 
ets into the estuary that drop salinities to lethal levels. 
The severity of the damage may be affected by local 
tidal conditions, proximity to the storm, wave surge, 
rainfall and other climatological factors. Runoff from 
storm events, along with dredge and fill activities and 
effluent discharges, can also increase turbidity and 
sedimentation in the aquatic environment (Killam et al. 
1 992). This can lead to silt settling out over oyster spat 
and inhibiting normal growth. This sedimentation also 
results in a soft muddy habitat that is undesirable for 
spat settlement. Currents are necessary for removal of 
feces and pseudofeces to prevent burial of the oyster 
reef. However, turbulent currents that carry sand or 
pebbles can damage oysters by eroding shell sur- 
faces. Suspended solids may clog gills and interfere 
with filter feeding and respiration. If covered with 
sediment, oysters can die within a week (Stanley and 
Sellers 1986). Despite initial mortality resulting from 
hurricanes, long-term oyster production may be en- 
hanced by the subsequent destruction of high-salinity 
predators and diseases, and the scouring of extant 
reefs making more clean shell available for spat settle- 
ment. 

The loss of suitable habitat is probably the most impor- 
tant factor in the decline of oyster populations in the 
Gulf of Mexico (Berrigan et al. 1991). Reef substrate 
which is necessary for spat settlement is removed 
during harvest, and fossil reefs are mined for shell 
material. The continuing development of Gulf coastal 
areas is resulting in habitat areas being filled or dredged 
to accommodate human needs. Spoil banks from 
dredging projects modify the bottom morphology of 
bay bottoms and alter current patterns causing condi- 
tions that can result in mortality (Hoese and Ancelet 
1987). Freshwater inflow into estuaries has been 
reduced due to the damming of rivers, leveeing of 
rivers preventing overflow into surrounding marshes, 
channelization, pumping for redistribution, and other 
construction projects that alter salinity regimes, reduce 
available nutrients, and allow the influx of predators. 
Development of coastal areas has also led to in- 
creased pollution and pollution-related mortality (Menzel 
et al. 1 966, Berrigan et al. 1 991 ). The development of 
power equipment for commercial oyster harvest has 
increased the potential for depleting and damaging 
oyster beds (Stanley and Sellers 1986). 


26 


American oyster, continued 


Individuals of this species in high salinity areas are 
more susceptible to disease infection by the patho- 
genic protozoan, dermo (Perkinsusmarinus) (Hofstetter 
1 977, Soniat et al. 1 989, Berrigan et al. 1 991 , Killam et 
al. 1 992). Dermo interferes with growth and reproduc- 
tion, and is associated with, and primarily responsible 
for, annual losses of 1 0% to 50% of the market oysters. 
Water temperature is an important factor in controlling 
the occurrence and effects of this organism. Repro- 
duction of dermo is drastically lowered in water tem- 
peratures below 20°C, and warm water temperatures 
during the summer months may promote it. The 
ectoparasitic gastropod, Boonea impressa, which in- 
fests the American oyster, is also capable of transmit- 
ting dermo from one oyster to another (White et al. 
1987). Troublesome boring organisms reduce the 
market value, as well as consume energy in shell 
growth and repair. The most common of these are 
Cliona, the boring sponge, and Diplothyra smithii, the 
boring clam. Oysters infested with burrowing clams 
and sponges have been indicated to be much more 
susceptible to predation by black drum and possibly 
other predators because of weakened shells (Cave 
1978). Intertidal oysters, because of their slower 
growth, thicker shells, and less relative time underwa- 
ter, seem to be less susceptible to this predation than 
subtidal oysters. Blooms of red tide are another source 
of natural mortality. High concentrations (500 cells/ml) 
of this diatom, Colchlodinium heterolobatum, can kill 
oyster larvae (Killam et al. 1992). The oyster crab 
(Pinnotheressp.) sometimes lives in the mantle cavity 
of the oyster where it may cause damage to the gills 
(Stanley and Sellers 1986). 

The American oyster also competes for space and food 
with other organisms. Competitors include bryozoans 
(Conopeum commensale), barnacles (Balanus sp.), 
slipper shells (Crepidula sp.), hooked mussel 
(Ischadium recurvum), jingle shells (Anomia sp.), 
anemones, serpulid worms (Eupomatus dianthus), 
tunicates, and algae (Marshall 1954, Schlesselman 
1955, MacKenzie 1970, Berrigan et al. 1991). The 
impact of competition for settlement space in the Gulf 
of Mexico has not been fully determined (Berrigan et al. 
1991), but heavy sets of barnacles can seriously re- 
duce the area of hard surface available to settling 
oysters (Ingle 1951). Young oysters can also be 
smothered by the excreta from polychaete worms 
(Polydora sp.) (Stanley and Sellers 1986). In some 
cases, these organisms have a purely commensal 
relationship with oysters, or do not seriously compete 
with them (Stanley and Sellers 1986, Berrigan et al. 
1991). 


Personal communications 

Van Hoose, Mark S. Alabama Division of Marine 
Resources, Dauphin Island, AL. 

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30 


American oyster, continued 


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31 


Atlantic rangia 


Rangia cuneata 
Adult 


2 cm 


(from Fischer 1978) 


Common Name: Atlantic rangia 

Scientific Name: Rangia cuneata 

Other Common Names: common rangia (Nelson et 

al. 1992); marsh clam (Burdon 1978); brackish water 

clam, road clam, wedge clam (LaSalle and de la Cruz 

1 985). 

Classification (Turgeon et al. 1988) 

Phylum: Mollusca 

Class: Bivalvia 

Order: Veneroida 

Family: Mactridae 

Value 

Commercial : The Atlantic rangia has been utilized for 
several thousand years along the Gulf coast, begin- 
ning with the Native Americans who made this clam a 
part of their diet (Tarver 1 972, Tarver and Dugas 1 973, 
LaSalle and de la Cruz 1 985). The commercial value 
of this clam in now mainly in the use of its shell (both 
fresh and fossil) in the manufacture of cement, glass, 
chemicals, chicken and cattle feed, wallboard and 
other building products, agricultural lime, road con- 
struction and as fill in nearshore oil exploration (Tarver 
and Dugas 1973, Arndt 1976, Fischer 1978). Rangia 
shell is also used as substrate to enhance oyster 
settlement in Florida and Louisiana (MacKenzie 1 996). 
Rangia are sometimes used for blue crab bait and 
some human consumption (Godcharles and Jaap 1 973, 
LaSalle and de la Cruz 1985). Preparations include 
chopped clam dishes, chowders, soups, and either raw 
on the half shell, or steamed with rice dishes (Fischer 
1978). It has also been canned occasionally for food 
products (Pf itzenmeyer and Drobeck 1 964, Tarver and 
Dugas 1973). Hand-collected rangia are sometimes 
brought to cannery processors and added to hard clam 
catches (Fischer 1978). 


Recreational : Recreational harvest of Atlantic rangia is 
not significant in Gulf of Mexico estuaries. 

Indicator of Environmental Stress The Atlantic rangia 
filter feeds on detritus, and is therefore susceptible to 
the accumulation of pollutants from the particles on 
which they feed. Because of this, they are commonly 
used for tests of toxicity and bioaccumulation of petro- 
leum products and by-products (Neff et al. 1976, Mo- 
rales-Alamo and Haven 1982, Ferrario et al. 1985, 
Jovanovich and Marion 1985, Bender et al. 1986), 
organochlorine insecticides (Lunsford and Blem 1 982), 
dioxins and furans from pulp mill effluent (Harrel and 
McConnell 1 995), and heavy metals (Olson and Harrel 
1973, Lytle and Lytle 1982, McConnell and Harrel 
1995). They have been used in the past to monitor 
radionuclides from radioactive debris resulting from 
atmospheric testing of nuclear weapons (Wolfe 1967, 
Wolfe and Schelske 1969). 

Ecological : The Atlantic rangia is an important compo- 
nent of estuarine ecosystems, and can account for a 
large portion of the benthic biomass in estuaries (Cain 
1975, LaSalle and de la Cruz 1985). This species is 
linked to primary producers and secondary consumers 
in estuarine areas, because they convert detritus and 
phytoplankton into biomass which can be utilized by 
many fishes, birds, and crustaceans (Tenore et al. 
1968, Hopkins and Andrews 1970, Cain 1975, Olsen 
1976a, LaSalle and de la Cruz 1985). 

Range 

Overall : The Atlantic rangia occurs along the U.S. 
Atlantic coast and in the Gulf of Mexico. Although there 
is an extensive range for this species in the fossil 
record, the present day range is more limited. Along 


32 


Atlantic rangia, continued 


Table 5.03. Relative abundance of Atlantic rangia in 
31 Gulf of Mexico estuaries (from Volume I). 


Life 


stage 


Estuary 


A S J L E 


Florida Bay 


Ten Thousand Islands 


Caloosahatchee River 


Charlotte Harbor 


Tampa Bay 


• 


• 


• 


• 


• 


Suwannee River 


® 


® 


® 


® 


® 


Apalachee Bay 


o 


O 


O 


o 


o 


Apalachicola Bay 


® 


® 


® 


® 


® 


St. Andrew Bay 


o 


o 


o 


o 


o 


Choctawhatchee Bay 


o 


o 


o 


o 


o 


Pensacola Bay 


o 


o 


o 


o 


o 


Perdido Bay 


® 


® 


® 


® 


® 


Mobile Bay 


® 


® 


® 


® 


® 


Mississippi Sound 


o 


o 


o 


o 


o 


Lake Borgne 


<§ 


® 


® 


® 


® 


Lake Pontchartrain 


® 


® 


® 


® 


® 


Breton/Chandeleur Sounds 


o 


o 


o 


o 


o 


Mississippi River 


o 


o 


o 


o 


o 


Barataria Bay 


® 


® 


® 


® 


® 


Terrebonne/Timbalier Bays 


® 


® 


® 


® 


® 


AtchafalayaA/ermilion Bays 


o 


o 


o 


o 


o 


Calcasieu Lake 


o 


o 


o 


o 


o 


Sabine Lake 


• 


• 


• 


• 


• 


Galveston Bay 


® 


® 


® 


® 


o 


Brazos River 


na 


na 


na 


na 


na 


Matagorda Bay 


o 


o 


o 


o 


o 


San Antonio Bay 


V 


V 


V 


V 


V 


Aransas Bay 


V 


V 


V 


V 


V 


Corpus Christi Bay 


V 


V 


V 


V 


V 


Laguna Madre 


Baffin Bay 


A S J L E 


Relative abundance: 

# Highly abundant 

® Abundant 

O Common 

V Rare 

blank Not present 

na No data available 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


the Atlantic coast, the Atlantic rangia is found from 
Chesapeake and Delaware Bays southward to Indian 
River, Florida. In the Gulf of Mexico, the Atlantic rangia 
is found from southwestern Florida to Texas, and to 
Alvarado, Veracruz, Mexico (Hopkins and Andrews 
1970, Andrews 1981, Godcharles and Jaap 1973, 
Fischer 1978, Fritz et al. 1990). 

Within Study Area : Along the U.S. Gulf coast, this 
species is found from the Corpus Christi Bay area to 
southwestern Florida, and is concentrated in brackish 
waters of Louisiana, particularly around Lake 
Pontchartrain, Maurepas, and Vermilion Bay (Table 
5.03) (Tarver 1972, Tarverand Dugas 1973, Andrews 
1 981 , LaSalle and de la Cruz 1 985). It is not common 
in the south Florida and south Texas estuaries, which 
have relatively high salinities (Nelson et al. 1992). 

Life Mode 

Eggs and larvae are known to have a brief planktonic 
and pelagic existence (Fairbanks 1 963, LaSalle and de 
la Cruz 1985). Juveniles and adults are semi-sessile 
estuarine benthic infauna capable of burrowing through 
sediments, and they typically have only a small portion 
of the shell protruding from the substrate. Juveniles 
and adults are generally restricted to shallower water 
along bay margins, presumably due to the concentra- 
tion of free-swimming larvae by wave action where the 
metamorphosis to a benthic existence occurs. 

Habitat 

Ty pe: All stages are found in river-influenced brackish 
water (riverine-oligohaline) and in subtidal oligohaline 
to polyhaline estuarine waters. This clam prefers a 
combination of low salinity, high turbidity, and a sub- 
strate of sand, mud and vegetation (LaSalle and de la 
Cruz 1985). 

Substrate : Juvenile and adult stages occur in soft 
sediments of sand and mud (Tarver 1 973, Godcharles 
and Jaap 1973, LaSalle and de la Cruz 1985). Larger 
sized Atlantic rangia tend to inhabit sandy bottom 
areas, suggesting that larger sized particles trap more 
food; sandy substrates facilitate burrowing, and excre- 
tory products do not accumulate (Tarver and Dugas 
1972). Sandy sediments of high organic content and 
phosphate are more favorable for growth and survivor- 
ship than silt/clay sediments that are also high in 
organic matter and phosphate (Tenore et al. 1968). 
There is also evidence that larvae settle preferentially 
in sandy versus silty substrate, and that they prefer 
substrate with some organic content (Sundberg and 
Kennedy 1993). In the Trinity River delta, Texas, 
Rangia isfound in soft mud-clay-silt substrates (Baldauf 
1970). The sediments that Rangia resides in can 
result in shell erosion and ultimate mortality because of 
the presence of acids formed in the breakdown of 


33 


Atlantic rangia, continued 


detritus. Fairbanks (1963) noted substantial shell 
erosion of rangia along the north shore of Lake 
Pontchartrain, due to the presence of carbonic acids 
produced by carbon dioxide reacting with high concen- 
trations of organic matter. 

Physical/Chemical Characteristics 
Temperature: Optimum conditions for embryos stud- 
ied in the laboratory are 18°-29°C (Cain 1973). The 
planktonic existence of larvae is greatly extended by 
low temperatures; larvae at survive 8° to 32°C, and 
growth is fastest at 20° to 32°C (Cain 1 973, Cain 1 974, 
LaSalle and de la Cruz 1985). Temperatures above 
35°C are known to be lethal to larvae. Survival has 
been observed at temperatures as high as 40°C for 
small and medium sized animals acclimated to sum- 
mer conditions (Lane 1986). The upper lethal limit 
(LT50) for large individuals was 38°C. A temperature 
of 36°C will begin causing mortalities after 3 days. 

Salinity: Embryos and larvae cannot tolerate pure fresh 
water (0% o ) (Cain 1972, Cain 1973, Cain 1974). Opti- 
mal salinities for embryos range from 6 to 10% o , with 
eggs surviving as low as 2%o. Larvae survive in 
salinities ranging from 2 to 20% o , and growth is fastest 
at 10 to 20% o . Juvenile and adult Atlantic rangia can 
tolerate a wide range of salinities, generally from to 
25%o, and have reported to be capable of living in fresh 
water (<0.3%o) for a period of at least 7 months (Hopkins 
and Andrews 1970) by osmoregulating with inorganic 
and intracellular free amino acids to control cell vol- 
umes (Anderson 1 975, Otto and Pierce 1 981 ). Uptake 
of osmotically active glycine from the environment 
increases as salinity increases, and when salinities 
drop below 5%o, the glycine is rapidly converted into 
protein. Spawning becomes physiologically impos- 
sible if salinities are <1%o or >15%o for long periods 
(Otto and Pierce 1981). 

Dissolved Oxygen (DO): This species is tolerant of 
temporary anoxic conditions (LaSalle and de la Cruz 
1985, Lane 1986). Individuals have survived a maxi- 
mum of 6.5 days in waters with ppm oxygen; how- 
ever, they are intolerant of exposure to air. 

Movements and Migrations : Planktonic egg and larval 
stages may be transported by tidal and river currents. 
Larvae are presumed to be negatively phototropic and 
are expected to be associated with the bottom of 
shallow bay margins. Juveniles and adults are seden- 
tary with only the posterior end and siphons slightly 
exposed, and limited capability of vertical movement 
through the sediments. Captive specimens have been 
observed to only move toward the sediment surface 
when covered by sand (Fairbanks 1963). Attached 
organisms (barnacles, mussels and algae) indicate a 
stationary position for long periods of time (Fairbanks 


1963, LaSalle and de la Cruz 1985). Although juve- 
niles and adults do not migrate, they are easily trans- 
ported by shifting water currents because of their small 
mass (LaSalle and de la Cruz 1985). 

Reproduction 

Mode : Reproduction is primarily sexual with separate 
sexes (gonochoristic), but there are rare cases of 
hermaphroditism (Olsen 1976b). Fertilization is exter- 
nal with the gametes released directly into the water. 

Spawning : The initiation of gametogenesis in the spring 
and early summer is typically triggered by a rise in 
water temperature to approximately 10°-16°C (Cain 
1 975, Jovanovich and Marion 1 985). Fairbanks (1 963) 
identified two distinct periods of spawning per year in 
Louisiana; a spring spawn (March-May) and a less 
intense period from late summer to November. In most 
areas Rangia spawn from March to May and late 
summer to November, but it may be continuous from 
March to November. Wolfe and Petteway (1 968) found 
spawning to occur from July to November with a peak 
in September in North Carolina. Ripe gametes have 
been reported July through November in Florida (Olsen 
1976b) and from early summer through October with 
fall peaks in Alabama (Jovanovich and Marion 1985). 
Heavy spawning is associated with a rapid increase or 
decrease in salinity of approximately 5%o (Cain 1 975). 
Spawning has also been stimulated in the laboratory at 
other temperatures and salinities by adjusting water 
conditions and introducing male gametes (Chanley 
1965, Cain 1973). Gametes are released through the 
exhalent siphon by both sexes (Sundberg and Kennedy 
1992). 

Fecundity : There is little available information on fe- 
cundity of Atlantic rangia (LaSalle and de la Cruz 
1985). 

Growth and Development 

Egg Size and Embryonic Development Egg develop- 
ment is oviparous. In laboratory studies, fertilized eggs 
(69 urn) have developed into ciliated blastulae 3 hours 
after fertilization (AF), and into pelagic trochophore 
larvae by 1 2 hours AF at 23° to 26°C (Fairbanks 1 963, 
Sundberg and Kennedy 1992). A similar study by 
Fairbanks (1963) described these developmental 
stages as occurring in older larvae than Sundberg and 
Kennedy (1 992) despite their being reared at the same 
temperature. This may have been due to his use of 
stripped eggs and sperm instead of naturally spawned 
gametes (Sundberg and Kennedy 1992). 

Age and Size of Larvae : The length of the larval period 
is dependent on temperature and food, but generally is 
short lived (Fairbanks 1963). In a laboratory study, 
trochophore larvae developed to the veliger stage (93 


34 


Atlantic rangia, continued 


(im) in 8 hours. Shelled larvae develop within 24 hours 
of fertilization (Chanley 1965, Sundbergand Kennedy 
1 992). Larval sizes range from 75-203 urn depending 
on the specific stage. These stages are extremely 
fragile and may not be picked up in normal larval 
sampling efforts. 

Juvenile Size Range : In laboratory studies, larval settle- 
ment and metamorphosis to the juvenile stage oc- 
curred after 6 or 7 days at a size of 175-180 |im 
(Chanley 1965, Sundberg and Kennedy 1992, 
Sundberg and Kennedy 1993). Field studies, how- 
ever, indicate a size at settlement of 300-400 urn 
(Fairbanks 1963, Cain 1975). Growth of juveniles is 
1 5-20 mm in the first year, 5-9 in the second and 4-5 in 
the third year (Fairbanks 1963). The growth rate of 
Atlantic rangia can be significantly inhibited by sus- 
pended solids above the substratum, and suspended 
solids tend to influence growth more so than the actual 
substrate (Fairbanks 1963). 

Age and Size of Adults : Size at sexual maturity ranges 
from 1 4 mm (Cain 1 972) to 24 mm (Fairbanks 1 963) in 
length, and is reached in 2-3 years (Fairbanks 1963). 
A maximum length of 7 cm has been recorded, and 
sizes to 5 cm are common (Fischer 1 978). A confirmed 
life span for this species has not been determined 
(LaSalle and de la Cruz 1985). Estimates range from 
4-5 years to a maximum of 15 years. 

Food and Feeding 

Trophic Mode : This species is a nonselective filter 
feeder. It controls food movement with the gill palps 
and ciliary currents over the gills (Darnell 1 958, Olsen 
1976a, LaSalle and de la Cruz 1985). 


catfish, blue catfish (Ictalurus furcatus), freshwater 
drum {Aplodinotus grunniens), spot, Atlantic croaker, 
black drum, sheepshead, pinfish, striped blenny 
(Chasmodesbosquianus), southern flounder, and sand 
seatrout. Invertebrate predators include white shrimp, 
Ohio shrimp (Macrobrachium ohione), blue crab, Har- 
ris mud crab (Rhithropanopeus harrisit), moon snails 
(Po//n/cesspecies), and oyster drill {Thais haemastoma) 
(Darnell 1958, Tarverand Dugas 1973, Levine 1980, 
LaSalle and de la Cruz 1 985). A potential predator of 
Atlantic rangia larvae are ctenophores, such as 
Mnemiopsis, which sometimes are abundant in estua- 
rine waters (LaSalle and de la Cruz 1985). 

Factors Influencing Populations Winter kills in the 
northern portion of the Atlantic rangia's range indicate 
that it has reached the limit of its temperature tolerance 
there (LaSalle and de la Cruz 1 985). Sporocysts and 
cercarial larvae, intermediate trematode stages of the 
fish intestinal parasite Cercaria rangiae, have been 
described from Rangia'm Galveston Bay, Texas (Wardle 
1 983); sporocysts concentrate in the gonadal tissue of 
the clam causing castration. Anthropogenic changes 
in river discharge patterns can result in flow regimes 
that can either enhance Rangia populations or cause 
their declines (Harrel 1993). Channelization of rivers 
may result in saltwater intrusions that produce favor- 
able brackish water conditions in what was once a 
freshwater habitat. Increased reservoir discharges 
into a river can flush saltwater from an estuary, reduc- 
ing Rangia abundance. Waste discharge into rivers 
can create toxic or anoxic conditions that also ad- 
versely affect Rangia. 

Personal communications 


Food Items : Food of the Atlantic rangia consists of 
diatoms, algae and detritus, with detritus comprising 
the greatest portion (Darnell 1 958, Olsen 1 976a, LaSalle 
andde la Cruz 1985). 


Harrel, Richard C. Lamar Univ., Dept. Biology, Beau- 
mont, TX. 

References 


Biological Interactions 

Predation : Atlantic rangia are preyed upon by fish, 
crustaceans, molluscs, and ducks (LaSalle and de la 
Cruz 1985). This species appears to be important to 
the diet of the migratory ducks, such as lesser scaup 
duck (Aythya affinis), greater scaup duck (Aythya 
mania), ring-neck duck (Aythya collaris), American 
black duck (Anas rubripes), mallard (Anas 
platyrhynchos), and the ruddy duck (Oxyura 
jamaicensis), and may be replaced in their diet under 
more saline conditions by the dwarf surfclam (Mulinia 
lateralis) (Tarver and Dugas 1973, LaSalle and de la 
Cruz 1985). Fishes that are known to prey on rangia 
include Atlantic stingray (Dasyatis sabina), spotted gar 
(Lepisosteus oculatus), alligator gar (L. spatula), 
longnose gar (L. osseus), gizzard shad, hardhead 


Anderson, J. W. 1975. The uptake and incorporation 
of glycine by the gills of Rangia cuneata (Mollusca: 
Bivalvia) in response to variations in salinity and so- 
dium. In Vernberg, F.J. (ed.), Physiological ecology of 
estuarine organisms, p. 239-257. Univ. South Carolina 
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Andrews, J. 1981. Texas shells, a field guide. Univer- 
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Arndt, R.H. 1976. The shell dredging industry of the 
gulf coast region. In Bouma, A. (ed.), Shell Dredging 
and its Influence on Gulf Coast Environments, Gulf 
Publishing Co., Houston, TX, p. 13-48. 


35 


Atlantic rangia, continued 


Baldauf, R.J. 1970. A study of selected chemical and 
biological conditions of the lower Trinity River and the 
upper Trinity Bay. Water Resources Institute, Texas 
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Barnes, R.D. 1987. Invertebrate Zoology. Saunders 
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37 


Mercenaria species 
Adult 


2 cm 


(from Goode 1884) 


Common Name: hard clam 
Scientific Name: Mercenaria species 
Other Common Names: Quahog, hard-shelled clam, 
littleneck, cherrystone clam, chowder clam (Stanley 
1985);pra/redusi7d(French),a/meyaGfe/sur(Spanish) 
(Fischer 1978). Mercenaria mercenaria is known as 
northern quahog, and M. campechiensis as southern 
quahog (Turgeon et al. 1988). Andrews (1979) refers 
to M. campechiensis as southern quahog, and subspe- 
cies M. campechiensis texana as Texas quahog. 
Classification (Turgeon et al. 1988) 
Phylum: Mollusca 
Class: Bivalvia 
Order: Veneroida 
Family: Veneridae 

Value 

Commercial : Although hard clams support a significant 
commercial fishery in the United States as a whole, the 
gulf coast of Florida supports only a very limited hard 
clam fishery (Schroeder 1924, Taylor and Saloman 
1 969). There was a substantial fishery in Florida's Ten 
Thousand Islands until the 1930's, and clams were 
taken to Key Westforcanning (Schroeder 1 924, Marelli 
pers. comm.). During 1992, 27.7 metric tons (mt) of 
hard clam meat valued at $64,000 was landed, on 
Florida's Gulf coast (Newlin 1993). No landings are 
reported for other Gulf coast states. The season for 
clams harvested in Florida is regulated, and harvest is 
restricted to approved shellfish areas (GSMFC 1993). 
Dredges can be used for harvest on private leases after 
posting a $3000 bond and securing a Special Activity 
License. The minimum allowable harvest size for 
clams is 7/8 inch (2.22 cm). In Texas, a commercial 
mussel and clam fisherman's license is required to 
commercially harvest hard clams (TPWD 1993). Har- 


vest is open year-round, but only from water approved 
by the State Commissioner of Health. The traditional 
and most popular method of harvesting hard clams has 
been by rakes or tongs (Eversole 1987). In North 
Carolina, they are harvested by "kicking" which uses 
the wash from a boat propeller to dislodge clams from 
the substrate. An otter trawl is towed behind the boat 
to collect the clams. 

Recreational : Hard clams are sometimes taken for 
home consumption by recreational fishermen. There 
is a significant recreational fishery for hard clams in the 
Tampa Bay area (Kunneke and Palik 1 984, Killam et al. 
1992). The bag limit in Florida is two bushels per 
person or boat (whichever is less) per day (GSMFC 
1993, Arnold pers. comm). Harvesting is done mostly 
by hand picking or treading. 

Indicator of Environmental Stress : Hard clams, like 
other bivalves, are used to study the uptake and 
bioaccumulation of heavy metals and toxic organic 
chemicals (Boehm and Quinn 1977, Moore 1985, 
Byrne 1989, Laughlin et al. 1989, Long et al. 1991). 
Because of their filter feeding life mode and benthic 
habitat, the presence of such compounds in clam 
tissues can be indicative of poor water quality and 
environmental stress (Eversole 1987). Evidence of 
past geologic events can be traced through fossil shell 
remains (Parker 1955, 1956). 

Ecological : Hard clams provide a food source to bot- 
tom feeding fishes and invertebrates. Their larval 
stages also provide food for larval and early juvenile 
fishes. Through their suspension feeding activities 
hard clams help to transfer phytoplankton primary 
productivity to the higher trophic levels within the 


38 


Hard clam, continued 


Table 5.04. Relative abundance of hard clam in 31 

Gulf of Mexico estuaries (Nelson et al. 1 992, Marelli 

pers. comm.). 

Life stage 


Estuary 


A S J L E 


Florida Bay 


Ten Thousand Islands 


O 


O 


o 


o 


o 


Caloosahatchee River 


Charlotte Harbor 


O 


O 


o 


o 


o 


Tampa Bay 


o 


O 


• 


o 


o 


Suwannee River 


o 


O 


o 


o 


o 


Apalachee Bay 


^o 


O 


o 


o 


o 


Apalachicola Bay 


St. Andrew Bay 


o 


o 


o 


o 


o 


Choctawhatchee Bay 


o 


o 


o 


o 


o 


Pensacola Bay 


Perdido Bay 


~o\ 


V 


V 


V 


V 


Mobile Bay 


JJ 


V 


V 


V 


V 


Mississippi Sound 


o 


o 


o 


o 


o 


Lake Borgne 


Lake Pontchartrain 


Breton/Chandeleur Sounds 


o 


o 


o 


o 


o 


Mississippi River 


Barataria Bay 


o 


o 


o 


o 


Terrebonne/Timbalier Bays 


V 


V 


V 


V 


V 


Atchafalaya/Vermilion Bays 


Calcasieu Lake 


Sabine Lake 


Galveston Bay 


o 


o 


o 


o 


o 


Brazos River 


na 


na 


na 


na 


na 


Matagorda Bay 


o 


o 


o 


o 


o 


San Antonio Bay 


o 


o 


o 


o 


o 


Aransas Bay 


o 


o 


o 


o 


o 


Corpus Christi Bay 


o 


o 


o 


o 


o 


Laguna Madre 


Baffin Bay 


A S J L E 


Relative abundance: 

# Highly abundant 
® Abundant 
O Common 
V Rare 
blank Not present 
na No data available 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


estuarine food web (Eversole 1987). 

Range 

Overall : Mercenaria campechiensisoccurs from Cape 
May, NJ, to the Yucatan Peninsula, most abundantly 
on Florida's Gulf coast. Populations inhabiting the 
muddier environments of the northern Gulf of Mexico 
are now recognized under the subspecific name M. 
campechiensls texana (Dillon and Manzi 1989b). 
Mercenaria mercenaria naturally ranges from Prince 
Edward Island, Canada, to the Atlantic coast of Florida, 
intertidally and subtidally to 1 5 m in estuaries and bays. 
It generally inhabits shallower waters of lower salinity 
than M. campechiensis. A hybrid zone between the 
two species occurs in the Indian River lagoon on 
Florida's Atlantic coast (Dillon and Manzi 1989a, Bert 
et al. 1 993, Bert and Arnold 1 995). Although probably 
not native to the Gulf of Mexico, M. mercenaria may 
have been locally introduced by aquaculture interests 
(Dillon pers. comm.). Populations of hard clams have 
also been introduced to the British Isles, parts of 
France, and California (Taylor and Saloman 1968, 
Abbott 1 974, Kunneke and Palik 1 984, Eversole 1 987). 

The most reliable physical character distinguishingM. 
mercenaria from M. campechiensis through most of 
their range is the strength of the ridges on their shells. 
M. mercenaria typically has thin, easily-eroded ridges, 
best adapted for life in silty mud. M. campechiensishas 
thick, resistant ridges, that seem adapted for coarse 
substrates, especially carbonate sands. A subspecies 
M. campechiensis texanahas been described from the 
northern Gulf of Mexico, which unlike typical M. 
campechiensis, has thin ridges (Dillon pers. comm.). 
This makes sense, as the northern Gulf contains 
substantial areas of silty mud substrate. However, 
these clams are considered a subspecies of M. 
campechiensis, in spite of their external morphological 
similarities to M. mercenaria. 

Within Study Area : Within U.S. estuaries of the Gulf of 
Mexico, M. campechiensis is found from south Florida 
to Texas. Hard clams are widely distributed, but not 
generally abundant in the nearshore waters of the Gulf 
coast states (Table 5.04). 

Life Mode 

Hard clam eggs and early larval stages are planktonic. 
The last larval stage (plantigrade) is semi-benthic 
alternating between swimming and crawling in search 
of a suitable settlement site. Juveniles and adults are 
semi-sessile benthic infauna capable of burrowing 
through sediments (Eversole 1987). 

Habitat 

Type : All life stages are estuarine or marine. Hard 
clams usually occur in dense groups in coastal bays, 


39 


Hard clam, continued 


sounds, and estuaries from intertidal zones to a depth 
of 15 m or more. Although they occur in the open 
ocean, hard clams appear to prefer relatively shallow 
waters (Killam et al. 1 992). They are typically found in 
waters less than 10 m deep (Sims and Stokes 1967, 
Taylor and Saloman 1 970, Godcharles and Jaap 1 973a, 
Godcharles and Jaap 1 973b, Killam et al. 1 992). Hard 
clams have been collected from grass flats on the 
shoreward side of barrier islands (Christmas and Lan- 
gley 1973, Craig and Bright 1986), and near oyster 
reefs (Swingle 1 971 ). In northern latitudes, Mercenaria 
campechiensis may generally occur in deeper waters 
with higher salinities (Eversole 1987) than does M. 
mercenaria. 


Temperature - Juveniles and Adults: Juveniles and 
adults can tolerate temperature extremes ranging from 
<0° to greater then 35°C (Eversole 1987). The upper 
lethal temperature of the hard clam is 45.2°C 
(Henderson 1 929), but temperatures above 30°C may 
alterclam behavior and physiology (Savage 1 976, Van 
Winkle et al. 1 976). Growth is negligible at <1 0°C and 
increases with rising temperatures to an optimum of 
about 20° to 23°C (Pratt and Campbell 1956). Opti- 
mum growth temperatures for Mercenaria 
campechiensis texana are from 15° to 35°C (Craig et 
al. 1988). In Florida, growth of M. campechiensis is 
optimal from 15° to 25°C, but is reduced at tempera- 
tures above 25°C. 


Substrate : Substrate appears to play an important role 
in distribution and growth (Wells 1 957, Craig and Bright 
1 986, Coen and Heck 1 991 ). Late larval stages attach 
to hard substrates with byssal threads. If no hard 
substrate is available, they attach to sediment par- 
ticles. Juvenile and adult clams occur primarily in soft 
bottom habitats of mud and sand. In one laboratory 
experiment, settling pediveligers were reported to pre- 
fer sand particles over mud (Keck et al. 1 974). Highest 
natural densities of clams occur in sand with coarse 
shell sediments, which provide spatial refugia so that 
the juvenile clams are better protected from predation 
(Wells 1 957, Walker et al. 1 980, Craig and Bright 1 986, 
Killam et al. 1992). Overall, hard clams can utilize a 
variety of unconsolidated substrates: firm sand, silty 
sand, sand/mud, sand/shell, sand/gravel, mud/sand/ 
gravel, and frequently near seagrasses and algae. 
Hard clams are rare on fine silt and clay bottoms (Pratt 
1 953, Saloman and Taylor 1 969, Taylor and Saloman 
1970, Godcharles and Jaap 1973a, Godcharles and 
Jaap 1973b, Kunneke and Palik 1984). 

Physical/Chemical Characteristics : 
Temperature - Eggs and Larvae: Spawning occurs 
generally from 22° to 30°C, with maximum spawning 
activity found between 24° to 26°C (Loosanoff 1937c, 
Carriker 1 961 ). Egg survival is high between 1 8° and 
28°C (Kennedy et al. 1974, Wright et al. 1983). Egg 
mortality at low (15°C) and high (33°C) temperatures 
may be reduced through acclimation (Loosanoff et al. 
1 951 ). Larvae can tolerate temperatures ranging from 
approximately 13° to greater than 30°C with growth 
rates increasing with an increase in temperature 
(Loosanoff et al. 1951, Davis and Calabrese 1964, 
Wright et al. 1983). Maximum larval growth generally 
occurs between 22° and 33°C depending on the salin- 
ity (Davis and Calabrese 1964, Lough 1975). The 
range of temperatures tolerated by larvae is reduced 
as salinity decreases (Eversole 1987). As tempera- 
tures approach 40°C larval mortality increases (Wright 
etal. 1983). 


Salinity - Eggs and Larvae: Egg development occurs at 
salinities of 20 to 33%o (Davis 1958). The optimum 
salinity for egg development to the straight hinged 
larval stage is approximately 27 to 28%o with metamor- 
phosis occurring at a minimum of 1 7.5% (Davis 1 958, 
Davis and Calabrese 1964, Castagna and Chanley 
1973). 

Salinity - Juveniles and Adults: Juveniles can tolerate 
salinities as low as 1 2 to 1 5%o, but death usually occurs 
at <1 0% o within several weeks (Chanley 1 958, Castagna 
and Chanley 1 973). The optimum salinity for growth is 
approximately 24 to 28%o (Chanley 1958). Optimum 
growth salinities for Mercenaria mercenaria texana are 
22 to 33%o, probably with no growth occurring below 
20% o (Craig et al. 1988). In the Indian River, Florida, 
hard clams are reported to do well in salinities above 
20%o (Arnold et al. 1991, Arnold et al. 1996). During 
periods of stress, such as sudden extreme changes in 
water salinity, hard clams can close their shells tightly 
and respire anaerobically (Lutz and Rhoads 1977, 
Eversole 1987). 

Turbidity: Hard clams prefer clear water in Tampa Bay 
(Kunneke and Palik 1984); secchi disc values range 
from 0.9 to 3.7 m in one study (Godcharles and Jaap 
1973b). Reduced survival has been noted at high 
turbidity (Loosanoff 1962). Eggs and larvae develop 
normally at silt concentrations of <0.75 g/l, but no egg 
development occurs at silt concentrations of 3.0 to 4.0 
g/l. Larval growth is retarded at 1.0 to 2.0 g/l and is 
negligible at 3.0 to 4.0 g/l (Davis 1 960). Huntington and 
Miller (1 989) found larval growth decreased only at the 
highest experimental levels of sediment load (2,200 
mg/l), but survival remained unaffected. Silt concen- 
trations can also influence growth of juvenile clams. 
Juveniles (9 mm) are not affected by sediment concen- 
trations of 25 mg/l, but experience a 16% reduction in 
growth at 44 mg/l of silt (Bricelj et al. 1984). Water 
currents are important to the growth and survival of 
hard clams by removing silts that would otherwise 
accumulate and produce undesirable soft sediments 


40 


Hard clam, continued 


(Killam et al. 1992). In addition, currents are also 
important for providing food, maintaining acceptable 
water quality, removing biodeposits, and transporting 
eggs and larvae. 

Dissolved oxygen (DO): One hundred percent egg 
mortality occurs at oxygen concentrations of 0.2 part 
per million (ppm). Embryos from Long Island Sound, 
New York develop normally at 0.5 ppm and above, and 
larval growth is lower at 2.4 ppm than at 4.2 ppm 
(Morrison 1971). However, larvae from Indian River 
Bay showed no significant differences in growth and 
survival when exposed to hypoxic conditions, but a 
decrease of growth was observed in larvae subjected 
to hyperoxic conditons (13.7 ppm) (Huntington and 
Miller 1 989). In Tampa Bay hard clams were found in 
oxygen saturation conditions, while from Charlotte 
Harbor they are taken at 4.6 to 9.6 parts ppm (mean = 
6.6 ppm), and at 4.0 to 7.8 ppm (mean = 5.8 ppm) from 
the Ten Thousand Island area (Taylor and Saloman 
1970, Godcharles and Jaap 1973b). 

pH: Normal development of embryos occurs between 
a pH of 7.00 and 8.50. Optimum larval growth occurs 
between pH 7.50 and 8.00 with a minimum of 6.25 and 
a maximum of 8.75. The pH must be greater than 7.0 
for successful recruitment of juveniles to occur 
(Calabrese and Davis 1966, Calabrese 1972). 

Migrations and Movements : Egg and larval stages are 
subject to tidal action and currents. Larvae are capable 
of migrating vertically throughout the water column to 
retain themselves in the estuary. Pediveliger larval 
stages crawl and swim in search of a settlement site. 
Juveniles and adults exhibit limited horizontal and 
vertical movement through the sediment, but do not 
migrate extensive distances (Eversole 1987). Upon 
removal from the sediment in Narragansett Bay, hard 
clams less than 83 mm in valve length (VL) are able to 
reburrow within a week (Rice et al. 1 989). Hard clams 
exceeding 83 mm VL demonstrate the least capability 
of reburrowing. 

Reproduction 

Mode : Hard clams are protandrous hermaphrodites 
which release their gametes into the water column for 
external fertilization. Mercenaria mercenaria exhibit 
consecutive hermaphroditism, passing through a pre- 
adult sexual phase at around 6-7 mm shell length. 
Individuals usually function as males during the pri- 
mary sexual phase, but their gonads have both male 
and female sex cells. The primary sex phase lasts 
throughout the first year. Following the primary sex 
phase, the clams experience a permanent sex change 
after which the male-female ratio changes to 50:50, 
and they will function primarily as male or female 
(Loosanoff 1937a, Merrill and Tubiash 1970, Walker 


and Stevens 1989). Subsequent reproductive efforts 
are sexual with separate male and female sexes 
(gonochoristic), with rare instances of hermaphrodit- 
ism. Mercenaria campechiensis also tends to be 
protandric in its development (Dalton and Menzel 
1983). Clams in the 60 mm size class have been 
reported as the most reproductively active (Belding 
1912), but there appears to be no evidence of repro- 
ductive senescence in larger, older clams (Peterson 
1983). 

Spawning : Spawning occurs generally from 20° to 
30°C, with maximum spawning activity found between 
24° to 26°C (Loosanoff 1937c, Carriker 1961, 
Hesselman et al. 1989), in the marine and estuarine 
subtidal seawater zone (Dalton and Menzel 1983). 
Spawning activity has bimodal annual peaks in the 
more southern portion of the hard clam's range, such 
as the Gulf of Mexico (Eversole 1 987). In Florida, these 
peaks occur in the spring (February-June) and fall 
(September-December) with spawning beginning in 
February-March and ending in October (Dalton and 
Menzel 1983). In the Tampa Bay area, spawning 
occurs during April and continues to August (Belding 
1912, Kunneke and Palik 1984, Hesselman et al. 
1989). Temperature influences gonadal development 
(Loosanoff 1937b, Porter 1964), and spawning may 
occasionally occur all year in warmer parts of the hard 
clam's range such as Florida (Dalton and Menzel 1 983, 
Hesselman et al. 1 989). When the water temperature 
averages >30°C gametogenesis is inhibited and spawn- 
ing ceases (Hesselman et al. 1989). In addition to 
climatic influences, spawning frequency may also be 
differently influenced by genetic factors in different 
populations of hard clam (Knaub and Eversole 1988). 
Spawning appears to coincide with high algal concen- 
trations during spring, fall and winter, allowing ample 
food resources for larval stages (Heffernan et al. 1 989). 
Gametes are broadcast into the water column, and 
fertilization is external (Belding 1912, Loosanoff 1 937b, 
Kunneke and Palik 1984, Eversole 1987). 

Fecundity : Egg production estimates range from 2-3 
million all the way up to 39.5 million per individual for an 
entire spawning season (Davis and Chanley 1956, 
Ansell 1967, Bricelj and Malouf 1980) with up to 24.3 
million eggs reported in a single spawn (Davis and 
Chanley 1956). Fecundity is directly related to clam 
size (Bricelj and Malouf 1980, Peterson 1983), and 
reported differences may be due to clam size and 
condition at time of spawning. 

Growth and Development 

Egg Size and Embryonic Development : Hard clam 
eggs develop oviparously. Unfertilized eggs range 50- 
97 urn in diameter (Carriker 1961, Bricelj and Malouf 
1980). A gelatinous envelope surrounds the egg 


41 


Hard clam, continued 


bringing the egg diameter up to approximately 1 25 \im. 
The gelatinous envelope imbibes water causing the 
egg to swell, providing buoyancy to the egg and further 
increasing the diameter to 270 u.m (Carriker 1961). 
Lipids stored in the egg provide energy and nutrients to 
the embryo, and are important to the embryo's devel- 
opment and survival (Lee and Heffernan 1991). Egg 
cleavage begins within 30 minutes of fertilization at 
27°-30°C and after 10 hours a ciliated gastrula has 
developed. The ciliated blastula emerges from the 
gelatinous egg and becomes a trochophore larva 
(Carriker 1961). 

Age and Size of Larvae : The first two larval stages, the 
trochophore and early veliger stages (85-90 u.m), are 
non-shelled and possess a ciliated velum for propul- 
sion (Carriker 1961 , Eversole 1987). By day 1 the first 
shelled stage, the straight hinged veliger, develops 
ranging in size from 90-140 urn. By day 3 the second 
shelled stage, the umboed veliger, develops. The 
umboed veliger stage may last 3 to 20 days, depending 
on water temperature and food availability, and ranges 
in size from 140 to 220 urn in length. The pediveliger 
stage follows lasting 6 to 20 days with a size range of 
170 to 220 |im. The pediveliger possesses a strong 
ciliated velum and foot that allow the larvae to swim and 
crawl in search of a suitable settlement site. At 200-230 
|im the velum is lost, and the newly settled plantigrades 
are referred to as spat. The spat use byssal threads to 
attach and detach from various substrates. For ap- 
proximately 2 weeks the spat alternate between crawl- 
ing and attaching to substrates. By 7-9 mm the byssal 
gland is lost and the juvenile plantigrade settles perma- 
nently to its benthic existence (Carriker 1 961 , Eversole 
1987). 

Juvenile Size Range : Juvenile growth is influenced by 
temperature, food availability, siphon nipping, and type 
of substrate (Pratt 1953, Pratt and Campbell 1956, 
Loosanoff and Davis 1963, Coen and Heck 1991, 
Coen et al. 1 994). Growth is more rapid in smaller hard 
clams, and most of it occurs during the initial several 
years of life, particularly the first year (Eversole et al. 
1986, Jones et al. 1990). Thereafter, the growth rate 
declines progressively with age (Gustafson 1955). 
Growth may be affected by substrate and current 
regime more than increased exposure time at low tide 
(Walker 1989). In Florida, Menzel (1961) found that 
Mercenaria campechiensisgrevj most during the spring 
through fall months with little growth occurring during 
winter. In contrast, M. mercenaria grew in spring and 
fall with very little growth in summer or winter, which 
agreeswith later work by Peterson etal. 1983, Peterson 
et al. 1985, and Jones et al. 1990. Growth rates of M. 
mercenaria imported into Texas remained different 
from native M. campechiensis texana which showed 
little growth occurring during summer (Craig et al. 


1988). Growth rates in M. campechiensis exceed 
those of M. mercenaria and their hybrids. Taylor and 
Saloman (1968) reported average growth of Tampa 
Bay hard clams over a four year period as age I - 50 
mm, age II - 73 mm, age 111-81 mm, and age IV - 90 mm. 
Growth is rapid and variable through the first three 
years and clams generally reach 50% of adult maxi- 
mum size. M. campechiensis reaches a commercially 
marketable size of 45 mm within 1 .5 to 2 years (Peterson 
et al. 1983, Kunneke and Palik 1984, Eversole et al. 
1986, Eversole 1987). Juvenile M. mercenaria were 
found to reach marketable size faster at lower stocking 
densities than those stocked at higher densities (Rice 
et al. 1989, Eversole et al. 1990). Those planted in 
subtidal areas also grew faster than clams in intertidal 
areas. By five years M. campechiensis reach 70% of 
their maximum size (Taylor and Saloman 1969). Hy- 
brid clams exhibit a growth rate greater than northern 
hard clams (Chestnut et al. 1 956, Haven and Andrews 
1 957, Menzel 1 964, Loosanoff and Davis 1 963, Taylor 
and Saloman 1969). Overall growth rates of southern 
populations of hard clams are more rapid than those of 
northern populations; however, populations in the south 
do not appear to live as long (Jones etal. 1990). Size 
appears to determine sexual maturity more than age 
does (Quayle and Bourne 1972, Eversole 1987). 
Maturity is achieved at approximately 30-40 mm in 
length at an age of 1 to 2 years depending on environ- 
mental conditions (Eversole et al. 1980, Bricelj and 
Malouf 1980). 

Age and Size of Adults : Hard clams in the Gulf of 
Mexico can live up to 28 years and maximum size can 
exceed 170 mm (Taylor and Saloman 1969, Kunneke 
and Palik 1984, Jones et al. 1990). On the Atlantic 
coast, two hard clams used in a growth experiment 
reached estimated ages of 33 and 36 years (Eversole 
1987). The annual mortality for clams raised under 
laboratory conditions is about 4% (Eversole et al. 
1986). The growth rate of hard clams decreases with 
increasing size and age (Eversole et al. 1986). 
Peterson's (1985) growth equation [length (in cm) = 
3.176 + 1.819 In (number of annual bands)] becomes 
a very poor predictor of age based on size after 4.5 
years. Growth rates for the hard clam also vary with 
geographical area (Jones et al. 1990). Growth in 
Florida Gulf of Mexico sites is most rapid in the spring. 

Food and Feeding 

Trophic Mode : Hard clams are selective, omnivorous 
filter-feeders, utilizing a siphon system to take in sus- 
pended particles and dissolved organics carried along 
in bottom currents (Eversole 1987). 

Food Items : Food is obtained from suspended par- 
ticles entering through the ventral inhalant siphon and 
passed to the gills. The particles are sorted in the gills, 


42 


Hard clam, continued 


and large particles are rejected. The rejected material 
is voided as pseudofeces through the inhalant siphon. 
The size range of particles ingested changes as the 
hard clam grows (Riisgard 1988). Food items include: 
marine diatoms, naked flagellates and other phytoplank- 
ton, protozoans, micro-crustaceans, larvae of other 
mollusks, rotifers, bacteria, and other zooplankton 
(Belding 1912, Loosanoff and Davis 1963, Eversole 
1987). 

Biological Interactions 

Predation : Predation is an important natural control of 
hard clam populations, and its impact is felt by all size 
classes (Killam et al. 1992). Blue crabs are a major 
predator of hard clams (Craig et al. 1988). Arnold 
(1 984) demonstrated the effects of blue crab predation 
in different substrates, with predation rates being higher 
in sand and sand/mud substrates. Clams greaterthan 
40 mm SL were not consumed, even by large crabs. 
Other predators include gastropods (oyster drills (Thais 
sp.), moon snails (Polinices duplicatus and Lunatia 
heros), and whelks (Busycon sp.)), starfish, stone 
crabs and other xanthid crabs, skates and rays, various 
bony fishes (sciaenids, puffers, flounders), and birds 
(Craig and Bright 1 986, Craig et al. 1 988, Bisker et al. 
1989, Killam et al. 1992). The fish species feed on 
juvenile seed clams, and in localized areas, skates and 
rays may be important predators (Killam et al. 1992). 
The importance of fish predation is minor, however, 
when compared with that of invertebrate predators. 
Starfish prey on both juvenile and adult hard clams. 
Small clams are attacked by individual starfish, but 
larger clams (>50 mm shell length) are usually at- 
tacked by several starfish. Several species of shore- 
birds prey on clams and other bivalves, however, their 
influence is restricted to hard clams exposed in the 
intertidal area. Herring gulls have been observed 
capturing hard clams, flying them up, and dropping 
them onto hard surfaces to break them open. Grass 
beds may serve as refuges from predation (Craig and 
Bright 1986, Coen and Heck 1991), although it has 
been suggested these areas can have higher preda- 
tion rates than bare areas (Coen and Heck 1991). 

Factors Influencing Populations : Recruitment success 
and predation are two of the factors most limiting to 
large populations in the Gulf of Mexico. The sub-lethal 
effects of siphon nipping by predators is known to 
impact growth (Coen et al. 1994). The oyster toadfish 
(Opsanus tau) reduces predation on juvenile hard 
clams from xanthid and portunid crabs by preying on 
these species in field experiments (Bisker et al. 1 989). 
Natural mortality decreases as clams reach sizes 
greater than 50 mm in length; however, fishing mortal- 
ity can become significant at this point (Eversole 1987). 
It has been noted that the settlement and survival of 
juveniles is enhanced in beds where abundance of 


large clams is low due to fishing pressure (Rice et al. 
1989). Possible reasons for this are the removal of 
competition and larviphagy from adults, and the distur- 
bance of sediment from fishing activities forming a 
more suitable substrate for settlement. A parasitic 
copepod, Ostrincola gracilis, occurs in the mantle 
cavity of the hard clam (Humes 1 953), but probably has 
little adverse impact on its host. Changes in the 
environment due to storm events can have either 
positive or negative effects on hard clam population 
(MacKenzie 1989). Storms can widen inlets that can 
lead to improved water circulation which can increase 
clam populations by increasing the water salinity. 
However, in some cases, wider inlets can cause swifter 
currents that sweep clam larvae out to sea or alter the 
sediment to a coaser less favorable texture. In the 
Indian River Lagoon of east central Florida, M. 
mercenaria x M. campechiensis hybrid clams have a 
high incidence of gonadal neoplasia, which may act as 
a barrier to gene flow, and reinforce reproductive 
isolation between the two species (Bert et al. 1993, 
Arnold pers. comm.). 

Personal Communications 

Arnold, W.S. Florida Marine Research Institute, St. 
Petersburg, FL. 

Dillon, Robert T. College of Charleston, Dept. Biology, 
Charleston, SC. 

Marelli, D. Florida Marine Research Institute, St. 
Petersburg, FL. 

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47 


Hard clam, continued 


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48 


Bay squid 


Lolliguncula brevis 
Adult 


2 cm 


(from Vecchione et al. 1989) 


Common Name: bay squid 

Scientific Name: Lolliguncula brevis 

Other Common Names: Atlantic brief squid (Turgeon 

et al. 1988), thumbstall squid (Andrews 1981); brief 

squid, short squid, least squid (Bane et al. 1985); 

common gulf squid (Dillion and Dial 1962); calmar 

doigtier (French), calamar dedal (Spanish) (Fischer 

1978). 

Classification (Turgeon et al. 1988) 

Phylum: Mollusca 

Class: Cephalopoda 

Order: Teuthoidea 

Family: Loliginidae 

Value 

Commercial : The bay squid has been neglected as a 
fishery resource primarily because of its small size 
(Hixon 1 980b). The low demand for squid and the high 
cost of capture makes a directed squid fishery in the 
U.S. Gulf of Mexico financially unfeasible (Hixon et al. 
1980). Squid sold through commercial fisherman are 
typically acquired as incidental catch from trawling for 
shrimp and fish (Fischer 1978, Voss and Brakonieki 
1984). The larger squid species (Loligo p/e/'/and L 
pealeii) are the ones usually taken. The bay squid is 
sometimes sold in Texas supermarkets, but, although 
edible, is not especially popular as a consumer food 
(Voss and Brakonieki 1984). This species is some- 
times used in neurologic research because of the large 
axon characteristic of the cephalopod molluscs. 

Recreational : Bay squid is often used as bait in off- 
shore sport fishing (Bane et al. 1985). 

Indicator of Environmental Stress : Bay squid is not 
typically used as an indicator species in studies of 


environmental stress. 

Ecological : The bay squid is one of the few cephalo- 
pods that can tolerate estuarine salinities, and is often 
an abundant pelagic species in estuaries (Dragovich 
and Kelly 1 967). It consumes shrimp and small fishes 
and is preyed upon by larger fishes. 

Range 

Overall : The range of the bay squid includes the 
western Atlantic Ocean from New Jersey, Delaware 
Bay southward to Florida, throughout the Gulf of Mexico 
and along the Caribbean mainland, and southward to 
Rio de la Plata in South America (Voss 1956, Fischer 
1 978, Hixon 1 980a, Hixon 1 980b, Andrews 1 981 ). It is 
not known from the Bahamas and Caribbean Islands 
except Cuba and Curacao (Fischer 1978). 

Within Study Area : Bay squid occur in U.S. Gulf of 
Mexico estuaries from Rio Grande, Texas, to Florida's 
Dry Tortugas, and are widely distributed along the Gulf 
coast during most of the year (Voss and Brakonieki 
1 984). They are common along the Texas coast during 
part of the year, but major concentrations determined 
by catch and observation are on both sides of the 
Mississippi River delta in waters of high productivity, off 
the Florida panhandle, and southwest Florida below 
Tampa (Table 5.05) (Voss and Brakonieki 1984). 

Life Mode 

This is a schooling, mobile, diumally active species that 
occurs in near-shore waters and in estuaries (Hargis 
and Hanlon 1984, Vecchione and Roper 1991). Eggs 
are attached to submerged hard structures and sub- 
strate, but have also been collected on soft muddy 
bottoms (Hall 1 970, Forsythe pers. comm.). Paralarvae, 


49 


Bay squid, continued 


Table 5.05. Relative abundance of bay squid in 31 
Gulf of Mexico estuaries (Nelson et al. 1992, 


uuiiiune peia. uuiiimi^. 


Life 


s stage 


Estuary 


A S J L E 


Florida Bay 


V 


V 


V 


V 


V 


Ten Thousand Islands 


V 


V 


V 


V 


V 


Caloosahatchee River 


o 


o 


o 


o 


o 


Charlotte Harbor 


o 


o 


o 


o 


o 


Tampa Bay 


® 


® 


® 


® 


® 


Suwannee River 


o 


o 


o 


o 


o 


Apalachee Bay 


o 


o 


o 


o 


o 


Apalachicola Bay 


® 


® 


® 


® 


® 


St. Andrew Bay 


® 


o 


® 


o 


o 


Choctawhatchee Bay 


o 


o 


o 


o 


o 


Pensacola Bay 


o 


o 


o 


o 


o 


Perdido Bay 


o 


o 


o 


o 


o 


Mobile Bay 


o 


o 


o 


o 


o 


Mississippi Sound 


• 


• 


• 


• 


® 


Lake Borgne 


® 


® 


Lake Pontchartrain 


o 


o 


Breton/Chandeleur Sounds 


o 


o 


Mississippi River 


Barataria Bay 


o 


o 


Terrebonne/Timbalier Bays 


o 


o 


AtchafalayaA/ermilion Bays 


o 


o 


Calcasieu Lake 


o 


o 


V 


Sabine Lake 


V 


V 


Galveston Bay 


o 


o 


o 


o 


o 


Brazos River 


o 


na 


o 


na 


na 


Matagorda Bay 


® 


® 


® 


® 


® 


San Antonio Bay 


® 


® 


® 


® 


® 


Aransas Bay 


o 


o 


o 


o 


o 


Corpus Christi Bay 


iO 


o 


o 


o 


o 


Laguna Madre 


o 


o 


o 


o 


o 


Baffin Bay 


o 


o 


A S J L E 


Relative abundance: 


® 
O 

V 
blank 


Highly abundant 

Abundant 

Common 

Rare 

Not present 


Life stage: 

A - Adults 

S - Spawning 

J - Juveniles 

L - Larvae (paralarvae) 

E - Eggs 


na No data available 


juveniles, and adults are pelagic. 

Habitat 

Type : The bay squid occurs in the upper salinity 
regions of estuaries around marsh grasses to the 
inshore continental shelf when the estuarine salinities 
are unfavorable. It is nektonic in the shallow waters of 
these areas with most specimens found in depths of 
<30 m. It has been observed as deep as 475 m on a 
steep rock face (Vecchione and Roper 1 991 ), although 
this is probably not typical. In areas where salinities are 
favorable, squid are found in relatively deep passes 
and/or channels where current velocity is usually high 
(Dragovich and Kelly 1 967, Hargis 1 979a, Hargis 1 979b, 
Laughlin and Livingston 1982, Hargis and Hanlon 
1984, Vecchione and Roper 1991). This species is 
unique among the cephalopods in that it can withstand 
low salinity waters (down to 17.5%o) and become 
common inhabitants of bays (Hixon 1980a, Hixon 
1 980b). Paralarvae are much more abundant near the 
bottom than near the surface in both coastal and 
estuarine waters (Vecchione 1 991 b). Overall paralarval 
abundance is much greater in coastal rather than 
estuarine areas. 

Substrate : Due to its pelagic life style, the bay squid 
occurs over a wide variety of bottom substrates, but 
appears to be found in association with soft mud 
bottoms (Dragovich and Kelly 1 967, Hargis and Hanlon 
1984). 

Physical/Chemical Characteristics: Abundance is gen- 
erally correlated with lower salinity and higher tem- 
perature (Hixon 1980a, Hixon 1980b). 

Temperature - Paralarvae: The reported temperature 
range for paralarval bay squid taken in nearshore 
waters off Louisiana is 1 1 -32°C, with the highest abun- 
dance occurring at 20-29°C (Bane et al. 1985). 

Temperature - Adults and Juveniles: Temperature 
tolerance ranges from 1 1 ° to 33°C, and possibly as low 
as 7°C. Low temperatures exclude squid from bays 
during the winter months, usually December to Febru- 
ary (Hixon 1980a, Hixon 1980b). Benson (1982) 
reports a range of 5-34. 9°C, and a preference of 13- 
16°C. 

Salinity - Paralarvae: Paralarval bay squid do not seem 
to be as euryhaline as the adults and were not found 
below 22%oOff of coastal Louisiana (Vecchione 1991b). 
In another study, salinities where paralarval bay squid 
were collected in nearshore Louisiana waters ranged 
from 20-36%o, with the highest abundance occurring at 
32-33%o (Bane et al. 1985). Tolerance of moderate 
salinities may develop ontogenetically late during 
paralarval development (Vecchione 1991b). 


50 


Bay squid, continued 


Salinity - Adults and Juveniles: Salinity ranges for 
juvenile and adult squid are 20-37% o , with the lower 
lethal limit being 17.5%o (Hixon 1980a, Hixon 1980b, 
Hendrix et al. 1981, Laughlin and Livingston 1982). 
The salinity range reported by Benson (1982) for bay 
squid is 5-35. 5%o, with a preference for >15%o. How- 
ever, these lower reported salinities may have been 
taken at surface rather than bottom waters where the 
squid were collected. It is also considered possible that 
squid make forays into lower salinity surface waters to 
feed and then return to deeper waters where the 
salinity is higher (Hendrix et al. 1981). 

Dissolved Oxygen: Evidence indicates that paralarval 
bay squid are capable of adjusting to low concentra- 
tions of dissolved oxygen (DO) (<2 mg/l), perhaps by 
increasing oxygen uptake rates (Vecchione 1991b). 
This may be an adaptation to survive the seasonally 
hypoxic bottom water where the the bay squid spawns. 
Adults have been observed in water with a DO content 
of 0.7 mg/l (Vecchione and Roper 1991). 

Migrations and Movements : Bay squid migration and 
abundance are regulated by temperature and salinity 
(Benson 1982, Laughlin and Livingston 1982). Squid 
move out of bays to a few miles offshore during 
December and February to avoid the cooler tempera- 
tures. They move back to the bays in the spring when 
temperatures increase. The spring movement is also 
related to salinity, spawning, and feeding (Hixon 1 980a, 
Hixon 1980b, Laughlin and Livingston 1982). Bay 
squid are able to move into bottom water layers which 
are higher in salinity due to stratification conditions that 
also result in hypoxic water layers (Vecchione 1 991 a). 
It is considered likely that the bay squid takes up 
oxygen in upper, more oxygenated water layers and 
then dives into the bottom waters facultatively. This 
could be a feeding or predator avoidance strategy 
(Vecchione 1991a), or possibly a behavioral mecha- 
nism for avoiding hypoosmotic stress in stratified wa- 
ters (Hendrix et al. 1981). 

Reproduction 

Mode : The bay squid is gonochoristic, with separate 
sexes. Transfer of sperm to the female is accom- 
plished by means of a spermatophore and specially 
adapted arms on the males. 

Mating/Spawning : Bay squid perform head-to-mantle 
mating (Juanico 1983). A knob on the female mantle 
wall is reportedly formed for the attachment of sper- 
matophores. However, it has also been suggested that 
this pad does not occur in virgin females, and is actually 
a tissue response to the implanted spermatophores 
(Vecchione pers. comm.). Duration of the spermato- 
phore attachment and in what quality it can persist 
while attached to the female is unknown (Juanico 


1983). In the northern Gulf of Mexico, spawning can 
occur year-round at depths of 2-18 m with major peaks 
from April to July and a lesser peak from October to 
November (Juanico 1983, Hargis and Hanlon 1984). 
In the northern Gulf of Mexico, bay squid eggs appear 
to hatch throughout the year except during the coldest 
months (Vecchione 1991b). Eggs are deposited on 
sandy bottoms, sometimes within estuaries (Benson 
1 982, Vecchione 1 991 b). In Galveston Harbor, Texas, 
egg capsules have been reported attached to crab 
traps so thickly as to make them useless (Vecchione 
1991b). 

Fecundity : As many as 2000 eggs have been produced 
in a single brood. With multiple broods, an estimated 
1400-6350 can be produced by one female during a 
breeding season (Hixon 1 980a). Eggs are enclosed in 
a capsule, the number per single capsule is limited by 
size of individual eggs and the size of the spawning 
female's nidamental apparatus (Boletzky 1986). 

Growth and Development 

Egg Size and Embryonic Development : Eggs are con- 
tained in clavate egg capsules that are between 1 and 
13 cm long (Hall 1970). One end of the capsule is 
bulbous and contains most of the embryos, and the 
opposite end is narrow and appears to be an attach- 
ment stalk. Capsules are not joined together, and are 
apparently attached directly to bottom sediments. The 
average number of eggs and embryos in a capsule is 
69. Eggs, on the average, measure 1 .8 mm long by 1 .3 
mm wide and are enveloped in a clear jelly-like matrix. 
Total embryonic lifespan is estimated as 35 to 40 days 
based on observed growth rates. Detailed descrip- 
tions of embryonic development can be found in the 
literature (Hall 1970, Hunter and Simon 1975). 

Age and Size of Larvae : The total length of a newly 
hatched bay squid is about 3.8 mm. Morphology and 
development of planktonic "paralarvae" are discussed 
by Vecchione (1 982). Due to the ambiguity of the term 
"larva" when applied to cephalopods, a new designa- 
tion has been proposed (Young and Harman 1988). 
Cephalopods in the first post-hatching growth stage 
that are pelagic in near-surface waters during the day, 
and that have a distinctively different mode of life from 
that of older conspecific individuals are defined as 
"paralarvae." Paralarvae appear to exist only in the 
Teuthoidea and Octopoda groups of cephalopod mol- 
luscs. 

Juvenile Size Range : Hixon (1 980) found growth among 
individuals to be highly variable with averages in nature 
of 8.6 and 7.9 mm/month for males and females 
respectively. There was no significant differences in 
growth rates recorded from nature and laboratory or 
between sexes. 


51 


Bay squid, continued 


Age and Size of Adults : The life cycle of this species is 
approximately one year (Hargis and Hanlon 1984). 
Males are sexually mature in about 6 months at a 
mantle length (ML) of about 40-60 mm (=1 3 g); females 
at 8 months when they are about 70-80 mm ML (=30 g) 
(Hixon 1 980a, Hixon 1 980b, Hargis and Hanlon 1 984). 
Males appear to mature at slightly smaller sizes (32 
mm ML) than females (63 mm ML) (Benson 1982). 
Adults have been collected with ML's up to 85 mm for 
males and 1 1 mm forfemales (Fischer 1 978). Growth 
morphometry of bay squid in Delaware Bay is de- 
scribed by Haefner (1964). 

Food and Feeding 

Trophic mode : Juveniles and adults are carnivores, 
consuming a variety of fish and crustaceans. Their 
high feeding and growth rates make this species an 
important predator in coastal estuaries (Hargis and 
Hanlon 1984). Preferred prey species typically seem 
to be highly visible nektonic species (Hargis 1979a, 
Hargis 1979b). The bay squid and cephalopods pos- 
sess a sophisticated receptor system analogous to the 
lateral line system in fishes and amphibians for the 
detection of small water movements (Budelmann and 
Bleckmann 1 988). This sensory apparatus could allow 
the normally visually oriented bay squid to locate prey 
under low visibility conditions (e.g. murky or deep 
water, or night). Feeding methods of this species are 
typical of loliginid squid (Hanlon et al. 1 983, Turk pers. 
comm.). Prey are seized with the squid's tentacles that 
are thrust quickly forward by means of an internal 
hydraulic mechanism. The captured animal is then 
"reeled in" and positioned near the mouth by retracting 
the tentacles. Prey items (e.g. fish) are injected with 
venom usually through bites behind the head with the 
squid's parrot-like beak. The venom acts as a tranquil- 
izer that paralyzes the prey. Once fish prey are 
paralyzed, the squid consumes the viscera, and then 
strips the flesh from the animal by means of perforating 
bites down the animal's sides. Shrimp prey are com- 
pletely eaten except for the head and the exoskeleton. 
A typical meal is cleared through the digestive system 
in approximately 30 minutes. 

Food Items : Planktonic copepods are likely the natural 
prey for paralarval bay squid (Vecchione 1 991 ). Juve- 
niles and adults feed on larger prey, mostly nektonic 
fishes and shrimps. Juveniles have a slight preference 
forcrustaceans, while adults seem to preferfish (Hargis 
and Hanlon 1984). Adults feed primarily on juvenile 
striped mullet, tidewatersilversides, and Atlantic croaker 
in the upper regions of the water column. They also 
show some preference for white shrimp. If prey move 
to the bottom without being detected they are not 
pursued. Juvenile bay squid prefer fish and shrimp 
equal to or smaller than their own size. Tidewater 
silversides, sheepshead minnows, and sailfin mollies 


have been observed as natural foods (Hargis 1979a, 
Hargis 1979b, Hixon 1980a). Seagrass has also been 
reported as a food item (Benson 1982). Polychaetes 
have also been reported as occurring in bay squid 
stomach contents (Vecchione 1991a). 

Biological Interactions 

Predation : The bay squid is preyed upon by larger 
fishes. 

Factors Influencing Populations : Greater abundances 
of bay squid are correlated with lower salinities and 
higher temperatures with respect to other squid spe- 
cies in the Gulf of Mexico (Hixon 1980). This species 
is most numerous in waters <30 m deep. 

Personal communications 

Turk, Phil. Marine Biomedical Institute, University of 
Texas Medical Branch, Galveston, TX. 

Forsythe, John. Marine Biomedical Institute, Univer- 
sity of Texas Medical Branch, Galveston, TX. 

Vecchione, Michael. NOAA NMFS Systematics Lab., 
National Museum of Natural History, Washington, DC. 

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of Mexico. Ph.D. dissertation, Univ. of Miami, Coral 
Gables, FL, 233 p. 

Hixon, R.F. 1980b. Potential commercial squid re- 
sources of the Gulf of Mexico — An updated review. 
Proceedings of a Workshop for Potential Fishery Re- 
sources of the Northern Gulf of Mexico, Miss. Ala. Sea 
Grant Publ. MASGP-80-012, p. 54-73. 


Vecchione, M. 1991b. Observations on the paralarval 
ecology of a euryhaline squid Lolliguncula brevis 
(Cephalopoda: Loliginidae). Fish. Bull., U.S. 89:515- 
521. 

Vecchione, M., and C.F.E. Roper. 1991. Cephalopods 
observed from submersibles in the western North 
Atlantic. Bull. Mar. Sci. 49:433-445. 

Vecchione, M., C.F.E. Roper, and M.J. Sweeney. 
1989. Marine flora and fauna of the eastern United 
States, Mollusca: Cephalopoda. NOAA Tech. Rep. 
NMFS 73, 23 p. 


53 


Bay squid, continued 


Voss, G.L. 1956. A review of the cephalopods of the 
Gulf of Mexico. Bull. Mar. Sci. Gulf Caribb. 6:85-178. 

Voss, G.L., and T.F. Brakonieki. 1984. Octopus and 
squid resource potential and fisheries in the northern 
Gulf of Mexico. NOAA, Program of Research Between 
Mexico-United States in the Gulf of Mexico. Meeting 
MEXUS-Gulf IX, Memoires, p. 25-30. 

Young, R.E., and R.F. Harman. 1988. "Larva," 
"paralarva" and "subadult" in cephalopod terminology. 
Malacologia 29:201-207. 


54 


Brown shrimp 


Penaeus aztecus 
Adult 


3 cm 


(from Perez-Farfante 1969) 


Common Name: brown shrimp 

Scientific Name: Penaeus aztecus 

Other Common Names: brownies, golden shrimp, 

green lake shrimp, native shrimp, red or red tail shrimp 

(Motoh 1977); crevette royale grise (French), camaron 

cafe norteno (Spanish) (Fischer 1978, NOAA 1985). 

Classification (Williams et al. 1989) 

Phylum: Arthropoda 

Class: Crustacea 

Order: Decapoda 

Family: Penaeidae 

Value 

Commercial : Shrimping has been ranked as the sec- 
ond most valuable commercial fishery in the U.S., and 
seventh in quantity (NMFS 1 993). U.S. landings of all 
shrimp species combined in the Gulf of Mexico were 
1 00.7 thousand mt in 1 992, and were valued at $316.6 
million. Total U.S. brown shrimp harvest in the Gulf of 
Mexico was 64,075 mt in 1991, and brown shrimp 
typically comprise 57% of the total Gulf of Mexico 
shrimp landings (NOAA 1 993). The fishery for Gulf of 
Mexico brown shrimp is considered to be fully exploited 
at this time (Nance and Nichols 1988, Nance 1989), 
and a longterm potential annual yield of 63,001 mt has 
been estimated (NOAA 1993). In 1991 an estimated 
5,000 offshore vessels were participating in the fishery 
with an unknown number of smaller boats fishing in the 
inshore and nearshore waters. The season begins in 
May, peaks from June to July and gradually declines 
through April. Major fishing grounds are off the coasts 
of Texas and Louisiana. Federal regulations have 
annually closed the offshore fishery along the coast of 
Texas from around mid-May to mid-July not more than 
55 days to allow shrimp to grow to larger sizes (Klima 
et al. 1 982, Klima et al. 1 987, Nance et al. 1 990). The 


majority of the brown shrimp are harvested for human 
consumption. In addition, a smaller bait shrimp fishery 
also exists (Swingle 1 972, Klima et al. 1 987, Nance et 
al. 1991). 

Recreational : Recreational shrimping has become in- 
creasingly popular along the Gulf coast in recent years 
(Christmas and Etzold 1977). Fishermen use small 
trawls for the most part, but seines, cast nets, and push 
nets are used as well. Approximately 4,000 mt (heads 
on) of total shrimp (brown, pink, and white) were taken 
by recreational shrimpers in 1 979 in Texas and Louisi- 
ana. Regulations pertaining to licensing and gear type 
vary among the Gulf states, and catches are limited by 
location and season of fishing (GMFMC 1981). 

Indicator of Environmental Stress : An experiment con- 
ducted by Miligan (1983) indicated dredge material 
free of significant concentrations of heavy metals, 
pesticides, and waste metabolites was non-toxic to 
brown shrimp. A second experiment demonstrated 
better growth for shrimp in rearing ponds treated with 
dredge material. Ward et al. (1981) determined a 
concentration of 1 .2 mg/l selenium (96 hours LC50) to 
be toxic to brown shrimp. Wofford et al. (1981) ob- 
served the bioaccumulation of phthalate esters (plas- 
ticizers) and demonstrated brown shrimp were better 
biodegraders of the ester than oysters. A study of the 
impact of production water from offshore oil platform 
found toxic effects occurred in the immediate outfall 
area on larval brown shrimp (Gallaway 1 980). Popula- 
tion studies conducted around brine disposal sites 
found no effects by brine on brown shrimp distribution 
(Reitsema et al. 1982). Studies in areas treated with 
aerial insecticides have found varying degrees of shrimp 
mortality (Christmas and Etzold 1977). Couch (1978) 


55 


Brown shrimp, continued 


Table 5.06. Relative abundance of brown shrimp in 
31 Gulf of Mexico estuaries (from Volume I). 


Life stage 


Estuary 


A S J L E 


Florida Bay 


V 


V 


V 


Ten Thousand Islands 


V 


V 


V 


Caloosahatchee River 


V 


Charlotte Harbor 


V 


V 


V 


Tampa Bay 


Suwannee River 


Apalachee Bay 


Apalachicola Bay 


® 


® 


® 


St. Andrew Bay 


® 


® 


® 


Choctawhatchee Bay 


® 


® 


® 


Pensacola Bay 


• 


• 


• 


Perdido Bay 


• 


• 


V 


Mobile Bay 


• 


• 


• 


Mississippi Sound 


• 


O 


• 


• 


® 


Lake Borgne 


® 


• 


• 


Lake Pontchartrain 


o 


® 


o 


Breton/Chandeleur Sounds 


® 


Mississippi River 


o 


Barataria Bay 


• 


• 


Terrebonne/Timbalier Bays 


• 


AtchafalayaA/ermilion Bays 


• 


® 


Calcasieu Lake 


• 


® 


Sabine Lake 


V 


® 


® 


Galveston Bay 


• 


• 


Brazos River 


® 


® 


Matagorda Bay 


• 


• 


• 


San Antonio Bay 


® 


• 


• 


Aransas Bay 


• 


® 


Corpus Christi Bay 


• 


o 


Laguna Madre 


o 


® 


V 


Baffin Bay 


• 


■ 


A S J L E 


Relative abundance: 

O Highly abundant 

® Abundant 

O Common 

V Rare 

blank Not present 


Life stage: 

A - Adults 

S - Spawning 

J - Juveniles 

L - Larvae/postlarvae 

E - Eggs 


has compiled a comprehensive review of the toxic 
responses of penaeid shrimp. 

Ecological : The brown shrimp is consumed by many 
finfish species and by large crustaceans. Large juve- 
nile stocks of these and other penaeid shrimp appear 
to be important in supporting large populations of 
certain juvenile fish species (Heftier 1 989). The loss of 
marsh habitat and reduction in freshwater inflow into 
the bays have come under scrutiny as major factors 
influencing shrimp production (Kutkuhn 1966, Minello 
and Zimmerman 1 983, Minello and Zimmerman 1 984). 

Range 

Overall : The brown shrimp extends farther north than 
any of the other western Atlantic species of Penaeus 
(Fischer 1 978). It is distributed from Martha's Vinyard, 
Massachusetts, around the tip of Florida and through- 
out the Gulf of Mexico to the northwestern Yucatan 
Peninsula. 

Within Study Area : In U.S. waters of the Gulf of Mexico, 
the brown shrimp is distributed throughout bays, estu- 
aries and coastal waters (Table 5.06). For the pur- 
poses of Table 5.06, all larval and postlarval stages of 
brown shrimp are considered together as "larvae" (L). 
However, the brown shrimp is uncommon in Florida 
Bay and is conspicuously absent along the western 
Florida coast from the Sanibel grounds to Apalachicola 
Bay. Its maximum density occurs along the coasts of 
Texas, Louisiana, and Mississippi (Allen et al. 1980, 
Williams 1984, NOAA 1985). 

Life Mode 

This species is found in neritic to estuarine habitats and 
is pelagic to demersal, depending on life stage. Eggs 
are denser than seawater and are demersal (Kutkuhn 
1966). Larval stages are planktonic, their position in 
the water column is dependent on time of day, water 
temperature and clarity (Temple and Fischer 1965, 
1967, Kutkuhn, et al. 1969). Nauplii are demersal, 
becoming pelagic as they develop through the 
protozoeae and mysis stages (Lassuy 1983). 
Postlarvae spawned in the fall may burrow into the 
sediments to escape cooler temperatures and over- 
winter (St. Amant et al. 1966, Aldrich et al. 1968). 
Postlarvae move into estuaries and transform into 
juveniles (Cook and Lindner 1970). Adults generally 
inhabit offshore waters ranging from 14 to 110 m in 
depth (Renfro and Brusher 1982). The brown shrimp 
is most abundant from March to December with opti- 
mum catches occurring from March to September 
(Copeland and Bechtel 1974). This species typically 
seems to have an annual life cycle; however, captive 
individuals have survived for over two years (Perez- 
Farfante 1969, Zein-Eldin pers. comm.). 


56 


Brown shrimp, continued 


Habitat 

Ty pe: Eggs occur offshore and are demersal. Larvae 
occur offshore and begin to immigrate to estuaries as 
postlarvae around 8 to 14 mm total length (TL) (Cook 
and Lindner 1 970, Zein-Eldin pers. comm.). In estuar- 
ies, postlarvae and small juveniles are associated with 
shallow vegetated habitats, but are also found over 
silty sand and non-vegetated mud bottoms. Juveniles 
and subadults are found from secondary estuarine 
channels out to the continental shelf, but prefer shallow 
marsh areas and estuarine bays, showing a prefer- 
ence for vegetated habitats. Adults occur in neritic Gulf 
waters (Perez-Farfante 1969, Copeland and Bechtel 
1974, Williams 1984, Minello et al. 1990, Zimmerman 
etal. 1990). 

Substrate : Substrate suitable for burrowing activity 
generally seems to be preferred (Minello et al. 1990). 
Postlarvae and juveniles inhabit soft, muddy areas, 
especially in association with plant-water interfaces. 
Adults are associated with terrigenous silt, muddy 
sand, and sandy substrates (Hildebrand 1 954, Ward et 
al. 1980, Lassuy 1983, Williams 1984). 

Physical/Chemical Characteristics : 
Temperature: Eggs will not hatch at temperatures 
below 24°C (Cook and Lindner 1 970). Postlarvae have 
been collected from temperatures of 12.6° to 30.6°C. 
Aldrich et al. (1968) demonstrated postlarval burrow- 
ing in temperatures below 18°C. Extended exposure 
to temperatures below 20°C may be detrimental to 
population survival (Zein-Eldin and Renaud 1986). 
Brown shrimp greater than 75 mm tolerate tempera- 
tures between 4° and 36°C, with a preferred range of 
14.9° to 31.0°C (Ward et al. 1980, Copeland and 
Bechtel 1974). Estuarine water temperature appears 
to affect growth more than salinity does (Herke et al. 
1987). Maximum growth, survival, and conversion 
efficiency occurs at 26°C (Ward et al. 1980, Copeland 
and Bechtel 1974). No growth occurs below 16°C and 
growth is reduced above 32.2°C (Ward et al. 1980, 
Lassuy 1983). 

Salinity: Brown shrimp are euryhaline to stenohaline 
depending on life stage. Larvae tolerate salinities 
ranging from 24.1 to 36%> (Cook and Murphy 1966). 
Postlarvae have been collected from salinities of 0.1 to 
69% , and have good growth at 2 to 40% o . Juvenile 
brown shrimp are distributed over to 45%o, but have 
been reported to prefer 10 to 20%o (Cook and Murphy 
1966, Copeland and Bechtel 1974, Zimmerman et al. 
1 990). Adults tolerate salinities of 0.8 to 45%o, but their 
optimum range is 24 to 38.9%o (Cook and Murphy 
1966). Salinity tolerance is significantly narrowed 
below 20°C (Copeland and Bechtel 1 974). Salinity and 
temperature effects are more conspicuous at either 
extremes (Ward et al. 1980, Zein-Eldin and Renaud 


1 986). 

Dissolved Oxygen: In one field study, abundance lev- 
els were lower in areas that had been altered by 
development where dissolved oxygen content had 
dropped below 3 ppm (Trent et al. 1976). Detailed 
laboratory studies of brown shrimp oxygen consump- 
tion and its interactions with temperature, salinity, and 
body size are presented by Bishop et al. (1980). 

Turbidity: The effects of turbidity on shrimp distribution 
and abundance are not well known (Kutkuhn 1966). 
General observations indicate that turbid water areas 
tend to have higher concentrations of young shrimp 
than clear water areas. Water turbidity has also been 
observed to strongly affect the brown shrimp's habitat 
selection preference for structure in laboratory experi- 
ments (Minello et al. 1990). Significant reductions in 
abundance occurred in habitats with structure when 
turbidity levels were high. 

Migrations and Movements : Brown shrimp postlarvae 
(10-15 mm TL) move into estuaries from February to 
April with the incoming tides and migrate to shallow and 
often vegetated nursery areas (Copeland and Truitt 
1 966, King 1 971 , Minello et al. 1 989b). In the northern 
Gulf of Mexico, estuarine recruitment may occur all 
year (Baxter and Renfro 1967). Rogers et al. (1993) 
hypothesized that the estuarine recruitment is en- 
hanced by downward migration of brown shrimp 
postlarvae as northerly cold fronts force out estuarine 
water, and upward migration into the tidal water column 
as waters is forced back into the estuary. When 
juveniles reach a size generally greater than 55-60 
mm, they move out into open bays. The sub-adults 
then migrate into the coastal waters (Minello et al. 
1989b). Emigration to offshore spawning grounds 
occurs from May through August, coinciding with full 
moons and ebb tides (Copeland 1 965). Some tagging 
studies in the northern Gulf indicate a west and south- 
ward movement of the adults with the prevailing cur- 
rents (Cook and Lindner 1970, Hollaway and Baxter 
1981); but other studies do not indicate a net move- 
ment in any direction when fishing effort is taken into 
account (Sheridan et al. 1 989, Sheridan pers. comm.). 

Reproduction 

Mode : Brown shrimp reproduce sexually by external 
fertilization in offshore Gulf of Mexico waters (Cook and 
Lindner 1970, Lassuy 1983). This species has sepa- 
rate male and female sexes (gonochoristic). 

Mating/Spawning : Mating probably occurs soon after 
the female molts and before the exoskeleton hardens 
(Cook and Lindner 1 970). A spermatophore is placed 
inside the thelycum of the female by the male before 
her eggs are spawned. Spawning occurs offshore 


57 


Brown shrimp, continued 


usually between depths of 46 to 91 m, but can range 
from 18 to 137 m (Renfro and Brusher 1982). The 
major spawning season is September through May; 
however, spawning may occur throughout the year at 
depths greater than 46 meters. In the northern Gulf of 
Mexico, there are two spawning peaks: September - 
November, and April - May. In waters off Texas, 
spawning occurs in spring and fall at depths greater 
than 14 m, and throughout the year at depths of 64 to 
110 m. In shallower water, peaks of spawning are 
during late spring and in the fall (Renfro and Brusher 
1982). Brown shrimp may spawn more than once 
during a season (Perez-Farfante 1969), and usually 
spawn at night (Henley and Rauschuber 1981). 

Fecundity : Reitsema et al. (1 982) found brown shrimp 
that averaged 192 mm TL released an average of 
246,000 viable eggs, of which 15 % hatched. 

Growth and Development 

Egg Size and Embryonic Development : Eggsare round, 
golden brown, and translucent measuring approxi- 
mately 0.26 mm in diameter (Cook and Murphy 1 971 ). 
They are demersal and hatch within 24 hours after 
release into the water column (Kutkuhn 1966, Christ- 
mas and Etzold 1977). 

Age and Size of Larvae : Larvae transform through 5 
naupliar stages with average total lengths of 0.35, 
0.39, 0.40, 0.44 and 0.50 mm respectively; 3 protozoeal 
stages, average total lengths of 0.96, 1.71, and 2.59 
mm; and 3 mysis stages, average total lengths of 3.3, 
3.8 and 4.3 mm, to become postlarvae at an average 
total length of 4.6 mm, in a period of 1 to 25 days (Cook 
. and Murphy 1 969, Cook and Murphy 1 971 ). Postlarvae 
enter the estuaries and transform into juveniles around 
25 mm TL. Larval growth rate estimates are: nauplii, 
0.1 -0.2 mm/day; protozoeae 0.3-0.35 mm/day; myses 
0.4-0.5 mm/day (Ward et al. 1980). Postlarval growth 
is at a maximum between 25 to 27° C, greater than 0.5 
mm/day. 

Juvenile Size Range : Estuarine juveniles range from 
25 to 90 mm. The shrimp spend about 3 months on the 
nursery grounds, and then move back offshore at sizes 
ranging from 80 to 1 00 mm TL (Copeland 1 965, Cook 
and Lindner 1970, Parker 1970). Growth rates are 
temperature dependent and tend to decrease after 
maturity. Juveniles have grown 3.3 mm/day at tem- 
peratures above 25°C; growth decreases from 29 to 
33°C (Zein-Eldin and Renaud 1986). 

Age and Size of Adults : Growth of offshore adults has 
not been studied in detail. Females usually reach 
sexual maturity at about 140 mm TL (Henley and 
Rauschuber 1981). Brown shrimp have lived over two 
years in captivity (Zein-Eldin pers. comm.). 


Food and Feeding 

Trophic Mode : Larvae are omnivorous, and feeding 
begins with the first protozoeal stage (Cookand Murphy 
1969). Juveniles and adults forage nocturnally on 
available food, and are more carnivorous, progressing 
from "encounter-feeders" to selective omnivore-preda- 
tors (GMFMC 1981, Zein-Eldin and Renaud 1986, 
Minello and Zimmerman 1991). 

Food Items : Larval stages feed on phytoplankton and 
zooplankton. Postlarvae feed on epiphytes, phytoplank- 
ton and detritus, but faster growth is attained on animal 
food (e.g. Artemia, fish meal, shrimp meal, and squid 
meal) (Gleason and Zimmerman 1 984, Zein-Eldin and 
Renaud 1 986, Zein-Eldin pers. comm.). Juveniles and 
adults prey on polychaetes, amphipods, and chirono- 
mid larvae, but also detritus and algae (GMFMC 1 981 , 
Zein-Eldin and Renaud 1986). Optimal growth of 
juveniles in a laboratory feeding study was obtained 
using a diet that consisted of a mixture of animal and 
plant material (McTigue and Zimmerman 1 991 ). Brown 
shrimp were found to rely more heavily on animal 
material in their diet than white shrimp, and this may be 
the result of interspecific competition. 

Biological Interactions 

Predation : Predation is probably the most usual direct 
cause of brown shrimp mortality in estuarine nurseries 
in the northern Gulf of Mexico (Minello et al. 1989b). 
Habitat location may affect the degree of predation with 
such factors as differences in vegetation, substrate, 
and waterturbidity altering mortality rates (Minello et al. 
1 989a). A wide variety of predators, including carnivo- 
rous fishes and crustaceans feed on this species. In 
estuarine waters, the southern flounder is considered 
the major predator of juvenile brown shrimp especially 
during the spring, but spotted seatrout, sand seatrout, 
and inshore lizard fish also prey heavily on penaeid 
shrimp (Stokes 1 977, Minello et al. 1 989a, Minello et al. 
1989b). Other piscine predators include: sand tiger 
shark, bull shark, dusky shark, ladyfish, gafftopsail 
catfish, hardhead catfish, sheepshead, rock sea bass, 
bluefish, comon snook, silver seatrout, pinfish, pigfish, 
gulf killifish, red snapper, lane snapper, southern king- 
fish, spot, silver perch, black drum, red drum, Atlantic 
croaker, crevalle jack, cobia, code goby, Spanish mack- 
erel, gulf flounder (Gunter 1945, Kemp 1949, Miles 
1 949, Springer and Woodburn 1 960, Harris and Rose 
1 968, Boothby and Avault 1 971 , Odum 1 971 , Carr and 
Adams 1 973, Diener et al. 1 974, Bass and Avault 1 975, 
Stokes 1 977, Overstreet and Heard 1 978a, Overstreet 
and Heard 1 978b, Danker 1 979, Overstreet and Heard 
1 982, Divita et al. 1 983, Saloman and Naughton 1 984, 
Sheridan et al. 1 984, Minello et al. 1 989a, Minello et al. 
1989b). Penaeid shrimp are an important link in the 
energy flow of food webs by feeding on benthic organ- 
isms, detritus, and other organic material found in 


58 


Brown shrimp, continued 


sediments (Odum 1971, Carrand Adams 1973). 

Factors Influencing Populations : Disease is second 
only to predation and periodic physical catastrophes in 
limiting numbers of penaeid shrimps in nature (Couch 
1 978). A high proportion (up to 40%) of postlarval and 
juvenile brown shrimp in Mississippi waters may be 
infected with the Baculovirus penaei (BP) virus 
(Overstreet 1994, Stuck pers. comm.), which may be 
highly pathogenic to these life stages (Couch et al. 
1975, Lightner and Redman 1991). The commercial 
fishery has a major impact on parental stock during a 
given year, but does not seem to affect production of 
young for recruitment into the next year's fishery. 
Environmental conditions, habitat alteration, food avail- 
ability and substrate type may also affect brown shrimp 
abundance and distribution (Christmas and Etzold 
1 977, Herke et al. 1 987, Minello et al. 1 989b, Minello et 
al. 1990). Salinity, turbidity, and light conditions can 
interact with the brown shrimp's preference for veg- 
etated areas, causing it to inhabit non-vegetated areas 
where it may be more vulnerable to predation (Minello 
et al. 1989b, Minello et al. 1990). 

Personal communications 

Nance, J.M. NOAA National Marine Fisheries Service, 
Galveston, TX. 


Baxter, K.N., and W.C. Renfro. 1966. Seasonal 
distribution and size distribution of postlarval brown 
and white shrimp near Galveston, Texas, with notes on 
species identification. Fish. Bull., U.S. 66:149-158. 

Bishop, J.M., J.G. Gosselink, and J.H. Stone. 1980. 
Oxygen consumption and hemolymph osmolality of 
brown shrimp, Penaeus aztecus. Fish. Bull., U.S. 
78:741-757. 

Boothby,R.N.,andJ.W.Avault,Jr. 1971. Food habits, 
length-weight relationship, and condition factor of the 
red drum (Sciaenops ocellata) in southeastern Louisi- 
ana. Trans. Am. Fish. Soc. 100(2):290-295. 

Carr, W.E.S., and C.A. Adams. 1973. Food habits of 
juvenile marine fishes occupying seagrass beds in the 
estuarine zone near Crystal River, Florida. Trans. Am. 
Fish. Soc. 102:511-540. 

Christmas, J.Y., and D.J. Etzold. 1977. The shrimp 
fishery of the Gulf of Mexico, United States: a regional 
management plan. Gulf Coast Res. Lab. Tech. Rep. 
Ser. No. 2, 128 p. 

Cook, H.L., and M.J. Lindner. 1970. Synopsis of 
biological data on the brown shrimp Penaeus aztecus 
aztecus Ives, 1891. FAO Fish. Rep. 57:1471-1497. 


Patella, F.J. NOAA National Marine Fisheries Service, 
Galveston, TX. 

Sheridan, P.F. NOAA National Marine Fisheries Ser- 
vice, Galveston, TX. 

Stuck, K. Gulf Coast Research Laboratory, Ocean 
Springs, MS. 

Zein-Eldin, Z.P. NOAA National Marine Fisheries 
Service, Galveston, TX. 

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Brown shrimp, continued 


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62 


Brown shrimp, continued 


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63 


Pink shrimp 


Penaeus duorarum 
Adult 


5 cm 


(from Fischer 1978) 


Common Name: Pink shrimp 
Scientific Name: Penaeus duorarum 
Other Common Names 

Brown spotted shrimp; Green shrimp, grooved shrimp, 
hopper, pink spotted shrimp, pink night shrimp, pushed 
shrimp, red shrimp, skipper, spotted shrimp (Costello 
and Allen 1 970, Motoh 1 977, McKenzie 1 981 , Bielsa et 
al. 1983, Williams 1984); crevette roche du nord 
(French), camaron rosado norteno (Spanish) (Fischer 
1978, NOAA 1985). 
Classification (Williams et al. 1989) 
Phylum: Arthropoda 
Class: Crustacea 

Order: Decapoda 

Family: Penaeidae 

Value 

Commercial : Shrimping is the second most valuable 
commercial fishery in the U.S., and ranks seventh in 
quantity (NMFS 1993). U.S. landings of all shrimp 
species combined in the Gulf of Mexico were 100.7 
thousand mt in 1992, and were valued at $316.6 
million. Total U.S. pink shrimp harvest in the Gulf of 
Mexico was 4,785 mt in 1 991 , and pink shrimp typically 
comprise 8% of the total Gulf of Mexico shrimp land- 
ings (NOAA 1 993). The pink shrimp is a commercially 
important species throughout the Gulf of Mexico, and 
its stocks have historically been considered quite stable 
compared to those of white and brown shrimp (Nance 
and Nichols 1 988). However, the Tortugas pink shrimp 
fishery has had considerable fluctuation in landings 
and effort since 1986 (Nance 1994, Sheridan 1996, 
Steele pers. comm.). Most of the commercial catch is 
taken by otter and roller-frame trawls, but other meth- 
ods include haul seines, cast, butterfly, drop, push, and 
channel nets (Costello and Allen 1970, Eldridge and 


Goldstein 1975, Eldridge and Goldstein 1977, Steele 
pers. comm.). Federal and some state laws may 
require the use of Turtle Excluder Devices (TEDs) 
year-round on shrimp trawls, but bait shrimpers (catch 
<16 kg/day, trawl <10.7 m) may be exempt from this 
rule (Nance pers. comm.). The major pink shrimp 
fishery is in the Tortuga and Sanibel grounds of south- 
west Florida. In Texas there is also a major fishery, but 
the pink shrimp is often difficult to distinguish from the 
brown shrimp, and is usually included with the brown 
shrimp fishery statistics. The pink shrimp fishery 
probably does not contribute more than 1 0% of the total 
catch off Texas (Klima et al. 1982), and catches are 
minor in Louisiana as well (Christmas and Etzold 
1977). The pink shrimp helps support an substantial 
bait shrimp industry that is mainly in western Florida 
from Tampa Bay north to Apalachee Bay (Christmas 
and Etzold 1 977). Bait harvests also occur in Biscayne 
Bay, along the Florida Keys, and along the east coast 
of Florida (Costello and Allen 1966, Joyce and Eldred 
1966, Steele pers. comm.). Bait harvest is prohibited 
in the Everglades National Park portion of Florida Bay 
(Schmidt pers. comm.). Bait shrimpers in Alabama and 
south Texas also utilize this species, but catches are 
small compared to those of brown and white shrimp 
(Swingle 1972, Sheridan pers. comm.). 

Recreational : Recreational shrimping has become in- 
creasingly popular along the Gulf coast in recent years 
(Christmas and Etzold 1977). Fishermen use small 
trawls for the most part, but seines, dip-nets, cast nets, 
and push nets are used as well (Christmas and Etzold 
1977, Killam et al. 1992). Regulations pertaining to 
licensing and gear type vary among the Gulf states, 
and catches are limited by location and season of 
fishing (GMFMC 1 981 ). In Tampa Bay, fishing effort is 


64 


Pink shrimp, continued 


Table 5.07. Relative abundance of pink shrimp in 
Gulf of Mexico estuaries (from Volume !). 


31 


Life 


1 stage 


Estuary 


A S J L E 


Florida Bay 


O 


m 


• 


Ten Thousand Islands 


• 


• 


Caloosahatchee River 


® 


Charlotte Harbor 


O 


® 


Tampa Bay 


O 


• 


• 


Suwannee River 


• 


o 


Apalachee Bay 


® 


o 


Apalachicola Bay 


V 


® 


o 


St. Andrew Bay 


® 


® 


V 


Choctawhatchee Bay 


V 


® 


V 


Pensacola Bay 


V 


o 


o 


Perdido Bay 


o 


o 


V 


Mobile Bay 


V 


o 


V 


Mississippi Sound 


o 


O 


o 


o 


o 


Lake Borgne 


V 


Lake Pontchartrain 


V 


Breton/Chandeleur Sounds 


o 


® 


Mississippi River 


Barataria Bay 


o 


o 


Terrebonne/Timbalier Bays 


V 


Atchafalaya/Vermilion Bays 


V 


Calcasieu Lake 


Sabine Lake 


Galveston Bay 


V 


V 


Brazos River 


o 


Matagorda Bay 


o 


V 


San Antonio Bay 


o 


o 


Aransas Bay 


o 


o 


Corpus Christi Bay 


o 


Laguna Madre 


o 


® 


Baffin Bay 


V 


o 


A S J L E 


Relative abundance: 

O Highly abundant 

® Abundant 

O Common 

V Rare 

blank Not present 


Life stage: 

A - Adults 

S - Spawning 

J - Juveniles 

L - Larvae/postlarvae 

E - Eggs 


highest during the fall (Christmas and Etzold 1977) 
when pink shrimp are moving from the estuaries into 
deeper waters (Costello and Allen 1970). 

Indicator of Environmental Stress : Penaeid shrimps 
are known to be very sensitive to certain classes of 
chemical pollutants (Couch 1978). Pesticides and 
other organic chemicals have been found to cause 
mortality in pink shrimp (Christmas and Etzold 1977, 
Couch 1978). Heavy metals have also been found to 
be detrimental. All of these compounds can enter 
estuarine systems as surface runoff, point source 
discharges, or atmospheric deposition. This species 
has been used by National Oceanic and Atmospheric 
Administration (NOAA), Technology Resources, Inc. 
and the Environmental Protection Agency (EPA) to 
study the effects of bioaccumulation of heavy metals, 
chlorinated hydrocarbons, and toxic substances from 
bottom sediments and dredge materials (Heitmuller 
and Clark 1 989, Parrish et al. 1 989, Long et al. 1 991 ). 

Ecological : Pink shrimp distribution seems to be corre- 
lated with seagrasses in general and shoalgrass 
{Halodule wrightt) in particular, and postlarvae may 
actively select this habitat (Costello et al. 1 986, Sheridan 
pers. comm.). Large populations of juvenile penaeid 
shrimp appear to be important in supporting large 
populations of certain juvenile fish species (Hettler 
1989). Penaeid shrimp also provide an important link 
in the estuarine food web by converting detritus into 
available biomass for fishes, birds, and other predators 
many of which are commercially or recreationally im- 
portant (Bielsa et al. 1983, Robblee et al. 1991). 

Range 

Overall : The pink shrimp ranges from lower Chesa- 
peake Bay to southern Florida, through the Gulf of 
Mexico to Cape Catoche and the Isla Mujeres at the 
tip of the Yucatan Peninsula. Maximum densities in 
the Gulf of Mexico occur along the coast of southwest- 
ern Florida and in the Gulf of Campeche (Perez- 
Farfante 1969). 

Within Study Area : The primary nursery ground is the 
Florida Bay region within Everglades National Park. 
This area is known as the "Tortugas Shrimp Sanctu- 
ary", and is closed to most commercial shrimping 
(Steele pers. comm.). However, it supports the fish- 
eries of the Tortugas fishing grounds (Beardsley 1970, 
Bielsa et al. 1983, Robblee et al. 1991). Highly 
productive fishery areas also occur at the Sanibel 
grounds, supported by the Charlotte Harbor-Pine 
Island Sound and Tampa Bay nurseries, and the Big 
Bend grounds which receives stockf rom Apalachicola 
Bay and nearby estuarine areas (Bielsa et al. 1983). 
Other areas of high abundance are in the Laguna 
Madre, Texas, and offshore from Brownsville and 


65 


Pink shrimp, continued 


Galveston, often associated with coarse substrate 
(Sheridan pers. comm.) (Table 5.07). For the pur- 
poses of Table 5.07, all larval and postlarval stages of 
pink shrimp are considered together as "larvae" (L). 

Life Mode 

Eggs and adults are demersal; larvae are planktonic to 
the postlarval stage (Costello and Allen 1 970). Postlar- 
val and juvenile stages are demersal in estuaries and 
coastal bays (Perez-Farfante 1 969, Costello and Allen 
1970, Williams 1984). Juvenile pink shrimp burrow 
during the day and are active nocturnally. The noctur- 
nal activity is most obvious during new and full moons 
(Hughes 1967, Williams 1984). In the Florida Bay 
region juvenile pink shrimp are most abundant be- 
tween September and December (Robblee et al. 1 991 , 
Schmidt 1993). 

Habitat 

Ty pe: Eggs and early planktonic larval stages are 
oceanic. Postlarval and juvenile stages occur in 
oligohaline to euhaline estuarine waters and bays, and 
adults occur in estuaries and nearshore waters to 64 m 
depth. Mature pink shrimp inhabit deep offshore 
marine waters with the highest concentrations in depths 
of 9 to 44 m. Largest numbers of pink shrimp occur 
where shallow bays and estuaries border on a broad 
shallow shelf (Perez-Farfante 1 969, Costello and Allen 
1970, McKenzie 1981, Bielsa et al. 1983, Williams 
1 984). Costello et al. (1 986) indicate optimum habitats 
have daily tidal flushing with marine water and large 
seagrass beds with high blade densities. Protozoeal 
and mysis stage larvae on the Tortugas Shelf were 
found in depths of 14.6 to 47.6 m (Jones et al. 1970). 
Larvae most generally occurred at depths of 18.3 to 
36.6 m. Older pink shrimp occurred almost entirely in 
inshore waters, and in Florida Bay appeared to be most 
abundant in shallow water habitats (Jones et al. 1 970, 
Robblee et al. 1 991 ). Optimum catches in Texas occur 
in secondary bays, but this species occurs from sec- 
ondary estuarine channels out to the continental shelf 
(Copeland and Bechtel 1974) 

Substrate : Pink shrimp inhabit a range of bottom sub- 
strates including shell-sand, sand, coral-mud, and 
mud. Immature pink shrimp prefer shell-sand or loose 
peat, and adults prefer shell-sand over loose peat 
(Williams 1958, Williams 1984). Juvenile shrimp are 
also commonly found in estuarine areas with seagrass 
where they burrow into the substrate by day and 
emerge and are active by night (Perez-Farfante 1 969, 
Costello and Allen 1970, Williams 1984). Juveniles 
have been frequently associated with seagrasses, and 
it has been suggested that the distribution of seagrasses 
may influence the geographic distribution of pink shrimp 
populations (Costello and Allen 1970). In inshore 
Florida waters, small juveniles were found close to 


shore in beds of shoal grass, Halodule wrightii, while 
large juveniles occurred in deeper waters in turtle 
grass, Thalassia testudinum (Robblee et al. 1991, 
Schmidt 1993). Turtle grass has also been found to 
provide a suitable habitat for many organisms that 
penaeids and other species utilize as food (Moore 
1963). 

Physical/Chemical Characteristics : 
Temperature: One laboratory study found larvae 
showed normal growth at 21° and 26°C, but died at 
temperatures exceeding 31 °C (Williams 1 955a). While 
larval development may be restricted to a narrower 
range, juveniles may be fairly tolerant of a wide range 
of temperatures (Williams 1955a). Juveniles tolerate 
temperatures between 4° to 38°C, but extended peri- 
ods of low water temperatures may result in death. In 
Texas, they become more abundant with increasing 
temperature, and optimal catches occur between 20° 
and 38°C (Copeland and Bechtel 1974). Adult pink 
shrimp tolerate temperatures between 10° to 35.5°C 
(Williams 1955a), and temperature may be a limiting 
factor in the northern part of their range (Hettler 1 992). 

Salinity: Pink shrimp show different degrees of salinity 
preference at different life stages (Bielsa et al. 1983). 
Postlarvae have been observed in salinities ranging 
from 12 to 43%» with little apparent differences in their 
growth (Williams 1 955a). At a constant temperature of 
24°C postlarvae showed no difference in growth at 
salinities ranging from 2 to 40% o (Zein-Eldin 1963). 
Juveniles have been observed between <1 to 47%o 
although they prefer salinities greater than 20%o 
(Costello and Allen 1 970, Copeland and Bechtel 1 974). 
Optimum catches in Texas occur between 20 and 35%o 
(Copeland and Bechtel 1974). Salinity does not ap- 
pear to be a major factor in the distribution of adults or 
in controlling spawning activity (Roessler et al. 1969). 
Adults are generally found in 25 to 45%o, although they 
have been found in salinities as high as 69%o. Abun- 
dances are reduced above 45%o. At their lower salinity 
tolerance, pink shrimp have been observed in 2.7%o in 
the western Gulf of Mexico; and close to 1%o in the 
Caloosahatchee estuary and Ten Thousand Islands of 
Florida. One study indicates a possible positive rela- 
tionship with freshwater runoff in the Everglades and 
landings in the Tortugas shrimping grounds (Browder 
1 985). Salinity requirements or preferences vary with 
geographic area and shrimp size (Costello and Allen 
1970). The pink shrimp appears to have superior 
osmoregulatory capabilities to those of the brown 
shrimp during periods of low water temperature, and 
thus shows a greater capability for overwintering in 
estuaries in the northern part of its range (Williams 
1955a). 


66 


Pink shrimp, continued 


Migrations and Movements : Larval stages are capable 
of vertical migration to control their position in the water 
column (Costello and Allen 1970, Allen et al. 1980). 
Both larval and juvenile stages show phototaxic re- 
sponses in their movements (Ewald 1965, Costello 
and Allen 1970, Jones et al. 1970). Larvae migrate 
vertically away from the water surface during the day, 
and juveniles move to the water surface during full 
moon tides. Pink shrimp postlarvae enter estuarine 
nursery areas during the summer months after 21 to 28 
days of larval and postlarval development and remain 
there for 2 to 6 months (Costello and Allen 1 970, Jones 
et al. 1970, Copeland and Bechtel 1974, Allen et al. 
1980). Entry into estuaries may be facilitated by net 
inflows of sea water after periods of low water levels. 
The annual rise in sea level that occurs during the 
warmer months when spawning is occurring may facili- 
tate current-borne movement of postlarvae from the 
continental shelf into these nursery areas (Allen et al. 
1980). Late juveniles and early adults (95-100 mm 
total length (TL)) migrate to deeper offshore waters as 
they grow, often migrating 150 nautical miles (Joyce 
1965, Costello and Allen 1970). There is no evidence 
that adults from different spawning stocks migrate to 
different spawning grounds (Costello and Allen 1 966). 
The intensity of the migrations at the surface appears 
to be associated with moon phase, with greater num- 
bers captured during full moon tides compared to 
captures during new and quarter moon tides (Beardsley 
1970, Costello and Allen 1970). Although emigration 
occurs throughout the year, the main activity peak 
occurs in the fall with a secondary peak in the spring. 
Decreasing watertemperature triggers the pink shrimp 
to move into deeper waters (Joyce 1 965, Costello and 
Allen 1970, Copeland and Bechtel 1974). In Florida 
during this time, maturing juveniles move from Florida 
Bay westward into the Tortugas fishery area (Costello 
and Allen 1966, Allen et al. 1980, Gitschlag 1986). 
Western Gulf of Mexico pink shrimp typically move 
southward as they mature into adults, but some move- 
ment to the north has been observed (Klima et al. 
1 987). Movement patterns are influenced by patterns 
in fishing effort (Sheridan et al. 1989, Sheridan pers. 
comm.). Shrimp stocks in northern Mexico and south 
Texas cross the U.S. -Mexico border and probably 
comprise a single management entity. The pink shrimp 
may also overwinter in estuaries by burrowing into 
sediment (Williams 1955b, Joyce and Eldred 1966, 
Costello and Allen 1970, Copeland and Bechtel 1974, 
Bielsaetal. 1983). 

Reproduction 

Mode : Sexual reproduction occurs through external 
fertilization by sexually dimorphic (gonochoristic) male 
and female individuals (Costello and Allen 1970, 
McKenzie 1981). 


Mating/Spawning : Spawning occurs in sea water at 
depths of 4 to 48 m and probably in deeper waters as 
well (Perez-Farfante 1 969). Mating may occur several 
times during a female's growth and development and 
is not always associated with spawning. Mating occurs 
between midnight and early morning between a hard- 
shell male and a soft-shell female (Eldred 1958). A 
spermatophore is placed on the female's abdomen 
during mating. When the female releases eggs the 
spermatophore releases sperm and fertilization occurs 
externally (Costello and Allen 1970, McKenzie 1981, 
Williams 1984). In one study, the smallest impreg- 
nated female observed was 89 mm, and the smallest 
ripe female was 101 mm. In the Gulf of Mexico, the two 
principal spawning grounds are the Sanibel and Tortuga 
shelf regions between depths of 15 to 48 m. The 
Tortugas shrimp grounds receives emigrants from 
nursery areas between Florida Bay and Indian Key, 
and the Sanibel grounds receives shrimp from nursery 
areas between Indian Key and Pine Island Sound. 
Although ripening females and postlarvae have been 
observed throughout the year, the number of larvae 
indicates the height of spawning activity occurs from 
April through September in the Florida Bay region 
(Costello and Allen 1970, Roesslerand Rehrer 1971, 
McKenzie 1 981 , Williams 1 984). Similar but season- 
ally more abbreviated patterns are seen in areas to the 
west and north of south Florida. Spawning occurs as 
water temperatures rise, and water temperature is 
apparently critical to reproductive development 
(Cummings 1 961 , Costello and Allen 1 966, Jones et al. 
1970, Allen et al. 1980, Bielsa et al. 1983). Most 
spawning activity in the Florida Tortugas grounds is 
during the waning moon (Costello and Allen 1970, 
Roesslerand Rehrer 1 971 ), and occurs between 20° to 
31 °C with maximum activity between 27° and 30.8°C 
(Roessler et al. 1 969, Jones et al. 1 970). 

Fecundity : Shrimp with a weight of 1 0.1-66.8 g contain 
44,000 to 534,000 developing ova (Martosubroto 1 974). 

Growth and Development 

Egg Size and Embryonic Development : The average 
egg diameter is 0.31-0.33 mm. At 27-29°C, nauplii 
emerge 13-14 hours afterthe eggs are spawned (Dobkin 
1961). 

Age and Size of Larvae : Pink shrimp larvae undergo 5 
naupliar stages with length ranges of 0.35-0.40, 0.40- 
0.45, 0.45-0.49, 0.48-0.55, and 0.53-0.61 mm. There 
are 3 protozoeal stages with length ranges of 0.86- 
1.02, 1.5-1.9, and 2.2-2.7 mm. There are 3 mysis 
stages with length ranges of 2.9-3.4, 3.3-3.9, and 3.7- 
4.4 mm. Two postlarval stages have been described, 
with length ranges of 3.8 to 4.8 mm, and 4.7 to nearly 
10.0 mm (Ewald 1965, Costello and Allen 1970, Allen 
et al. 1980). The pink shrimp grows from nauplius to 


67 


Pink shrimp, continued 


postlarva in 2 to 3 weeks depending on the tempera- 
ture and location. Metamorphosis from protozoea to 
postlarva occurs in 15 days at 26°C, and in 25 days at 
21°C(Ewald 1965). 

Juvenile Size Range : Reported juvenile growth rates 
vary from 7 to 52 mm/month (Williams 1 955a, Eldred et 
al. 1 961 , Iversen and Jones 1 961 ), and subadults and 
adults grow approximately to 22 mm/month (Costello 
and Allen 1960, Iversen and Jones 1961, McCoy and 
Brown 1 967). Sexual maturity occurs at 85 mm TL for 
females and 74 mm TL for males (Dobkin 1 961 , Bielsa 
etal. 1983). 

Age and Size of Adults : The average sizes of large 
male and female pink shrimp are 1 70 mm and 210 mm 
TL, respectively. The average maximum age is 83 
weeks with an absolute maximum age of 2 years 
(Bielsa etal. 1983). 

Food and Feeding 

Trophic Mode : Pink shrimp are omnivorous consumers 
in marine and estuarine systems (Bielsa et al. 1983). 
Larvae in the naupliar stages do not feed, but first 
protozoea were observed to begin feeding immedi- 
ately when food became available (Ewald 1 965). Lar- 
vae and postlarvae feed on various plankton species. 
Juveniles and adults are opportunistic and forage 
primarily at night, on benthic prey, in shallow grass 
beds (Bielsa et al. 1983, Williams 1984, Nelson and 
Capone 1990, Schmidt 1993). 

Food Items : Larvae raised in hatchery conditions are 
fed various cultures of algae initially, and increasing 
amounts of brine shrimp nauplii as they became older 
(Ewald 1 965). Typical juvenile and adult prey includes 
nematodes, polychaetes, ostracods, copepods, di- 
noflagellates, annelids, gastropods, mollusks, filamen- 
tous green and blue-green algae, vascular detritus, 
and inorganic material (Bielsa et al. 1983, Williams 
1984, Nelson and Capone 1990, Schmidt 1993). 

Biological Interactions 

Predation : Many inshore fish species utilize the pink 
shrimp in their diet. Sport fishes such as snook, spotted 
seatrout, and gray snapper feed heavily on this spe- 
cies, but it is found in varying amounts in the diets of 
other fishes. These include lemon shark (Negaprion 
brevirostris), hardhead catfish, gafftopsail catfish (Bagre 
marinus), pinfish, pigfish (Orthopristis chrysoptera), 
sheepshead, crevalle jack, red drum, code goby, Span- 
ish mackerel, and red snapper (Lutjanus campechanus) 
(Kemp 1949, Miles 1949, Springer and Woodburn 
1 960, Odum 1 971 , Carr and Adams 1 973, Overstreet 
and Heard 1 978, Overstreet and Heard 1 982, Saloman 
and Naughton 1984, Sheridan et al. 1984, Schmidt 
1986, Harrigan et al. 1989, Heftier 1989). Many reef 


species, such as mutton snapper (Lutjanus analis), red 
grouper (Epinephelus morio), black grouper 
(Mycteroperca bonaci), and even pelagic species such 
as king mackerel (Scomberomorus cavalla) have been 
found to prey on pink shrimp (Bielsa et al. 1983). In 
addition, several birds prey on this species. These 
include wading birds, feeding opportunistically in coastal 
areas and seabirds foraging in mixed species flocks on 
concentrations of prey. Pink shrimp are probably an 
easy target for diving seabirds during periods of con- 
gregated movement. This species has also been 
found in the stomachs of some marine mammals 
(Tursiops truncatus and Stenella coeruleoalba), and 
may possibly be a prey item of marine reptiles (Bielsa 
et al. 1983). The bay squid (Lolliguncula brevis) is 
known to consume penaeid shrimp, and may include 
the pink shrimp as a prey item (Hargis 1979). 

Factors Influencing Populations : Disease is second 
only to predation and periodic physical catastrophes in 
limiting numbers of penaeid shrimps in nature (Couch 
1 978). A significant number of pink and brown shrimp 
in the Gulf of Mexico may be infected with the 
Baculoviruspenaei (BP) virus (Overstreet 1 994, Stuck 
pers. comm.). This virus is highly pathogenic to the 
early life stages of penaeid shrimp (Lightner and 
Redman 1 991 ), and it may be responsible for epizootic 
mortalities of pink shrimp (Couch et al. 1 975). Penaeid 
shrimp infected with symbiotic organisms may be weak- 
ened and more susceptible to mortality in waters with 
low DO (Overstreet 1978). Distribution, abundance, 
and recruitment of the pink shrimp may be limited by 
salinity, freshwater runoff , temperature, seagrass habi- 
tat, and substrate (Williams 1 965, Bielsa 1 983, Browder 
1 985, Hettler 1 992, Schmidt 1 993). Recruitment over- 
fishing by commercial shrimpers does not appear to be 
a problem for this species, but annual catch is man- 
aged to prevent the parent stock from falling below the 
level considered necessary to maintain recruitment 
(Nance 1989, Klima et al. 1990). Environmental 
changes may cause variable recruitment (Klima et al. 
1 990, Sheridan 1 996). The pink shrimp may compete 
for or be displaced by brown shrimp from habitats. This 
species can be difficult to distinguish from the brown 
shrimp, often resulting in unreliable data (Sheridan 
pers. comm.). 


68 


Pink shrimp, continued 


Personal communications 

Nance, J.M. NOAA National Marine Fisheries Service, 
Galveston, TX. 

Patella, F.J. NOAA National Marine Fisheries Service, 
Galveston, TX. 

Schmidt, T.W. South Florida Research Center, Ever- 
glades National Park, Homestead, FL. 

Sheridan, P.F. NOAA National Marine Fisheries Ser- 
vice, Galveston, TX. 

Steele, P. Florida Marine Research Inst., St. Peters- 
burg, FL. 

Stuck, K. Gulf Coast Research Laboratory, Ocean 
Springs, MS. 

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aquatic invertebrates from the United States and 
Canada: Decapod crustaceans. Amer. Fish. Soc. 
Spec. Pub. No. 17. American Fisheries Society, 
Bethesda, MD, 77 p. 

Zein-Eldin, Z.P. 1963. Experimental growth studies 
with postlarval brown shrimp. U.S. Fish Wildl. Serv. 
Circ. No. 161. 


72 


White shrimp 


Penaeus setiferus 
Adult 


(from Perez-Farfante 1969) 


Common Name: white shrimp 
Scientific Name: Penaeus setiferus 
Other Common Names: Blue shrimp, blue-tailed 
shrimp, common shrimp, Daytona shrimp; gray shrimp, 
green shrimp, green-tailed shrimp, lake shrimp, rain- 
bow shrimp, southern shrimp (Perez-Farfante 1969, 
Lindner and Cook 1 970, Motoh 1 977, McKenzie 1 981 , 
Muncy 1984); crevette ligubam du nord (French), 
camaron bianco norteno (Spanish) (Fischer 1978, 
NOAA1985). 

Classification (Williams et al. 1989) 
Phylum: Arthropoda 
Class: Crustacea 

Order: Decapoda 

Family: Penaeidae 

Value 

Commercial : Shrimping has been ranked as the sec- 
ond most valuable commercial fishery in the U.S., and 
seventh in quantity (NMFS 1993). U.S. landings of all 
shrimp species combined in the Gulf of Mexico were 
1 00.7 thousand mt in 1 992, and were valued at $316.6 
million. Total U.S. white shrimp harvest in the Gulf of 
Mexico was 32,012 mt in 1991, and white shrimp 
typically comprise 31% of the total Gulf of Mexico 
shrimp landings (NOAA 1 993). White shrimp were the 
targeted species in the U.S. shrimp fishery until the 
mid-1 930's; other species were darker and not as 
marketable. The species is fished for throughout the 
nearshore Gulf of Mexico and along the southeast U.S 
Atlantic coast. Maximum catches in the Gulf occur 
along the Louisiana coast west of the Mississippi Delta 
(Christmas and Etzold 1977). Catches of young-of- 
the-year shrimp occur almost entirely during summer 
and fall, while the spring white shrimp fishery consists 
of adults that have overwintered in the estuaries (Christ- 


mas and Etzold 1 977, Nance et al. 1 991 ). The Gulf of 
Mexico white shrimp fishery is considered fully ex- 
ploited, and a longterm potential annual yield of 34,403 
mt has been estimated (NOAA 1993). It has been 
suggested that commercial harvest has reached a 
point at which overfishing can occur (Nance and Nichols 
1988, Nance 1989). There is also a bait fishery for 
white shrimp throughout the bays and nearshore wa- 
ters from June to October. This catch, as well as most 
of the commercial catch, is obtained using otter trawls. 
Federal and some state laws may require the use of 
Turtle Excluder Devices (TEDs) on shrimp trawls, but 
bait shrimpers (catch <16 kg/day, trawl <10.7 m) may 
be exempt from these regulations (Nance pers. comm.). 
Other methods include haul seines and cast, butterfly, 
drop, push, and channel nets (Eldridge and Goldstein 
1975, Eldridge and Goldstein 1977). White shrimp 
form the mainstay for the Texas commercial bay fish- 
ery (Christmas and Etzold 1977). They also form an 
important part of the catch in Alabama where it is one 
of the primary species harvested for bait (Swingle 
1 972). Highest catches occur in fall months using otter 
trawls. 

Recreational : Recreational shrimping has become in- 
creasingly popular along the Gulf coast in recent years 
(Christmas and Etzold 1977). Fishermen use small 
trawls for the most part, but seines, cast nets, and push 
nets are used as well. Approximately 4,000 mt (heads 
on) of total shrimp (brown, pink, and white) were taken 
by recreational shrimpers in 1 979 in Texas and Louisi- 
ana. Regulations pertaining to licensing and geartype 
vary among the Gulf states, and catches are limited by 
location and season of fishing (GMFMC 1981). 


73 


White shrimp, continued 


Table 5.08. Relative abundance of white shrimp in 
31 Gulf of Mexico estuaries (from Volume /). 


Life 


stage 


A S J L E 


Florida Bay 


Ten Thousand Islands 


Caloosahatchee River 


Charlotte Harbor 


Tampa Bay 


Suwannee River 


V 


V 


V 


Apalachee Bay 


® 


• 


Apalachicola Bay 


® 


• 


V 


St. Andrew Bay 


o 


o 


Choctawhatchee Bay 


o 


® 


Pensacola Bay 


o 


® 


Perdido Bay 


o 


o 


Mobile Bay 


o 


• 


Mississippi Sound 


• 


O 


• 


® 


o 


Lake Borgne 


® 


• 


Lake Pontchartrain 


® 


• 


Breton/Chandeleur Sounds 


o 


O 


o 


o 


o 


Mississippi River 


o 


o 


Barataria Bay 


® 


• 


• 


V 


Terrebonne/Timbalier Bays 


o 


® 


o 


Atchafalaya/Vermilion Bays 


® 


• 


® 


Calcasieu Lake 


o 


• 


• 


Sabine Lake 


• 


• 


• 


Galveston Bay 


o 


• 


• 


Brazos River 


o 


• 


® 


Matagorda Bay 


® 


• 


• 


San Antonio Bay 


• 


• 


• 


Aransas Bay 


o 


® 


o 


Corpus Christi Bay 


® 


® 


Laguna Madre 


o 


® 


V 


Baffin Bay 


V 


V 


• 


A S J L E 


Relative abundance: 

# Highly abundant 

® Abundant 

O Common 

V Rare 

blank Not present 


Life stage: 

A - Adults 

S - Spawning 

J - Juveniles 

L - Larvae/postlarvae 

E - Eggs 


Indicator of Environmental Stress Pesticides have 
been found to have adverse effects on shrimp popula- 
tions along the coast of the Gulf of Mexico (Christmas 
and Etzold 1977, Couch 1978). White shrimp at 
locations in Galveston treated by aerial sprays of 
Malathion have experienced mortalities of up to 80%. 
The use of this pesticide has increased to the point that 
currently much of the Gulf coast uses some form of it in 
mosquito control programs. Other pesticides, as well 
as industrial and agricultural discharges, pose serious 
threats when used or discharged in drainage areas 
where they can enter water systems. The effects of 
petroleum products on penaeid shrimp is not well 
known. Mortality and pathological conditions have 
been induced in species exposed to different concen- 
trations of these chemicals. Penaeid shrimp are sen- 
sitive to heavy metals (Couch 1978). Jackson (1975) 
found mercury to be two orders of magnitude more 
toxic than zinc for juvenile white shrimp, with higher 
mortalities occurring at higher temperatures. Mortali- 
ties were also higher during spring compared to winter. 

Ecological : Penaeid shrimp provide an important link in 
the estuarine food web by converting detritus and 
plankton into available biomass for fishes and other 
predators. White shrimp are preyed on by many 
species of estuarine and coastal finfish. Abundant 
juvenile penaeid shrimp appear to be important in 
supporting large populations of certain fish species 
(Hettler 1 989). The postlarvae and juveniles are more 
tolerant of lower salinities than other Penaeus species 
(Williams 1984, Zein-Eldin and Renaud 1986), and 
may venture further into brackish marshes. White 
shrimp remain in estuaries longer and grow largerthan 
brown shrimp (Christmas and Etzold 1 977). They may 
be displaced by brown shrimp from Spartina marshes 
to nearby mud substrates in areas where they are 
sympatric (Giles and Zamora 1973, Zimmerman and 
Minello1984). 

Range 

Overall : The white shrimp ranges from Fire Island, New 
York, to the St. Lucie Inlet, Florida, on the Atlantic 
coast. In the Gulf of Mexico, it is found from Ochlockonee 
River, Florida, to Campeche, Mexico. It is rarely found 
near the Dry Tortugas, Florida, and is absent around 
the southernmost portion of the Florida peninsula. The 
centers of abundance occur off Georgia and northeast- 
ern Florida for the Atlantic coast; and Louisiana, Texas 
and Tabasco for the Gulf of Mexico (Williams 1984, 
Klima et al. 1987), but greatest densities occur off the 
coast of Louisiana (Klima et al. 1982). NOAA (1985) 
reports the range within the Gulf of Mexico from 
Apalachee Bay, Florida, to northeast Campeche Bay, 
Mexico. Perez-Farfante (1 969) distinguishes the area 
of Ciudad, Mexico as the southern limit in the Gulf of 
Mexico. 


74 


White shrimp, continued 


Within Study Area : Postlarval to subadult white shrimp 
are well established throughout the Texas, Louisiana, 
and Mississippi estuaries and nearshore Gulf waters, 
utilizing the nursery habitat generally trom June/July 
through October/November (Christmas and Etzold 
1 977) (Table 5.08). For the purposes of Table 5.08, all 
larval and postlarval stages of white shrimp are consid- 
ered together as "larvae" (L). 

Life Mode 

Eggs are spawned from spring through fall in offshore 
waters, where they hatch and develop into larvae 
(Etzold and Christmas 1977, Klima et al. 1982). Eggs 
are demersal and larval stages are planktonic. 
Postlarvae become benthic upon reaching the nursery 
areas of estuaries, and begin development into the 
juvenile stage (Perez-Farfante 1 969, Lindnerand Cook 
1970, McKenzie 1981, Muncy 1984, Williams 1984). 
As juveniles approach adulthood, they move out of 
estuaries into coastal waters where they mature and 
spawn. Both juveniles and adults are demersal in 
estuarine and coastal waters, and are usually found at 
depths of <30 m (Perez-Farfante 1969, Lindner and 
Cook 1970, Etzold and Christmas 1977, McKenzie 
1981, Muncy 1984, Williams 1984). 

Habitat 

Ty pe: The white shrimp is neritic to estuarine, and 
pelagic to demersal, depending on the life stage. Eggs 
and early planktonic larval stages occur in nearshore 
marine waters. Postlarvae seek estuarine habitats of 
shallow water with muddy/sand bottoms high in or- 
ganic detritus, or abundant in marsh grass in oligohaline 
to euhaline salinities. Juveniles prefer lower salinity 
waters, and are frequently found in tidal rivers and 
tributaries throughout their range (Christmas and Etzold 
1977). Juveniles and sub-adults move into offshore 
waters during fall and winter. Adults generally inhabit 
nearshore waters of the Gulf in depths less than 27 m, 
and are usually more abundant at a depth of 14 m 
(Perez-Farfante 1 969, Lindner and Cook 1 970, Rent ro 
and Brusher 1982, Muncy 1984, Williams 1984). 

Substrate : Postlarvae and juveniles inhabit mostly 
mud or peat bottoms with large quantities of decaying 
organic matter or vegetative cover (Williams 1955b, 
Williams 1958). Adults are found on bottoms of soft 
mud or silt in offshore waters (Perez-Farfante 1969, 
Lindner and Cook 1 970, Muncy 1 984, Williams 1 984). 
It has been suggested that white shrimp densities are 
related to the amount of marsh vegetation available in 
intertidal estuarine habitats (Turner 1977), but other 
studies have found abundances to be quite variable in 
relationship to vegetation (Minello et al. 1990, 
Zimmerman et al. 1990, Zimmerman pers. comm.). 


Physical/Chemical Characteristics : 
Temperature: This species is tolerant of temperatures 
ranging from approximately 7° to 38°C (Williams 1 955b, 
Joyce 1965, Zein-Eldin and Griffith 1969). Sudden 
changes in temperature, however, can be detrimental. 
White shrimp are more tolerant of high temperatures 
and less tolerant of low temperatures than brown or 
pink shrimp (Christmas and Etzold 1977). Postlarval 
white shrimp have been collected in temperatures from 
12.6° to 30.6°C. Juveniles have been collected in 
temperatures ranging from 6.5° to 39.0°C, with peaks 
in abundance between 15° and 33°C (Zein-Eldin and 
Renaud 1986). Normal growth of juveniles occurs 
between 15°-16° and 25°-30°C with growth rates de- 
creasing as temperatures approach > 35°C (Zein-Eldin 
and Griffith 1 969) or drop below 1 5°C (Christmas and 
Etzold 1977, St. Amant and Lindner 1966). 

Salinity: White shrimp can be considered euryhaline 
since most life stages tolerate fairly wide salinity ranges 
(Gunter 1961, Zein-Eldin and Griffith 1969, Lindner 
and Cook 1970, Copeland and Bechtel 1974). This 
species is apparently more tolerant of lower salinities 
than brown shrimp (Gunter 1 961 ), and does not appear 
to be affected by sudden salinity drops as the brown 
shrimp is (Minello et al. 1 990). White shrimp postlarvae 
have been collected in salinities ranging from 0.4 to 
37.4% . Juveniles seem to prefer or tolerate lower 
salinities than do other penaeid species (Williams 
1955a). They prefer salinities less than 10%o (Zein- 
Eldin and Renaud 1 986), and have been found several 
kilometers upstream in rivers and tributaries (Christ- 
mas and Etzold 1977). Collections of juveniles have 
occurred in salinities from 0.3%o in Florida to as high as 
41.3%o in the Laguna Madre of Texas (Gunter 1961, 
Joyce 1965). Adults are usually found offshore in 
waters with salinities greater than 27%o (Muncy 1 984). 
Size appears to be related to salinity tolerance (Will- 
iams 1955a, Joyce1965). In laboratory studies no 
growth differences were detected over a salinity range 
from 2 to 40%o (Zein-Eldin and Griffith 1969). 

Migrations and Movements : White shrimp postlarvae 
migrate into the estuarine nurseries through passes 
from May to November, with peaks in June and a 
second peak in September for the northwest Gulf of 
Mexico (Baxter and Renfro 1967, Klima et al. 1982). 
Juveniles migrate farther up the estuary into less saline 
waterthan brown or pink shrimp (Perez-Farfante 1 969). 
As shrimp grow and mature they leave the marsh 
habitat for deeper, higher salinity parts of the estuary 
prior to their emigration to Gulf waters (Lindner and 
Cook 1 970). The emigration of juveniles and subadults 
from estuaries usually occurs in late August and Sep- 
tember, and appears to be related to the size of the 
shrimp and the environmental conditions within the 
estuarine system (Klima et al. 1982). One factor that 


75 


White shrimp, continued 


may influence this emigration is sharp drops in water 
temperature occurring during the fall and winter (Pullen 
and Trent 1 969). After leaving the estuaries, there is a 
general westward movement of adult white shrimp in 
offshore waters combined with movement to deeper 
waters (Baxter and Hollaway 1981, Hollaway and 
Sullivan 1982, Lyon and Boudreaux 1983). In April to 
mid-May, white shrimp move back to nearshore and 
inshore waters (Hollaway and Sullivan 1982). 

Reproduction 

Mode : Reproduction is by external fertilization be- 
tween sexually dimorphic male and female individuals 
(Perez-Farfante 1 969, Lindner and Cook 1 970, Muncy 
1984). Although this species has separate male and 
female sexes (gonochoristic), hermaphroditism has 
been reported in white shrimp parasitized by Thelohania 
sp. (Rigdonet al. 1975). 

Mating/Spawning : The external genital organ (thelycum) 
in female white shrimp is open, unlike those in brown 
shrimp, making copulation possible between two hard- 
shelled individuals (Overstreet 1978, Muncy 1984). 
The male places a spermatophore on the female's 
abdomen, and when eggs are released the spermato- 
phore releases sperm fertilizing the eggs externally 
(Perez-Farfante 1969). Spawning along the Atlantic 
coast probably begins in May and extends through 
September (Lindner and Anderson 1956, Williams 
1984); in the Gulf, the season probably extends from 
March to September or October (spring to late fall) 
(Franks et al. 1972). Spawning occurs offshore at 
depths of 9 to 34 m deep and peaks in the summer 
(June-July). There is also some suggestion of limited 
spawning within estuaries and bays (Lindner and Cook 
1970, Whitaker pers. comm.). Females that spawn 
early may spawn a second time in late summer or fall, 
and possibly up to 4 times in a season (Lindner and 
Anderson 1956, Lindner and Cook 1970, Whitaker 
pers. comm.). The ability of shrimp over one year old 
to spawn is unknown, but considered possible (Lindner 
and Cook 1 970, Zein-Eldin pers. comm.). Othershrimp 
species with similar methods of reproduction have 
been found to spawn again in their second year. Rapid 
temperature changes, such as the sudden increases 
and decreases that occur in the summer and fall, seem 
to trigger spawning (Henley and Rauschuber 198.1). 

Fecundity : A large female is estimated to produce 0.5 
to 1.0 million eggs at a single spawning (Anderson et 
al. 1949, Lindner and Cook 1970, Williams 1984). 

Growth and Development 

Egg Size and Embryonic Development : Egg develop- 
ment is oviparous. Fertilized eggs are demersal, 
nonadhesive, spherical, and are approximately 0.28 
mm in diameter (Lindner and Cook 1970). Ripe eggs 


are 0.2 to 0.3 mm in diameter and hatch in 10 to 12 
hours after fertilization (Klima et al. 1982). 

Age and Size of Larvae : Eggs hatch into planktonic 
nauplii approximately 0.3 mm TL (Klima et al. 1982). 
Larvae transform through 5 naupliar stages, 3 
protozoeal stages and 3 mysis stages (Perez-Farfante 
1969). The length of larval life is from 10 to 12 days, 
depending on local food, habitat, and environmental 
conditions. They enter the estuaries as postlarvae at 
total lengths (TL) of approximately 7 mm. Rapid growth 
rates of 20-40 mm/month occur in nursery areas (Wil- 
liams 1955a, Lindner and Anderson 1956, Perez- 
Farfante 1 969, Lindner and Cook 1 970). Growth is far 
more strongly affected by changes in temperature than 
salinity (Zein-Eldin and Griffith 1969), with little or no 
growth occuring below 18°C (Zein-Eldin and Renaud 
1986). Postlarvae develop into juveniles at about 25 
mm TL (Christmas et al. 1976). 

Juvenile Size Range : Juveniles can attain lengths of 98 
to 146 mm TL in 4 to 6 weeks after entering estuarine 
areas (Zein-Eldin and Renaud 1986). Emigration of 
subadults occurs through the summer and fall at a size 
of 100 to 120 mm TL. Sexual maturity is generally 
reached at 140 mm TL in the northern Gulf of Mexico 
(Perez-Farfante 1969, Lindner and Cook 1970). 

Age and Size of Adults : The white shrimp has a life 
expectancy of 18 months, although some have been 
maintained in the laboratory for 3 to 4 years (Klima et 
al. 1982). Females become sexually mature at about 
165 mm TL and ripe sperm first appears in males at 
about 119 mm TL (Burkenroad 1939, Lindner and 
Cook 1970). 

Food and Feeding 

Trophic Mode : White shrimp are omnivorous at all life 
stages, but may depend more heavily on plant matter 
than animal matter (McTigue and Zimmerman 1991). 
Larval white shrimp are planktivorous, while adults and 
juveniles are scavengers. 

Food Items : Penaeid larvae subsist on egg yolk until 
the Protozoea I stage when active feeding begins 
(Lindner and Cook 1 970). Larvae are reported to feed 
on plankton and suspended detrital material, and in the 
laboratory, they have been successfully fed micro- 
scopic green algae and brine shrimp nauplii. Both 
juveniles and adults are omnivorous. Juveniles com- 
bine detrital feeding with scavenging on the bottom 
sediment. As they mature, they combine predation 
with detrital feeding. Foods consist of detritus, insects, 
annelids, gastropods, and fish, and copepods, bryozo- 
ans, sponges, corals, filamentous algae, and vascular 
plant stems and roots (Darnell 1958, Perez-Farfante 
1969, Christmas and Etzold 1977). 


76 


White shrimp, continued 


Biological Interactions 

Predation : Finfish prey heavily on this species. Known 
predators include tiger shark {Galeocerdo cuvier), At- 
lantic sharpnose shark (Rhizoprionodon terraenovae), 
bull shark, ladyfish (Elops saurus), hardhead catfish, 
crevalle jack, red snapper (Lutjanus campechanus), 
southern kingfish (Menticirrhus americanus), spotted 
seatrout, sand seatrout, red drum, black drum, cobia 
(Rachycentron canadum), code goby, Spanish mack- 
erel, southern flounder, and gulf flounder (Gunter 1 945, 
Kemp 1949, Miles 1949, Darnell 1958, Springer and 
Woodburn 1960, Boothby and Avault 1971, Stokes 
1977, Overstreet and Heard 1978a, Overstreet and 
Heard 1978b, Danker 1979, Creel and Divita 1982, 
Overstreet and Heard 1982, Saloman and Naughton 
1984, Sheridan et al. 1984). Some predation by bay 
squid (Lolliguncula brevis) is possible (Hargis 1979). 
Penaeid shrimp are an important link in the energy flow 
of food webs by feeding on benthic organisms, detritus, 
and other organic material found in sediments (Odum 
1 971 , Carr and Adams 1 973). 

Factors Influencing Populations : The commercial 
shrimp fishery may be impacting the white shrimp 
population (Nance and Nichols 1988, Nance 1989, 
Nance et al. 1989). Catch statistics indicate that 
current harvest levels may be over-exploiting the re- 
source, causing a decline in adult recruitment. Patho- 
gens also affect the white shrimp. It is susceptible to 
diseases and parasites, but the extent of resultant 
mortality is largely unknown (Couch 1978, Muncy 
1 984). Predation and episodic catastrophes probably 
play more important roles as limiting factors of natural 
populations. Penaeid shrimp infected with biosymbionts 
may be weakened and die in low oxygen situations 
(Overstreet 1978). In the Mississippi Sound, adult 
white shrimp are infected with a cestode which invades 
the hepatopancreas (Muncy 1 984). White shrimp tend 
to aggregate, forming a patchy distribution pattern in 
estuaries. The environmental factors that govern this 
type of distribution are not known (Zimmerman et al. 
1990, Zimmerman pers. comm.). Suitable estuarine 
habitat is critical to survival and recruitment of juveniles 
(Turner 1 977, Nance et al. 1 989). However, develop- 
ment has destroyed or altered large portions of these 
estuarine areas to a point of low productivity (Christ- 
mas and Etzold 1977). Continued loss of this habitat 
may result in declines in recruitment and harvest 
(Christmas and Etzold 1 977, Nance et al. 1 989). Epi- 
sodic weather events such as hurricanes and freezes 
also impact white shrimp populations (Kutkuhn 1962, 
Barrett and Gillespie 1973). Hurricanes can result in 
high mortality of a spawning class by causing adverse 
environmental conditions. Such conditions include 
high tides and extensive flooding, higher salinities, 
excessive turbulence, turbidity, and habitat destruc- 
tion. Freezes can cause mass mortalities by reducing 


the watertemperature to lethal levels. Other factors felt 
to be related to penaeid shrimp population dynamics 
are productivity of estuarine nursery areas, food avail- 
ability and content, refuge from predation, amount of 
freshwater inflow, light intensity, tide, and rainfall (Christ- 
mas and Etzold 1977, Gracia 1991). 

Personal Communications 

Nance, J.M. NOAA National Marine Fisheries Service, 
Galveston, TX. 

Patella, F.J. NOAA National Marine Fisheries Service, 
Galveston, TX. 

Whitaker, J.D. South Carolina Wildlife and Marine 
Resources Department, Charleston, SC. 

Zein-Eldin, Z.P. NOAA National Marine Fisheries 
Service, Galveston, TX. 

Zimmerman, R.J. NOAA National Marine Fisheries 
Service, Galveston, TX. 

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78 


White shrimp, continued 


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79 


White shrimp, continued 


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80 


Grass shrimp 


Palaemonetes pugio 
Adult 


1 cm 


(from Heard 1979) 


Common Name: grass shrimp 

Scientific Name: Palaemonetes pugio 

Other Common Names: daggerblade grass shrimp 

(Williams et al. 1989), glass shrimp 

Classification (Williams et al. 1989) 

Phylum: Arthropoda 

Class: Crustacea 

Order: Decapoda 

Family: Palaemonidae 

There are several Palaemonetes species in U.S. es- 
tuarine waters, which are known collectively as "grass 
shrimp" (Camp pers. comm.). For the purposes of this 
life history summary, "grass shrimp" refers specifically 
to P. pugio, also known as "daggerblade grass shrimp" 
(Williams et al. 1 989). Closely related "sister species" 
include P. vulgaris (marsh grass shrimp), P. interme- 
dius (brackish grass shrimp), P. kadiakensis (Missis- 
sippi grass shrimp), and P. paiudosus (riverine grass 
shrimp) (Hedgepeth 1966, Williams et al. 1989). 

Value: 

Commercial : The grass shrimp has little commercial 
value. It is available for sale through commercial 
biological suppliers for use in toxicity testing (Buikema 
et al. 1 980). It is also sometimes sold in pet stores as 
live food for aquarium fish (Anderson 1985). 

Recreational : The grass shrimp has little recreational 
value (Anderson 1 985). Anglers catch grass shrimp to 
use as live bait for game fish (Huner 1979). In Louisi- 
ana, preserved grass shrimp are also sold as bait in 
some fishing shops. 


Indicatorof Environmental Stress : This species is often 
used for LD50 bioassays for petroleum hydrocarbons 
because it is usually a common inhabitant of estuarine 
systems. It has also been used to study toxicity and 
bioaccumulation of heavy metals, insecticides, petro- 
leum hydrocarbons, and suspended particulate sedi- 
ments (Schimmel and Wilson 1977, Anderson 1985, 
Khan et al. 1 989, Moore 1 989, Rice et al. 1 989, Thorpe 
and Costlow 1989, Burton and Fisher 1990, Fisherand 
Clark 1990, Lindsay and Sanders 1990, Rule and 
Alden 1990, Long et al. 1991). 

Ecological : This grass shrimp and other members of its 
genus are among the most widely distributed and 
abundant shallow water benthic macroinvertebrates in 
Gulf of Mexico estuaries (Odum and Heald 1972, 
Anderson 1985, Zimmerman et al. 1990). Its abun- 
dance in estuaries can enable it to have a substantial 
impact on the dominant energy sources of these sys- 
tems while channeling significant quantities of that 
energy through its own population (Welsh 1975). The 
grass shrimp's importance as a prey item in the diet of 
many estuarine fishes and as a link in the marine food 
web makes this a valuable species ecologically. It is 
also important in estuarine trophic dynamics in speed- 
ing detrital breakdown by breaking up large detrital 
particles during its feeding activities. This serves to 
prevent blockages or accumulations from occurring 
due to pulses of detrital material into the environment. 
The grass shrimp also transfers refractory organic 
matter and detritus to higher trophic levels by repack- 
aging this material into feces, heterogeneous frag- 
ments, dissolved organic material, and shrimp biom- 
ass, thus making this food source more available to a 
variety of trophic levels (Welsh 1 975, Anderson 1 985, 
Killametal. 1992). 


81 


Grass shrimp, continued 


Table 5.09. Relative abundance of grass shrimp in 
31 Gulf of Mexico estuaries (from Volume /)■ 


Life 


i stage 


Estuary 


A S J L E 


Florida Bay 


O 


O 


O 


o 


o 


Ten Thousand Islands 


o 


O 


O 


o 


o 


Caloosahatchee Rivet 


• 


• 


• 


• 


• 


Charlotte Harbor 


Tampa Bay 


Suwannee River 


Apalachee Bay 


• 


• 


• 


• 


• 


Apalachicola Bay 


• 


• 


• 


• 


• 


St. Andrew Bay 


® 


® 


® 


® 


® 


Choctawhatchee Bay 


® 


® 


® 


® 


® 


Pensacola Bay 


• 


• 


• 


• 


• 


Perdido Bay 


Mobile Bay 


Mississippi Sound 


Lake Borgne 


• 


• 


• 


• 


• 


Lake Pontchartrain 


o 


O 


o 


o 


o 


Breton/Chandeleur Sounds 


® 


® 


® 


® 


® 


Mississippi River 


o 


o 


o 


o 


o 


Barataria Bay 


® 


® 


® 


® 


® 


Terrebonne/Timbalier Bays 


® 


® 


® 


® 


® 


AtchafalayaA/ermilion Bays 


• 


• 


• 


• 


• 


Calcasieu Lake 


Sabine Lake 


Galveston Bay 


• 


• 


• 


• 


• 


Brazos River 


® 


® 


® 


® 


® 


Matagorda Bay 


• 


• 


• 


• 


• 


San Antonio Bay 


® 


® 


® 


® 


® 


Aransas Bay 


® 


® 


® 


® 


® 


Corpus Christi Bay 


• 


• 


• 


• 


• 


Laguna Madre 


Baffin Bay 


A S J L E 


Relative abundance: 


Highly abundant 
Abundant 
Common 
Rare 


® 

o 

blank Not present 


Life stage: 

A - Adults 

S - Spawning 

J - Juveniles 

L - Larvae/postlarvae 

E - Eggs 


Range 

Overall : The range of the grass shrimp is probably 
discontinuous from Quebec to Nova Scotia, and Maine 
to Texas (Williams 1984). 

Within Study Area : This is a ubiquitous species, along 
with its congeners, throughout the estuaries of the Gulf 
coast from Florida Bay, Florida, to the Laguna Madre, 
Texas (Table 5.09). It is often replaced in higher 
salinities by Palaemonetes vulgaris and/or P. interme- 
dius, and by P. kadiakensis and P. paludosus in fresh 
water (Hedgepeth 1966). 

Life Mode 

Eggs are carried by the female, and the larvae are 
planktonic. Juveniles and adults are littoral or estua- 
rine and benthic, appearing to prefer vegetated areas 
(Williams 1984). In Georgia salt marshes, juveniles 
and adults are segregated by habitat (Kneib 1987a). 
Movements and distribution patterns may be influ- 
enced by both photoperiod and tidal cycles (Anderson 
1 985, Kneib 1 987a). Juveniles and adults are omnivo- 
rous in their feeding habits. 

Habitat 

Type : The grass shrimp occupies habitats ranging 
from estuarine to riverine (Knowlton and Williams 1970). 
It is usually found near the water's edge in shallows of 
bays and creeks, or in marshes, submerged vegetation 
and oyster reefs (Williams 1984, Anderson 1985). 
Although most common in shallow waters, it has been 
collected in waters as deep as 1 7 m. During periods of 
extreme heat or cold it retreats to deeper channel 
areas. It is often abundant in turbid waters possibly to 
avoid predators, but turbidity is not a necessary habitat 
requirement (Anderson 1985, Killam et al. 1992). It 
also uses seagrass and other aquatic vegetation as 
refuge from predation and as foraging areas (Killam et 
al. 1992). Juveniles are found primarily on vegetated 
marsh surfaces in the intertidal region, while adults 
inhabit subtidal areas (Anderson 1985, Kneib 1987a). 

Substrate : Vegetated or oyster shell substrate is pre- 
ferred (Williams 1984, Anderson 1985). 

Physical/Chemical Characteristics 
Temperature: The grass shrimp is eurythermal and 
both juveniles and adults can tolerate from 5° to 38°C, 
depending on geographic location (Wood 1 967, Christ- 
mas and Langley 1 973, Anderson 1 985). In laboratory 
studies an estimated 80% of larvae completed meta- 
morphosis to postlarval stages at temperatures of 
20°C to 30°C at salinities ranging from 1 1 to 33% , with 
optimum development occurring at 20° to 27°C and 1 7 
to 27% (Sastry and Vargo 1977, McKenney and Neff 
1 979). Juveniles and adults have optimum survival at 
temperatures ranging from 18° to 25°C in salinities of 


82 


Grass shrimp, continued 


4 to 1 6%o (Wood 1967). Growth of juveniles is greatest 
at temperatures between 25° and 32°C and salinities 
between 16 and 22%°. Below 14°C growth decreases, 
and is negligible at 11°C (Wood 1967). Breeding 
temperatures vary with geographic location of the 
study, and range between 17° to 38°C (Sastry and 
Vargo 1977, Wood 1967). 

Salinity: The effects of salinity on larval growth and 
development are unclear and may vary with geo- 
graphic location and individual populations. Larval 
survival, however, is generally poor at salinities of less 
than 15%o (Kirby and Knowlton 1976, McKenney and 
Neff 1 979). The upper and lower 96 hour LC50 values 
for larval grass shrimp in laboratory studies occurred at 
16 and 46%o respectively (Kirby and Knowlton 1976). 
The optimum salinity for complete larval development 
is reportedly from 20 to 25%o (McKenney and Neff 
1979, Knowlton and Kirby 1984). Larval and juvenile 
grass shrimp are more tolerant of low salinities and 
high temperatures than of high salinities and high 
temperatures (Wood 1967). Juveniles and adults are 
capable of tolerating salinities ranging from to 55%o 
(freshwater to hypersaline), but are most common in 
oligohaline to euhaline salinities of 2 to 36% (Wood 
1 967, Kirby and Knowlton 1 976, Williams 1 984, Ander- 
son 1985). In southwestern Florida, they were most 
common from 10 to 15%o in one study (Rouse 1969), 
and in waters with salinities of <20%o in another (Odum 
and Heald 1 972). Salinity appears to affect maturation 
and spawning age, with individuals from higher salinity 
waters reaching maturity faster than those in lower 
salinity waters (Alon and Stancyk 1 982). The 96 hour 
LC50 values for adults is 0.5%° and 44%o (Kirby and 
Knowlton 1976). 

Dissolved Oxygen (DO): Data on the DO requirements 
of the grass shrimp are limited (Killam et al. 1 992). It is 
apparently well adapted to low oxygen conditons, and 
collections have been made in waters with DO levels 
that ranged from 2.8 to 1 1 ppm (Welsh 1 975, Barrett et 
al. 1978, Rozas and Hackney 1984). In laboratory 
tests, it is able to tolerate DO levels less than 1 .0 ppm 
(Anderson 1985). Grass shrimp can cope with brief 
periods of low DO by climbing out of water on Spartina 
stalks for a few hours, particularly during warm summer 
nights (Wiegert and Pomeroy 1981). This species is 
also able to tolerate anoxic conditions by decreasing its 
oxygen consumption as DO declines (Welsh 1975). 

Migrations and Movements : There is little indication of 
extensive migrations. The grass shrimp does, how- 
ever, move to deeper waters with the onset of espe- 
cially high or low temperatures. The extent of its 
movements among various depths may be related to 
the distribution of oyster shell substrates. It tends to 
migrate in the direction of tidal currents, but avoids fast 


currents (Thorp 1 976, Anderson 1 985). There is some 
evidence that grass shrimp may be more active at night 
(Rozas and Hackney 1984). 

Reproduction 

Mode : Sexes in the grass shrimp are separate 
(gonochoristic). This species is sexually dimorphic 
and has external fertilization (Burkenroad 1947, 
Knowlton and Williams 1970). Eggs develop ovipa- 
rously. 

Mating and Spawning : When females become sexu- 
ally mature, they molt into breeding-form and become 
receptive to males (Burkenroad 1 947, Anderson 1 985, 
Killam et al. 1 992). The breeding-form is characterized 
by extra setae on the pleopods, enlargement of the 
abdominal brood pouch, and development of periodic 
chromatophores and is recognized by males through 
antennal contact on some part of the female's body 
(Burkenroad 1947). Mating must occur within 7 hours 
of the female's molting, and oviposition must occur 
within 7 hours after transfer of sperm. Spawning 
usually occurs a few hours after mating (Burkenroad 
1947). Fertilization is external and occurs with disso- 
lution of the spermatophore as eggs are released by 
the female (Burkenroad 1 947, Anderson 1 985). Eggs 
are extruded onto the female's pleopods and are held 
there until they hatch, usually in 1 2 to 60 days, depend- 
ing on temperature. A new brood of eggs is deposited 
1 to 2 days after hatching of the previous brood 
(Knowlton and Williams 1 970). The spawning season 
is from February to October, but may vary with geo- 
graphic location. Two spawning peaks have been 
noted in Galveston Bay, Texas, one in the early sum- 
mer and the other in early fall (Wood 1967). The 
presence of ovigerous females suggests that spawn- 
ing occurs throughout the year in southwest Florida 
(Rouse 1969, Williams 1984, Anderson 1985). 

Fecundity : The number of eggs produced increases as 
the female grows. Fecundity estimates range from 
<100 to >700 eggs per female (Welsh 1975, Wood 
1967, Sikora 1977), but eggs probably number from 
300 to 500 most commonly (Anderson 1 985, Killam et 
al. 1992). Females can molt again within a few days 
after spawning and produce a second brood (Knowlton 
and Williams 1970, Anderson 1985). Peak egg pro- 
duction occurs in May and is continuous through the 
summer months, but begins to wane in September 
(Knowlton and Williams 1970). 

Growth and Development 

Egg Size and Embryonic Development : Eggs are 0.6 
to 0.9 mm in diameter (Holthius 1952, Broad 1957) 
and develop oviparously (Anderson 1 985). Hatching 
occurs in 12 to 60 days depending on geographical 
location. The period of incubation is usually shorter in 


83 


Grass shrimp, continued 


areas with warmer water than in cooler locations. 

Age and Size of Larvae : Newly hatched larvae are 2.6 
mm. They go through 3-11 zoeal stages (molts), 
ending at about 6.3 mm. The zoeal stages last from 
1 1 days to several months depending on environmen- 
tal conditions including the amount of food (Broad 
1957). In a study conducted in Georgia, it was 
suggested that settlement from the plankton by ad- 
vanced zoeal stages and metamorphosis to the 
postlarva stage is triggered when larvae enter veg- 
etated habitats (Kneib 1987b). 

Juvenile Size Range : Growth to maturity in Texas is 
reported to take 2 to 3 months in summer and 4 to 6 
months in winter. Females are mature at a size of 
approximately 18-24 mm TL (total length) and males 
at approximately 1 5 mm TL (Broad 1 957, Wood 1 967, 
Knowlton and Williams 1 970, Alon and Stancyk 1 982). 

Age and Size of Adults : The life span of this species 
is 6 to 13 months. The older overwintering shrimp 
usually spawn early in the year as adults, and 
postlarvae that survive the winter spawn the following 
spring. In South Carolina, habitats with consistently 
higher salinities (>20% o ) may provide more optimal 
conditions, resulting in faster growth and earlier spawn- 
ing, than fluctuating, lower salinity habitats (<20%o) 
(Alon and Stancyk 1982). Reported maximum sizes 
for males and females are 33 mm and 50 mm TL, 
repectively (Holthuis 1952). . 

Food and Feeding 

Trophic mode : This species is an opportunistic, om- 
nivorous feeder (Anderson 1 985, Kneib 1 987a, Nelson 
and Capone 1990). It probably uses tactile cues and/ 
or chemoreceptors on its legs in order to find relatively 
sedentary benthic prey, but may rely on the sensitivity 
of its compound eyes to detect nektonic prey (Kneib 
1987a). 

Food Items : Planktonic larvae feed on zooplankton, 
algae, and detritus. Juveniles and adults eat a variety 
of animal and plant matter including detritus, polycha- 
etes, meiofauna, blue crab megalopae, larval fish, 
algae and dead animal matter (Heard 1 979, Anderson 
1985, Kneib 1987a, Nelson and Capone 1990, Olmi 
1990). Grass shrimp are known to consume the 
epiphytic organisms attached to seagrasses while 
living in this habitat (Morgan 1980). When epiphyte 
abundance is high, grass shrimp are capable of using 
them to completely satisfy their dietary needs. 

Biological Interactions 

Predation : Wading birds such as the clapper rail (Rallus 
longirostris) utilize the grass shrimp as food (Heard 
1 982). It has also been found in the stomach contents 


of juvenile American alligators (Piatt et al. 1990). 
Piscine predators include: longnose gar (Lepisosteus 
osseus), blue catfish (Ictalurus furcatus), gafftopsail 
catfish (Bagre marinus), hardhead catfish, gulf killifish, 
yellow bass (Morone mississippiensis), largemouth 
bass (Micropterus salmoides), snook, gray snapper, 
silver perch, Atlantic croaker, spotted seatrout, sand 
seatrout, red drum, black drum, pinfish, sheepshead, 
bighead searobin (Prionotus tribulus), Spanish mack- 
erel, king mackerel (S. cavalla), and southern flounder 
(Gunter 1945, Kemp 1949, Miles 1949, Darnell 1958, 
Harrington and Harrington 1961, Linton and Rickards 
1965, Boothby and Avault 1971, Diener et al. 1974, 
Bass and Avault 1975, Danker 1979, Levine 1980, 
Overstreet and Heard 1 982, Rozas and Hackney 1 984, 
Perschbacherand Strawn 1 986, Morales and Dardeau 
1987, Peters and McMichael 1987, Hettler 1989). 
Penaeid shrimp may also prey upon juvenile grass 
shrimp (Kneib 1987b). Blue crabs in Florida are known 
to occasionally prey on grass shrimp during the winter 
(Laughlin 1982), and small juvenile blue crabs have 
been observed capturing and consuming grass shrimp 
when both were held in aquaria set up with marsh 
habitats (Pattillo pers. obs.). 

Factors Influencing Populations : 
Temperature and salinity are considered to be the 
major factors affecting the distribution of grass shrimp 
(Wood 1 967, Killam et al. 1 992). Although this species 
can tolerate wide ranges of these two parameters, 
reproduction, optimal growth, and survival can be 
negatively affected by extreme conditions. Grass 
shrimp abundance can be affected by habitat alter- 
ations that destroy vegetation on which this species 
depends (Trent et al. 1 976, Anderson 1 985). The loss 
of vegetation also results in a reduction of detrital input 
into surrounding systems which can cause a decrease 
in grass shrimp abundance. Palaemonetes pugio is 
not as tolerent to higher salinities as some of its sister 
species, and this may contribute to its replacement in 
high salinity waters by P. vulgaris and/or P. interme- 
dius (Williams 1985). Predation by fishes can have a 
major influence in the distribution and longevity of 
grass shrimp (Alon and Stancyk 1982, Kneib 1987b). 
Displacement of grass shrimp from their preferred 
habitats of submerged macrophytes makes them more 
vulnerable to predation (Anderson 1 985). Adult grass 
shrimp prey on the larvae of killifish (Fundulus sp.) and, 
by so doing, contribute to the control of one of their 
principal predators (Kneib 1 987a). Diseases and para- 
sites do not appear to have any major effect on the 
abundance and growth of grass shrimp in the Gulf of 
Mexico (Anderson 1985). 


84 


Grass shrimp, continued 


Personal communications 

Camp, David K. Florida Marine Research Inst., St. 
Petersburg, FL. 

Peterson, Mark S. Gulf Coast Research Lab., Ocean 
Springs, MS. 

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Broad, A.C. 1957. Larval development of 
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87 


Spiny lobster 


Panulirus argus 
Adult 


5 cm 


(from Williams 1965) 


Common Name: spiny lobster 
Scientific Name: Panulirus argus 
Other Common Names: crawfish, Florida spiny lob- 
ster, western Atlantic spiny lobster, Caribbean spiny 
lobster, rock lobster, bug, langouste blanche (French), 
langosta comun (Spanish) (Fischer 1 978, NOAA 1 985, 
Williams et al. 1989). 
Classification (Williams et al. 1989) 
Phylum: Arthropoda 
Class: Crustacea 

Order: Decapoda 

Family: Palinuridae 

Value 

Commercial : Spiny lobster are typically marketed as 
tails either fresh or frozen (Fischer 1978). U.S. land- 
ings in 1992 were 2,222.6 mt valued at $20.2 million 
(NMFS 1993). Florida, with landings of 1,814.4 mt 
valued at 14.6 million, accounted for 81% of the total 
catch and 73% of the value. In 1 992, all reported Gulf 
landings were from the west coast of Florida (Newlin 
1993), mostly from the Florida Keys in Monroe County 
(Lyons pers. comm.). Reported landings for Florida's 
1995-96 fishing season were considerably higher at 
3,1 86 mt (Matthews pers. comm.). Fishermen use top- 
entry wood-slat traps and juvenile lobsters to attract 
adults into the trap (Lyons 1986, Marx and Herrnkind 
1 986). A few are harvested by divers and as incidental 
catch by shrimp trawlers (Hunt 1 994). Florida issues a 
special permit required for the commercial harvest of 
this species (GMFMC 1987). Spiny lobster is a valu- 
able commercial species and supports Florida's sec- 
ond most valuable shellfishery (Schomer and Drew 
1982, Marx and Herrnkind 1986). In Florida state 
waters, lobsters must measure at least three inches 
(76 mm) carapace length (CL) and tails must be at least 


140 mm in length to be legal for harvest (Hunt pers. 
comm.). Florida has maintained a closed harvest 
season since 1 91 9 (Lyons 1 986). Dates forthe closure 
have changed several times, but have always occurred 
during the spring-summer spawning season. Similar 
regulations apply in offshore federal waters of the Gulf 
of Mexico as well (GMFMC 1996a). The fishery ap- 
pears to be fully exploited in the U.S. and may be 
overexploited in Puerto Rico (NOAA 1 992). Capitaliza- 
tion of the fishery is considered to be excessive. 
Current regulations have reduced the number of traps 
in the Florida fishery from 939,000 to approximately 
61 3,000, while landings have remained high (Matthews 
pers. comm.). Although there is interest in mariculture 
of palinurid lobsters, successful rearing of the larval 
stages has been problematic (Van Olst et al. 1980). 

Recreational : Divers, using either skin- or SCUBA- 
diving gear catch lobsters recreationally using gloves 
and small hand held nets (Marx and Herrnkind 1986). 
The recreational harvest is typically about 20% of the 
commercial landings (Bertelson and Hunt 1991), and 
most of this fishery is in the Florida Keys. Recreational 
diving can substantially impact local spiny lobster 
populations when divers congregate in specific areas 
(Blonder et al. 1 990). Recreational fishing is typically 
closed in Florida from early April to early August 
(GMFMC 1 982, NOAA 1 992), although there has been 
a special two-day non-trap recreational season in late 
July (Hunt pers. comm.). Lobsters must measure at 
least three inches (76 mm) CL and tails must be at least 
140 mm in length, and possession limits are enforced. 
Similar recreational regulations apply in offshore fed- 
eral waters of the Gulf of Mexico as well (GMFMC 
1 996b). In Florida state waters, a special lobster stamp 
must be purchased in addition to a recreational saltwa- 


88 


Spiny lobster, continued 


Table 5.10. Relative abundance of spiny lobster in 
31 Gulf of Mexico estuaries (Nelson et al. 1992, 
Hunt, Lyons pers. comm.). 

Lit 6 SlclCJG 


Estuary 


A M J L E 


Florida Bay 


V 


V 


® 


Ten Thousand Islands 


V 


Caloosahatchee River 


Charlotte Harbor 


V 


V 


Tampa Bay 


V 


V 


Suwannee River 


Apalachee Bay 


V 


V 


Apalachicola Bay 


St. Andrew Bay 


V 


V 


Choctawhatchee Bay 


Pensacola Bay 


Perdido Bay 


Mobile Bay 


Mississippi Sound 


V 


Lake Borgne 


Lake Pontchartrain 


Breton/Chandeleur Sounds 


Mississippi River 


Barataria Bay 


Terrebonne/Timbalier Bays 


AtchafalayaA/ermilion Bays 


Calcasieu Lake 


Sabine Lake 


Galveston Bay 


Brazos River 


Matagorda Bay 


San Antonio Bay 


Aransas Bay 


Corpus Christi Bay 


Laguna Madre 


V 


V 


Baffin Bay 


A M J L E 


Relative abundance: 

# Highly abundant 
® Abundant 
O Common 
V Rare 
blank Not present 


Life stage: 

A - Adults 
M - Mating 
J - Juveniles 
L - Larvae 
E - Eggs 


ter fishing license. 

Indicator of Environmental Stress The spiny lobster is 
not typically used in studies of environmental stress. 

Ecological : Spiny lobsters are frequently the dominant 
carnivores in their habitat and have important ecologi- 
cal effects on marine benthic communities (Marx and 
Herrnkind 1 986). The loss of spiny lobster from habi- 
tats through overfishing could have serious conse- 
quences. Removal of such a large sized and abundant 
carnivore may result in loss of diversity and significant 
shift in food webs in simpler ecosystems (Davis 1 977). 

Range 

Overall : The spiny lobster is found in coastal and 
shallow continental shelf waters along the western 
Atlantic coast from North Carolina to Brazil, including 
Bermuda, and throughout the Gulf of Mexico. Genetic 
studies indicate that spiny lobsters throughout the 
Caribbean are genetically similar, suggesting a single 
population (Silberman and Walsh 1994, Silberman et 
al. 1 994). A few specimens have been collected in the 
Gulf of Guinea, West Africa (Lewis 1951, Williams 
1984, NOAA 1985, Marx and Herrnkind 1986). 

Within Study area : The species is abundant off the 
southern Florida coast from Florida Bay to Dry Tortugas 
and is found throughout the Gulf of Mexico in warm 
offshore waters. The southern edge of Florida Bay is 
the major nursery area for juvenile spiny lobster in 
South Florida (Field and Butler 1994, Herrnkind and 
Butler 1994). Rare collections are made in inshore 
waters of south Texas (Moore 1 962, Marx and Herrnkind 
1986, Tunnell pers. comm., Hockeday pers. comm.). 
(Table 5.10). 

Life Mode 

Eggs are carried on the female's pleopods. Egg 
bearing females are found in reef areas at approxi- 
mately 24 to 30°C. Larvae (phyllosoma stage) are 
planktonic and their distribution is regulated by ocean 
currents. Larvae metamorphose to the puerulus stage 
offshore, and move shoreward at the water's surface 
(Acosta et al. in press). Benthic juveniles show a 
combination of crepuscular and nocturnal activity. 
Juveniles reside in shallow nearshore waters in 
seagrass, mangrove, or hardbottom nursery areas 
until they approach maturity, and then move out to reef 
habitats (Moe 1 991 , Herrnkind et al. 1 994, Acosta et al. 
in press). Lobsters found offshore are principally adult 
stage (Witham et al. 1968, Williams 1984, Marx and 
Herrnkind 1 986). Adults also have a combined pattern 
of crepuscular and nocturnal activity (Andree 1981). 


89 


Spiny lobster, continued 


Habitat 

Type : Spiny lobster phyllosome larvae are planktonic 
and inhabit oceanic waters (Lyons 1986). They are 
found in the epipelagic zone of the Caribbean Sea, Gulf 
of Mexico, and the Straits of Florida (GMFMC 1987). 
The postlarval swimming puerulus stage enters estua- 
rine nursery areas. After pueruli molt into juveniles, 
they become demersal and littoral, and utilize the 
coastal waters of bays, lagoons, and reef flats, seeking 
shelter associated with the substrate (Moore 1962, 
Witham et al. 1968, Herrnkind et al. 1994). They are 
solitary and reside in algal clumps for about 3 months 
(Witham et al. 1 964, Andree 1 981 , Marx and Herrnkind 
1985a, Butler and Herrnkind 1991, Butler et al. in 
press) . These clumps provide an epif aunal food source, 
and protection from predation and physical distur- 
bance (Marx and Herrnkind 1985b). When they reach 
15-16 mm CL, they begin to enter holes and crevices 
in rocks, corals, and sponges and start associating with 
similar-sized juveniles (Marx and Herrnkind 1985a, 
Lyons 1986). Juveniles become gregarious at about 
20-25 mm CL and congregate in rocky dens (Childress 
and Herrnkind 1994, Childress and Herrnkind 1996). 
Larger dens are occasionally shared with stone crabs, 
spider crabs, small grouper, and other fishes (Davis 
and Dodrill 1 989). Juveniles can use these areas for 1 5 
months to 3 years (Lyons 1 986, Davis and Dodrill 1 989, 
Forcucci et al. 1994). They spend this time foraging 
and seeking dens appropriate for their increasing size 
(Lyons 1 986). Appropriate sized dens appear to be an 
important defense against predation (Eggleston et al. 
1992). As juveniles become older they move from 
inshore nursery areas to begin adult life in seaward 
waters. Adults occur on reefs and rubble areas from 
shore to 80 m (Moore 1 962, Eldred et al. 1 972, Williams 
1984, NOAA 1985, Lyons 1986, Marx and Herrnkind 
1986). 

Substrate : Adults are found among reefs, jetties, off- 
shore oil platforms, and rubble, while young pueruli 
and juveniles occur among seagrasses, algal beds 
(especially the red algae Laurencia), sponges, tidal 
channels, and holes and crevices among jetties, rocky 
outcrops, and corals (Khandker 1964, Schomer and 
Drew 1982, Williams 1984, NOAA 1985, Marx and 
Herrnkind 1 985a, Davis and Dodrill 1 989, Tunnell pers. 
comm., Hockeday pers. comm.). 

Physical/Chemical Characteristics : 
Temperature: The spiny lobster can survive exposure 
to 13°C, but generally inhabits areas with an annual 
minimum temperature of at least 20°C (Marx and 
Herrnkind 1986). Temperature tolerance may vary 
with developmental stage, location, and salinity. Tem- 
perature and salinity interact in their effect on postlarval 
survival, time to metamorphosis, and size at metamor- 
phosis (Field and Butler 1 994). Temperature has been 


found to significantly affect all measured aspects of 
juvenile growth, including survival, intermolt period, 
postmolt size change, feeding, and weight gain (Lellis 
and Russell 1990). Early juveniles do not generally 
survive below 10°C, nor above 35°C (Witham 1974, 
GMFMC 1982). Growth of juveniles and adults is 
optimal at 26 to 28°C, and spawning activity is related 
to temperature. 

Salinity: In afactorial experiment, survival of postlarvae 
to the first benthic juvenile stage was found to be 
highest at 22°C and 35%o, and declined markedly at 
temperatures and salinities above and below those 
values (Field and Butler 1 994). Juveniles and adults 
are known to occur in mesohaline to euhaline salinities 
(5-40%o) (Witham et al. 1968, Witham 1974, GMFMC 
1982, Lellis and Russell 1990). Older juveniles are 
able to use marginal inshore habitats because they are 
highly mobile and can retreat from unsuitable condi- 
tions (Marx and Herrnkind 1986). 

Movements and Migrations : Local movements are 
reported in response to temperature, salinity, currents, 
wave surge, turbulence, and food availability. Adults 
sometimes move to offshore water to mate. Males 
return to shallower water after mating, followed by 
females after their larvae have been released. Larvae 
are dispersed by oceanic currents. Pueruli swim 
shoreward at night during dark lunar phases, moving 
from the open ocean into shallow nearshore waters, 
and are aided in movements into nursery areas by wind 
driven and tidal currents (Calinski and Lyons 1983, 
Acosta et al. in press). Peak influxes occur from 
December through April (Acosta et al. in press). Juve- 
niles residing in algal clumps may move to different 
clumps depending on food abundance, presence of 
other juveniles, and the quality of shelter provided by 
their original clump (Marx and Herrnkind 1 985b, Butler 
et al. in press). As juveniles approach maturity, they 
move to deeper offshore waters, traveling as much as 
210 km in the process. Adult movement patterns are 
not fully understood. They may occupy particular reefs 
or dens for several years, or move many kilometers for 
unknown reasons (Hunt et al. 1991). Offshore move- 
ment during autumn is prompted by periods of cold 
temperatures and possibly photoperiod. Mass migra- 
tions during this period can involve thousands of lob- 
sters moving in separate single-file queues of up to 50 
individuals. Movement in this type of formation may 
conserve energy during locomotion (Davis 1977, 
Herrnkind 1 980, Lyons et al. 1 981 , Schomer and Drew 
1982, NOAA 1985, Marx 1986, Marx and Herrnkind 
1986, Davis and Dodrill 1989, Yeung and McGowan 
1991, Lozano-Alvarez et al. 1991). 


90 


Spiny lobster, continued 


Reproduction 

Mode : Reproduction is sexual, sexes are separate 
(gonochoristic), and fertilization is external. Hermaph- 
roditism has not been reported (GMFMC 1982). 

Mating and Spawning : Mating may occur up to a month 
prior to spawning, and consists of placement of a 
spermatophore by the male onto the female's sternum. 
In Florida, the mating season is principally from March 
to August, but some may occur throughout the year 
(Hunt et al. 1991). After mating, the spermatophore 
adheres to the female's sternum; at spawning she 
scratches it to initiate and achieve fertilization. Spawn- 
ing occurs offshore in open waters and is principally 
associated with reef habitats. The season extends 
from March to July with some spawning occurring in 
August. In the Florida Keys, it peaks in May and June. 
Some spawning throughout the year has been re- 
ported (Little 1977, Warner et al. 1977, Lyons 1981, 
Lyons et al. 1 981 , GMFMC 1 982, Gregory et al. 1 982, 
Williams 1 984, NOAA 1 985, Marxand Herrnkind 1 986). 

Fecundity : Fecundity is proportional to size (Mora- 
Alves and Bezerra 1968). Recent Florida fecundity 
studies show that a 76 mm CL female lobster can lay 
320,000 eggs, an 87 mm CL female 500,000 eggs, a 
1 1 3 mm CL female 1 ,000,000 eggs, and a 1 41 mm CL 
female was observed with 1 ,952,000 eggs (Matthews 
pers. comm.). A second and potentially a third mating 
and spawning may occur during the season, increas- 
ing the spawning potential two or three fold (Hunt et al. 
1 991 ). It has been estimated that nearly half of the egg 
pool is contributed by females in the 75-85 mm CL size 
class (Gregory et al. 1982). 

Growth and Development 

Egg Size and Embryonic Development : Eggs are spheri- 
cal and about 0.5 mm in diameter. Embryonic develop- 
ment lasts about 3 weeks. During this time the eggs 
adhere to pleopodal setae on the underside of the 
female's abdomen. The phyllosome larvae emerge 
from the egg membrane and disperse in the water 
column (Marx and Herrnkind 1986). 

Age and Size of Larvae : Phyllosome larvae develop 
through about 1 1 stages increasing in size from 2 mm 
total length at hatching to nearly 34 mm before meta- 
morphosis. Duration of the phyllosome stages is about 
6 to 1 2 months (Richards and Potthoff 1 981 , Marx and 
Herrnkind 1986, Acosta et al. in press). 

Juvenile Size Range : The phyllosome larvae meta- 
morphose into a transparent swimming stage called a 
puerulus which may last several weeks. They begin to 
acquire reddish-brown pigment within 3 to 6 days after 
arriving in nursery areas, and within days molt into the 
first juvenile stage. Juveniles are 6 mm CL when they 


first settle out of the water column beginning the spiny 
lobster's benthic juvenile phase (Eldred et al. 1972, 
Andree 1981, Marx and Herrnkind 1986, Butler and 
Herrnkind 1 991 ). Growth of juveniles is estimated at 5 
mm carapace length (CL) per month (Eldred et al. 
1972). Other estimates are 12 mm in first year of 
benthic existence (GMFMC 1982), from 6 mm to 90 
mm CL in the first three years of life (Sutcliffe 1 957), 5.4 
mm per molt (Warner etal. 1977), 0.46 mm CL/ week 
(23.9 mm CL/year) (Hunt and Lyons 1986), 0.76 mm 
CL/week (Davis and Dodrill 1989), and 0.95 mm CL/ 
week (Forcucci et al. 1994). In general, there are 4 
molts per year (GMFMC 1982). Growth decreases 
dramatically between 74 mm CL (0.46 mm CL/week) 
and 76 mm CL (0.23 CL/week) signifying a shift in 
energy use from growth to the onset of maturation 
(Hunt and Lyons 1986). Difference of sex does not 
appear to affect growth rates in juveniles (Davis and 
Dodrill 1989, Forcucci et al. 1994). Injury appears to 
have the greatest effect on growth rates in lobsters less 
than 60 mm CL, and confinement of juveniles in traps 
may also affect growth (Hunt and Lyons 1 986, Forcucci 
etal. 1994). 

Age and Size of Adults : Onset of maturation begins 
near 70 mm CL in south Florida, but a few are reproduc- 
tively functional at 66 mm CL (Warner et al. 1977, 
Gregory et al. 1 982, Hunt and Lyons 1 986). Histologi- 
cal examination of ovaries, however, indicates that 
most south Florida spiny lobsters are not reproduc- 
tively active until reaching 90-95 mm CL (Lyons 1 986). 
Injury does not affect growth rate in adults as much as 
in juveniles (GMFMC 1982, Hunt and Lyons 1986). 
Adult males grow faster than adult females, and growth 
rates during the summer are faster than in the winter 
(Davis and Dodrill 1 989). Intermolt periods range from 
3 to 6 months for subadults and adults (Andree 1 981 ). 

Food and Feeding 

Trophic Mode : Throughout their benthic juvenile and 
adult stage, spiny lobsters are nocturnal predators, 
locating their food by means of antennae and chemore- 
ceptive filaments that line the antennules and dactyls 
of the legs (Marx and Herrnkind 1986). The lobster's 
mandibles are used to crush the shells of molluscs, 
crustaceans, and urchins. Spiny lobsters are probably 
the dominant carnivores in their habitat and have 
important ecological effects on the marine benthic 
commuinity (Marx and Herrnkind 1986). 

Food Items : Spiny lobster phyllosome larvae are pre- 
sumed to feed on plankton; laboratory-reared 
phyllosomes fed on chaetognaths, euphasiids, fish 
larvae, medusae and ctenophores (Marx and Herrnkind 
1 986). Pueruli stage lobsters are not known to feed at 
all. The spiny lobster is a nocturnal forager throughout 
the benthic juvenile and adult stages (Cox et al. 1 997). 


91 


Spiny lobster, continued 


It preys on a wide variety of slow-moving and sedentary 
animals such as molluscs, crustaceans, and echino- 
derms. Young juveniles can be considered general 
opportunistic feeders that consume a large variety of 
organisms (Andree 1 981 , Herrnkind et al. 1 988). The 
only major difference between the diets of younger and 
older juveniles is the size of the prey; smaller lobsters 
feed on smaller species of gastropods, bivalves, and 
crustaceans as well as smaller size classes of com- 
monly eaten larger species. Small quantities of algae, 
sea grass, detritus, foraminiferans, polychaetes, and 
sponges have also been found in fecal samples. Older 
juveniles were found to feed on molluscs, crustaceans, 
and other fauna that exist on the algal clumps in which 
they reside (GMFMC 1 982, Marx and Herrnkind 1 985a). 
Larger juveniles and adults are higher trophic level 
carnivores that forage considerable distances from 
their dens in search of prey, principally bivalves, snails, 
hermit crabs, other crustaceans, and fish (Crawford 
and DeSmidt 1923, Davis 1977, GMFMC 1982, 
Schomerand Drew 1982, Marx and Herrnkind 1986). 

Biological Interactions 

Predation : Larvae are preyed on by a number of 
pelagic fishes, including skipjack tuna (Katsuwonus 
pelanus) and blackfin tuna (Thunnus atlanticus) 
(GMFMC 1 982). Postlarvae are preyed on most heavily 
as they cross the reef track (Acosta 1 997). Blue crabs 
and octopuses have been observed eating early juve- 
niles (Andree 1 981 ). Juveniles are presumably subject 
to predation by numerous fishes while occupying the 
mangrove and grass flat habitats (GMFMC 1982). 
Major predators of adult and sub-adult stages include 
skates (Dasyatis species), sharks (especially nurse 
shark, Ginglymostoma cirratum), various snappers 
(Lutjanus species), grouper (Mycteroperca and 
Epinephelus species), jewfish, grunts, barracudas, 
and octopus (Andree 1 981 , GMFMC 1 982, Smith and 
Herrnkind 1992). Dolphins (Tursiops) and loggerhead 
turtles (Caretta caretta) also prey on lobster. A small 
snail, Murexpomum, is known to kill lobsters in traps by 
boring through the carapace (GMFMC 1982). The 
degree of predation risk in an area appears to influence 
the distribution and abundance of lobsters present 
there (Eggleston and Lipcius 1 992, Mintz et al. 1 994). 

Factors Influencing Populations : Extreme tempera- 
tures and salinities (Field and Butler 1994) and sedi- 
mentation (Herrnkind et al. 1988) reduce survival of 
postlarvae and juveniles. The cascading effects of 
environmental disturbance can result in declines in 
lobster populations (Butler et al. 1995). Although 
Florida Bay is a major nursery area for juvenile spiny 
lobster, recruitment within the northern portion of the 
bay may be limited by physical hydrology, and by 
seasonal extremes of temperature and salinity (Field 
and Butler 1994). Illegal harvest out-of-season and of 


undersize lobsters (shorts) are no longer considered 
serious problems in the now-limited entry fishery (Lyons 
pers. comm.). The widespread use of shorts as trap 
attractants by commercial fishermen may have an 
adverse impact on recruitment to the adult population 
due to increased mortality of the shorts (GMFMC 1 982, 
Lyons 1986). However, this impact may diminish as 
the number of traps in the fishery is reduced consider- 
ably by limited entry (Lyons pers. comm.). Ocean 
dumping of dredged material creates silt that settles 
over larvae and suffocates them (GMFMC 1982). Oil 
and tar pollution of marine waters can potentially 
impact the open ocean epipelagic habitat of larvae 
(GMFMC 1982). Shallow water mangrove and grass 
flat nursery areas are subject to abuses of dredge and 
fill, modified discharges, and coastal development, all 
of which destroy necessary habitat needed to sustain 
spiny lobster population levels (Herrnkind et al. 1 988). 
Damage to reef areas from pollution, ship groundings, 
anchors, and collectors also remove habitat necessary 
for sustaining this species (Andree 1981, GMFMC 
1 982). Large amounts of rainfall that significantly lower 
the salinity of estuarine nursery areas can cause 
mortality in postlarval lobsters, affecting their recruit- 
ment to these areas (Witham et al. 1968, Field and 
Butler 1994). Loss or degradation of inshore nursery 
habitat could have a serious effect on continued lobster 
recruitment and production (Little 1977, Butler et al. 
1995, Butler and Herrnkind 1997). However, artificial 
habitats that mimic mimic natural shelters are useful in 
mitigating loss of shelter (Herrnkind et al. 1997). The 
inability of lobsters to survive low temperatures (<10° 
C) probably limits latitudinal and depth distribution of 
this species and prevents its spread northward and 
across deep ocean basins (Witham 1974, Marx and 
Herrnkind 1986). The density of lobsters in a given 
habitat can enhance gregariousness, which in turn can 
influence the relative impact of lobster size, shelter 
size, and predation risk upon den choice (Eggleston 
and Lipcius 1992). 

Personal communications 

Butler, Mark J. Old Dominion University, Norfolk, VA. 

Hockeday, D. Pan American University, Edinburg, TX. 

Hunt, John H. Florida Div. Marine Resources, Mara- 
thon, FL. 

Jury, Steven H. NOAA SEA Division, Silver Spring, 
MD. 


92 


Spiny lobster, continued 


Lyons, William G. Florida Marine Research Inst., St. 
Petersburg, FL. 

Matthews, Thomas R. Florida Div. Marine Resources, 
Marathon, FL. 

Tunnell, J.W. Corpus Christi State University, Corpus 
Christi, TX. 

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Press, New York, NY, 390 p. 

Warner, R.E., C.L. Combs, and D.R. Gregory, Jr. 
1 977. Biological studies of the spiny lobster, Panulirus 
argus (Decapoda: Palinuridae) in south Florida. Proc. 
Ann. Gulf Caribb. Fish. Inst. 29:166-183. 


95 


Spiny lobster, continued 


Williams, A. B. 1965. Marine decapod crustaceans of 
the Carolinas. Fish. Bull., U.S. 65:1-298. 

Williams, A.B. 1984. Shrimps, Lobsters, and Crabs of 
the Atlantic Coast of the Eastern United States, Maine 
to Florida. Smithsonian Institution Press, Washington, 
DC, 550 p. 

Williams, A.B. 1988. Lobsters of the World - An 
Illustrated Guide. Osprey Books, Hunnington, NY, 186 
P- 

Williams, A.B., LG. Abele, D.L. Felder, H.H. Hobbs, 
Jr., R.B. Manning, P.A. McLaughlin, and I. Perez- 
Farfante. 1989. Common and scientific names of 
aquatic invertebrates from the United States and 
Canada: Decapod crustaceans. Am. Fish. Soc. Spec. 
Pub. No. 17. American Fisheries Society, Bethesda, 
MD, 77 p. 

Witham, R. 1974. Preliminary thermal studies on 
young Panulirus argus. Fla. Sci. 36:154-158. 

Witham, R., R.M. Ingle, and E.A. Joyce, Jr. 1968. 
Physiological and ecological studies of Panulirus argus 
from the St. Lucie estuary. Fla. Board Cons. Mar. Res. 
Lab., Tech. Ser. No. 53, 31 p. 

Witham, R., R.M. Ingle, and H.W. Sims, Jr. 1964. 
Notes on postlarvae of Panulirus argus. Q. J. Fla. 
Acad. Sci. 27:289-297. 

Yeung, C, and M.F. McGowan. 1991. Differences in 
inshore-offshore and vertical distribution of phyllosoma 
larvae of Panulirus, Scyllarus and Scyllarides in the 
Florida Keys in May-June, 1 989. Bull. Mar. Sci. 49:699- 
714. 


96 


Callinectes sapidus 
Adult 


5 cm 


(fromGoode 1884) 


Common Name: blue crab 

Scientific Name: Callinectes sapidus 

Other Common Names: jimmies (males), sooks (adult 

females), common edible crab, sallies, spongers, 

sponge crab, berry crab, soft shell, soft shelled crab, 

hard crab; crabe bleu (French), cangrejo azul, jaiba 

azu/ (Spanish) (Fischer 1978, NOAA 1985). 

Classification (Williams et al. 1989) 

Phylum: Arthropoda 

Class: Crustacea 

Order: Decapoda 

Family: Portunidae 

Value 

Commercial : Commercial blue crab landings have 
been reported from the Gulf of Mexico since 1880, 
although the data are not continuous prior to 1948 
(Steele and Perry 1990). With the introduction of the 
wire crab trap and improved shipping methods came 
an increased availablility of fresh raw product, which 
stimulated processing capacity, market development, 
and consumer demand. Since 1984, Gulf landings 
have increased greatly, at least partially as a result of 
increased fishing effort. Declining catches and in- 
creased regulation of otherfisheries may have prompted 
many fishermen to turn to crabbing to supplement their 
income. 

The commercial value of the Gulf of Mexico blue crab 
fishery is difficult to estimate. Many blue crab fisher- 
men use unsurveyed market channels which lead to 
under-reporting of landings (Roberts and Thompson 
1982, Keithlyetal. 1988). In additon, large numbers of 
blue crabs are harvested as incidental catch during 
shrimping operations (Adkins 1 972b, Steele and Perry 
1990). These crabs are sold, eaten, given away, or 


swapped for supplies and thus not reported as land- 
ings. With this under-reporting noted, the following 
landings are presented. In 1994, 24,123 mt of blue 
crab, valued at $32.5 million, were reported in the Gulf 
region (NMFS 1997). The contribution of the Gulf of 
Mexico to total U.S. blue crab landings reached a peak 
of 38% in 1987, but has remained below 30% since 
1990 . The annual proportional contribution of each 
Gulf State to harvest is variable (Perry pers. comm.). 
However, since 1 972, Louisiana has consistently con- 
tributed the highest proportion of Gulf landings, fol- 
lowed by Florida (Steele and Perry 1 990). The propor- 
tional contribution of each state to the total Gulf harvest 
from 1980 to 1994 is Louisiana 59.9%, Florida 18.0%, 
Texas 15.0%, Alabama 4.9%, and Mississippi 2.2% 
(Perry pers. comm.). In 1994, 98.9% of the Gulf of 
Mexico blue crab harvest was by crab pots (traps), 
whereas only 1.1% was by trawl (Perry pers. comm.), 
and these proportions are consistent with previous 
years (Perry et al. 1984). The seasonal variation in 
harvest is similar among the Gulf States. Highest 
catches usually occur from May through August, with 
peaks in June and July. 

There is a tremendous domestic consumer demand for 
blue crab, and the landings are believed to be totally 
consumed by the domestic market. The main commer- 
cial outlets for blue crab are seafood restaurants and 
retail seafood markets. Approximately 75% of the hard 
crab landings are sold as processed product, the other 
25% are assumed to be sold live for boiling or steaming 
(Perry etal. 1984). There is also a small soft shell crab 
fishery, which supports local demand for fresh soft 
shell crabs. Soft shell crabs demand a higher price, 
and are most abundant during the late spring, summer, 
and fall, when crabs are actively molting (Perry pers. 


97 


Blue crab, continued 


Table 5. 1 1 . Relative abundance of blue crab in 
Gulf of Mexico estuaries (from Volume !). 

Life stage 


31 


Estuary 


A M J L E 


Florida Bay 


® 


® 


® 


® 


V 


Ten Thousand Islands 


® 


® 


® 


® 


V 


Caloosahatchee River 


® 


® 


• 


Charlotte Harbor 


® 


® 


® 


® 


® 


Tampa Bay 


r® 


® 


® 


® 


® 


Suwannee River 


• 


• 


• 


• 


® 


Apalachee Bay 


• 


• 


• 


• 


® 


Apalachicola Bay 


• 


• 


• 


• 


® 


St. Andrew Bay 


• 


® 


• 


® 


o 


Choctawhatchee Bay 


® 


® 


® 


® 


V 


Pensacola Bay 


® 


® 


® 


® 


V 


Perdido Bay 


® 


O 


® 


o 


o 


Mobile Bay 


• 


• 


• 


• 


V 


Mississippi Sound 


Lake Borgne 


• 


• 


• 


• 


• 


Lake Pontchartrain 


® 


o 


o 


V 


Breton/Chandeleur Sounds 


® 


® 


® 


® 


® 


Mississippi River 


o 


o 


o 


o 


o 


Barataria Bay 


® 


o 


® 


® 


® 


Terrebonne/Timbalier Bays 


® 


® 


® 


• 


® 


AtchafalayaA/ermilion Bays 


® 


® 


® 


® 


Calcasieu Lake 


• 


o 


• 


o 


Sabine Lake 


• 


® 


® 


® 


Galveston Bay 


® 


o 


® 


® 


® 


Brazos River 


o 


o 


o 


o 


o 


Matagorda Bay 


® 


o 


® 


• 


o 


San Antonio Bay 


• 


o 


• 


• 


• 


Aransas Bay 


® 


o 


• 


o 


o 


Corpus Christi Bay 


® 


o 


• 


® 


® 


Laguna Madre 


® 


o 


® 


® 


® 


Baffin Bay 


® 


® 


o 


o 


A M J L E 


Relative abundance: L 

9 Highly abundant fi 
® Abundant N 
O Common J 
V Rare L 
blank Not present 

E 


ife stage: 

- Adults 

1 - Mating 

- Juveniles 

- Larvae (zoeae anc 
megalopae) 

■Eggs 


1 


comm.). The soft shell crab fishery is primarily in 
Louisiana and Florida (NMFS 1997), and actual land- 
ings are probably greater than reported (Perry pers. 
comm.). 

Since the commercial harvest of blue crabs is primarily 
in state, not federal, territorial waters, the fisheries are 
managed by the state resource agencies in coopera- 
tion with the Gulf States Marine Fisheries Commission 
(GSMFC) (Steele and Perry 1990). State regulations 
for Gulf of Mexico commercial blue crab fisheries have 
been summarized by the GSMFC (1993), but these 
regulations are subject to annual revision. A five inch 
minimum carapace width generally applies Gulf-wide, 
and there are additional regulations for fishing season, 
location, gear type and quantity, mandatory release of 
gravid females, etc. 

Recreational : The blue crab supports a considerably 
large recreational fishery. Estimates for recreational 
landings vary widely, ranging from 4% of the commer- 
cial landings in Mississippi in 1 971 (Herring and Christ- 
mas 1974) to 400% of the commercial landings in 
Louisiana in 1 968 (Lindall and Hall 1 970, Adkins 1 972b). 
They are taken in the estuaries and nearshore Gulf 
waters by dip nets, baited lift nets, baited strings, "fold- 
up" traps, crab pots, and recreational shrimp trawls. No 
reliable estimates are available for Alabama or the 
west coast of Florida because reports for recreational 
landings do not exist (Lindall and Hall 1970, Killam et 
al. 1 992). Regulations similar to the commercial fish- 
ery apply to recreational fishing, with marked traps 
being labeled with name, address, saltwater stamp 
number, and date set out (TPWD 1987b, GSMFC 
1 993). In Mississippi crabs can be taken by handline, 
drop net, dip net, hook and line, and crab pots/traps 
(MDWC 1 988). The smaller crabs are considered to be 
excellent bait for game fishes such as red drum. 

Indicator of Environmental Stress This species is well 
known to be susceptible to low dissolved oxygen (DO) 
in estuarine waters during the summer (May 1973, 
Lowery and Tate 1986). The blue crab is sensitive to 
chemical pollution, and is commonly used in pollution 
studies due to its widespread distribution in the nation's 
estuaries, and its commercial, recreational, and eco- 
logical importance. Cadmium, mercury, and several 
chlorinated hydrocarbons have been found to be acutely 
toxic to megalopal blue crabs in low concentrations 
(Millikin and Williams 1984). Toxicity for several pes- 
ticides has been determined for juvenile stages as well 
as adults. Kepone released into the James River, 
Virginia from 1 950 to 1 975 may have affected juvenile 
crab abundance and fishery landings (Van Engel 1 982). 
In a laboratory study, Kepone concentrations of 0.5 
and 0.75 parts per billion (ppb) were sublethal to blue 
crab zoeae, whereas 1 .0 ppb caused a survival rate of 


98 


Blue crab, continued 


5% to the first crab stage, compared with 22% in the 
control group (Bookout et al. 1980). Juvenile blue 
crabs exposed to Kepone were shown to have a 96 
hour LC50 at concentrations greater than 210 ppb 
(Schimmel and Wilson 1 977). Mirex has been reported 
to be toxic to blue crab zoeae at concentrations of 1 .0 
and 10 ppb, whereas 0.01 and 0.1 ppb were sublethal 
(Lowe et al. 1971, Bookout and Costlow 1975). DDT 
and its derivatives tend to accumulate in the hepato- 
pancreas of adult crabs (Sheridan 1975) and have 
been demonstrated to cause high mortalities when 
combined with low temperatures in natural habitats 
(Koenig et al. 1 976). Juvenile blue crabs (27 mm CW) 
died within a few days exposure to DDT concentrations 
greater than 0.5 ppb (Lowe 1 965). Mass mortalities of 
blue crab occurred in South Carolina, North Carolina, 
and Georgia in 1966, and it was speculated that 
pesticides were responsible (Newman and Ward 1 973). 
Lipid-rich blue crab eggs may serve as a route for 
exporting lipophilic compounds such as kepone (Rob- 
erts and Leggett 1980). 

Ecological : The blue crab performs a variety of func- 
tions in the estuarine ecosystem, and plays an impor- 
tant role in trophic dynamics (Van Den Avyle and 
Fowler 1984). At different stages in its life cycle, it 
serves as predator and prey to plankton, small inverte- 
brates, fish, and other crabs. It has been characterized 
as an opportunistic benthic omnivore whose food hab- 
its are governed by availability of food items (Darnell 
1959). 

Range 

Overall : The blue crab is a cosmopolitan species found 
in coastal waters, primarily in bays and brackish estu- 
aries. It occurs occasionally from Nova Scotia, Maine, 
and northern Massachusetts to northern Argentina, 
and also Bermuda and the Antilles (Millikin and Will- 
iams 1984, Williams 1974, Williams 1984). It is found 
north of Cape Cod only during favorable warm periods 
that allow it to move into these waters. This species 
has also been introduced into coastal waters of Europe 
and Japan. 

Withinthe Study Area : This species is abundant through- 
out the nearshore and estuarine areas of the Gulf of 
Mexico (Table 5.11) (Millikin and Williams 1984, Will- 
iams 1 974, Williams 1 984). For the purposes of Table 
5.11, all zoeal and megalopal stages are considered 
together as "Larvae". 

Life Mode 

The blue crab spends most of its life in estuaries and 
nearshore Gulf waters. Eggs are carried externally by 
the female for approximately two weeks. Egg-bearing 
females are commonly known as sponge or berry 
crabs. Eggs hatch near the mouths of estuaries, and 


the zoeal larvae are carried offshore. Zoeae are 
planktonic, and remain in offshore waters for up to one 
month. Metamorphosis to the megalopal stage follows 
the seventh zoeal molt. Re-entry to estuarine waters 
occurs during the megalopal stage. Juveniles and 
adults tend to be demersal and estuarine. Adult males 
spend most of their time in low salinity waters; females 
move into these lower salinities as they approach their 
terminal molt to mate. After mating, females move to 
higher salinity areas of estuaries and nearshore envi- 
ronments for spawning (Dudley and Judy 1 971 , Millikin 
and Williams 1984, Van Den Avyle and Fowler 1984, 
Williams 1984). 

Habitat 

Type : The blue crab is dependent on estuaries during 
portions of its life. Depending on the life stage, indi- 
viduals can be neritic, estuarine and/or riverine. Zoeae 
are found in oceanic habitats (Williams 1 984), and they 
are positively phototropic (Costlow et al. 1959). The 
megalopae swim freely and may be found in the surf 
area near the bottom in nearshore or lower estuarine 
high-salinity areas. In Tampa Bay, the primary habitat 
that megalopae use for settlement appears to be 
seagrass or vegetated bottom (Killam et al. 1992). In 
the northern Gulf of Mexico, megalopae move into 
nearshore marshes where molt to the first crab stage 
occurs (Perry pers. comm.). Within an estuarine sys- 
tem, habitat is partitioned for use by blue crabs based 
on size class, and may be related to food availability, 
predator avoidance, nutritional requirements, repro- 
ductive success, and growth (Steele and Bert 1994). 
Juveniles have been found in greatest numbers in low 
to intermediate salinities characteristic of upper and 
middle estuarine waters (Steele and Perry 1 990). They 
prefer seagrass as nursery habitat but also utilize salt 
marsh habitat (Thomas et al. 1 990, Killam et al. 1 992). 
Juveniles and adults tend to be demersal and estua- 
rine. Adult males spend most of theirtime in low salinity 
water and females move from higher to lower salinities 
as they approach their terminal molt in order to mate 
(Dudley and Judy 1971, Millikin and Williams 1984, 
Van Den Avyle and Williams 1984, Williams 1984). 
Although juvenile and adult blue crab distributions are 
affected by salinity (Killam et al. 1 992, Steele and Bert 
1994), other factors such as substrate type and food 
availability also play a major role (Steele and Perry 
1990). 

Substrate : Juveniles and adults are found on muddy 
and sandy bottoms. Juveniles have been found in 
greatest abundances in association with soft mud 
bottoms (Van Engel 1958, Perry 1975, Perry and 
Mcllwain 1986). 

Physical/Chemical Characteristics : Environmental re- 
quirements affecting the growth, survival, and distribu- 


99 


Blue crab, continued 


tion of the blue crab vary with the life stage and sex of 
the individual (Killam et al. 1 992). The eggs of the blue 
crab are the most sensitive to change in environmental 
conditions such as temperature and salinity, while 
juveniles and adults have greater tolerances to 
flucutations. Juveniles and adults are also more mo- 
bile, and can avoid degraded areas if possible. 

Temperature - Eggs: Eggs have been successfully 
hatched under laboratory conditions in temperatures 
ranging from 19° to 29°C (Sandoz and Rogers 1944). 

Temperature - Larvae: Megalopal survival is highest at 
temperatures between 21.5° and 34.5°C, but larval 
development is fastest between 24° to 31 °C (Costlow 
1967, Copeland and Bechtel 1974). 

Temperature - Juveniles and Adults: Blue crabs have 
been collected at temperatures from 3° to 35°C 
(Copeland and Bechtel 1 974). Adults cease feeding at 
temperatures below 1 0.8°C, and burrow in mud at 5°C. 
Mortalities of blue crabs have been related to extreme 
cold and sudden drops in water temperature (Van 
Engel 1982, Couch and Martin 1982). Tagatz (1969) 
evaluated maximum and minimum median thermal 
tolerance limits (48 hours) of juvenile and adult blue 
crab from St. Johns River, Florida, and found them to 
be 3°C and 37°C. However, thermal limits are highly 
dependent on acclimation temperature and salinity. 
Adult males are more tolerant of temperature extremes 
than females and juveniles. Temperature apparently 
plays a key role in molting (Copeland and Bechtel 
1974). 

Salinity: This species is euryhaline and has been found 
from freshwater to hypersaline lagoons (0-50% o ). Up- 
per and lower lethal limits (LC-50s) determined for two 
different Gulf of Mexico populations were 56%o and 
67%o for the upper limits, and 0%o and 1 %o for the lower 
limits (Guerin and Stickle 1990). 

Salinity - Eggs: Eggs have been observed to hatch 
under laboratory conditions in salinities ranging from 
1 0.3 to 32.6%o, but the optimum salinities ranged from 
23%o to 28%o (Sandoz and Rogers 1944). 

Salinity - Larvae: Early zoeae are found at high 
salinities, usually 20%o or greater (Dittel and Epifanio 
1 982). Megalopae may be transported to lower salini- 
ties, and have been found in waters as low as 5%o 
(Costlow 1 967, Benson 1 982). Highest survival occurs 
between 1 6 and 43%o, but larval development is fastest 
from 11.5 to 35.5%o at 24° to 31 °C (Costlow 1967, 
Copeland and Bechtel 1974). 

Salinity - Juveniles: Juvenile crabs are found in lower 
salinity waters, typically 2-21 %o. Reported salinity 


values for juveniles vary, and specific salinities are not 
critical to postlarval crabs. 

Salinity - Adults: Adult males are usually found at less 
than 1 0%o. Egg-bearing females (sponge) are found in 
23-33%o and 19-29°C waters (Millikin and Williams 
1 984, Van Den Avyle and Fowler 1 984, Williams 1 984). 
The interaction of salinity and temperature reveals the 
blue crab to be less tolerant of low salinities at high 
temperatures and high salinities at low temperatures 
(McKenzie 1970). 

Dissolved Oxygen (DO): The blue crab is very sensi- 
tive to low DO conditions. Survival times of 2 hours at 
parts per million (ppm) DO (32°C and 15%o salinity) 
and 4.3 hours at ppm DO (25°C and 15%o salinity) 
were reported by Lowery and Tate (1986). The occur- 
rence of dead crabs in traps is fairly common during 
warmwaterconditions. The fishermen usually remedy 
the problem by moving their traps into shallower water 
to avoid any low DO water layers. Often the presence 
or boundary of a low DO water mass can be inferred by 
the placement of crab traps in any given area. Mass 
mortalities have been reported to be associated with 
low DO conditions (May 1973). 

Migration and Movements : Migrations within estuarine 
systems are related to phases of life cycle, season, 
and, to a lesser extent, the search for favorable envi- 
ronmental conditions. Most crabs move to relatively 
deeper, warmer waters during winter, but some juve- 
niles will burrow in shallow water substrate for protec- 
tion. Blue crab return to rivers, tidal creeks, salt 
marshes and sounds when conditions become more 
favorable. They also move out of waters with low DO 
levels, and in some cases will actually leave the water 
to escape anoxic conditions (Lowery 1 987, Killam et al. 
1992). In Mobile Bay, large masses of migrating blue 
crabs and other animals occasionally occur while at- 
tempting to avoid low DO conditions, and such events 
are referred to as "jubilees" (Lowery pers. comm.). 
Blue crabs are recruited to Gulf estuaries as megalopae, 
with molt to the first crab stage occurring in nearshore 
waters (Thomas et al. 1990, Perry et al. 1995). 
Oesterling and Evink (1977) proposed a larval dis- 
persal mechanism for the northeastern Gulf in which 
larvae could be transported 300 km or more. If such 
mechanisms do exist, larvae produced by spawning 
females in one estuary could be responsible for recruit- 
ment in others. In the Gulf of Mexico, immature 
females approaching their final molt during the spring, 
move to lower salinities to mate, and then, typically, 
migrate backtohighersalinity waters within theestuary 
during June and July (Adkins 1972b, Millikin and Will- 
iams 1984). In Florida, females may leave estuaries 
after mating and move along the coast to specific 
spawning areas near Apalachicola Bay (Oesterling 


100 


Blue crab, continued 


and Evink 1977). Adult males appear to remain in 
lower salinity waters, and rarely move to higher salini- 
ties. Adults are known to migrate between estuaries 
along the Florida Gulf coast (Adkins 1 972b, Oesterling 
1976). Movement of mated females from Lakes 
Pontchartrain and Borgne into Mississippi waters oc- 
curs in the fall and early winter months (Perry 1975). 

Reproduction 

Mode : Sexes are separate (gonochoristic), fertilization 
is internal, and eggs develop oviparously (Williams 
1965). 

Mating and Spawning : Mating normally occurs in low 
salinity waters in the upper reaches of the estuary. 
Females mate while in the soft shell stage during their 
pubertal or terminal molt. The females are vulnerable 
to cannibalism and predation during these molts, and 
as a result, the recognition of amorous males inter- 
ested in mating is important. Females approaching 
their pubertal orterminal molts initiate mating behavior 
upon recognition of a mature male via olfactory and 
visual stimuli (Teytaud 1971). Males recognize the 
females via a pheromone that triggers male mating 
behavior (Gleeson 1980). Males protect their mates 
during the females molt. The males accomplish this by 
grasping the females with their first pair of walking legs 
and "cradle-carry" her in an upright position under- 
neath the male. The males transmit their spermato- 
phores by tube-like pleopods into the females seminal 
receptacle (Cronin 1 974). The sperm are stored in the 
seminal receptacle to be released later. Soon after 
mating, females move to the higher salinity waters near 
the mouths of estuaries or into the Gulf of Mexico in 
preparation for spawning. 

Spawning may occur any time from 2 to 9 months after 
mating, but usually occurs during the spring by females 
that mated in August-September of the previous year 
(Van Engel 1 958, Williams 1 965). In the northern Gulf 
of Mexico, larvae have been found throughout the year 
except January and February, but their occurrence is 
low from December to April (Stuck and Perry 1981). 
Two spawning peaks typically occur in the Gulf, one in 
late spring and the other during late summer or early fall 
(More 1 969, Jaworski 1 972, Stuck and Perry 1 981 ). In 
Florida's St. Johns River, spawning occurs from Feb- 
ruary through October, with peak occurrence from 
March through October (Tagatz 1968a). The primary 
spawning grounds along the Gulf coast of Florida are 
located off Apalachicola Bay (Oesterling 1976). Eggs 
are fertilized as they are passed from the ovaries to the 
seminal receptacle and are extruded out to the pleo- 
pods (Millikin and Williams 1984). Egg extrusion may 
be completed within 2 hours (Van Engel 1958). Fe- 
males may ovulate more than once and sperm can 
survive forat least one year in their seminal receptacle. 


Fecundity : Fecundity estimates range from 723,500 to 
2,1 73,300 eggs per spawning (Truitt 1 939), but gener- 
ally between 1 ,750,000 and 2,000,000 eggs are pro- 
duced per spawning (Millikin and Williams 1984). The 
egg mass (sponge) ranges from 24 to 98 g, with an 
average of 37 g (Tagatz 1965). Females may ovulate 
and spawn more than once (Millikin and Williams 
1 984). Second spawnings can occur for some females 
later in the summer after the first one, and it is possible 
for a third one to occur, possibly as late as the succeed- 
ing spring or at an age of three years (Williams 1 965). 

Growth and Development 

Egg Size and Embryonic Development : Approximate 
ages (after fertilization and extrusion) of blue crab egg 
masses (sponges) can be estimated according to 
coloration. Yellow to orange egg masses are from 1 to 
7 days old. Brown to black egg masses are from 8 to 
15 days old (Bland and Amerson 1974). Hatching 
occurs from 14 to 17 days after egg extrusion at 26°C, 
and 12 to 15 days at 29°C (Churchill 1921). Freshly 
extruded eggs in the early stages of development are 
273 x 263 urn, and enlarge to 320 x 278 urn before 
hatching (Davis 1 965). Hatching occurs in high salinity 
waters in the lower estuary, and in adjacent Gulf 
waters. In laboratory experiments, successful hatch- 
ing did not occur below 20% o (Costlow and Bookout 
1959). 

Age and Size of Larvae : Newly hatched blue crab 
larvae are 0.25 mm in carapace width (CW) and usually 
develop through seven zoeal stages. Laboratory stud- 
ies indicate that 31 to 43 days are required to complete 
the zoeal larval stages at 25°C and 26%o salinity 
(Costlow and Bookout 1959). After the final zoeal 
stage when approximately 1 mm CW, larvae metamor- 
phose into the megalopal larval stage (Costlow and 
Bookout 1959). The optimal salinity and temperature 
combination for zoeal and megalopal development is 
30% o and 25°C (Bookout et al. 1 976, Costlow 1 967). At 
30%o and 25°C, 6 to 12 days were required to develop 
through the megalopal larval stage into the first crab 
Guvenile) stage at 2.2-3.0 mm CW (Costlow 1 967). In 
Mississippi Sound, settlement of blue crab megalopae 
is episodic, occurring primarily from late summer to 
early fall (Perry et al. 1 995). Settlement in Mississippi 
Sound was associated with spring tides and onshore 
winds, rather than with salinity, temperature, or lunar 
period (Perry et al. 1 995). Megalopal settlement in the 
northern Gulf of Mexico may be asynchronous among 
sites (Rabalais et al. 1995). 

Juvenile Size Range : Juvenile blue crabs may reach 
maturity within one year along the Gulf coast (Perry 
1975), while populations in more temperate climates 
may take up to 20 months (Millikin and Williams 1 984). 
Salinities from 6 to 30%o do not differentially affect 


101 


Blue crab, continued 


growth of juveniles (Millikin and Williams 1 984). Tagatz 
(1 968b) observed that growth per molt remained simi- 
lar regardless of temperature (summer vs. winter) in 
the St. Johns River, Florida, but that intermolt intervals 
were three to four times longer in the winter. Juvenile 
blue crabs may range in size from approximately 2 mm 
CW when the first crab stage is attained, to over 150 
mm CW. Maturity in blue crabs is attained over a wide 
range of carapace widths (Perry pers. comm.). Guillory 
and Hein (in press) sampled 2,925 blue crabs in 
Louisiana estuarine waters, and reported that 50% of 
males were mature by 1 10-1 15 mm CW, and 50% of 
females were mature by 1 25-1 30 mm CW. The small- 
est mature male was 96 mm CW, and the smallest 
mature female 1 1 3 mm CW. One hundred percent of 
the males were mature by 130 mm CW, and 100% of 
the females by 160 mm CW. 

Age and Size of Adults : Tagatz (1 968b), sampling blue 
crabs from St. Johns River, Florida, reported mean 
carapace widths and ranges: adult males averaged 
147 mm, ranging from 117 mm to 181 mm; adult 
females averaged 148 mm, ranging from 128 to 182 
mm. Tagatz (1965) reported a maximum carapace 
width of 246 mm (male), and a heaviest weight of 550 
g (male), from commercial catches in the St. Johns 
River, Florida. Adult males generally weigh more than 
females of a given size (excluding gravid females) 
(Millikin and Williams 1 984). Females may vary in size 
from mature at 51 mm to immature at 177 mm. Fe- 
males mate at their terminal molt, males continue to 
grow and molt after reaching sexual maturity. The blue 
crab has an estimated life span of 3-4 years (Tagatz 
1 968a). Growth equations for the blue crab have been 
calculated by Pullen and Trent (1970). 

Food and Feeding 

Trophic Mode : This crab is an omnivore, scavenger, 
detritivore, predator, and cannibal that feeds on a wide 
variety of plants and animals, selecting whatever is 
locally available at any time (Costlow and Sastry 1 966, 
Laughlin 1982). Its feeding habits change with its 
ontogeny. Larval blue crabs are believed to feed on 
phytoplankton and zooplankton, while juveniles and 
adults are described as general scavengers, bottom 
carnivores, detritivores, and omnivores, that consume 
whatever is in the area (Costlow and Sastry 1966, 
Laughlin 1982). 

Food Items : Food habits of the blue crab are variable, 
changing with season of the year, geographic location, 
and the developmental stages of its life cycle (Laughlin 
1982, Steele and Perry 1990). Zoea consume phy- 
toplankton and copepod nauplii. Aquaculture proto- 
cols recommend that zoeal stages be fed sea urchin 
embryos, Artemia nauplii, and/or rotifers (Millikin and 
Williams 1 984, Schmidt 1 993). The megalopal stage is 


omnivorous and consumes fish larvae, small shellfish 
and aquatic plants. The diet of juveniles and adults 
consists mainly of molluscs, crustaceans, and fish 
(Tagatz 1968a, Jaworski 1972, Alexander 1986). 
Laughlin (1982) evaluated stomach contents of blue 
crabs from Apalachicola Bay, Florida and observed the 
following: small juveniles (less than 31 mm carapace 
width) fed mainly on bivalves, plant matter, ostracods, 
and detritus; intermediate juveniles (31-60 mm) fed 
mostly on fishes, gastropods, and xanthid crabs; large 
juveniles and adults (greater than 60 mm) fed on 
bivalve molluscs, fishes, xanthid crabs, and smaller 
blue crabs. Molluscs known to be food items for blue 
crab include American oyster, hard clams, coot clam 
(Mulina lateralis), Atlantic ribbed mussel (Geukensia 
demissa), darkfalsemussel (Mytilopsis leucophaeata), 
scorched mussel (Brachidontes exustus), Atlantic 
rangia, and marsh periwinkle (Littorina irrorata) (Millikin 
and Williams 1984). The blue crab has been charac- 
terized as an opportunistic benthic omnivore, whose 
food habits are governed by availability of food items 
(Darnell 1959, Seed and Hughes 1997). Feeding 
generally decreases as temperature decreases, espe- 
cially from 34° to 13°C (Leffler 1972). 

Biological Interactions 

Predation : Blue crab postlarvae can be 1 to 1 00 times 
more abundant in estuaries of the U.S. Gulf Coast (AL, 
MS, TX) than along the East Coast (DE, VA, NC, SC), 
but this does not necessarily result in elevated abun- 
dance of juveniles and higher fishery landings (Heck 
and Coen 1995). Abundances of blue crab juveniles 
are similar in estuaries of the two regions, suggesting 
that there is higher mortality of recently-metamor- 
phosed juveniles in the Gulf region, possibly as a result 
of predation (Heck and Coen 1995). Numerous spe- 
cies of fish, mammals, and birds prey on the blue crab 
(Killam et al. 1992). Different species of shrimp, 
including Palaemonetes pugio, have been found to 
prey on blue crab megalopae (Olmi 1990). Fish that 
consume zooplankton, such as herring and menhaden 
species, are also probably important predators of blue 
crab larvae (Millikin and Williams 1 984, Schmidt 1 993). 
Major fish predators on juveniles are snook, black 
drum, juvenile and adult red drum, Atlantic croaker, 
spotted seatrout, and sheepshead (Fontenot and 
Rogillio 1 970, Boothby and Avault 1 971 , Adkins 1 972b, 
Fore and Schmidt 1973, Bass and Avault 1975, 
Overstreet and Heard 1978a, Overstreet and Heard 
1978b). They have also been found in the stomach 
contents of the sandbar shark (Carcharhinus plumbeus) 
and spot (Levine 1980, Medved and Marshall 1981, 
Rozas and Hackney 1984). In addition, adult blue 
crabs will often cannibalize juveniles (Costlow and 
Sastry 1 966, Martinez pers. comm.). Several freshwa- 
ter fishes may prey on blue crab in oligohaline waters, 
including alligator gar (Lepisosteus spatula), spotted 


102 


Blue crab, continued 


gar (Lepisosteus oculatus), and largemouth bass 
(Micropterus salmoides)(Lambou 1961). The primary 
mammalian predator (other than humans) is the rac- 
coon (Procyon lotor) (Steele and Perry 1 990, Killam et 
al. 1992). Avian predators include the clapper rail, 
great blue heron, American merganser, and hooded 
merganser. Other vertebrate predators include the 
Kemp's ridley sea turtle and the American alligator 
(Byles 1989, Piatt et al. 1990). 

Factors Influencing Populations : Natural mortality rates 
of juvenile (5-20mm CW) blue crab have been esti- 
mated at 70-91 %/day in Alabama, 68-88%/day in 
Virginia, and 25-38%/day in New Jersey (Heck and 
Coen 1995). Estimated natural mortality rates were 
lower at sites with seagrass, and higher at sites with 
sand substrate. Estimation of fishery mortality is com- 
plicated by: (1 ) the lack of data on incidental harvest by 
non-directed fisheries, (2) inadequate recreational catch 
statistics, and (3) widespread under-reporting of soft 
and hard crab harvest (Adkins 1 972b, Steele and Perry 
1 990). In addition to catches made by the recreational 
and commercial fisheries, large numbers of blue crabs 
are harvested incidentally by the shrimp trawl fishery 
(Adkins 1972b, Steele and Perry 1990). At present, 
increases in fishing effort have resulted in only slight 
declines in catch per fisherman, indicating that the 
fishery has remained fairly stable. Destruction of 
wetland habitat due to dredging, filling, impoundment, 
flow alteration, and pollution has been suggested to 
cause a decrease in fishery production, and, therefore, 
may be a significant factor in determining blue crab 
production (Steele and Perry 1990). 

The blue crab can be infected by several diseases 
caused by viral, bacterial and fungal agents that result 
in mortality or morbidity (Steele and Perry 1 990, Messick 
and Sinderman 1992). A variety of ecto-commensal 
symbionts and parasites are associated with blue 
crabs (Perry pers. comm.). Heavy infestations of 
symbionts may interfere with metabolic processes. 
Infested crabs are more vulnerable to predations, and 
less tolerant of unfavorable environmental conditions 
(Overstreet 1978). The cypris stage of the parasitic 
sacculinid barnacle, Loxothylacus texanus, infects soft 
juveniles retarding their growth (Overstreet 1978, 
Overstreet et al. 1983, Hochberg et al. 1992), and 
resulting in their loss to the fishery (Adkins 1972a). 
Predation and cannibalism may significantly affect 
abundance (Adkins 1972a, Heck and Coen 1995). 
Abiotic environmental variables may affect survival 
directly or indirectly. Mortality of blue crabs exposed to 
low dissolved oxygen coupled with high temperatures 
is common during the summer (May 1973, Tagatz 
1 969). Abiotic factors can influence blue crab popula- 
tions indirectly through predator-prey relationships if 
they exert a greater influence on the distribution of food 


organisms than they do on the blue crab (Laughlin 
1982). 

Personal communications 

Martinez, Janet. U.S. Army Corps of Engineers, 
Galveston, TX. 

Lowery, Tony A. NOAA/NOS SEA Division, Silver 
Spring, MD. 

Perry, Harriet M. Gulf Coast Research Lab., Ocean 
Springs, MS. 

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16 p. 


Texas Parks and Wildlife Department (TPWD). 1 987b. 
Texas Saltwater Fishing Guide. Texas Parks and 
Wildlife Department, Austin, TX, PWD-BR-3400-204- 
7/87, 16 p. 

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recognition in the blue crab, Callinectes sapidus 
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Thomas, J.L., R.J. Zimmerman, and T.J. Minello. 1 990. 
Abundance patterns of juvenile blue crabs {Callinectes 
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Mar. Sci. 46:115-125. 

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Spec. Pub. No. 17, 77 p. 


107 


Stone crab 


Menippe species 


Adult 


/ 


ki 


V.^' ! ^^ "'■* ' ^-l. J J 


Vx^^skL 


HllfcMl. 1 n 11 * 


]L±i0*\ '£±<lJr ^4^.. w ■ '^j^M&ffi*^ 1 ^ 


^7 


Ti 


(from Goode 1884) 


5 cm 7 


Common Name: stone crab 

Scientific Name: Menippe species 

Other Common Names: Florida stone crab, gulf stone 

crab (Williams et al. 1 989); cangrejo de piedra negro, 

cangrejo moro (Spanish), crabe caillou noir (French) 

(Fischer 1978, NOAA 1985). 

Classification 

Phylum: Arthropoda 

Class: Crustacea 

Order: Decapoda 

Family: Xanthidae 

Stone crabs (genus Menippe) have recently under- 
gone taxonomic revision, and two species are now 
recognized in U.S. waters of the Gulf of Mexico: Menippe 
mercenaria, the Florida stone crab; and Menippe adina, 
the gulf stone crab (Williams and Felder 1 986, Williams 
et al. 1 989). A third species, the Cuban stone crab (M. 
nodifrans), is smaller and occurs in the Caribbean but 
is not common in U.S. Gulf of Mexico estuaries (Fischer 
1978, Williams etal. 1989). M. mercenaria occurs from 
North Carolina around peninsular Florida to the Big 
Bend region near Apalachicola Bay, and also in the 
Caribbean, the Yucatan, and Belize. M. adina occurs 
in the Gulf of Mexico from Florida's Big Bend region 
westward through Texas to northern Mexico (Williams 
and Felder 1 986). The two species are sympatric in the 
Big Bend region of northwest Florida, and they often 
hybridize there. Their evolutionary divergence may 
have occurred as a result of geologic events and 
oceanic processes within the past 3 million years (Bert 
1986). It has been hypothesized that the Miocene 
glaciation may have caused two populations of an 
ancestral Menippe species to become isolated, result- 
ing in allopatric speciation (Brown and Bert 1993). 
Specific differences in coloration and morphometries 


(Williams and Felder 1 986, Bert et al. 1 996), megalopal 
morphology (Martin et al. 1988, Guillory et al. 1995), 
habitat utilization (Wilber 1992), low salinity tolerance 
(Stuck and Perry 1992), low temperature tolerance 
(Brown and Bert 1 993), and isozyme markers (Cline et 
al. 1992) have been described. 

The life histories of these two species are summarized 
together here because their biology is very similar, and 
because much of the existing literature does not distin- 
guish between them. They are referred to individually 
here as "Florida stone crab" and "gulf stone crab", and 
collectively as "stone crabs". It is presumed that life 
history characteristics of the two species are similar, 
but known differences are noted. 

Value 

Commercial : The commercial importance of stone 
crabs comes from the meat of their highly esteemed 
claws. The large claws contain much of the crab's 
muscle mass, can weigh over 300 g (Stuck 1 989), and 
have a high market value. The claw is removed after 
capture, and the crab is released. This makes the 
stone crab fishery unique because the harvested ani- 
mal does not necessarily die (Restrepo 1992). Crabs 
that survive de-clawing can then regenerate new claws, 
but regeneration to legal size (70 mm propodus length) 
may take a year or more. The major (crusher) claw is 
typically on the right and the minor (pincer) claw on the 
left, although crabs that have lost a right claw may 
regenerate a crusher on the left after one or more 
molts, indicating a reversal of handedness (Cheung 
1976, Simonson and Steele 1981, Simonson 1985). 
Most of the legal-sized harvested claws are crushers, 
and most of the harvested crushers are right-handed 
(Sullivan 1 979, Simonson and Hochberg 1 992). Males 


108 


Stone crab, continued 


Table 5.12. Relative abundance of Florida stone 

crab (M. mercenaria) in 31 Gulf of Mexico estuaries 

(from Volume I). ... 

Life stage 


Estuary 


A M J L E 


Florida Bay 


O 


O 


V 


V 


o 


Ten Thousand Islands 


O 


O 


o 


o 


o 


Caloosahatchee River 


V 


V 


Charlotte Harbor 


O 


O 


o 


o 


o 


Tampa Bay 


O 


O 


o 


o 


o 


Suwannee River 


O 


O 


o 


o 


o 


Apalachee Bay 


O 


o 


o 


o 


o 


Apalachicola Bay 


V 


V 


V 


V 


V 


St. Andrew Bay 


Choctawhatchee Bay 


Pensacola Bay 


Perdido Bay 


Mobile Bay 


Mississippi Sound 


Lake Borgne 


Lake Pontchartrain 


Breton/Chandeleur Sounds 


Mississippi River 


Barataria Bay 


Terrebonne/Timbalier Bays 


Atchafalaya/Vermilion Bays 


Calcasieu Lake 


Sabine Lake 


Galveston Bay 


Brazos River 


Matagorda Bay 


San Antonio Bay 


Aransas Bay 


Corpus Christi Bay 


Laguna Madre 


Baffin Bay 


A M J L E 


Relative abundance: 

# Highly abundant 
Abundant 
Common 
Rare 
Not present 


® 

o 

blank 


Life stage: 

A - Adults 
M - Mating 
J - Juveniles 
L - Larvae 
E - Eggs 


Table 5.13. Relative abundance of gulf stone crab 

(M. adina) in 31 Gulf of Mexico estuaries (from 

Volume !). 

Life stage 


Estuary 


A M J L E 


Florida Bay 


Ten Thousand Islands 


Caloosahatchee River 


Charlotte Harbor 


Tampa Bay 


Suwannee River 


V 


V 


V 


V 


V 


Apalachee Bay 


o 


o 


o 


o 


o 


Apalachicola Bay 


o 


o 


o 


o 


o 


St. Andrew Bay 


V 


V 


V 


V 


V 


Choctawhatchee Bay 


V 


V 


V 


V 


V 


Pensacola Bay 


V 


V 


V 


V 


V 


Perdido Bay 


V 


V 


V 


V 


V 


Mobile Bay 


o 


V 


o 


V 


V 


Mississippi Sound 


o 


o 


o 


o 


o 


Lake Borgne 


V 


V 


Lake Pontchartrain 


V 


V 


Breton/Chandeleur Sounds 


o 


o 


o 


o 


o 


Mississippi River 


o 


o 


Barataria Bay 


V 


o 


Terrebonne/Timbalier Bays 


o 


o 


Atchafalaya/Vermilion Bays 


V 


< 


Calcasieu Lake 


V 


o 


Sabine Lake 


V 


V 


Galveston Bay 


o 


o 


o 


o 


o 


Brazos River 


na 


na 


Matagorda Bay 


o 


o 


o 


o 


o 


San Antonio Bay 


o 


o 


o 


o 


o 


Aransas Bay 


o 


o 


o 


o 


o 


Corpus Christi Bay 


o 


o 


o 


o 


o 


Laguna Madre 


V 


V 


M 


V 


V 


Baffin Bay 


o 


o 


o 


o 


o 


A M J L E 


Relative abundance: 

O Highly abundant 
® Abundant 
O Common 
V Rare 
blank Not present 
na No data available 


Life stage: 

A - Adults 
M - Mating 
J - Juveniles 
L - Larvae 
E - Eggs 


109 


Stone crab, continued 


tend to have larger claws and are therefore more likely 
to be harvested by the fishery. Male stone crabs are 
recruited into the fishery during theirthird year, andean 
live to at least 8 years (Restrepo 1989). Most crabs 
with legal-sized claws in Florida are 3 or 4 years old 
(Sullivan 1979). Both claws can be removed if they are 
legal size, but it is illegal to remove claws from a gravid 
female (Bert pers. comm.). 

Southwest Florida is the major area of commercial 
harvest in the U.S. (NOAA 1985), although landings 
are also reported from South Carolina, Texas, Louisi- 
ana, Mississippi, and northwest Florida (Bert 1992). 
Stone crab fisheries also exist in the Caribbean, and 
landings have been reported from Cuba, Mexico, and 
the Dominican Republic (Fischer 1978). Florida has 
kept fishery statistics since 1 962 (Williams and Felder 
1 986). In 1 990, the Florida fishery reported landings of 
1,225 metric tons, with a dockside value of over $15 
million (Restrepo 1992). The stone crab fishery has 
been ranked as Florida's eighth most valuable (Adams 
and Prochaska 1992). Recent dockside prices have 
been near $4.75/lb for medium and $7.50/lb for jumbo 
claws (Newlin 1993), and consumer demand contin- 
ues to be strong. Most of the claws harvested in Florida 
are marketed fresh or frozen and consumed locally. 
The same appears to be true of the Texas fishery, 
although some Texas claws are transported to meet 
increasing demand in Florida (Landry 1 992, Tobb pers. 
comm.). Catches along the Texas coast are primarily 
incidental to the blue crab fishery (Stuck 1 987, Landry 
1 992, Pattillo pers. obs.). Texas reported 39,000 kg of 
gulf stone crab claws landed in 1 992, about one fourth 
of which came from the Galveston region (Newlin 
1993). The prospect of a limited fishery in Barataria 
Bay, Louisiana, and the lower Mississippi Sound and 
adjacent nearshore waters has been studied and is 
considered feasible if regulations are enacted to pre- 
vent overharvest and minimize gear conflict (Horst and 
Bankston 1986, Stuck 1987, Stuck 1989, Baltz and 
Horst 1 992). However, it has been suggested that only 
a fairly low percentage of the available stone crab 
claws in the northern Gulf of Mexico (Mississippi) 
would be of legal size, i.e. >70 mm propodus length 
(Perry et al. 1995). 

In the south Florida stone crab fishery, stationary traps 
made of wood, plastic, or wire are baited with fish 
scraps, deployed on the bottom and marked with a 
buoy, and checked every few days for crabs (Overbey 
1992). According to Florida regulations, claws must 
have a propodus length of >70 mm (2.75 in) to be legal 
for harvest, and commercial stone crabbers must have 
a Saltwater Products License (GSMFC 1993). Legal 
size is generally attained by males at approximately 80 
mm carapace width (CW), and by females at 90 mm 
CW (Simonson 1985, GSMFC 1993). This minimum 


size is intended to allow crabs to reproduce at least 
once before being vulnerable to the fishery. Egg- 
bearing females are protected, and the fishery is open 
from mid-October to mid-May (Ehrhardt et al. 1990, 
GSMFC 1 993, NOAA 1 993). Similar regulations apply 
in offshore federal waters of the Gulf of Mexico as well 
(GMFMC 1996a). The Florida stone crab fishery is 
spatially separated from the pink shrimp trawl fishery to 
minimize gear conflict (Overbey 1 992). In Texas, only 
right claws with propodus length >63 mm may be 
harvested, and the possession or sale of ovigerous 
(sponge) crabs and left claws is prohibited (GSMFC 
1993). 

Recreational : Many of the Florida permit holders can 
be considered recreational because their harvest is for 
home consumption, but the total recreational harvest is 
probably much smaller than the commercial (GMFMC 
1978, Zuboy and Snell 1982, Lindberg and Marshall 
1 984, NOAA 1 985). Some of the recreational harvest 
is with gear similar to the commercial fishery, i.e., crab 
traps, and a Saltwater Products License is required to 
use traps (GSMFC 1 993). Stone crabs are also taken 
by hand or dipnet while wading or diving (GMFMC 
1978, Williams 1984), or removed from their burrows 
with a hook attached to a long handle (Savage et al. 
1 975). In offshore federal waters of the Gulf of Mexico, 
recreational regulations include a 2.75 in (70 mm) 
minimum claw size, closed season from mid-May to 
mid-October, and prohibition of claw removal from 
egg-bearing females (GMFMC 1996b). 

Indicator of Environmental Stress : Stone crabs are not 
typically used in studies of toxicity, bioaccumulation, 
and environmental stress. 

Ecological : Stone crabs have a large claw adapted for 
crushing shells, and are formidable predators of mol- 
luscs. They are known to prey on juvenile oysters on 
reefs. The burrows of gulf stone crabs in mud flats 
remain filled with seawater at low tide, and can provide 
a unique intertidal refuge for small fishes and other 
organisms (Powell and Gunter 1968). 

Range 

Overall : The Florida stone crab occurs from North 
Carolina around peninsular Florida to the Big Bend 
region, and also in the Bahamas, Cuba, Jamaica, the 
Yucatan peninsula, and Belize. The gulf stone crab 
occurs in the Gulf of Mexico from Florida's Big Bend 
region westward through Texas to Tamaulipas in north- 
ern Mexico (Williams and Felder 1986). The two 
species co-occur and are known to hybridize in the Big 
Bend region of northwest Florida. 

Within Study Area : Within U.S. estuaries of the Gulf of 
Mexico, the Florida stone crab occurs from Florida Bay 


110 


Stone crab, continued 


to Apalachicola Bay, Florida, and is especially abun- 
dant in the southwest Florida region (NOAA 1985) 
(Table 5.1 2). The gulf stone crab occurs from Suwannee 
River, Florida westward to Laguna Madre and Baffin 
Bay, Texas, and is relatively abundant in the south 
Texas estuaries (Table 5.13). The two species are 
sympatric in Suwannee River, Apalachee Bay, and 
Apalachicola Bay, and are known to hybridize in this 
region. 

Life Mode 

Eggs are maintained by the female beneath her abdo- 
men until hatching. Zoeal larvae are planktonic. The 
megalopal stage is a transition from the planktonic 
larval life mode to the epibenthic life mode of juveniles 
(Stuck and Perry 1 992). As megalopae transform into 
juveniles, they settle out and are found in areas provid- 
ing cover such as rubble and seagrass beds. Adults 
and juveniles are demersal, with adults often forming 
deep burrows in mud sediments. Juveniles usually do 
not form burrows, but use readily available crevices or 
existing cavities in close proximity to food (Lindberg 
and Marshall 1984). Adult males may exhibit agonistic 
behavior and compete for burrows, but it is not known 
whetherthey establish and defend territories or whether 
their distribution changes between mating and non- 
mating seasons (Wilber 1 986). Stone crabs have been 
suggested to be nocturnal; however, equal activity at 
mid-day and mid-night has been observed, suggesting 
a crepuscular activity cycle (Powell and Gunter 1968, 
Lindberg and Marshall 1984). 

Habitat 

Type : All life stages are marine to estuarine. Adult 
Florida stone crabs are generally found in deeper 
waters of estuaries or in nearshore waters of the Gulf 
of Mexico. Adults burrow under rock ledges, coral 
heads, dead shell, or grass clumps (Costello et al. 
1979, Bert and Stevely 1989). In seagrass flats and 
along tidal channels they inhabit burrows and are 
rarely found on shallow flats during spring and early 
summer. Juveniles are found in estuaries around 
pilings, among shells and rocks, and in grass beds 
(NOAA 1 985). They can change coloration patterns to 
blend with the background (Bert et al. 1978, Lindberg 
and Marshall 1984, Williams 1984). Maturing crabs 
movetodeeperestuarineand nearshore waters. Adults 
have been collected at depths ranging from 5 to 54 m, 
but are not generally abundant in offshore waters 
(Bullis and Thompson 1965, Bert and Stevely 1989, 
Stuck 1 989). The Florida stone crab occurs at greatest 
densities in seagrass, rocky outcrops, and hard bot- 
tom. It rarely occupies oyster bars, while the gulf stone 
crab commonly inhabits oyster bars, sandy or muddy 
bottoms, as well as seagrass or rocky habitats (Bert 
and Harrison 1 988). Gulf stone crabs occur both sub- 
and intertidally, whereas the Florida stone crab is 


primarily subtidal (Wilber 1989a, Wilber 1992). In 
addition, males are more likely to be found in intertidal 
areas in the summer, and females in subtidal habitats 
(Wilber 1989a). Highest catches of gulf stone crab in 
Mississippi Sound are in the immediate vicinity of 
barrier island passes in depths less than 12 m, and they 
are not generally abundant in offshore waters (Stuck 
1989). 

Substrate : Florida stone crabs appear to require sub- 
strate suitable for refuge, using either available struc- 
ture or excavated burrows. They are found in rock or 
shell substrates, seagrass meadows, and pilings 
(Costello et al. 1979), and are known to excavate 
burrows in emergent hard substrate or in seagrass 
( Thalassia) beds (Bert and Stevely 1 989). In one study 
in Galveston Bay, gulf stone crabs were found to be 
more abundant on oyster reefs than in vegetated or 
non-vegetated habitat (Zimmerman et al. 1989). 

Physical/Chemical Characteristics : 
Temperature - Larvae: Florida stone crab larvae do not 
develop beyond the megalopal stage at temperatures 
below 20° C (Ong and Costlow 1970). Optimal 
conditions for zoeae appear to be 30°C at 30 to 36%o. 
Megalopae are sensitive to low salinities and extreme 
temperatures (Lindberg and Marshall 1984). In a 
factorial experiment of salinity and temperature, sur- 
vival of Florida stone crab larvae (zoeae) was found to 
be highest at 30°C and 30%o, and diminished at salini- 
ties and temperatures above and below these values 
(Brown et al. 1 992). The early zoeal stages (zoeae 1 - 
3) were strongly affected by both temperature and 
salinity, whereas the later stages (zoeae 4-5) were less 
affected by salinity. Larval developmental rate and 
molting frequency were accelerated by increasing tem- 
perature, but not by salinity. 

Temperature - Juveniles and Adults: Juvenile and 
adult stone crabs are eurythermal and, in general, can 
tolerate waters ranging from 8°-32°C. In cooler tem- 
peratures they become inactive and may seal their 
burrows with mud (Powell and Gunter 1 968). Muscular 
movements of juvenile Florida stone crab virtually 
cease below 15°C (Brown et al. 1992). In Mississippi 
Sound, juvenile gulf stone crabs have been collected at 
temperatures from 7°-33°C, but mostly above 25°C 
(Stuck and Perry 1992). Molting and spawning are 
affected by temperature (Lindberg and Marshall 1984, 
Williams 1984), and low temperatures are known to 
inhibit molting (Brown et al. 1992). Ovigerous gulf 
stone crab females are not generally found at <18°C, 
and are most common at >22°C (Stuck and Perry 
1992). In a factorial experiment of salinity and tem- 
perature, survival of juvenile Florida stone crab was 
found to be 100% at 15°, 20°, and 25°C (Brown et al. 
1992). 


111 


Stone crab, continued 


Salinity - Larvae: Ong and Costlow (1 970) reported that 
Florida stone crab zoeae have low survival rates at low 
salinities (20-25%o) at 20°C; and complete mortality 
occurs in a salinity of 10%o. At 23°-25°C, low survival 
of zoeae has been observed below 27%o (Porter 1 960). 
It has been suggested that gulf stone crab larvae may 
be more tolerant of low salinities than Florida stone 
crab larvae. In Mississippi Sound, gulf stone crab 
megalopae are commonly found in salinities of 15- 
25%o, and have been collected from salinities as low as 
9% (Stuck and Perry 1992). 

Salinity - Juveniles and Adults: Juveniles and adults of 
both species are considered euryhaline, although they 
are usually found in higher salinities. It has been 
suggested that M. mercenaria may be less tolerant of 
lower salinities and/or prefer higher salinities than M. 
adina (Williams and Felder 1986). Juvenile Florida 
stone crabs are generally found in salinities >24%o 
(Bender 1971). In Mississippi Sound, gulf stone crab 
juveniles have been collected in salinities from <4 to 
34%o, although they are most abundant in salinities 
from 20-29% o (Stuck and Perry 1 992). Gulf stone crab 
adults are found in salinities above 1 3%o in Mississippi 
Sound (Stuck 1989, Stuck and Perry 1992), but they 
have been reported from salinities as low as 1 1 .6%o in 
Texas (Powell and Gunter 1 968). In a factorial experi- 
ment of salinity and temperature, survival of juvenile 
Florida stone crab was found to be 1 00% at 25, 30, 35, 
and 40% o (Brown et al. 1 992). In a similar experiment 
comparing survival of juvenile gulf stone crab and 
Florida stone crab, it was found that gulf stone crab had 
greater tolerance for low salinity and low temperature 
than did Florida stone crab (Brown and Bert 1993). 
This may be due to species-specific differences, or to 
local adaptation of populations. These differences 
generally reflect the known biogeographic and in- 
shore/offshore distribution of the two species (Brown 
and Bert 1993). 

Dissolved Oxygen (DO): Adults are fairly tolerant of 
periods of low DO, although long-term effects are not 
well known (Lindberg and Marshall 1984). 

Turbidity: Stone crabs may become more active in 
turbid waters, possibly as a result of waves and turbu- 
lence that agitate the bottom substrate (Savage et al. 
1975). 

Migrations and Movements : Movements by Florida 
stone crabs of up to 30 km/year have been recorded in 
Florida's Everglades National Park (Bert and Harrison 
1988), but most movements appear to be short-range 
and along shore (1.6-8.0 km) (Ehrhardt 1990). Minor 
movements by the females from grass flats to deeper 
waters to avoid especially high or low temperatures 
have been noted (Lindberg and Marshall 1984, NOAA 


1985, Wilber 1986). In northwest Florida's "hybrid 
zone", adult females may migrate into intertidal oyster 
habitats (Wilber and Herrnkind 1 986). This is followed 
by the gradual emigration of nearly all crabs from the 
intertidal region in the late fall and early winter, prob- 
ably in response to falling temperature. 

Reproduction 

Mode : Stone crabs have separate male and female 
sexes (gonochoristic), and exhibit sexual dimorphism 
(Savage 1971, Bert and Stevely 1989). 

Mating and Spawning : Mating occurs from November 
to March, but primarily in January and February. It is 
sequenced with the spawning season, generally from 
March to November. In Florida Bay, peak mating 
periods have been noted in April and October (Bert and 
Stevely 1989). Mating takes place within a burrow or 
crevice (Savage 1971, Bert and Stevely 1989, Wilber 
1 989b). Males will guard the females after copulation, 
and for longer periods after females molt if another 
male stone crab is present. Sperm are transferred from 
the male to the female within spermatophores which 
are stored by the female in the seminal receptacle. 
Only a portion of the sperm is used at a spawning 
period, some being maintained for later spawns. A 
female can spawn up to six times before mating again. 
After hatching one batch of eggs, a female may deposit 
a new egg mass within a week. Fertilized eggs are 
released into a basket formed by the female's ex- 
tended abdomen and the exopods of her abdominal 
appendages. The eggs are attached to hairs on the 
exopods by a secretion. Temperature and photoperiod 
are primary regulators of spawning frequency (Bert et 
al. 1 978, Lindberg and Marshall 1 984, Williams 1 984, 
Bert et al. 1986). In south Florida, most spawning of 
Florida stone crabs is from March to October, with 
peaks in May and September (Sullivan 1979). How- 
ever, spawning can also occur throughout the year in 
warm areas such as Florida Bay. Ovigerous gulf stone 
crabs occur in Mississippi Sound from March through 
October, with apparent spawning peaks in June and 
September (Stuck and Perry 1992). Evidence indi- 
cates that females molt and mate soon after spawning 
is terminated. The movement of adult females to 
oyster reefs in the fall suggests this may be an impor- 
tant mating habitat for first and second year adults 
(Wilber 1986). 

Fecundity : A single female can produce between 4 and 
6 egg masses (sponges) during a spawning season, 
averaging 4.5 spawnings per molt (Cheung 1 969). Ten 
spawnings during an intermolt period have been re- 
ported from a single female held in the laboratory 
(Yang 1971). Each sponge may contain 0.5 to 1.0 
million eggs. Wilber (1989a) observed a maximum 
number of five clutches carried by a single female in a 


112 


Stone crab, continued 


93 day period. Fecundity is higher in larger females 
(Sullivan 1979). 

Growth and Development 

Egg Size and Development : Fertilized eggs are main- 
tained by the female until hatching, usually 9 to 1 4 days 
(Lindberg and Marshall 1984). The embryonic dura- 
tion of eggs held in the laboratory at temperatures of 29 
to 30°C was approximately 10 days (Yang 1971). 

Age and Size of Larvae : Stone crabs typically pass 
through five (sometimes six) zoeal stages with one 
molt per stage, and then metamorphose into 
megalopae. Each zoeal stage lasts three to six days 
(Porter 1960), and total time from hatch to metamor- 
phosis is 21 to 28 days (Brown et al. 1992). Fastest 
larval growth of Florida stone crabs was achieved in the 
laboratory at 30°C and 30-35%o, in which the megalopal 
stage was reached in 1 4 days and first crab stage in 21 
days (Ong and Costlow 1970). At 25°C and 30%o, 
laboratory-reared gulf stone crab megalopae devel- 
oped in 17 days (Martin et al. 1988). Development of 
planktonic larvae to first crab stage usually requires 27 
to 30 days, but may be affected by diet. The megalopal 
stage of gulf stone crab is thought to last 4 to 7 days 
(Stuck and Perry 1992). 

Juvenile Size Range : Megalopae metamorphose to 
juveniles and settle at 1.5 to 2.0 mm carapace width 
(CW) (Bert et al. 1986). Intermolt period for post- 
settlement juveniles <10 mm CW is approximately 36 
days (Brown et al. 1 992). Juveniles molt several times, 
and growth can vary from 1 to 40 mm CW in their first 
year. At a size of about 35 mm CW, the carapace 
shape transforms to the adult coloration. Size in- 
creases in increments of approximately 1 5% per molt. 

Age and Size of Adults : 

Female M. mercenaria begin to reach sexual maturity 
at about 40 mm CW and some mate during the winter 
at age 1 , although most mature later at age 2 (60-70 
mm CW) or age 3 (70-80 mm CW). Males are generally 
mature at 70 mm CW, at age 2. In laboratory studies, 
measured growth of adults has been approximately 1 5 
to 20% of the carapace width per molt, which is 
comparable with field growth observations (Simonson 
1 985, Tweedale et al. 1 993). After four years of age, 
crabs generally molt only once per year, typically in the 
fall. Terminal molts have been suggested to occur 
around 1 1 2 mm CW, but crabs can reach sizes of 1 30 
to 145 mm CW (Bert et al. 1978, Sullivan 1979, 
Lindberg and Marshall 1 984, Bert et al. 1 986). Recruit- 
ment into the Florida stone crab fishery probably oc- 
curs at about age 2 (Ehrhardt and Restrepo 1989, 
Restrepo 1989). The maximum age of Florida stone 
crabs has been estimated as six to eight years or more 
(Bert et al. 1 986, Restrepo 1 989). Gulf stone crabs are 


morphometrically similar to Florida stone crabs, and 
their carapace widths at 50% sexual maturity have 
been estimated at 71 mm for males, and 73 mm for 
females (Perry et al. 1995). 

Food and Feeding 

Trophic Mode : Stone crabs are high trophic level 
predators and are primarily carnivorous at all life stages 
(Bert and Stevely 1989). After feeding to satiation, 
these crabs can live for two weeks without feeding 
again (Bert et al. 1986). 

Food Items : It has been suggested that larvae have 
specific dietary requirements, apparently met by only 
certain types of planktonic animals (Guillory et al. 
1995). Juveniles feed on small molluscs, polychaete 
worms and crustaceans. Juveniles in captivity are 
known to consume small bivalves, oyster drills, beef 
liver and chicken parts, polychaetes, and each other. 
Adults use their heavy chelae to crush all types of 
molluscs, and are known to prey on oysters (Williams 
1984, NOAA 1985, Bert et al. 1986) and mussels 
(Brachidontes spp.) (Powell and Gunter 1968). Stone 
crabs are also known to consume carrion and veg- 
etable matter such as seagrass (NOAA 1985). 

Biological Interactions 

Predation : Larvae are preyed on by other planktivores, 
while the larger juveniles are prey for black sea bass, 
groupers, common octopus (Octopus vulgaris), and 
other large predators (Lindberg and Marshall 1984, 
Lindberg et al. 1992). Adults can usually defend 
against predators, but may be vulnerable to attack 
when caught in crab traps. 

Factors Influencing Populations : Although "harvested" 
crabs are released alive, subsequent mortality of 
declawed crabs has been estimated at 50% and has a 
significant impact on stone crab populations. After 
removal from traps, crabs are sometimes held onboard 
and declawed while enroute to port; mortality of these 
crabs is higher if they are held too long and not kept 
moist, and if the claws are not severed along the 
natural fracture plane (Simonson and Hochberg 1 986). 
The Florida stone crab fishery is considered to be fully 
exploited. Recent annual harvests have been over 
1 ,000 metric tons per year (mt/y), although long-term 
potential yield has been estimated as 976 mt/y (NOAA 
1993), and Zuboy and Snell (1982) estimated a maxi- 
mum sustainable yield (MSY) of 853 mt/y. Declines in 
catch per unit effort (CPUE) have been observed in 
recent years, further suggesting that the fishery is fully 
utilized (Phares 1992). Mariculture methods have 
been developed to produce stone crab megalopae 
(McConnaughey and Krantz 1 992), although commer- 
cial-scale mariculture of stone crab claws is not yet 
feasible. 


113 


Stone crab, continued 


Personal communications 

Bert, Theresa M. Florida Marine Research Institute, St. 
Petersburg, FL. 

Tobb, Mark. Lu Belle's Seafood Brokerage, Port 
Aransas, Texas. 

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115 


Stone crab, continued 


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117 


Bull shark 


Carcharhinus leucas 


Adult 


-^ir****?^' 


"•' -'' /l^^y-^ ..'rjyl^.W', -r. , t 7. : 


<^ [ffflr _, 


Xx^ 


50 cm 


(from Fischer 1978) 


Common Name: bull shark 

Scientific Name: Carcharhinus leucas 

Other Common Names: cub shark, requiem taureau 

(French), tiburon sarda (Spanish) (Fischer 1978). 

Classification (Robins et al. 1991) 

Phylum: Chordata 

Class: Chondrichthyes 

Order: Lamniformes 

Family: Carcharhinidae 

Value 

Commercial : The bull shark is becoming more impor- 
tant in the commercial shark fishery of the Gulf of 
Mexico as the market demand for sharks increases 
(Branstetter pers. comm., NOAA 1992, NMFS 1993). 
The flesh is edible, but it is primarily used for fish meal. 
The hide is processed into leather and has good quality 
(Castro 1983, NOAA 1992). This species was once 
sought for its liver which contains large amounts of 
vitamin A; however, synthetic substitutes have re- 
duced the demand for this product (Fischer 1978, 
NOAA 1 992, NMFS 1 993). Bull sharks will take almost 
any bait, but may prefer shark or ray. Recently, many 
Gulf of Mexico shrimp fishermen have changed to 
longline rigs to catch sharks because of the high export 
demand for shark fins. A Fishery Management Plan 
(FMP) has been developed for sharks in the western 
Atlantic, Caribbean Sea, and Gulf of Mexico (NMFS 
1993). Some of the features of this plan include an 
annual permit required for commercial shark fishing 
vessels in the U.S. exclusive economic zone, and an 
annual quota of 2,436 mt dressed weight for large 
coastal species during the 1993 fishing year. Future 
quotas will be based on the shark fishery rebuilding 
program (NMFS 1993). 


Recreational : In general, shark populations in the Gulf 
of Mexico and Atlantic waters of the southeast U.S. are 
suffering from overfishing to which they are especially 
vulnerable (NOAA 1992). Most sharks caught by 
recreational anglers are released or discarded, but 
some are used as mounted trophies or for home 
consumption. In the Gulf of Mexico, the bull shark 
comprises 7% by number and 11% by weight of the 
sharks caught by recreational fishermen (Casey and 
Hoey 1985). The recreational bag limit is four sharks 
per boat per trip (NMFS 1 993). 

Indicator of Environmental Stress : This species is not 
typically used in studies of environmental stress, but 
monitoring by the Florida Department of Health and 
Rehabilitative Services has shown high concentra- 
tions of mercury present in shark flesh sold in the retail 
market (NMFS 1993). 

Ecological : Sharks are often studied as top trophic 
level predators (Casey and Hoey 1 985). The bull shark 
is a top trophic level carnivore in many estuarine 
systems, and is one of the most common species of 
inshore sharks in the Gulf of Mexico (Casey and Hoey 
1985, Shipp 1986). 

Range 

Overall : This is a cosmopolitan species in both tropical 
and subtropical areas with range extensions into some 
temperate regions. In the western Atlantic, it extends 
from Cape Cod, Massachusetts to southern Brazil, 
including Bermuda, Gulf of Mexico, and Caribbean 
islands (Fischer 1978, Lee et al. 1980, Garrick 1982). 
It is most abundant in Gulf of Mexico and Caribbean 
Sea (Garrick 1982, Castro 1983). In the Pacific, it is 
known from Anacapa Island off the California coast to 


118 


Bull shark, continued 


Table 5.14. Relative abundance of bull shark in 31 
Gulf of Mexico estuaries (from Volume I). 

Life stage 


Estuary 


A M J P 


Florida Bay 


V 


V 


o 


V 


Ten Thousand Islands 


o 


V 


o 


o 


Caloosahatchee River 


o 


o 


o 


Charlotte Harbor 


o 


V 


o 


o 


Tampa Bay 


o 


V 


o 


o 


Suwannee River 


o 


V 


o 


o 


Apalachee Bay 


o 


V 


o 


o 


Apalachicola Bay 


o 


V 


o 


o 


St. Andrew Bay 


o 


V 


o 


o 


Choctawhatchee Bay 


o 


V 


o 


o 


Pensacola Bay 


o 


V 


o 


o 


Perdido Bay 


V 


V 


V 


V 


Mobile Bay 


o 


V 


o 


o 


Mississippi Sound 


o 


o 


o 


Lake Borgne 


o 


o 


Lake Pontchartrain 


o 


o 


Breton/Chandeleur Sounds 


® 


o 


Mississippi River 


V 


V 


Barataria Bay 


o 


V 


V 


Terrebonne/Timbalier Bays 


o 


o 


V 


Atchafalaya/Vermilion Bays 


o 


Calcasieu Lake 


V 


V 


V 


Sabine Lake 


V 


Galveston Bay 


V 


o 


Brazos River 


na 


Matagorda Bay 


o 


San Antonio Bay 


o 


Aransas Bay 


o 


Corpus Christi Bay 


o 


Laguna Madre 


V 


Baffin Bay 


V 


A M J P 


Relative abundance: 

O Highly abundant 

® Abundant 

O Common 

V Rare 

blank Not present 

na No data available 


Life stage: 

A - Adults 
M - Mating 
J - Juveniles 
P - Parturition 


Ecuador and possibly to northern Peru (Lee et al. 
1980). 

Within Study Area : This species is common in inshore 
waters and estuaries from Texas to Florida, and is fairly 
abundant in Louisiana and Florida estuaries (Table 
5.14). It is generally the most common shark species 
in brackish water areas of the Gulf of Mexico, and is 
known to enter fresh water (Shipp 1986). 

Life Mode 

Bull sharks are demersal predators. They are euryha- 
line and occur from the nearshore marine zone to 
freshwater rivers (Fischer 1 978, Lee et al. 1 980, Shipp 
1986). 

Habitat 

Ty pe: This species is predominantly a coastal species 
that is frequently found in shallow waters, especially in 
bays and river estuaries (Fischer 1 978, Lee et al. 1 980, 
NMFS1993). 

Substrate : No particular substrate preference by this 
species has been noted, but it is considered a bottom 
dweller (Fischer 1978). 

Physical/Chemical Characteristics 
Temperature: Thomerson and Thorson (1977) sug- 
gested water temperatures to be the limiting factor for 
the advancement of bull shark up the Mississippi River. 
Only when temperatures are above 24°C, particularly 
during the summer and fall, do the sharks ascend the 
Mississippi River. Snelson and Williams (1981) col- 
lected juvenile bull shark in temperatures from 20 to 
32°C, and reported that two individuals had succumbed 
to hypothermal stress around a temperature of 8°C, 
during January. Branstetter (pers. comm.) suggests 
that 18°C is the minimum temperature necessary 
before bull sharks advance into estuaries. 

Salinity: The bull shark occurs in brackish or freshwa- 
ter, mainly as pups and juveniles but also as adult 
females. This occurrence may be related to inshore 
migrations of the females for parturition (Garrick 1 982, 
Snelson et al. 1 984). As a result, juveniles often spend 
considerable time in these brackish waters (Garrick 
1982). Branstetter (1986) noted that the fishery for 
these is located primarily near freshwater inflows. One 
study reported the collection of juveniles from a salinity 
range of 1.6 to 2.3%o (Kelley 1965). Thomerson and 
Thorson (1977) report that the bull shark is the only 
shark known to withstand the osmotic demands of 
either fresh water or sea water for periods of at least 
months and probably years. Other sharks may be 
capable of withstanding these osmotic conditions, but 
do not typically enter freshwater (Branstetter pers. 
comm.). 


119 


Bull shark, continued 


Movements and Migrations : Movements of sharks to 
estuarine nursery areas appears to be mainly for 
parturition (Lineaweaverand Backus 1970). Females 
move towards whelping grounds in the spring, but do 
not actually enter them until parturition is eminent. 
Other movements are probably associated with chang- 
ing temperatures. Springer (1940) suggested a north 
and south migration coinciding with spring and fall on 
the northern Gulf coast. 

Reproduction 

Mode : This species has separate male and female 
sexes (gonochoristic). The male inseminates the 
female with the assistance of modified pelvic fins 
known as clasper organs. Fertilization is internal, and 
development is viviparous (Castro 1983). 

Mating and Parturition : Descriptions of mating are 
unavailable due to a lack of detailed observations and 
reports (Castro 1983). Mating takes place in coastal 
waters during June and July in the Gulf of Mexico, with 
pups being born the following year in April, May, and 
June (Clark and Schmidt 1965). Gestation probably 
lasts 10 to 11 months (Clark and Schmidt 1965, 
Branstetter 1981). In warmer waters, mating and 
parturition can occur year-round (Castro 1983). 

Fecundity : Snelson et al. (1986) took a 249 cm total 
length (TL) female with 12 near term embryos. Most 
other investigators report litters of six to eight. 

Growth and Development 

Embryonic Development : Development is viviparous 
with embryos initially dependent on stored yolk, but 
later nourished by the mother through a placental 
connection. Dodrill (1977) proposed that during uter- 
ine development one or more pups may develop to 
extraordinary size at the expense of other litter mates. 

Juvenile Size Range : Pups measure around 75 cm at 
birth (Castro 1983). Size at birth is highly variable 
ranging from 60 to greater than 75 cm (Branstetter 
1986, Branstetter and Stiles 1987). Caillouet et al. 
(1969) showed no significant differences between 
lengths or weights for male and female neonates 
shortly after birth. Juvenile weights increased rapidly 
as maturity approached (Branstetter 1 981 ). Branstetter 
and Stiles (1 987) estimated growth rates were 1 5 to 20 
cm/year for the first five years, 1 cm/year for 6 to 1 
year old sharks, 5 to 7 cm/year for 1 1 to 16 year old 
sharks and less than 4 to 5 cm/year for sharks older 
than 16 years. 

Age and Size of Adults : The smallest reported mature 
male and female are 212 cm TL and 228 cm TL 
respectively (Branstetter 1981). Males mature at 210- 
220 cm TL or 1 4 to 1 5 years of age, and females mature 


at >225 cm TL or over 1 8 years of age (Branstetter and 
Stiles 1987). Females grow larger than males (Clark 
and Von Schmidt 1965, Branstetter 1986). The bull 
shark is thought to live to 20 years and possibly longer, 
and may reach lengths of 2.7 m and weights near 270 
kg(Shipp1986). 

Food and Feeding 

Trophic Mode : Larvae development is in uterine and 
nutrients are derived from the mother. At parturition the 
bull shark is considered a juvenile. Both juveniles and 
adults are carnivorous predators, but they will also 
scavenge (Shipp 1986). The bull shark typically feeds 
during the evening around bridges, passes, and chan- 
nels. Although usually a sluggish moving fish, it is 
capable of great speed when pursuing prey (Fischer 
1978, Shipp 1986). 

Food Items : The bull shark is an opportunistic predator 
(Lee et al. 1980). Reported stomach contents have 
included species of loliginid squid and several fishes 
(longspine porgy, sand perch, striped anchovy, men- 
haden). Jaws commonly contained spines from rays 
(Branstetter 1981). Other bony fishes reported from 
the stomachs of bull sharks are sheepshead, various 
jacks, common snook, little tunny, hardhead catfish, 
trunkfish, tarpon, mullets (Clark and Von Schmidt 
1965); American eel, white perch, Atlantic croaker 
(Schwartz 1 960), mackerels, tunas, and carrion (Fischer 
1978). Bull sharks are also known to feed on other 
sharks, preying heavily on small sandbar sharks, as 
well as rays, molluscs, sea urchins, crabs, shrimp, 
porpoises, and sea turtles (Fischer 1978, Lee et al. 
1 980, Castro 1 983). Snelson et al. (1 984) suggest that 
saltwater catfishes (hardhead and gafftopsail) and 
stingrays are very important food items in the diet of bull 
sharks. This shark is considered to be potentially 
dangerous to humans. Its habits frequently place it in 
the vicinity of swimmers and fishermen, and it has been 
reponsible for several documented attacks (Lee et al. 
1980, Shipp 1986). 

Biological Interactions 

Predation: The bull shark is not known to be a prey item 
for other species. 

Factors Influencing Populations : The bull shark is a top 
trophic level carnivore with slow growth and relatively 
low reproductive capacity. It is therefore vulnerable to 
overfishing, and probably should be managed conser- 
vatively (Casey and Hoey 1 985, NMFS 1 993). A major 
commercial fishery for these sharks is not recom- 
mended, and if sport fishing pressures increase there 
may be need to further regulate the fishery (Casey and 
Hoey 1 985, NOAA 1 992). Shark mortality also occurs 
in the form of bycatch from the commercial swordfish, 
tuna, and shrimp fisheries (NMFS 1 993). The loss and 


120 


Bull shark, continued 


degradation of habitat, especially nursery areas, is 
another factor that may affect shark abundance. 

Personal communications 

Branstetter, Steve. Florida Marine Research Institute, 
St. Petersburg, FL. 

References 

Branstetter, S. 1981. Biological notes on the sharks of 
the north central Gulf of Mexico. Contrib. Mar. Sci. 
24:13-34. 

Branstetter, S.G. 1986. Biological parameters of the 
sharks of the northwestern Gulf of Mexico in relation to 
their potential as a commercial fishery resource. Ph.D. 
dissertation, Texas A&M Univ., College Stn, TX, 1 38 p. 

Branstetter, S., and R. Stiles. 1987. Age and growth 
of the bull shark, Carcharhinus leucas, from the north- 
ern Gulf of Mexico. Environ. Biol. Fishes 20:169-181. 

Caillouet, C.W., Jr., W.S. Perret, and B.J. Fontenot, Jr. 
1969. Weight, length and sex ratio of immature bull 
sharks, Carcharhinus leucas, from Vermilion Bay, Loui- 
siana. Copeia 1969:196-197. 

Casey, J.G., and J.J. Hoey. 1985. Estimated catches 
of large sharks by U.S. recreational fishermen in the 
Atlantic and Gulf of Mexico. NOAA Tech. Rep. NMFS 
31. 

Castro, J.I. 1983. The Sharks of North American 
Waters. Texas A&M Univ. Press, College Stn., TX, 1 80 
P- 

Clark, E., and K. von Schmidt. 1965. Sharks of the 
central Gulf coast of Florida. Bull. Mar. Sci. 15:13-83. 

Dodrill, J.W. 1977. A hook and line survey of the 
sharks found within five hundred meters of shore along 
Melbourne Beach, Brevard County, Florida. M.S. 
thesis, Fla. Inst. Tech., Melbourne, FL, 304 p. 

Fischer, W. (ed.). 1978. FAO Species Identification 
Sheets for Fishery Purposes, Western Central Atlantic 
(Fishing Area 31), Vol. I. Food and Agriculture Orga- 
nization of the United Nations, Rome. 

Garrick.J.A.F. 1982. Sharks of the genus Carcharhinus. 
NOAA Tech. Rep. NMFS Circ. 445, 194 p. 

Kelley, J.R., Jr. 1965. A taxonomic survey of the fishes 
of Delta National Wildlife Refuge with emphasis upon 
distribution and abundance. M.S. thesis, Louisiana St. 
Univ., Baton Rouge, LA, 133 p. 


Lee, D.S., C.R. Gilbert, OH. Hocutt, R.E. Jenkins, D.E. 
McAllister, and J. R. Stauffer, Jr. 1980. Atlas of North 
American Freshwater Fishes. N.C. St. Mus. Nat. Hist., 
NC Biol. Surv. Pub. No. 1980-12, 867 p. 

Lineaweaver, T.H., III, and R.H. Backus. 1970. The 
Natural History of Sharks. J.B. Lippincott Co. .Philadel- 
phia, PA, 256 p. 

National Marine Fisheries Service (NMFS). 1993. 
Fishery management plan for sharks of the Atlantic 
Ocean. NOAA NMFS Office of Fisheries Conservation 
and Management, Silver Spring, MD, 276 p. 

National Oceanic and Atmospheric Administration 
(NOAA). 1992. Status of fishery resources off the 
southeastern United States for 1991. NOAA Tech. 
Memo. NMFS-SEFSC-306, 75 p. 

Nelson, D.M., M.E. Monaco, CD. Williams, T.E. Czapla, 
M.E. Pattillo, L. Coston-Clements, L.R. Settle, and E.A. 
Irlandi. 1992. Distribution and abundance of fishes 
and invertebrates in Gulf of Mexico estuaries, Vol. I: 
Data summaries. ELMR Rep. No. 10. NOAA/NOS 
SEA Division, Rockville, MD, 273 p. 

Robins, C.R., R.M. Bailey, C.E. Bond, J.R. Brooker, 
E.A. Lachner, R.N. Lea, and W.B. Scott. 1991. Com- 
mon and scientific names of fishes from the United 
States and Canada, Fifth Edition. Am. Fish. Soc. Spec. 
Pub. 20. AFS, Bethesda, MD, 183 p. 

Schwartz, F.J. 1960. Additional comments on adult 
bull sharks Carcharhinus leucas (Muller and Henle), 
from Chesapeake Bay, Maryland. Chesapeake Sci. 
1:68-71. 

Shipp, R.L. 1986. Guide to fishes of the Gulf of Mexico. 
Dauphin Island Sea Lab, Dauphin Island, AL, 256 p. 

Snelson, F.F., and S.E.Williams. 1981. Notes on the 
occurrence, distribution, and biology of elasmobranch 
fishes in the Indian River Lagoon system, Florida. 
Estuaries 4:110-120. 

Snelson, F.F., Jr., T.J. Mulligan, and S.E. Williams. 
1984. Food habits, occurrence and population struc- 
ture of the bull shark, Carcharhinus leucas, in Florida 
coastal lagoons. Bull. Mar. Sci. 34:71-80. 

Springer, S. 1940. The sex ratio and seasonal 
distribution of some Florida sharks. Copeia 1 940: 1 88- 
194. 

Thomerson, J.E., and T.B. Thorson. 1977. The bull 
shark, Carcharhinus leucas, from the upper Missis- 
sippi River near Alton, Illinois. Copeia 1977:166-168. 


121 


Megalops atlanticus 
Adult 


20 cm 


(fromGoode 1884) 


Common Name: tarpon 

Scientific Name: Megalops atlanticus 

Other Common Names: Tarpum, caffum, silverfish, 

silver king, jewfish, big scale; grande ecaille, grand 

ecoy,palika (French); sabalo, sabaloreal, tarpon(Span- 

ish) (Gunter 1 945, Wade 1 962, Hildebrand 1 963, Hoese 

and Moore 1977, Fischer 1978, NOAA 1985). 

Classification (Robins et al. 1991) 

Phylum: Chordata 

Class: Osteichthyes 

Order: Elopiformes 

Family: Elopidae 

Value 

Commercial : There is no commercial fishery for tarpon 
in the United States. Its flesh is generally considered 
to be fatty and of second rate quality, but in Central 
America and West Africa, it is marketed locally and 
consumed fresh or salted (Breder 1944, Wade 1962, 
Hildebrand 1 963). Historically, there was a substantial 
fishery for tarpon in Ceara, Brazil in the 1960's (de 
Menezes and Paiva 1966, Cyr pers. comm.). Their 
large scales are sometimes used for ornamental pur- 
poses (artificial pearls, wind chimes, etc.) (Manooch 
1984). 

Recreational : The tarpon is considered a superb in- 
shore game fish, and it is valuable to the economies of 
areas where it is fished (Hoese and Moore 1 977, Killam 
et al. 1 992). Its fighting ability and aerial acrobatics are 
famous, and it is sought for sport throughout most of its 
range. Fishing occurs primarily from March through 
June and from October to November from bridges, 
piers, and anchored boats (Manooch 1984, NOAA 
1985). Tarpon fishing in the state of Florida is regu- 
lated, with anglers required to purchase a permit before 


they can harvest a fish (Crabtree et al. 1 992). In Texas, 
fishing is currently allowed on a catch and release 
basis only (TPWD 1 993). Proposed regulations would 
allow the harvest of a single tarpon over 80 inches 
(203.2 cm) with the purchase of tag from Texas Parks 
and Wildlife Department (TPWD) (Hegen pers. comm.). 

Indicator of Environmental Stress : Because of its high 
trophic level, the tarpon was chosen as a test species 
in a study of the effects of chlorinated hydrocarbon 
insecticides (Wade 1969). The tarpon is also consid- 
ered a natural monitor of toxic pollutants in inshore 
areas because of its freedom from reliance on dis- 
solved oxygen for survival. Oxygen depletion could 
result in an immediate kill of other fish species, mask- 
ing the ultimate cause of death that would occur when 
toxicants are present (Harrington 1966). 

Ecological : The tarpon is a high trophic level carnivore, 
preying mainly on fish (Wade 1969). 

Range 

Overall : The tarpon occurs in the eastern Atlantic 
Ocean along the coast of west Africa, and in the 
western Atlantic along the coasts of North, Central, and 
South America (Wade 1969). Its range in the western 
Atlantic is from Nova Scotia to central Brazil, and 
throughout the West Indies. However, it is only rarely 
found north of the Carolinas. It has also been reported 
at the Pacific terminus of the Panama Canal (Wade 
1962, Hildebrand 1963, Harrington 1966, Wade 1969, 
Hoese and Moore 1977). Centers of abundance are 
the Gulf of Mexico, coastal Florida, Central America, 
and Brazil (Hildebrand 1963, de Menezes and Paiva 
1 966, Wade 1 969, Fahay 1 973, Smith 1 980, Cyr pers. 
comm.). Its range in the eastern Atlantic is from Ireland 


122 


Tarpon, continued 


Table 5.1 5. Relative abundance of tarpon in 31 Gulf 
of Mexico estuaries (Nelson et al. 1992, Crabtree 
pers. comm., Cyr pers. comm.). 

I—ITG ST3Q0 


Estuary 


A S J L E 


Florida Bay 


O 


O 


Ten Thousand Islands 


O 


O 


Caloosahatchee River 


® 


® 


V 


Charlotte Harbor 


® 


® 


o 


Tampa Bay 


® 


o 


V 


Suwannee River 


^o 


o 


o 


Apalachee Bay 


o 


o 


o 


Apalachicola Bay 


o 


o 


o 


St. Andrew Bay 


o 


V 


o 


Choctawhatchee Bay 


o 


o 


o 


Pensacola Bay 


o 


o 


o 


Perdido Bay 


V 


V 


Mobile Bay 


o^ 


o 


o 


Mississippi Sound 


o 


o 


o 


Lake Borgne 


o 


o 


V 


Lake Pontchartrain 


o 


o 


Breton/Chandeleur Sounds 


Mississippi River 


o 


Barataria Bay 


V 


V 


Terrebonne/Timbalier Bays 


V 


Atchafalaya/Vermilion Bays 


V 


Calcasieu Lake 


Sabine Lake 


V 


Galveston Bay 


V 


V 


Brazos River 


na 


Matagorda Bay 


o 


o 


San Antonio Bay 


o 


o 


Aransas Bay 


V 


V 


V 


Corpus Christi Bay 


V 


V 


V 


Laguna Madre 


V 


V 


Baffin Bay 


V 


A S J L E 


Relative abundance: 

# Highly abundant 
® Abundant 
O Common 
V Rare 
blank Not present 
na No data available 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


to the Congo, with reports of occurrence from Ber- 
muda, the Azores, and the Formigas (Wade 1962, 
Wade 1969, Twomey and Byrne 1985), but it is most 
common from Senegal to the Congo (Wade 1969). 

Within Study Area The tarpon occurs from the Rio 
Grande to Florida Keys with high numbers noted in: 
south Texas; Calcasieu Lake, Louisiana; Grand Isle, 
Louisiana; western Florida; the waterways and rivers 
among the Ten Thousand Islands and the interior 
waterways of the Florida Keys (Hildebrand 1 963, Wade 
1969). Greatest densities in the in the U.S. Gulf of 
Mexico probably occur along the coast of southwest- 
ern Florida (Shipp 1986) (Table 5.15). 

Life Mode 

Tarpon are known to form schools while feeding 
(Hildebrand 1963, Harrington 1966). Little information 
is available on eggs. Early larval forms are pelagic and 
planktonic, while later larval stages, juveniles, and 
adults are pelagic and nektonic (Gehringer 1 959, Smith 
1 980). Adults are known to actively feed both day and 
night (Wade 1962). 

Habitat 

Type: 

Larvae: Stage I (leptocephali) are found in warm, 
western Atlantic epipelagic waters north of the equator. 
They occur in the upper 100 m of water (Wade 1962) 
in euhaline salinities offshore as far as 250 km in 
depths ranging from 90 to 1400 m (Gehringer 1959, 
Wade 1 962, Smith 1 980, Crabtree et al. 1 992). Stage 
II (shrinking) larvae have been recorded from depths of 
<1 to 12 m in inshore waters (Erdman 1960, Tagatz 
1973, Tucker and Hodson 1976). They have been 
collected in salt marshes, rivers, mangrove swamps, 
estuaries, and upper reaches of bays as far north as 
Cape Fear River, North Carolina (Erdman 1960, 
Harrington and Harrington 1960, Harrington 1966, 
Tagatz 1 973, Tucker and Hodson 1 976) in mesohaline 
to euhaline salinities (Wade 1 962, Tagatz 1 973, Tucker 
and Hodson 1976). The stage III (growing) larvae are 
found along beaches in lagoons, salt marshes, tidal 
ponds and potholes, and tidal rivers and canals 
(Harrington 1958, Harrington 1960, Wade 1962, 
Hildebrand 1963, Jones etal. 1978). They occur rarely 
as far north as North Carolina (Tucker and Hodson 
1 976). Juveniles are recovered from salinities ranging 
from freshwater to hypersaline (Breder 1944, Gunter 
1 945, Simpson 1 954, Tabband Manning 1 961 , Rickards 
1 968, Randall 1 959, Wade 1 969, Franks 1 970, Kushlan 
and Lodge 1974, Marwitz 1986). Smaller juveniles 
occur in shallow streams, lakes, marshes, lagoons, 
ponds, ditches, canals, rivers, estuaries, mangrove 
swamps, pools, and drainage ditches nearly or com- 
pletely landlocked except for periods of extreme high 
water, also in headwaters of small freshwater streams 


123 


Tarpon, continued 


(Henshall 1 895, Breder 1 944, Randall 1 959, Harrington 
and Harrington 1960, Tabb et al. 1962, Wade 1962, 
Hildebrand 1963, Rickards 1968, Wade 1969, Odum 
1 971 , Hoese and Moore 1 977, Howells 1 985, Marwitz 
1986). They are usually found in organic-stained 
brackish waters that can be either stagnant or flowing 
(Randall 1959, Wade 1962, Rickards 1968) in depths 
of 1 .5 to 1 5 m (Simpson 1 954, Randall 1 959, Rickards 

1968, Wade 1969, Franks 1970). Tarpon 305 to 487 
mm are common in headwaters of brackish and fresh- 
water streams. Movement to deeper rivers, canals, 
pools, lakes, and eventually to the ocean occurs as 
they grow larger (Hildebrand 1 963, Wade 1 969) At this 
time, they are found in waters 0.9 to 2.5 m deep (Gunter 
1 945, Tabb and Manning 1 961 , Rickards 1 968, Wade 

1969, Franks 1970). Adults are primarily found in 
coastal inshore waters, inlets, estuaries, and passes 
between islands, but they also occur in deeper rivers, 
canals, streams, and lakes (Breder 1944, Hildebrand 
1963, Wade 1969, Kushlan and Lodge 1974, Hoese 
and Moore 1 977, Loftus and Kushlan 1 987) in fresh to 
euhaline salinities (Breder 1944, Randall 1959, Tabb 
et al. 1962, Kushlan and Lodge 1974, Loftus and 
Kushlan 1 987). Adults are found over a wide variety of 
water depths that range from shallow waters to deep 
(90-1400 m) offshore spawning sites (Killam et al. 
1 992). In summer, they have been reported in offshore 
areas such as coral reefs as far as 70 miles west of Key 
West, Florida, in the Dry Tortugas National Park 
(Schmidt pers. comm.). 


Caldwell 1 955, Randall 1 959, Tabb and Manning 1 961 , 
Wade 1962, Rickards 1968, Franks 1970, Marwitz 
1 986). Loss of equilibrium or death has been observed 
from 9.5° to 1 8.2°C in vitro with the greatest occurrence 
at 1 4.0°C (Howells 1 985). Otherstudies report mortali- 
ties occurring between 1 2° to 1 4°C and 1 2° to 1 6°C for 
sudden cold snaps, but resistance to cold might be 
greater during slow temperature falls (Tabb and Man- 
ning 1961, Rickards 1968). 

Salinity - Eggs and Larvae: Stage I larval specimens 
have been collected from waters at 28.5 to 39%o (Wade 
1962, Smith 1980, Zale and Merrifield 1989, Crabtree 
et al. 1 992), and it is assumed that eggs require similar 
conditions for proper development (Zale and Merrifield 
1 989). Early larvae (Stage I) are possibly stenohaline, 
seeming to prefer high salinities as they are generally 
not found in low or fluctuating salinities, and probably 
stay well offshore until the approach of metamorphosis 
(Smith 1980). 

Salinity - Juveniles and Adults: All developmental 
forms except Stage I larvae are euryhaline. They have 
been recorded from 0.0 to 47%o, but seem to prefer 
salinities between 5.1 and 22.3%o (Gunter 1945, 
Simpson 1954, Odum and Caldwell 1955, Gunter 
1956, Simmons 1957, Randall 1959, Tabb and Man- 
ning 1961, Harrington 1966, Rickards 1968, Wade 
1969, Franks 1970, Tagatz 1973, Tucker and Hodson 
1976, Marwitz 1986). 


Substrate : Juveniles and adults are generally found 
over soft mud bottoms that sometimes contain hydro- 
gen sulfide; but, they also occur over sand, firm mud, 
sandy mud with no vegetation, and peat (Gunter 1 945, 
Simpson 1954, Randall 1959, Tabb and Manning 
1961, Tabb et al. 1962, Rickards 1968, Wade 1969, 
Franks 1970). 

Physical/Chemical Characteristics : 
Temperature - Eggs and Larvae: The physical and 
chemical requirements of tarpon are not completely 
known. Stage I larval specimens have been collected 
from waters at 22.2° to 30.0°C (Wade 1962, Smith 
1980, Zale and Merrifield 1989, Crabtree et al. 1992), 
and it is assumed that eggs require similar conditions 
for proper development (Zale and Merrifield 1989). 
They appear to prefer warmer waters (Jones et al. 
1 978). Stage II larvae have been recorded in tempera- 
tures ranging 19.8° to 30.8°C (Tagatz 1973, Tucker 
and Hodson 1976). Stage III larvae have been col- 
lected in waters 25° to 27°C (Harrington 1966). 

Temperature - Juveniles and Adults: The known tem- 
perature ranges are similar for both juveniles and 
adults (Wade 1962). They have been recorded from 
16° to 40°C (Gunter 1945, Simpson 1954, Odum and 


Turbidity: Stage I larvae only occur in clear offshore 
waters (Zale and Merrifield 1989). In subsequent life 
history stages, the tarpon appears to be tolerant of high 
turbidities. 

Dissolved Oxygen: Tarpon have been considered to 
be obligate air breathers (Wade 1 962), able to breathe 
by means of rolling and gulping air which is held in a 
highly vascularized air bladder (Odum and Caldwell 
1955, Wade 1969). However, more recent evidence 
suggests that they are not obligate air breathers and 
can survive at least two weeks without air breathing in 
well oxygenated water (Killam et al. 1992). Larvae 
have been observed to die if prevented from surfacing 
as larger fish do (Harrington 1 966). Their air breathing 
capability allows them to survive in waters with a 
dissolved oxygen content as low as 0.00 to 0.81 parts 
per million (Odum and Caldwell 1955). 

Movements and Migrations : Leptocephalus larvae are 
probably transported into estuaries by tidal currents 
(Killam et al. 1 992). In the Everglades, tarpon are able 
to move between bodies of water during high water 
periods, resulting in their occurrence in isolated ponds 
(Loftus and Kushlan 1987). As juvenile tarpon grow, 
they move from nursery grounds to deeper inshore 


124 


Tarpon, continued 


waters and finally to the ocean (Wade 1969). This 
move typically occurs when juveniles reach approxi- 
mately 400 mm SL, after nearly one year of growth 
(Killam et al. 1 992). It could be speculated that this shift 
in habitat occurs after tarpon reach a sufficient size to 
avoid most predators, or it may be related to the the 
increasing food requirements of juveniles. Adult and 
large juvenile tarpon are capable of extensive move- 
ments, but patterns of coastal migration other than 
inshore-offshore movements in response to the sea- 
sonal temperature changes are not evident (Randall 
1959, Hildebrand 1963, Moe 1972). Adult tarpon are 
reported to be most abundant in inshore waters from 
April to November (Breuer 1 949, Hoese 1 958, Springer 
and Pirson 1958). Assemblages of sexually maturing 
tarpon during spring and summer may be preparatory 
to an offshore spawning migration from the inshore 
feeding areas (Moe 1 972, Crabtree et al. 1 992, Killam 
et al. 1 992). They have been observed in large schools 
2-5 km offshore, swimming together in a circular mo- 
tion referred to as a "daisy chain" (Crabtree et al. 1 992). 
These schools can range from 25 to more than 200 
individuals. Based on collections of larvae (Crabtree et 
al. 1 992, Crabtree 1 995), it has been inferred that adult 
tarpon migrate from inshore feeding areas to offshore 
(up to 250 km) spawning areas from May through July. 

Reproduction 

Mode : This species has separate male and female 
sexes (gonochoristic), and fertilization is external 
through the release of milt and roe into the water 
column. 

Spawning : The exact locations of spawning areas are 
not well known. They are apparently restricted to 
offshore waters such as the east coast of Florida to 
Cape Hatteras, Florida Straits, west central Florida, 
southwestern Gulf of Mexico, outer continental shelf 
and slope of the eastern Gulf of Mexico, Gulf Stream, 
and Caribbean Sea. Spawning activity has not been 
documented, but adult tarpon have been observed in 
large schools or aggregations known as "daisy chains" 
off of the Florida Gulf Coast (Crabtree et al. 1992). 
Larvae with estimated ages of 2 to 25 days have been 
collected over the continental shelf and slope of the 
Florida Gulf coast, indicating spawning in the immedi- 
ate vicinity (Crabtree et al. 1992). Similar exhaustive 
larval sampling efforts have not yet occurred in the 
northwest Gulf of Mexico, the Yucatan Peninsula, or 
elsewhere, so other spawning locations remain un- 
known (Cyr pers. comm.). The estimated spawning 
season of Florida tarpon is from April to July, with near 
ripe females and milt producing males occurring in 
March and April respectively, and spent females occur- 
ring in July and August (Breder 1 944, Hildebrand 1 963, 
Eldred 1967, Jones et al. 1978, Randall 1969, Wade 
1969, Smith 1980, Crabtree et al. 1992, Killam et al. 


1992, Cyr pers. comm.). Crabtree et al. (in press) 
reported that spawning of tarpon in the tropical waters 
of Costa Rica is not seasonal, and that reproductively 
active females were caught during all months. 

Fecundity : One female tarpon, 2,032 mm, was re- 
ported to contain approximately 12,202,000 eggs 
(Babcock 1 936, Wade 1 962). Crabtree et al. (in press) 
examined the gonads of 737 Florida tarpon, and re- 
ported that fecundity ranged from 4.5 to 20.7 million 
oocytes per female, and that fecundity is positively 
correlated with fish weight. 

Growth and Development 

Egg Size and Embryonic Development : No information 
is available on ripe eggs, but ovarian eggs in spent 
females were non-adhesive, opaque, and ranged 0.6 
to 1.7 mm in diameter (Randall 1959, Wade 1962). 
Fertilized eggs have not been successfully collected 
and identified (Crabtree 1995). 

Age and Size of Larvae : Larval development is often 
described in three stages: Stage I, a fully formed 
leptocephalus; Stage II, a period of marked shrinking 
during which the larva gradually loses its leptoceph- 
alus form; Stage III, begins with a second period of 
length increase and ends with the onset of the juvenile 
stage (Wade 1 962). Larvae are reported to occur in the 
Gulf of Mexico from June through August (Ditty et al. 
1988). Crabtree et al. (1992) described the age, size, 
and growth of tarpon leptocephalus larvae collected off 
of the Florida Gulf Coast. These collections occurred 
over depths ranging from 90 to 1 ,400 m, at sea surface 
temperatures of 27 to 30°C, and salinities of 35 to 36%<>. 
In June 1981 a total of 54 larvae were collected, 
ranging from 7.3 to 23.8 SL. In 1989, a total of 275 
larvae were collected, ranging from 5.5 to 24.4 mm SL, 
and with an estimated age of two to 25 days. Based on 
the collected specimens, standard length (in mm) and 
age (in days) can be described by the equation SL = 
2.78 + 0.92(age). Estimated size at hatching was 2.78 
± .63 mm, and estimated hatching dates were from 
May 12 to July 10. Based on back-calculation of 
hatching dates, it can be inferred that peak hatching 
activity occurs approximately one week after a full 
moon, and one week after a new moon (Crabtree 
1995). Alternately, it is possible that larval survival, not 
spawning activity, is associated with lunar phase 
(Crabtree 1995). 

Juvenile Size Range : The minimum size described for 
juveniles is 25.2 mm SL (Wade 1 962). Juvenile growth 
is seasonal, averaging about 30 mm per month during 
the summer and early fall (Rickards 1 968, Killam et al. 
1992). Cyr (1991) examined length-frequencies of 
juvenile tarpon from the east coast of Florida, and 
found that average first year growth (October to Octo- 


125 


Tarpon, continued 


ber) was 230 mm, corresponding to a size-specific 
growth rate of 0.5% SL/day April to September, and 
0.11 SL/day September to February. The body is 
opaque at 25.2 mm SL with pigment mostly above the 
lateral line. Scale formation begins along the lateral 
line at about 29.7 mm SL (Harrington 1966), and the 
lateral pores are visible at 51.0 mm SL (Wade 1962). 
By at least 1 40 mm SL two specialized ray scales cover 
the uppermost and lowest caudal rays (Jones et al. 
1978). At 194.1 mm SL, the filamentous ray of the 
dorsal becomes grooved on the underside, the anal 
ray has a scaly sheath and the last ray is produced. The 
caudal fin is scaly (Wade 1962, Jones et al. 1978). 
Juveniles become darker dorsally with age (Harrington 
1958). 

Age and Size of Adults : From 1988 through 1993, 
Crabtree et al. (1995) examined 1,469 juvenile and 
adult tarpon from south Florida, ranging from 102 to 
2,045 mm fork length (FL), and estimated their ages 
based on otoliths. All fish older than ten years were 
sexually mature. All males were sexually mature by 
1,175 mm FL, but the smallest mature female was 
1,285 mm FL (Cyr pers. comm.). Tarpon are long- 
lived, with ages of males estimated at to 43 years, and 
females at to 55 years. Growth is rapid until age 1 2, 
after sexual maturity is attained, then slows consider- 
ably. For any given age greater than four years, 
females tend to be larger than males. It has been 
suggested that tarpon scales are not appropriate for 
age estimation, as they would indicate a maximum age 
of only 15 years. A VonBertalanffy growth equation 
based on otolith age estimates more accurately pre- 
dicts the known maximum size of tarpon. Ages 
exceeding 50 years have been reported in captive fish 
(Killam et al. 1992). Crabtree et al. (1995) examined 
eighteen captive tarpon with oxytetracycline-marked 
otoliths, and found growth rates that varied from 95 mm 
in 20 months, to 235 mm in 21 months. Crabtree et al. 
(in press) estimated the ages of 87 tarpon from tropical 
Costa Rican waters, and reported that most were 1 5 to 
30 years old, with a maximum age of 48 years. The 
Costa Rican tarpon sampled were significantly smaller 
than Florida tarpon, and apparently reached maturity 
at a smaller size. 

Food and Feeding 

Trophic Mode : The tarpon is strictly carnivorous, prey- 
ing on a wide variety of animal species (Wade 1 962, de 
Menezes and Paiva 1966, Odum 1971). Feeding 
begins in Stage II larvae (Mercado and Ciardelli 1 972). 

Food Items : Metamorphic larvae and small juveniles 
are primarily plankton feeders, preying on copepods 
(cyclopoid and harpacticoid), mosquito larvae, and 
detritus (Randall 1 959, Harrington and Harrington 1 960, 
Harrington and Harrington 1961, Wade 1962, Odum 


1971). Large juveniles (>45 mm SL) begin gradually 
switching from copepods to small fish such as killi- 
fishes (Fundulussp.), mosquitofish (Gambusiaaffinis), 
silversides (Membras martinica and Menidia sp.), and 
mullet (Mugil sp.), and to caridean shrimp, ostracods, 
and insects (Simpson 1 954, Harrington and Harrington 
1 960, Harrington and Harrington 1 961 , Tabb and Man- 
ning 1961, Hildebrand 1963, Rickards 1968, Odum 
1 971 ). Adults are strictly carnivorous and feed prima- 
rily on mid-water prey (Killam et al. 1992). They are 
predominately piscivorous with fish composing up to 
95% of their total food volume (Harrington and 
Harrington 1961). Fish prey includes such species as 
mullet, marine catfishes (hardhead and gafftopsail), 
pinfish, sunfish (Lepomis species), sardines, needle- 
fish, silversides, cutlassfish (Trichiurus lepturus), and 
anchovies. Shrimp are also an important diet compo- 
nent. Otherfood items include insects, blue crabs, and 
ctenophores (Gunter 1945, Miles 1949, Harrington 
and Harrington 1961, Wade 1962, Hildebrand 1963, 
Rickards 1968, Odum 1971). 

Biological Interactions 

Predation : Predation of adults is limited to other large 
predators such as sharks, porpoises, and alligators, 
while the young fall victim to a variety of fish, including 
ladyfish (Elopssaurus), spotted seatrout, othertarpon, 
and to piscivorous birds that include kingfishers, peli- 
cans, and herons (Randall 1959, Wade 1962, 
Hildebrand 1963, Rickards 1968, Killam et al. 1992). 

Factors Influencing Populations : Althoughjuvenileand 
adult tarpon are able to penetrate coastal freshwater 
habitats, they are sensitive to low temperatures and 
may be susceptible to fish kills during winter months 
(Loftus and Kushlan 1987). The development of wet- 
land areas utilized as nursery habitat by tarpon to 
provide marketable real estate, highway and bridge 
construction, etc. may be impacting juvenile survival 
and recruitment (Randall 1959, Robins 1978). The 
impoundment of estuarine areas for mosquito control 
has reduced available habitat for juveniles and may 
also be affecting recruitment (Cyr 1991, Killam et al. 
1992). The tarpon is very sensitive to chemicals, and 
the wide-spread use of pesticides may have a negative 
impact on this species (Robins 1 978). Possible com- 
petition may exist between tarpon and such frequently 
associated species as common snook, spotted seatrout, 
and ladyfish (Wade 1962, Rickards 1968). Recorded 
parasites include: isopods (Cymothoa destrum, Nercilia 
acuminata), remoras (Echeneis naucrates), copepods 
(Paralebion pearsei), trematodes (Bivescula tarponis), 
and parasites of the family Hemiuridae (Wade 1962). 


126 


Tarpon, continued 


Personal communications 


Crabtree, Roy E. Florida Marine Research Institute, St. 
Petersburg, FL. 

Cyr, Ned. National Marine Fisheries Service, Silver 
Spring, MD. 

Hegen, Ed. Texas Parks and Wildlife Department, 
Rockport, TX. 

Schmidt, Thomas W. South Florida Research Center, 
Everglades National Park, Homestead, FL. 

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P- 


129 


Alabama shad 


Alosa alabamae 
Adult 


10 cm 


(from Fischer 1978) 


Common Name: Alabama shad 

Scientific Name: Alosa alabamae 

Other Common Names: white shad, gulf shad, Ohio 

shad (Daniell 1872, Hildebrand 1963); alose de 

/'Alabama (French), sabalo de Alabama (Spanish) 

(Fischer 1978). 

Classification (Robins et al. 1991) 

Phylum: Chordata 

Class: Osteichthyes 

Order: Clupeiformes 

Family: Clupeidae 

Value 

Commercial : The Alabama shad is not an important 
food fish, and no commercial landings have been 
recorded since 1902 (Hildebrand 1963, Mills 1972). 
However, it was historically seined from rivers and 
marketed fresh in some local areas in the 1800's 
(Fischer 1978, Mettee pers. comm.). 

Recreational : The Alabama shad has potential as a 
recreational fish, and its taste compares favorably with 
the more sought-after shad species. Despite this, it is 
generally considered to be undesirable and too bony 
for eating, thus receiving little attention from anglers 
(Laurence and Yerger 1967, Mills 1972). Fish caught 
are not usually kept, although some anglers fish forthis 
species to use as bait, or as recreation while waiting for 
more desirable game fish to bite (Hildebrand 1963, 
Laurence and Yerger 1967, Mills 1972). 

Indicator of Environmental Stress The Alabama shad 
is not typically used in studies of environmental stress, 
but its decline in numbers throughout its range may be 
at least a partial result of river impoundment, 
channelization, and siltation (Lee et al. 1980). 


Ecological : All shad species are important forage fish 
for predators (Eddy and Underhill 1982). Diminished 
numbers of Alabama shad have led to its listing under 
state endangered species laws in Kentucky, Missouri, 
and Tennessee (Johnson 1 987). It is being considered 
as a candidate species under the federal Endangered 
Species Act (NMFS 1997). 

Range 

Overall : The Alabama shad originally inhabited most 
principal stream tributaries and major river drainages 
of the Gulf coast from the Suwanee River in Florida to 
Grand Isle, Louisiana (Behre 1 950, Bailey et al. 1 954, 
Hildebrand 1963, Laurence and Yerger 1967, Moore 
1968, Mills 1972, Walls 1976). It formerly ascended 
the Mississippi River and many of its major tributaries, 
including the Red, Ouachita, Arkansas, Missouri, Ohio, 
and Tennessee Rivers, but has become rare or extir- 
pated this far inland (Hildebrand 1963, Laurence and 
Yerger 1967, Mills 1972, Lee et al. 1980). 

Within Study Area : This fish is indigenous to the coastal 
waters of the northeastern Gulf of Mexico and its 
drainages. It is found from Grand Isle, Louisiana to the 
Suwanee River in Florida (Table 5.16) (Behre 1950, 
Hildebrand 1963, Laurence and Yerger 1967, Moore 
1968, Swingle 1971, Mills 1972, Millican et al. 1984). 
Within its current range it is probably most common in 
the Apalachicola River system (Laurence and Yerger 
1967, Mills 1972, Mettee pers. comm.). 

Life Mode 

Eggs and larvae are pelagic and planktonic, and have 
been collected only at night (Mills 1 972). Juveniles are 
pelagic, nektonic, and schooling (Laurence and Yerger 
1967, Mills 1972). Adults are pelagic, schooling, and 


130 


Alabama shad, continued 


Table 5.16. Relative abundance of Alabama shad in 
31 Gulf of Mexico estuaries (Nelson et al. 1992, 
Mettee pers. comm.). ^ Q siaQe 


Estuary 


A S J L E 


Florida Bay 


Ten Thousand Islands 


Caloosahatchee River 


Charlotte Harbor 


Tampa Bay 


Suwannee River 


V 


V 


V 


V 


V 


Apalachee Bay 


Apalachicola Bay 


o 


o 


o 


o 


o 


St. Andrew Bay 


V 


V 


Choctawhatchee Bay 


V 


V 


Pensacola Bay 


Perdido Bay 


Mobile Bay 


V 


V 


Mississippi Sound 


V 


V 


V 


V 


V 


Lake Borgne 


V 


V 


Lake Pontchartrain 


V 


Breton/Chandeleur Sounds 


V 


Mississippi River 


Barataria Bay 


Terrebonne/Timbalier Bays 


Atchafalaya/Vermilion Bays 


Calcasieu Lake 


Sabine Lake 


Galveston Bay 


Brazos River 


Matagorda Bay 


San Antonio Bay 


Aransas Bay 


Corpus Christi Bay 


Laguna Madre 


Baffin Bay 


A S J L E 


Relative abundance: 

% Highly abundant 

® Abundant 

O Common 

a/ Rare 

blank Not present 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


anadromous (Laurence and Yerger 1 967, Turner 1 969. 

Habitat 

Ty pe: Eggs and larvae are riverine and have been 
collected only at night in areas with appreciable current 
(Mills 1972). Young juveniles are freshwater riverine 
and nektonic. Older juveniles descend rivers and 
move into estuarine and Gulf waters (Mills 1972). 
Adults are anadromous, inhabiting neritic waters of the 
Gulf and migrating into estuaries and then up major 
river systems to spawn. They occur in fresh to euhaline 
waters in both rivers and bays (Hildebrand 1963, 
Laurence and Yerger 1967, Moore 1968, Swingle 
1971, Mills 1972, Douglas 1974, Swift et al. 1977). 

Substrate : Eggs and larvae have been collected over 
coarse sand and gravel (Mills 1972). Juveniles and 
adults are found over a wide variety of substrates due 
to their anadromous nektonic life history. 

Physical/Chemical Characteristics : Eggs and larvae 
have been collected from freshwater at 1 9-23°C (Mills 
1 972). Juveniles have been found in a water tempera- 
ture range of 13.3 to 28.1 °C and are considered 
euryhaline along with adults (Mills 1 972, Douglas 1 974, 
Walls 1 976) because they occur in both freshwater and 
seawater at different times in their life cycle (Laurence 
and Yerger 1967, Mills 1972). Adults occur in water 
temperatures of 1 2. 1 to 23°C. Below 1 7°C, males are 
reported to outnumber females, but at 1 9.5°C, females 
may occur in larger numbers than males (Laurence 
and Yerger 1967, Mills 1972). 

Migrations and Movements : The Alabama shad is an 
anadromous species, and could be considered the 
only anadromous clupeid along the Gulf coast (Mettee 
et al. 1 996). Juveniles are present in freshwater rivers 
and streams from late May to early July. They leave 
these areas to enter saltwater at the end of their first 
summer when they reach a fork length (FL) of 1 20 mm, 
but they will migrate at smaller sizes in cold weather 
(Hildebrand 1963, Laurence and Yerger 1967, Mills 
1 972). Juvenile shad have been taken in the rivers as 
late as November (Mills 1972, Beecher and Hixson 
1 982). Adults leave salt water and ascend freshwater 
rivers and streams in the spring to spawn (Hildebrand 
1963, Eddy and Underhill 1982). Adults first begin to 
arrive at freshwater spawning areas in Apalachicola 
River during late January and February when water 
temperatures are 1 5° (Laurence and Yerger 1 967). In 
Alabama's Choctawhatchee and Conecuh Rivers, adult 
shad are reported to arrive in March, spawn in April, 
then migrate seaward (Mettee et al. 1 995, Mettee et al. 
1 996). In the Mississippi River valley, arrival has been 
reported from May to July (Fischer 1980). Abundance 
in the Apalachicola River generally peaks during late 
March through late April when water temperatures are 


131 


Alabama shad, continued 


about 17°C, and then drops as water temperatures 
increase (Laurence and Yerger 1967, Mills 1972). 
Males, especially older ones, enter freshwater earlier 
and at lower temperatures than females, but when 
water temperatures reach 19.5°C, females begin to 
outnumber males at the spawning areas (Laurence 
and Yerger 1967, Mills 1972). After spawning the 
adults return downriver to estuarine and marine wa- 
ters. 

Reproduction 

Mode : Species in the herring family (Clupeidae) have 
separate male and female sexes (gonochoristic), and 
fertilization is external through the broadcast of milt and 
roe. 

Spawning : Eggs are partially developed when females 
arrive in spawning areas, then complete maturation 
(Mettee et al. 1 995). Spawning occurs in the headwa- 
ters of the major drainages along the northern Gulf of 
Mexico during spring months (March-April) when water 
temperatures are 1 9° to 23°C. It takes place in fresh- 
water rivers and streams over coarse sand and gravel 
with water currents of 0.5-1.0 m/sec (Laurence and 
Yerger 1967, Mills 1972). Alabama shad are repeat 
spawners, but some spawning mortality occurs. The 
spawning population is dominated by two year old fish. 
This group produces the most viable offspring and its 
dominance has been interpreted as an adaptation to 
increase populations (Laurence and Yerger 1 967, Mills 
1972). 

Fecundity : Reported fecundity estimates range from 
46,400 to 257,655 eggs produced by female shad 
(Laurence and Yerger 1 967, Mills 1 972). Fecundity will 
vary considerably with total length, weight, and age. A 
decrease in the number of repeat spawners present in 
the population results in an increase in overall fecun- 
dity (Laurence and Yerger 1967, Leggett 1969, Mills 
1972). 

Growth and Development 

Egg Size and Embryonic Development Embryonic 
development is oviparous. Well developed uterine 
eggs averaged 1.159 mm in diameter (Mills 1972). 
Eggs are released in the spring with partially and 
completely spent females being collected December 
through April (Laurence and Yerger 1 967, Turner 1 969). 

Age and Size of Larvae : Little information is available 
on the age and size of larval Alabama shad. 

Juvenile Size Range : This stage ranges in size from 25 
to 142 mm FL. Modal growth of most juveniles varies 
from 1 to 30 mm/month. Maturity in males is reached 
during their first year or shortly after. One fish measur- 
ing 128 mm FL was collected with mature gonads, but 


was considered atypical (Laurence and Yerger 1967, 
Mills 1972). 

Age and Size of Adults : Alabama shad are reported to 
live up to 4 years, based on scale aging studies 
(Laurence and Yerger 1967, Leggett 1969). Average 
sizes for these age classes are: 269 mm total length 
(TL) for Class I males; 340.4 mm TL for Class II males 
and 368.3 mm for Class II females; 365.8 mm TL for 
Class III males and 388.6 mm TL for Class III females; 
and average measurements for Class IV fish were 
383.5 and 408.9 mm TL for males and females respec- 
tively (Laurence and Yerger 1967). This information 
corresponds well with Mills (1972) who reported aver- 
age size for males as Class 1-219 and 155 mm FL, 
Class II - 316 and 326 mm FL, Class III - 334 mm FL; 
and for females as Class I - unknown, Class II - 340 mm 
FL, Class III - 356 and 370 mm FL. Females are larger 
than males in every year class (Laurence and Yerger 
1 967, Mills 1 972). Average sizes and weights for this 
shad are 31 2 mm FL and 474 g for males, and 347 mm 
FL and 737 g for females. The largest reported fish 
measured 450 mm TL (Douglas 1974). A length/ 
weight equation has been derived by Laurence and 
Yerger (1967). Recent otolith aging studies of Ala- 
bama shad in the Choctawhatchee River suggest that 
fish may live up to six years (Mettee et al. 1995). 

Food and Feeding 

Trophic Mode : The feeding habits of the Alabama shad 
are not well known. Stomach contents of adults and 
juveniles suggest that they are opportunistic carni- 
vores (Hildebrand 1963, Laurence and Yerger 1967, 
Mills 1972). Adults generally do not feed during their 
spawning migration (Hildebrand 1963, Laurence and 
Yerger 1967, Mills 1972). 

Food Items : Stomach contents of some migrating 
adults show insects, plant material, and detritus 
(Hildebrand 1963, Laurence and Yerger 1967). Juve- 
niles are opportunists and will feed on whatever is 
available, especially fish and larval, pupal, and adult 
insects (Laurence and Yerger 1967). They also feed 
on copepods, Cladocera (waterf leas), worms, spiders, 
detritus, and plant material. Food habits of shad in 
marine and estuarine environments are not well known. 

Biological Interactions 

Predation : All shad species are important forage fish 
for piscivorous fish and birds. 

Factors Influencing Populations : Declines in popula- 
tions may be at least partially due to dams barring this 
species from its historical spawning grounds, and 
possibly also to channelization of rivers and siltation of 
spawning areas (Hildebrand 1963, Lee et al. 1980). 


132 


Alabama shad, continued 


Personal Communications 


Geological Survey of Alabama, 


Mettee, Maurice F. 
Tuscaloosa, AL. 

References 


Bailey, R.M., H.E.Winn, and C.L.Smith. 1954. Fishes 
form the Escambia River, Alabama and Florida, with 
ecologic and taxonomic notes. Proc. Acad. Nat. Sci. 
Phila. 106:109-134. 

Beecher, H.A., and W.C. Hixson. 1982. Seasonal 
abundance of fishes in three northwest Florida rivers. 
Fla. Sci. 45(3):145-171. 

Behre, E.H. 1950. Annotated list of the fauna of the 
Grand Isle region, 1928-1946. Occas. Pap. Mar. Lab., 
Louisiana St. Univ. 6(6):1-66. 

Daniell, W.C. 1872. Letters referring to experiments of 
W.C. Daniell, M.D., in introducing shad into the Ala- 
bama River. Comm. Rept. U.S. Comm. Fish. 2:387- 
390. 

Douglas, N.H. 1974. Freshwater Fishes of Louisiana. 
Claitor's Publ. Div., Baton Rouge, LA, 443 p. 

Eddy, S., and J.C. Underhill. 1982. How to Know the 
Freshwater Fishes. W.C. Brown, Dubuque, IA, 215 p. 

Fischer, W. (ed.). 1978. FAO Species Identification 
Sheets for Fishery Purposes, Western Central Atlantic 
(Fishing Area 31), Vol. II. U.N. FAO, Rome. 

Hildebrand, S.F. 1963. Family Clupeidae. In Fishes 
of the Western North Atlantic, p. 257-454. Sears 
Found. Mar. Res., Yale Univ., New Haven, CT. 


Leggett, W.C. 1969. A study of the reproductive 
potential of the American shad (Alosa sapidissima) in 
the Connecticut River, and of the possible effects of 
natural or man induced changes in the population 
structure of the species on its reproductive success. 
Conn. Res. Comm. Proj., 72 p. 

Mettee, M.F., P.E. O'Neil, and J.M. Pierson. 1996. 
Fishes of Alabama and the Mobile Basin. Oxmoor 
House, Birmingham, AL, 820 p. 

Mettee, M.F., P.E. O'Neil, T.E. Shepard, and P.L 
Kilpatrick. 1995. Status survey of gulf sturgeon 
(Acipenser oxyrinchus) and Alabama shad (Alosa 
alabamae) in the Choctawhatchee, Conecuh, and Ala- 
bama River systems, 1992-1995. Geological Survey 
of Alabama, Tuscaloosa, AL, 30 p. 

Millican, T., D.Turner, and G. Thomas. 1984. Check- 
list of the species of fishes in Lake Maurepas, Louisi- 
ana. Proc. Louis. Acad. Sci. 47:30-33. 

Mills, J. G., Jr. 1972. Biology of the Alabama shad in 
northwest Florida. Fla. Board Cons. Mar. Res. Lab. 
Tech. Ser. No. 68, 24 p. 

Moore, G.A. 1968. Fishes. /nVertebratesofthe United 
States, p. 21-165. McGraw-Hill Book Co., New York, 
NY. 

National Marine Fisheries Service (NMFS). 1997. 
Revision of candidate species list under the Endan- 
gered Species Act. Fed. Reg. 62(134):37560-37563. 

Nelson, D.M. (ed.), et al. 1992. Distribution and 
abundance of fishes and invertebrates in Gulf of Mexico 
estuaries, Vol. I: Data summaries. ELMR Rep. No. 1 0. 
NOAA/NOS SEA Div., Rockville, MD, 273 p. 


Johnson, J.E. 1987. 
States and Canada. 
Bethesda, MD, 42 p. 


Protected fishes of the United 
American Fisheries Society, 


Laurence, G.C., and R.W. Yerger. 1967. Life history 
studies of the Alabama shad, Alosa alabamae, in the 
Apalachicola River, Florida. Proc. Southeast. Assoc. 
Game Fish Comm. 20:260-273. 


Lee, D.S., et al. 
Freshwater fishes. 
NC, 854 p. 


1980. Atlas of North American 
NO. St. Mus. Nat. Hist., Raleigh, 


Swift, O, R.W. Yerger, and P.R. Parrish. 1977. Distri- 
bution and natural history of the fresh and brackish 
water fishes of the Ochlockonee River, Florida and 
Georgia. Bull. Tall Timbers Res. Sta., No. 20, 1 1 1 p. 

Swingle, H.A. 1971. Biology of Alabama Estuarine 
Areas - Cooperative Gulf of Mexico Estuarine Inven- 
tory. Ala. Mar. Res. Bull. 5:1-123. 

Turner, W.R. 1969. Life history of menhadens in the 
eastern Gulf of Mexico. Trans. Am. Fish. Soc. 
98(2):21 6-224. 

Walls, J.G. 1976. Fishes of the northern Gulf of 
Mexico. TFH Pub., Neptune City, NJ, 432 p. 


133 


Gulf menhaden 


Brevoortia patronus 
Adult 


5 cm 


(from Fischer 1978) 


Common Name: gulf menhaden 
Scientific Name: Brevoortia patronus 
Other Common Names: Pogy, shad, large-scale men- 
haden, sardine, menhaden ecailleux (French), lacha 
escamuda (Spanish) (Fischer 1978, NOAA 1985). 
Classification (Robins et al. 1991) 
Phylum: Chordata 
Class: Osteichthyes 

Order: Clupeiformes 

Family: Clupeidae 

Value 

Commercial : The Gulf menhaden fishery dates back to 
the turn of the century, and developed into a major 
industry after World War 1 1 (Lassuy 1 983, Smith 1 991 ). 
This is a unique American fishery that is vertically 
integrated, that is, menhaden processing companies 
generally own the vessels, the gear, the processing 
facilities, and often the spotter aircraft used to find the 
fish schools (Newlin 1 993, Smith pers. comm.). Crews 
are hired to fish for the length of the fishing season. 
Although schools of Atlantic thread herring are occa- 
sionally harvested by this fishery, vessels are designed 
to fish specifically for menhaden, and are not convert- 
ible to other fisheries (Smith pers. comm.). Except for 
a few small bait purse-seiners, vessels from other 
fisheries do not "free-lance" and sell their catch to the 
menhaden plants. The gulf and Atlantic menhaden 
fisheries combined supported the second largest com- 
mercial landings by weight in 1995 (O'Bannon 1996). 
Landings of gulf menhaden in that year were 463,900 
mt valued at $51 .9 million. Landings of gulf menhaden 
in 1996 have been estimated at 479,400 mt (Smith 
1997). Traditionally the majority of the landings are 
taken in the north central Gulf of Mexico. Menhaden 
are harvested from April to October as they move into 


moreshallow inshore areasfromtheirwintering grounds 
on the middle part of the continental shelf (Lewis and 
Roithmayr 1 981 , Vaughan and Merriner 1 991 ). Pres- 
ently, the gulf menhaden purse-seine fishery for reduc- 
tion extends for 28 weeks, from mid-April through late 
October (Smith pers. comm.). Up to 90% of the catch 
is made within ten miles of the northern Gulf of Mexico 
shoreline (Leard et al. 1995). Fishing grounds in the 
Gulf extend from Apalachee Bay, Florida to Matagorda 
Bay, Texas, but the heaviest fishing is in Louisiana and 
Mississippi waters (Christmas and Etzold 1 977, Nelson 
and Arenholz 1986). This fishery is currently consid- 
ered to be fully exploited and appears reasonably 
stable under present conditions of age composition, 
life span, and effects of environmental factors (Vaughan 
and Merriner 1991). At present, long-term average 
annual yields of 544.3 thousand mt are considered 
realistic. 

From 1990 to 1993, approximately 86% of the gulf 
menhaden catch for reduction came from the Louisi- 
ana coast, 6% from Texas, 5% from Mississippi, and 
3% from Alabama (Leard et al. 1995, Smith pers. 
comm.). Five reduction plants operated in 1996, at 
Moss Pt. MS, Empire LA, Morgan City LA, Abbeville 
LA, and Cameron LA (Smith 1996). Menhaden 
schools are located by spotter planes who notify large, 
refrigerated carrier vessels, known locally as pogy 
boats. Two purse seine boats from the carrier vessel 
encircle the school with a net. The captured school is 
then pumped into the hold of the carrier vessel and 
taken to the reduction plant on shore for processing 
(Simmons and Breuer 1964, Nicholson 1978, Smith 
1 991 ). Menhaden are used primarily forthe production 
of fish meal, fish oil, and fish solubles. The fish meal 
and oil are in high demand for use in poultry and other 


134 


Gulf menhaden, continued 


Table 5.17. Relative abundance of gulf menhaden 
in 31 Gulf of Mexico estuaries (from Volume I). 


Life stage 


Estuary 


A S J L E 


Florida Bay 


V 


Ten Thousand Islands 


V 


Caloosahatchee River 


V 


Charlotte Harbor 


V 


Tampa Bay 


• 


• 


V 


Suwannee River 


V 


o 


o 


Apalachee Bay 


® 


® 


® 


Apalachicola Bay 


® 


® 


® 


St. Andrew Bay 


® 


• 


o 


Choctawhatchee Bay 


® 


• 


• 


Pensacola Bay 


® 


• 


o 


Perdido Bay 


o 


® 


o 


V 


Mobile Bay 


• 


• 


• 


• 


Mississippi Sound 


• 


® 


• 


• 


® 


Lake Borgne 


• 


• 


• 


Lake Pontchartrain 


• 


® 


Breton/Chandeleur Sounds 


• 


Mississippi River 


® 


Barataria Bay 


• 


o 


Terrebonne/Timbalier Bays 


® 


® 


Atchafalaya/Vermilion Bays 


• 


o 


Calcasieu Lake 


• 


® 


Sabine Lake 


o 


• 


Galveston Bay 


• 


Brazos River 


® 


Matagorda Bay 


• 


• 


San Antonio Bay 


o 


® 


Aransas Bay 


® 


® 


Corpus Christi Bay 


o 


® 


o 


Laguna Madre 


o 


® 


Baffin Bay 


V 


• 


V 


A S J L E 


Relative abundance: 


® 

O 

blank 


Highly abundant 

Abundant 

Common 

Rare 

Not present 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


domestic animal feeds, aquaculture feeds, cosmetics, 
and margarine. Most fish meal is used domestically, 
but a portion is exported. In the past most fish oil was 
exported, but it is now being used domestically in a 
greater variety of products and markets (Smith pers. 
comm.). There has been an increasing use of whole 
menhaden in the past few years as bait for crabs and 
crayfish (Christmas et al. 1 988, 0'Bannon 1 993). Small 
quantities of menhaden are also used for canned pet 
food (O'Bannon 1993). 

Recreational : The gulf menhaden has little sport fish 
value since it is a filter feeder and has a poor tasting 
meat (Simmons and Breuer 1964). It is an important 
forage fish for many sport and food fish and is also used 
for fishing bait. Gulf menhaden are considered to be 
excellent bait for crevalle jack, tarpon, king mackerel 
(Scomberomorus cavalla), and other large game fish. 

Indicator of Environmental Stress : Gulf menhaden 
larvae have been used to study uptake and effects of 
heavy metals on the early life stages of fishes (Hanson 
and Hoss 1 986). Juveniles have been used to assess 
the effects of the uptake of aldrin and dieldrin from 
agricultural applications (Ginn and Fisher 1 974). Stout 
et al. (1981) reviewed chlorinated hydrocarbon levels 
in the products of gulf menhaden and reported that 
levels have decreased with restriction of their use. The 
chlorinated hydrocarbon levels present are generally 
safely below U.S. FDA tolerance limits. 

Ecological : Gulf menhaden are an important link in the 
food chain between primary producers, phytoplankton 
and detritus, and top predators. It is an extremely 
important forage fish for a variety of piscivorous birds 
and fish (Gunter and Christmas 1960, Palmer 1962, 
Christmas et al. 1988). It is also important in the 
translocation of energy between estuarine and off- 
shore ecosystems (Deegan 1 985). Larval gulf menha- 
den are one of the dominant species of ichthyoplankton 
in the Gulf of Mexico during the winter months (Raynie 
and Shaw 1994). 

Range 

Overall : This species is restricted to the Gulf of Mexico, 
ranging from southwestern Florida near Cape Sable to 
Vera Cruz, Mexico on the Yucatan Peninsula. It occurs 
in estuarine and nearshore marine waters in depths up 
to 111 m, and is most abundant from Apalachicola, 
Florida to Galveston, Texas (Reintjes and Pacheco 
1 966, Lewis and Roithmayr 1 981 , Nelson and Arenholz 
1 986, Powell and Phonlor 1 986, Christmas et al. 1 988, 
Ahrenholz1991). 

Within Study Area : Within U.S. Gulf of Mexico estuar- 
ies, the gulf menhaden occurs from Florida to Texas, 
but the principal area of abundance in this region is 


135 


Gulf menhaden, continued 


from Calcasieu Lake, Louisiana to between Mobile Bay 
and Perdido Bay, Alabama (Table 5.17) (Reintjes and 
Pacheco 1966, Dugas 1970, Lewis and Roithmayr 
1 981 , Powell and Phonlor 1 986, Christmas et al. 1 988, 
Nelson et al. 1992). 

Life Mode 

This is an estuary dependent, marine migratory spe- 
cies (Ahrenholz 1991). Eggs and larvae spend 3-5 
weeks in offshore waters as currents carry them into 
estuaries. Juveniles are nektonic and adults are pe- 
lagic (Tagatz and Wilkens 1973, Wagner 1973, Perry 
and Boyes 1978, Deegan 1985). Schooling behavior 
first appears during late larval development, and con- 
tinues throughout the gulf menhaden's life span (Christ- 
mas et al. 1983). 

Habitat 

Type : Food availability is probably the most important 
requirement for determining habitat suitability (Christ- 
mas et al. 1 982, Deegan 1 990). The gulf menhaden is 
estuarine dependent, spending most of its life in estu- 
aries and nearshore waters of the Gulf of Mexico 
(Lewis and Roithmayr 1 981 , Christmas et al. 1 982). It 
spawns in coastal and offshore waters in the winter. 
Larvae are found in greatest densities nearthe surface 
(Govoni et al. 1989), and over the inner to middle 
continental shelf. Larvae are known to occur from 
September through April (Ditty et al. 1 988), with peak 
densities in January and February (Ditty 1 986, Shaw et 
al. 1985b). They spend 3-5 weeks in offshore waters 
before moving into the quiet, low salinity shallows of 
marshes and estuaries and their tributaries, where 
they transform intojuveniles. Juveniles move to deeper, 
open estuarine waters, and individuals greater than 50 
mm SL are found primarily in this area. They remain in 
open water habitats until the following fall. Adults live 
in estuaries and nearshore waters during the spring 
and summer, and occur in depths of 1 .8 to 1 4.6 m (Fore 
and Baxter 1972, Christmas and Waller 1975, Lewis 
and Roithmayr 1978, Simoneaux 1979, Christmas et 
al. 1982, Deegan 1985, Nelson and Ahrenholz 1986, 
Deegan 1990, Ahrenholz 1991). During the fall and 
winter months they are found offshore at depths of 7.3 
to 87.8 m. 

Substrate : This fish inhabits the water column, and no 
direct use of the substrate is apparent. It is generally 
caught over soft mud bottoms, and it is assumed soft 
mud substrates are preferred because of the abun- 
dance of benthic organisms and the richer organic 
content (Christmas et al. 1982, Lassuy 1983). 

Physical/Chemical Characteristics : 
Temperature: Eggs have been collected in the wild 
from 17 to 20°C (Christmas et al. 1988). Water 
temperature preference for juveniles and adults is 


between 12° and 30°, but they have been taken in 
waters over a range extending from 2.5 to 35.5°C. 
Temperature tolerances have also been observed to 
be quite wide at lower salinities. Active avoidance of 
temperatures above 30°C has been reported, as well 
as a kill occurring at 39°C (Miller 1 965, Holcomb 1 970, 
Copeland and Bechtel 1971, Wagner 1973, Gallaway 
and Strawn 1 974, Christmas and Waller 1 975, Pineda 
1975). Gunter and Christmas (1960) reported that 
fishery activities in Mississippi Sound begin in the 
spring as water temperatures reached 23°C, and slow 
in the fall at approximately the same temperature. 

Salinity: This species has been collected in salinities 
ranging from fresh to hypersaline. Gravid adults, 
fertilized eggs, and early larvae are typically associ- 
ated with the higher salinities of the open Gulf of 
Mexico, generally 29%o and higher. Post-larvae and 
juveniles occupy a wider range of tolerance, generally 
occurring from 5 to about 30% o . However, they may 
also enter freshwater tributaries (Mettee et al. 1996). 
Non-gravid and developing adults occupy mid-range 
salinities in the deeper part of estuaries, with high 
abundances at 20-25%o reported (Wagner 1 973, Pineda 
1975, Perry and Boyes 1978, Marotz et al. 1990), but 
are capable of tolerating ranges from to 67%o (Etzold 
and Christmas 1979). Mass mortalities have been 
reported under hypersaline conditions of 80%oorgreater 
(Springer and Woodburn 1 960, Holcomb 1 970, Tagatz 
and Wilkens 1 973, Wagner 1 973, Gallaway and Strawn 
1 974, Shaw et al. 1 985a, Christmas et al. 1 988). 

Dissolved Oxygen: Christmas (1 981 ) suggests a mini- 
mum dissolved oxygen (DO) concentration of 3 parts 
per million (ppm); however, the empirical basis for this 
minimum was not given. Marotz et al. (1 990) found that 
in estuarine waters with DO concentrations below 2 
ppm, seaward movements of gulf menhaden increased. 

Movements and Migrations : Gulf menhaden migration 
patterns coincide with productivity peaks occurring in 
different areas of an estuarine system (Deegan 1985, 
Deegan 1 990). Larvae are carried shoreward from the 
central breeding grounds offshore for 3 to 5 weeks by 
currents, and then are distributed along nearshore 
areas throughout the range, predominantly by longshore 
current (Shaw et al. 1 985b). Larvae can begin migrat- 
ing into estuaries in October, and continue through late 
May. Peak influxes of larvae moving into Texas and 
Louisiana tidal passes occur during November-De- 
cember and February-April. During flood tides, larval 
gulf menhaden may be dense in the the mid-stream of 
tidal passes, to maximize transport into estuarine ar- 
eas (Raynie and Shaw 1994). They are then carried 
through open bays and into shallow estuarine areas 
(tidal creeks and ponds) by tidal flow when about 1 5-25 
mm. They may then enter brackish and/or freshwater 


136 


Gulf menhaden, continued 


areas and utilize such areas as nursery grounds 
(Simoneaux 1979). As juveniles grow, they begin to 
move into deeper, higher salinity areas of the estuary 
(Suttkus 1956, Dugas 1970, Fore 1970, Holcomb 
1970, Fore and Baxter 1972, Tagatz and Wilkens 
1973, Dunham 1975, Hinchee 1977, Perry and Boyes 
1978, Allshouse 1983, Guillory et al. 1983, Marotz 
1984, Deegan 1985, Shaw et al. 1985a, Shaw et al. 
1985b, Deegan 1990). This migration appears to be 
size related, but may also be influenced by environ- 
mental parameters (Marotz 1984, Deegan 1985, 
Deegan 1990). Larvae show a diel pattern in vertical 
distribution, in which they concentrate at the water 
surface by day, but are more vertically dispersed at 
night (Sogard et al. 1 987). This is thought to be due to 
a slow sinking in the water column as a result of passive 
depth maintenance during the night time nonfeeding 
period. During daylight hours, larvae are actively 
swimming, and maintain their position close to the 
surface. 

The gulf menhaden does not exhibit an extensive 
migratory pattern (Ahrenholz 1 991 ). Adults and matur- 
ing juveniles (80-1 05 mm SL) migrate from estuaries to 
open Gulf waters to overwinter or spawn from late 
summer to winter, with peak movement occurring from 
Octoberto January (Roithmayrand Waller 1963, Dugas 
1970, Holcomb 1970, Tagatz and Wilkens 1973, 
Deegan 1985, Ahrenholz 1991). Some emigration of 
larger individuals occurs throughout the year (Marotz 
1984, Marotz et al. 1990). In Louisiana, most move- 
ment of older fish is inshore/offshore with little east- 
west movement noted (Shaw et al. 1 985a, Shaw et al. 
1 985b). Tagging studies by Kroger and Pristas (1 974) 
indicate localized populations with little movement 
occurring between fishing grounds east and west of the 
Mississippi River Delta. However, there is evidence 
from other tagging studies that gulf menhaden which 
leave estuaries and enter the Gulf of Mexico in the 
edges of their range (e.g. Florida) tend to disperse or 
"drift" towards the center of the range (e.g. Louisiana) 
as they age (Ahrenholz 1 981 , Ahrenholz pers. comm.). 

The gulf menhaden has been reported to begin migra- 
tion from Tampa Bay, Florida in June and July (Springer 
and Woodburn 1960). Migration from Pensacola Bay, 
Florida has been reported to occur by September 
(Tagatz and Wilkens 1973). One study reports large 
schools in Louisiana migrating offshore in June (Wagner 
1973). Adults in the Gulf begin an apparent offshore 
movement in October from the shallow waters inshore. 
Movement back into estuaries after overwintering and/ 
or spawning in the open Gulf occurs from March to April 
(Christmas 1 981 , Lewis and Roithmayr 1 981 ). Christ- 
mas (1981) speculates that this inshore movement is 
"by random movement, probably in search of high food 
concentrations." This leads the menhaden back into 


the food rich estuarine waters. Some studies indicate 
that the lipid content of the menhaden is related to the 
time of movement. Lipid and energy content increase 
as fish metamorphose from larvae to subadults. Fish 
with high lipid content are the first to migrate offshore 
in response to small changes in temperature, and 
those with lower lipid content migrate later or not at all 
(Wagner 1973, Deegan 1985, Deegan 1986). 

Reproduction 

Mode : Reproduction is sexual, with separate male and 
female sexes (gonochoristic). Milt and roe are broad- 
cast, and fertilization is external. 

Spawning : Actual spawning in the wild has not been 
observed (Guillory et al. 1 983). Information is based on 
capture of eggs, larvae, spent adults, and laboratory 
fertilizations. Most spawning probably occurs off the 
Mississippi and Atchafalaya River deltas from nearshore 
to about 97 km offshore, in waters from 2 to 1 28 m deep 
(Roithmayr and Waller 1963, Etzold and Christmas 
1 979, Lewis and Roithmayr 1 981 , Shaw et al. 1 985a, 
Shaw et al. 1985b, Sogard et al. 1987), with most 
spawning in waters less than 18 m deep (Christmas 
and Waller 1975, Christmas et al 1988). Adults are 
intermittent spawners, having as many as five peaks 
during a season in different parts of the Gulf. A 
spawning season usually runs from October through 
March, but can begin as early as August and last as late 
as May. Separate peaks can be observed during the 
season from November to April (Miller 1965, Tagatz 
and Wilkens 1 973, Sabins and Truesdale 1 974, Etzold 
and Christmas 1979, Lewis and Roithmayr 1981, 
Allshouse 1983, Guillory et al. 1983, Marotz 1984, 
Shaw et al. 1985a, Christmas 1988, Warlen 1988, 
Marotz etal. 1990). 

Fecundity : Actual fecundity for menhaden is difficult to 
determine as they are intermittent, fractional spawners 
(Lewis and Roithmayr 1 981 ). Studies have shown that 
fecundity increases significantly with age and length 
(Suttkus and Sundararaj 1961, Lewis and Roithmayr 
1 981 ). Mean number of eggs per fish are: 21 ,960 in 
age classes I; 68,655 in age class II; and 122,062 in 
age class III (Suttkus and Sundararaj 1961). Lewis and 
Roithmayr (1981) have developed equations to de- 
scribe fecundity based on age, length, and weight. 

Growth and Development 

Egg Size and Embryonic Development : Eggs are plank- 
tonic and pelagic. They are spherical with unsculptured 
chorion, a faintly segmented yolk, and a single oil 
droplet. Observed mean total diameters of eggs have 
ranged from 1 .22 ± 0.04 to 1 .30 mm ± 0.05. Hatch rate 
can vary from 1 to 3 days depending on the ambient 
water temperature. In one study, eggs incubated at 1 9° 
to 20°C and 30%<= salinity hatched in 40 to 42 hours. 


137 


Gulf menhaden, continued 


Hatching of menhaden eggs occurs mostly from Octo- 
ber to March (Hettler 1 984, Shaw et al. 1 985a, Christ- 
mas et al. 1988, Powell 1993). 

Age and Size of Larvae : Larvae are 2.6 to 3.1 mm SL 
immediately after hatching. Growth rate at 20° ± 2°C 
averaged 0.30 ± 0.03 mm/day through 90 days of 
rearing, but growth rate can vary with age and tempera- 
ture (Chen et al. 1992, Powell 1993). Transformation 
from the larval to juvenile form began at approximately 
1 9 mm and was completed at approximately 25 mm SL 
(Hettler 1984). One field study of larvae showed 
metamorphosis beginning at 20-21 mm SL and being 
completed at 30-35 mm SL. Other studies have 
reported metamorphosis taking place when larvae 
reach a total length (TL) of 30-40 mm TL and 30-33 mm 
TL (Tagatz and Wilkens 1973, Guillory et al. 1983, 
Deegan 1985, 1986). By May, most larvae have 
metamorphosed into juveniles (Tagatz and Wilkens 
1973). Size-selective mortality may be significant for 
larval gulf menhaden, with the smaller larvae more 
vulnerable to predation (Grimes and Isely 1 996). This 
may result in overestimation of larval growth, as smaller 
larvae are removed from the population. Growth of 
larval fish proceeds through a series of ontogenetic 
intervals, with periods of rapid growth followed by 
periods in which structures form (Raynie and Shaw 
1994). Raynie and Shaw (1994) reported that the 
growth rate of larval gulf menhaden was lower in 
estuaries than in coastal waters, as they approached 
metamorphosis to the juvenile stage. 

Juvenile Size Range : Juveniles may grow as much as 
20-30 mm/month and become sub-adults at SL's greater 
than 85 mm. 

Age and Size of Adults : Menhaden mature after two 
seasons of growth and have a maximum life span of 
five years (Nelson and Ahrenholz 1981). Nicholson 
(1978) developed the following year class size infor- 
mation based on fork length (FL) data from ports 
throughout the Gulf of Mexico: 
Age-0: 1 02-1 23 mm FL range with 1 1 5 mm mean FL, 
22-47 g range with 32 g mean weight (W). 
Age-I: 147-165 mm FL range with 155 mm mean FL, 
65-101 g range with 78 g mean W. 
Age II: 181-188 mm FL range with 184 mm mean FL, 
122-148 g range with 133 g mean W. 
Age III: 201-214 mm FL range with 207 mm mean FL, 
170-217 g range with 190 g mean W. 
Nicholson (1978) also presents a length-weight equa- 
tion for gulf menhaden based on these data. 

Aging of gulf menhaden based on scale analysis is 
problematic, and length-frequency data are not reli- 
able forassigning age classes. However, otolith analy- 
sis suggests that age IV fish do exist in the population 


(Vaughan et al. 1996). The bulk of the population is 
composed of fish from age classes I and II, with few 
class III and even fewer class IV fish present (Christ- 
mas et al. 1 988, NOAA 1 992). Sizes at maturity range 
from 147-165 mm FL (Nicholson 1978). Lewis and 
Roithmayr (1981) found no maturing ova in fish less 
than 100 mm FL. Growth information has been com- 
pared from Florida and Louisiana by Springer and 
Woodburn (1 960); they found that Florida's menhaden 
seemed to grow at a slower rate that those in Louisi- 
ana, and that both groups experienced "a sudden burst 
of growth after May." Maximum lengths up to 250 mm, 
and weights up to 300 g have been recorded. Slight 
sexual dimorphism has been reported for menhaden, 
but it is insufficient to readily distinguish the sexes 
(McHugh et al. 1959, Turner 1969, Hoese and Moore 
1977, NOAA 1992). 

Food and Feeding 

Trophic Mode : Larvae are selective carnivores feeding 
on zooplankters. Metamorphosis of larvae into juve- 
niles is accompanied by loss of teeth. Juveniles and 
adults then become omnivorous filter feeders at the 
first and second trophic level of the food web utilizing 
phytoplankton, zooplankton, and detritus (Guillory et 
al. 1983, Govoni et al. 1983, Deegan 1985, Deegan 
1986, Deegan et al. 1990, Ahrenholz 1991). Food 
availability affects swimming speeds, with increased 
swimming speeds associated with increased food avail- 
ability in the water column (Durbin et al. 1981). Gulf 
menhaden are unique in that much of their stored 
energy is lipid which results in the highest energy 
content per gram weight found among estuarine spe- 
cies. As predators, gulf menhaden ingest large num- 
bers of planktonic larvae of other species, but the 
effects of this predation have not been quantified. Its 
role as an important forage species is also in need of 
more research (Christmas et al. 1988). 

Food Items : Small larvae feed on larger phytoplankton 
and some zooplankton (Ahrenholz 1991). As larvae 
grow, phytoplankton is replaced in importance by larger 
zooplankton, such as copepods, tintinnids, pteropods, 
and invertebrate eggs (Ahrenholz 1991, Chen et al. 
1 992). The diet of the remaining developmental stages 
of this species consists of phytoplankton, zooplankton, 
and detritus (Deegan 1985, Deegan 1986). 

Biological Interactions 

Predation : Gulf menhaden are potential prey fora large 
variety of predators throughout their life cycle (Ahrenholz 
1991). Many invertebrate predators (e.g. chaetog- 
naths), especially in oceanic waters, probably prey on 
this species (Ahrenholz 1 991 ). Other potential inverte- 
brate predators include squids, ctenophores, and jelly- 
fishes. Predation of larval gulf menhaden may be size- 
selective, with predation highest for smaller larvae 


138 


Gulf menhaden, continued 


after hatching, reaching a plateau at five to eight days, 
then declining after 14 days (Grimes and Isely 1996). 
In estuarine and marine waters, juvenile and adult gulf 
menhaden are prey items for several fish species. 
Piscine predators include sported seatrout, silver perch, 
silver sea trout (Cynoscion nothus), red drum, Spanish 
mackerel, king mackerel (Scomberomorus cavalla), 
bluefish, and sharks (Simmons and Breuer 1964, 
Fontenot and Rogillio 1 970, Reintjes 1 970, Swift et al. 
1 977, Etzold and Christmas 1 979, Levine 1 980). Men- 
haden are also thought to be an important forage 
species for piscivorous birds such as brown pelicans, 
and are known prey of the osprey and common loon 
(Ahrenholz 1 991 ). Marine mammals are also reported 
to prey on menhaden. 

Factors Influencing Populations : Gulf menhaden are 
frequently involved in "fish kills" along the Gulf coast. 
They are extremely sensitive to hypoxia, which is 
common in Gulf estuaries during the summer months. 
Dead-end sloughs, bayous, and harbors are particu- 
larly dangerous to menhaden during the summer. 
Postlarvae and juveniles are highly susceptible to such 
kills, as their mobility and ability to avoid hypoxia is 
limited (Lassuy 1983, Shipp 1986). Decaying menha- 
den remove still more oxygen from the water which can 
cause a fish kill to spread over a larger area. Gulf 
menhaden are susceptible to parasitic copepods and 
two major diseases, "spinning disease" and ulcerative 
mycosis (UM). Ulcerative mycosis was previously 
thought to be associated with infection by oomycete 
fungi (Noga et al. 1988), but it is now suspected to be 
a condition resulting from the destruction of epidermal 
tissue by the toxins released by the dinoflagellate 
Pfiesteria piscicida (Burkholder et al. 1 995, Ahrenholz 
pers. comm.). 

The timing of migrations from nursery areas to open 
bay habitats varies between different estuarine sys- 
tems. This may be a response to differences in timing 
of primary productivity and thus food availability (Deegan 
1990). Larvae occur in high concentrations at the 
Mississippi River plume front (Govoni et al. 1 989). This 
may provide larvae with an enhanced feeding environ- 
ment, but may also make them more susceptible to 
predation. The construction of water control structures 
in wetlands may seriously affect the recruitment of 
young gulf menhaden into nursery areas (Marotz et al. 
1 990). Some gulf menhaden are landed as bycatch on 
commercial shrimping vessels, but the impact of these 
landings on the menhaden population has not been 
studied, and remains largely unknown (Vaughan pers. 
comm.). 

Gulf menhaden are generally shorter-lived and have 
higher natural mortality than Atlantic menhaden (B. 
tyrannus), resulting in high interannual variation in 


fishable stock (Vaughan et al. 1 996). The gulf menha- 
den population is considered stable and capable of 
supporting an annual harvest, although declines in 
landings have been noted since the peak landings of 
the 1 980's (Christmas et al. 1 988, NOAA 1 992, Vaughan 
et al. 1996). To maintain this valuable resource, the 
Menhaden Advisory Committee and the Gulf States 
Marine Fisheries Commission impose fishing limits to 
regulate the fishery and monitor development activities 
that impact the population (Christmas et al. 1988, 
NOAA 1992). 

Personal communications 

Ahrenholz, Dean W. NOAA National Marine Fisheries 
Service, Beaufort, NC. 

Lowery, Tony A. NOAA SEA Division, Silver Spring, 
MD. 

Smith, Joseph W. NOAA National Marine Fisheries 
Service, Beaufort, NC. 

Vaughan, D.S. NOAA National Marine Fisheries Ser- 
vice, Beaufort, NC. 

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patronus, growth rates between an offshore spawning 
ground and an estuarine nursery. Fish. Bull., U.S. 
92:890-894. 


Reintjes, J.W. 1970. 
changing estuaries. 
22:87-90. 


The Gulf menhaden and our 
Proc. Gulf Caribb. Fish. Inst. 


Reintjes, J.W., and A.L. Pacheco. 1966. The relation 
of menhaden to estuaries. In Smith, R.F., A.H. Swartz, 
and W.H. Massman (eds.), A symposium on estuarine 
fisheries, p. 50-58. Am. Fish. Soc. Spec. Pub. No. 3. 
American Fisheries Society, Washington, DC, 154 p. 

Robins, C.R., R.M. Bailey, C.E. Bond, J.R. Brooker, 
E.A. Lachner, R.N. Lea, and W.B. Scott. 1 991 . Com- 
mon and scientific names of fishes from the United 
States and Canada, Fifth Edition. Am. Fish. Soc. Spec. 
Pub. No. 20. American Fisheries Society, Bethesda, 
MD, 183 p. 

Roithmayr, CM., and R.A. Waller. 1963. Seasonal 
occurrence of Brevoortia patronus in the northern Gulf 
of Mexico. Trans. Am. Fish. Soc. 92(3):301-302. 


142 


Gulf menhaden, continued 


Sabins, D.S., and F.M. Truesdale. 1974. Diel and 
seasonal occurrence of immature fishes in a Louisiana 
tidal pass. Proc. Conf. Southeast. Assoc. Game Fish 
Comm. 28:161-171. 

Shaw, R.F., J.H. Cowan Jr., and T.L. Tillman. 1985a. 
Distribution and density of Brevoortia patronus (gulf 
menhaden) eggs and larvae in the continental shelf 
waters of western Louisiana. Bull. Mar. Sci. 36(1 ):96- 
103. 

Shaw, R.F., W.J. Wiseman, Jr., R.E. Turner, L.J. 
Rouse, Jr., and R.E. Condrey. 1985b. Transport of 
larval gulf menhaden Brevoortia patronus in continen- 
tal shelf waters of western Louisiana: a hypothesis. 
Trans. Am. Fish. Soc. 114:452-460. 

Shipp, R.L. 1986. GuidetofishesoftheGulf of Mexico. 
Dauphin Island Sea Lab, Dauphin Island, AL, 256 p. 

Simmons, E.G., and J. P. Breuer. 1964. The Texas 
menhaden fishery. Texas Parks and Wildlife, Austin, 
TX, 16 p. 

Simoneaux, L.F. 1979. The distribution of menhaden, 
genus Brevoortia, with respect to salinity, in the upper 
drainage basin of Barataria Bay, Louisiana. M.S. 
thesis, Louisiana St. Univ., Baton Rouge, LA, 96 p. 

Smith, J.W. 1991. The Atlantic and Gulf menhaden 
purse seine fisheries: Origins, harvesting technolo- 
gies, biostatistical monitoring, recenttrends in fisheries 
statistics, and forecasting. Mar. Fish. Rev. 53(4): 28- 
41. 

Smith, J.W. 1996. Status of the menhaden fisheries: 
A report to the Gulf Menhaden Advisory Committee 
and the National Fish Meal and Oil Association. NOAA 
NMFS SEFSC Beaufort Lab., October 1996, 10 p. 

Smith, J.W. 1997. Forecast for the 1997 gulf and 
Atlantic menhaden purse-seine fisheries and review of 
the 1996 fishing season. NOAA NMFS SEFSC Beau- 
fort Lab., March 1997, 12 p. 

Sogard, S.M., D.E. Hoss, and J.J. Govoni. 1987. 
Density and depth distribution of larval gulf menhaden, 
Brevoortia patronus, Atlantic croaker, Micropogonias 
undulatus, and spot, Leiostomus xanthurus, in the 
northern Gulf of Mexico. Fish. Bull., U.S. 85:601-609. 

Springer, V.G., and K.D. Woodburn. 1960. An ecologi- 
cal study of the fishes of the Tampa Bay area. Fla. 
Board Conserv. Mar. Lab. Prof. Pap. Ser. 1, 104 p. 


Stout, V.F., C.R. Houle, and F.L Beezhold. 1981. A 
survey of chlorinated hydrocarbon residues in menha- 
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Suttkus, R.D. 1956. Early life history of the Gulf 
menhaden, Brevoortia patronus, in Louisiana. Trans. 
N. Am. Wildl. Conf. 21:390-407. 

Suttkus, R.D. , and B.I. Sundararaj. 1961. Fecundity 
and reproduction in the largescale menhaden, 
Brevoortia patronus. Tulane Stud. Zool. 8:177-182. 

Swift, C.R.W.Yerger, and P.R. Parrish. 1977. Distri- 
bution and natural history of the fresh and brackish 
water fishes of the Ochlockonee River, Florida and 
Georgia. Bull. Tall Timbers Res. Stn. No. 20, 111 p. 

Tagatz, M.E., and P.H. Wilkens. 1973. Seasonal 
occurrence of young gulf menhaden and other fishes in 
a northwestern Florida estuary. NOAA Tech. Rep. 
NMFS SSRF-672, 14 p. 

Turner, W.R. 1969. Life history of menhadens in the 
eastern Gulf of Mexico. Trans. Am. Fish. Soc. 98(2):21 6- 
224. 

Vaughan, D.S., E.J. Levi, and J.W. Smith. 1996. 
Population characteristics of Gulf Menhaden, Brevoortia 
patronus. NOAA Tech. Rep. NMFS 125, 18 p. 

Vaughan, D.S., and J. F. Merriner. 1991. Assessment 
and management of Atlantic menhaden, Brevoortia 
tyrannus, and gulf menhaden, Brevoortia patronus, 
stocks. Mar. Fish. Rev. 53(4): 49-57. 

Wagner, P.R. 1973. Seasonal biomass, abundance, 
and distribution of estuarine dependent fishes in the 
Caminada Bay System of Louisiana. Ph.D. disserta- 
tion, Louisiana St. Univ. Baton Rouge, LA, 207 p. 

Warlen, S.M. 1988. Age and growth of larval gulf 
menhaden, Brevoortia patronus, in the northern Gulf of 
Mexico. Fish. Bull., U.S. 86:77-90. 


143 


Yellowfin menhaden 


Brevoortia smithi 
Adult 


5 cm 


(from Fischer 1978) 


Common Name: yellowfin menhaden 

Scientific Name: Brevoortia smithi 

Other Common Names: yellowfin shad (Hildebrand 

1963), yellowtail (Reintjes 1969), Atlantic finescale 

(Gunter and Hall 1963), menhaden jaune (French), 

lacha amarilla (Spanish) (Fischer 1978). 

Classification (Robins et al. 1991) 

Phylum: Chordata 

Class: Osteichthyes 

Order: Clupeiformes 

Family: Clupeidae 

Value 

Commercial : Separate commercial harvest statistics 
are not reported forthis species (Fishcher 1 978). It co- 
occurs with gulf menhaden, but is not abundant enough 
to contribute appreciably to the commercial menhaden 
catch (Dahlberg 1970, Hettler 1984). In some areas it 
was historically separated from the rest of the catch 
because it was considered to have superior flavor 
compared to other menhaden, and marketed fresh in 
some local markets (Hildebrand 1963, Fischer 1978). 
It is not specifically sought by any commercial fishery; 
however, it is harvested as crab bait on both coasts of 
Florida (Ahrenholz 1991, Hettler pers. comm.). 

Recreational : Menhaden are not sought by sport fish- 
ermen as they are filter-feeders and are not caught by 
hook and line. However, they are important forage fish 
for many game species, and are often used as bait 
(Hildebrand 1963, Simmons and Breuer 1964). 

Indicator of Environmental Stress : The yellowfin men- 
haden is not well studied due to its low abundance and 
lack of importance as a commercial species (Ahrenholz 
1991). 


Ecological : Menhaden serve as an important link in the 
food chain between primary producers, phytoplankton 
and detritus, and top predators. They are extremely 
important forage fish for a variety of piscivorous birds 
and fish (Gunter and Christmas 1960, Palmer 1962, 
Christmas et al. 1 988). They are also important in the 
translocation of energy between estuarine and off- 
shore ecosystems (Deegan 1985). 

Range 

Overall : The yellowfin menhaden is found from 
Chandeleur Sound, Louisiana eastward and south- 
ward to Caloosahatchee River, Florida with distribution 
continuous around Florida to as far north as Cape 
Lookout, North Carolina (Dahlberg 1 970, Christmas et 
al. 1983, Hettler 1984, Vaughan 1991). Yellowfin 
menhaden on each side of the Florida peninsula are 
probably members of genetically separate populations 
(Ahrenholz 1 991 ). Levi (1 973) reported the collection 
of this species off Grand Bahama Island. 

Within Study Area : Within U.S. Gulf of Mexico estuar- 
ies, this species has been reported from Chandeleur 
Sound, Louisiana to Florida Bay, Florida (Dahlberg 
1970) (Table 5.18). 

Life Mode 

Yellowfin menhaden are a euryhaline species, inhab- 
iting coastal and tidal waters (Vaughan 1991). They 
are an estuarine dependent, marine migratory species 
(Ahrenholz 1991). Eggs and larvae of yellowfin men- 
haden are planktonic (Hettler 1968). Juvenile and 
adults are pelagic (Dahlberg 1970) and aggregate in 
loosely scattered schools (Reintjes 1960). These 
schools are typically much smaller in size than those of 
other menhaden species (Dahlberg 1970). 


144 


Yellowfin menhaden, continued 


Table 5.18. Relative abundance of yellowfin 

menhaden in 31 Gulf of Mexico estuaries (from 

Volume I). ... 

Life stage 


Estuary 


A S J L E 


Florida Bay 


® 


® 


Ten Thousand Islands 


• 


® 


Caloosahatchee River 


o 


V 


Charlotte Harbor 


O 


o 


Tampa Bay 


® 


® 


Suwannee River 


Apalachee Bay 


V 


V 


V 


Apalachicola Bay 


St. Andrew Bay 


Choctawhatchee Bay 


Pensacola Bay 


Perdido Bay 


Mobile Bay 


Mississippi Sound 


V 


Lake Borgne 


V 


V 


Lake Pontchartrain 


V 


V 


Breton/Chandeleur Sounds 


Mississippi River 


Barataria Bay 


Terrebonne/Timbalier Bays 


Atchafalaya/Vermilion Bays 


Calcasieu Lake 


Sabine Lake 


Galveston Bay 


Brazos River 


Matagorda Bay 


San Antonio Bay 


Aransas Bay 


Corpus Christi Bay 


Laguna Madre 


Baffin Bay 


A S J L E 


Relative abundance: 

# Highly abundant 

® Abundant 

O Common 

V Rare 

blank Not present 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


Habitat 

Type : The yellowfin menhaden is a neritic species 
(Dahlberg 1970, Hettler pers. comm.). Larvae and 
juveniles probably occur in all tidal waters of the 
spawning area (Gunterand Hall 1963, Reintjes 1969, 
Ahrenholz 1991). Adults frequent estuaries and tidal 
embayments during a portion of the year, and are 
typically found in depths less than 1 8 m (Reintjes 1 960, 
Turner 1969, Dahlberg 1970). 

Substrate : This species inhabits the water column, and 
no substrate preference is apparent. 

Physical/Chemical Characteristics : Eggs have been 
collected in waters with surface temperatures ranging 
from as low as 1 6.4° (Reintjes 1 962) to 25.4°C (Houde 
and Swanson 1975) and salinities as low as 20.1%o 
(Reintjes 1962) to 33%o (Houde and Swanson 1975). 
Juveniles have been reported from a temperature 
range of 17.0° to 26.1 °C and in salinities of 0.19 to 
27.2% (Gunterand Hall 1 963, Wang and Raney 1 971 ). 

Migrations and Movements : This species has no ap- 
parent systematic, annual migratory behavior. There 
is some evidence, however, for an increased north- 
ward distribution in late summer, and a southward 
movement of the species during the spawning season 
(Reintjes 1 969, Turner 1 969, Dahlberg 1 970, Ahrenholz 
1991). 

Reproduction 

Mode : Reproduction is sexual, with separate male and 
female sexes (gonochoristic). Milt and roe are broad- 
cast, and fertilization is external. 

Spawning : The yellowfin menhaden is a winter spawner. 
The spawning season appears to be relatively short, 
and occurs nearshore, apparently in tidal waters 
(Reintjes 1960, Dahlberg 1970, Ahrenholz 1991). 
Spawning may occur as early as November, but is 
probably most common from February to March 
(Ahrenholz 1991). Yellowfin menhaden reportedly 
spawn laterthan gulf menhaden (Hettler 1 968, Reintjes 
1969). Larvae are known to occur in Gulf of Mexico 
waters from December through March (Ditty et al. 
1988). 

Fecundity : Determinate fecundity is likely for menha- 
den, but this condition has not been demonstrated, nor 
has batch fecundity been estimated for any menhaden 
species (Ahrenholz 1991). 

Growth and Development 

Embryonic Development Embryos develop ovipa- 
rously. Egg diameters range from 1.21 to 1.48 mm 
(Houde and Swanson 1 975, Ditty et al. 1 994). The time 
of hatching varies with temperature. Hatching occurs 


145 


Yellowfin menhaden, continued 


in less than 24 hours above 22°C (Houde and Swanson 
1975), 34 hours at 21 °C, 26 hours at 26°C, and within 
46 hours at 19°C (Reintjes 1962, Hettler 1968). 

Age and Size of Larvae : The standard length (SL) of 
larvae at hatching is about 3.0 mm (Houde and Swanson 
1975). Larvae begin transforming at about 14.0 mm, 
with transformation being complete between 20 and 23 
mm (Houde and Swanson 1975). Larval growth is 
rapid, and is probably dependent on temperature and 
food availability (Reintjes 1 969, Ahrenholz 1 991 ). Larval 
growth at 20°C averaged 0.36 mm/day over a 32 day 
period, and 0.45 mm/day at over 20 days at 26°C 
(Hettler 1984). 

Juvenile Size Range : Juveniles reach a fork length 
(FL) of 160 mm by the end of their first summer and 
approximately 220 mm by the end of their second 
summer. Sexual maturity is attained during the second 
winter for most individuals (Reintjes 1969). In one 
study, the smallest ripe adults reported were a 1 86 mm 
FL female and a 215 mm FL male (Hettler 1968). 

Age and Size of Adults : Adults differ from juveniles and 
young adults in that their scales are more strongly 
serrated and their bodies are not as deep. The largest 
recorded total length (TL) for a specimen is 330 mm 
(Hildebrand 1963), and the maximum life span is 
thought to be somewhere between 5 and 12 years 
(Ahrenholz 1991). 

Food and Feeding 

Trophic Mode : Menhaden selectively sight-feed on 
individual planktonic organisms from the larval stage 
into the prejuvenile stage. After metamorphosis, juve- 
nile yellowfin menhaden become filter-feeding plankti- 
vores (Ahrenholz 1991). 

Food Items : The diet of this species consists of phy- 
toplankton, small zooplankton, and detritus strained 
from the water column (Ahrenholz 1 991 , Hettler pers. 
comm.). 

Biological Interactions 

Predation : Menhaden are potential prey throughout 
their life cycle (Ahrenholz 1991). Larval and juvenile 
piscivorous fish and some invertebrates (e.g., cha- 
etognaths) can prey on menhaden larvae. Other 
potential invertebrate predators may include squids, 
ctenophores, and jellyfish. Many piscivorous fishes 
(sciaenids, bluefish, bonito, etc.) prey opportunistically 
on juvenile and adult menhaden. Menhaden are also 
an important forage item for piscivorous birds such as 
the brown pelican and the common loon. Marine 
mammals are also reported to prey on menhaden. A 
potential also exists for menhaden to feed on their own 
eggs. 


Factors Influencing Populations : There is little pub- 
lished information on yellowfin menhaden due to its low 
abundance and lack of commercial importance 
(Ahrenholz 1991). This species is known to hybridize 
with Atlantic menhaden (B. tyrannus) and gulf menha- 
den (B. patronus) (Dahlberg 1970, Ahrenholz 1991). 
Parasitic copepods have been found on yellowfin men- 
haden, and parasitic isopods have been found on 
yellowfin x gulf menhaden hybrids (Ahrenholz 1991). 

Personal communications 

Hettler, William F., Jr. NOAA National Marine Fisher- 
ies Service, Beaufort, NC. 

Smith, Joseph W. NOAA National Marine Fisheries 
Service, Beaufort, NC. 

References 

Ahrenholz, D.W. 1991. Population biology and life 
history of the North American menhadens, Brevoortia 
spp. Mar. Fish. Rev. 53(4): 3-19. 

Christmas, J.Y., D.J. Etzold, and L.B. Swanson. 1 983. 
The menhaden fishery of the Gulf of Mexico United 
States: A regional management plan. Gulf States Mar. 
Fish. Comm. Pub. No. 8, Gulf States Marine Fisheries 
Commission, Ocean Springs, MS. 

Christmas, J.Y., D.J. Etzold, L.B. Simpson, and S. 
Meyers. 1988. The menhaden fishery of the Gulf of 
Mexico United States: a regional management plan, 
1 988 revision. Gulf States Mar. Fish. Comm. Pub. No. 
18, Gulf States Marine Fisheries Commission, Ocean 
Springs, MS, 77 p. 

Dahlberg, M.D. 1970. Atlantic and Gulf of Mexico 
menhaden genus Brevoortia (Pisces: Clupeidae). Bull. 
Fla. St. Mus. 15(3):91-162. 

Deegan, L.A. 1985. The population ecology and 
nutrient transport of gulf menhaden in Fourleague Bay, 
Louisiana. Ph.D. dissertation., Louisiana St. Univ., 
Baton Rouge, LA, 136 p. 

Ditty, J.G..E.D. Houde, and R.F.Shaw. 1994. Egg and 
larval development of Spanish sardine, Sardinella aurita 
(Family Clupeidae), with a synopsis of characters to 
identify clupeid larvae from the northern Gulf of Mexico. 
Bull. Mar. Sci. 54(2):367-380. 

Ditty, J. G., G.G. Zieske, and R.F. Shaw. 1988. Sea- 
sonality and depth distribution of larval fishes in the 
northern Gulf of Mexico above latitude 26°00'N. Fish. 
Bull., U.S. 86(4):81 1-823. 


146 


Yellowfin menhaden, continued 


Fischer, W. (ed.). 1978. FAO Species Identification 
Sheets for Fishery Purposes, Western Central Atlantic 
(Fishing Area 31), Vol. II. Food and Agriculture Orga- 
nization of the United Nations, Rome. 

Gunter, G., and J.Y. Christmas. 1960. A review of 
literature on menhaden with special reference to the 
Gulf of Mexico menhaden, Brevoortia patronus Goode. 
U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish., 363 p. 

Gunter, G., and G.E. Hall. 1963. Biological investiga- 
tions of the St. Lucie estuary (Florida) in connection 
with Lake Okeechobee discharges through the St. 
Lucie Canal. Gulf Res. Rep. 1(5):1 89-307. 

Heftier, W.F. 1968. Artificial fertilization among yellow- 
fin and gulf menhaden {Brevoortia) and their hybrids. 
Trans. Am. Fish. Soc. 97(2):1 19-123 

Heftier, W.F. 1984. Description of eggs, larvae and 
early juveniles of gulf menhaden, Brevoortia patronus 
and comparisons with Atlantic menhaden, B. tyrannus 
and yellowfin menhaden, B. smithi. Fish. Bull., U.S. 
82(1):85-95. 

Hildebrand, S.F. 1963. Family Clupeidae. In Fishes 
of the Western North Atlantic, pp. 1 1 1 -1 47. Memoir 1 , 
Part 3. Sears Found. Mar. Res., Yale Univ., New 
Haven, CT. 


Reintjes, J.W. 1969. A field guide and key to the North 
Atlantic menhadens, genus Brevoortia. Unpublished 
manuscript, 40 p. 

Robins, OR., R.M. Bailey, C.E. Bond, J.R. Brooker, 
E.A. Lachner, R.N. Lea, and W.B. Scott. 1 991 . Com- 
mon and scientific names of fishes from the United 
States and Canada, Fifth Edition. Am. Fish. Soc. Spec. 
Pub. 20. American Fisheries Society, Bethesda, MD, 
183 p. 

Simmons, E.G., and J. P. Breuer. 1964. The Texas 
menhaden fishery. Texas Parks Wildl. Dept., Austin, 
TX, 16 p. 

Turner, W.R. 1969. Life history of menhadens in the 
eastern Gulf of Mexico. Trans. Am. Fish. Soc. 98:216- 
224. 

Vaughan, D.S. 1991. Menhaden: the resource, the 
industry, and a management history. Mar. Fish. Rev. 
53:1-2. 

Wang,J.C.S.,andE.C.Raney. 1971. Distribution and 
fluctuations in the fish fauna of the Charlotte Harbor 
Estuary, Florida. Charlotte Harbor Estuarine Studies, 
Mote Marine Lab., Sarasota, FL, 64 p. 


Houde, E.D.,and L.J. Swanson. 1975. Description of 
eggs and larvae of yellowfin menhaden, Brevoortia 
smithi. Fish. Bull., U.S. 73(3):660-673. 

Levi, E.J. 1973. Juvenile yellowfin menhaden from the 
Bahama Islands. Trans. Am. Fish. Soc. 102(4):848. 

Nelson, D.M. (ed.)., M.E. Monaco, CD. Williams, T.E. 
Czapla, M.E. Pattillo, L. Coston-Clements, L.R. Settle, 
andE.A. Irlandi. 1992. Distribution and abundance of 
fishes and invertebrates in Gulf of Mexico estuaries, 
Vol. I: Data summaries. ELMR Rep. No. 10. NOAA/ 
NOS SEA Div., Rockville, MD, 273 p. 

Palmer, R.S. 1962. Handbook of North American 
birds. Vol. I. Loons through Flamingos. Yale Univ. 
Press, New Haven, CT. 

Reintjes, J.W. 1960. Continuous distribution of men- 
haden along the south Atlantic and Gulf coasts of the 
United States. Proc. Gulf Caribb. Fish. Inst. Ann. Ses. 
12:31-35. 

Reintjes, J.W. 1 962. Development of eggs and yolk- 
sac larvae of yellowfin menhaden. Fish. Bull., U.S. 
62:93-102. 


147 


Gizzard shad 


Dorosoma cepedianum 


Adult M 


r " : '' : '^^%^^ 


Ss£^"* 


^^t~^ 


5 cm 


(from Fischer 1978) 


Common Name: gizzard shad 
Scientific Name: Dorosoma cepedianum 
Other Common Names: eastern gizzard shad, skip- 
jack, hickory shad, mud shad, sawbelly, jackshad, 
aucun(French Canadian), a/osenoyer(French),sa£>a/o 
molleja (Spanish) (Fischer 1978). Occasionally re- 
ferred to as threadfin shad, the accepted common 
name for Dorosoma petenense (Mi Her 1 960, Robins et 
al. 1991). 

Classification (Robins et al. 1991) 
Phylum: Chordata 
Class: Osteichthyes 
Order: Clupeiformes 
Family: Clupeidae 

Value 

Commercial : This species has little commercial value, 
although it is sometimes reportedly harvested by net 
from freshwater lakes and reservoirs, and processed 
for animal feed or fertilizer. It is occasionally eaten, but 
is not popular because of poor flavor, undesirable 
texture, and being too bony. Gizzard shad are sold as 
live bait for striped bass in Alabama (Mettee pers. 
comm.). 

Recreational : The gizzard shad is generally consid- 
ered a "trash" and/or nuisance fish by anglers, but 
small sport fisheries have developed around dams and 
other congregation points (Manooch 1984). It is some- 
times used as live bait, especially for striped bass 
(Mettee pers. comm.). Its greatest value is as forage 
forcommercial and recreational fish species, and it has 
been introduced into reservoirs as a prey species 
(Manooch 1984, Guest et al. 1990). 


Indicator of Environmental Stress : Gizzard shad are 
not typically used in studies of environmental stress, 
but their populations have been used to assess the 
management needs of fresh water lakes and reser- 
voirs (Jenkins 1970). 

Ecological : The gizzard shad is an important forage 
fish (Lee 1 980), and is often the primary prey of game 
fish in some reservoirs (Guest et al. 1990). In estuar- 
ies, this species is important in converting detritus, 
algae, and benthic invertebrates into forage fish biom- 
ass available to predatory fish (Lippson et al. 1979). 

Range 

Overall : The gizzard shad occurs from the Great Lakes 
(except Lake Superior) and St. Lawrence River to 
southeastern South Dakota and central Minnesota, 
south across New Mexico, east to the Gulf of Mexico 
and throughout Mississippi and the Great Lakes drain- 
ages to about 40° N latitude on the Atlantic coast 
(Fischer 1978, Lee 1980). The populations that exist 
in the interior of the United States are generally land- 
locked from the coastal populations which occur from 
the St. Lawrence River southward along the Atlantic 
coast to central Florida and the Gulf of Mexico, and 
south to northeastern Mexico (Fischer 1 978). In south- 
ern Florida it is found occasionally in freshwater canals, 
and rarely in the Tampa Bay area (Springer and 
Woodburn 1960, Springer 1961, Loftus and Kushlan 
1987). 

Within Study Area : The gizzard shad occurs in estua- 
rine and coastal fresh waters from the Rio Grande, 
Texas, to southern Florida. It is abundant in some 
estuaries, especially those with high freshwater inflow 
(Table 5.19) (Fischer 1 978, Loftus and Kushlan 1 987). 


148 


Gizzard shad, continued 


Table 5.19. Relative abundance of gizzard shad in 
31 Gulf of Mexico estuaries (Nelson et al. 1992, 


>nee pers. comm.;. 


Life 


stage 


Estuary 


A S J L E 


Florida Bay 


Ten Thousand Islands 


Caloosahatchee River 


Charlotte Harbor 


Tampa Bay 


Suwannee River 


o 


O 


o 


o 


Apalachee Bay 


o 


O 


O 


o 


o 


Apalachicola Bay 


o 


O 


O 


o 


o 


St. Andrew Bay 


Choctawhatchee Bay 


o 


O 


O 


o 


o 


Pensacola Bay 


o 


O 


O 


o 


o 


Perdido Bay 


V 


V 


V 


V 


V 


Mobile Bay 


® 


If) 


® 


o 


o 


Mississippi Sound 


® 


® 


o 


o 


o 


Lake Borgne 


• 


o 


• 


o 


o 


Lake Pontchartrain 


o 


o 


Breton/Chandeleur Sounds 


o 


Mississippi Rivet 


o 


® 


o 


Barataria Bay 


o 


o 


Terrebonne/Timbalier Bays 


o 


o 


AtchafalayaA/ermilion Bays 


o 


o 


Calcasieu Lake 


o 


o 


Sabine Lake 


o 


Galveston Bay 


o 


Brazos River 


o 


na 


Matagorda Bay 


® 


® 


San Antonio Bay 


o 


o 


Aransas Bay 


V 


V 


Corpus Christi Bay 


o 


o 


Laguna Madre 


V 


Baffin Bay 


® 


® 


A S J L E 


Relative abundance: 

Highly abundant 

® Abundant 

O Common 

V Rare 

blank Not present 

na No data available 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


Life Mode 

This is generally a pelagic fish occurring at or near the 
surface of shallow, quiet waters for all life stages (Miller 
1 960). Young-of-the-year gizzard shad form compact 
schools, but in subsequent years aggregations occur 
with no true schooling. An upstream spring "run" 
occurs in rivers prior to the spawning season (Swift et 
al. 1977). 

Habitat 

Type : The gizzard shad is nektonic in fresh to polyhaline 
waters. It prefers areas with warm water and high 
phytoplankton production, and occurs in the littoral and 
limnetic regions of lakes and reservoirs, and in rivers, 
canals and coastal bays. This species commonly 
enters brackish and occasionally marine waters (Lee 
etal. 1980). 

Substrate : This species is widely distributed over mud 
bottoms, but also occurs over hard bottom lake shores. 
It is taken over mud, vegetation, rubble, sand, gravel, 
boulders, and bedrock (Nash 1950). 

Physical/Chemical Characteristics 
Temperature: This species is not considered hardy, 
and is susceptible to changes in temperature and low 
dissolved oxygen (Manooch 1984). Juveniles and 
adults have been collected from 5.0° to 34.9°C and 
suffer high mortality rates when temperatures fall to 
2.2°C. Northern populations are susceptible to cold- 
induced winter kills (Bodola 1 966, Perret 1 971 , Jester 
and Jensen 1 972, Juneau 1 975, Pineda 1 975, Tarver 
andSavoie 1976). 

Salinity: Eggs, larvae and small juveniles are limited to 
freshwater. Juveniles less than 40 mm are found in 
1.1 %o or less (Renfro 1960, Swingle 1971). Larger 
juveniles, usually greater than 70 mm TL, begin to 
enter brackish and more saline waters with one being 
collected at 41.3%o (Renfro 1960, Dunham 1972). 
Although adults are euryhaline (2-33.7%=,), they are 
rare in "pure saltwater" (Gunter 1942, Gunter 1945, 
Perret 1 971 , Pineda 1 975). They prefer oligohaline to 
mesohaline salinities with the greater abundance oc- 
curring below 1 5%o. One study reported captures from 
4 to 20%o (Wagner 1973). 

Dissolved Oxygen: The lowest reported dissolved oxy- 
gen (DO) concentration where this species has been 
collected is 4.6 parts per million (ppm) (Chambers and 
Sparks 1959). 

Movements and Migrations As larvae, there is a gen- 
eral movement from surface to midwater as size in- 
creases. Juveniles slowly make their way to more 
saline waters with age, but do not enter until about 70 
mm TL. Adults are concentrated in deeper water 


149 


Gizzard shad, continued 


during the fall and winter. Adults in salt water migrate 
upstream to spawn during spring months (Gunter 
1938, Gunter 1945, Pineda 1975, Jones et al. 1978). 
The increased abundance in inshore waters during 
winter months (November-February) may be due to 
this upstream spawning movement (Chambers and 
Sparks 1959). 

Reproduction 

Mode : Reproduction is sexual, with separate male and 
female sexes (gonochoristic). Milt and roe are broad- 
cast, and fertilization is external. 

Spawning : Spawning takes place in freshwater sloughs, 
ponds, lakes, and rivers, from mid-March to late Au- 
gust, with a peak from April to June in temperate 
waters. A second spawn may occur in late summer in 
some areas. This spawning period is generally later 
and more prolonged than that of Alabama shad l/\losa 
alabamae) or American shad (Alosa sapidissima) (Swift 
et al. 1 977, Lippson et al. 1 979). Eggs are scattered in 
open water or along the shoreline. Several individuals 
of each sex are often involved at the time of gamete 
release, which usually takes place at midday with rising 
temperatures that range from 10 to 28.9°C. They are 
reported to be most active around 18°C (Miller 1960, 
Bodola 1 966, Kelley 1 965, Jones et al. 1 978, Manooch 
1984). 

Fecundity : Reported fecundity ranges from 3,000 to 
543,900, but can change with age, averaging 59,480 at 
Age 1, 378,990 at Age II and declining to21 5,330 at Age 
VI (Bodola 1966, Manooch 1984). 

Growth and Development 

Egg Size and Embryonic Development Eggs are de- 
mersal and adhesive, sticking to the substrate (rocks, 
sticks, roots, etc.) if it is not covered with sediment. 
Fertilized eggs are creamy yellow, nearly transparent, 
and 0.75 mm in size. When eggs are first extruded they 
are hard and irregularly shaped, but become spherical 
after contact with water. The incubation period is 
temperature dependent and lasts from 36 hours to 1 
week. Egg hatching occurs after 95 hours at 1 7°C and 
36 hours at 27°C (Lippson and Moran 1974, Jones et 
al. 1978). 

Age and Size of Larvae : At hatching larvae are around 
3.25 mm TL. This stage lasts for a few weeks, during 
which the alimentary canal develops into the form 
necessary for omnivorous filter-feeding (Miller 1960). 

Juvenile Size Range : The juvenile stage is reached at 
about 20 mm TL. Juveniles mature in about 2 or 3 
years, with some females maturing as soon as 1 year. 
Average length at maturity is 178-279 mm TL. 


Age and Size of Adults : In Florida, gizzard shad aver- 
aged about 254 mm after the first year, 31 7.5 mm after 
the second and 345.4 mm after the third with none 
surviving to the fourth year. In other areas, particularly 
temperate freshwater locations, growth is much slower 
with a life span extending to almost 10 years (Miller 
1960), but most fish die before they are 7 years old 
(Manooch 1984). This species has attained lengths up 
to 520.7 mm TL, but does not commonly grow larger 
than 254 to 355.6 mm TL (Miller 1960). 

Food and Feeding 

Trophic Mode : Gizzard shad are primarily filter-feeders 
(Miller 1 963). For a short period after hatching, larvae 
are carnivorous. Juveniles and adults become filter- 
feeders. They may feed both on the bottom and in the 
water column, and may or may not be selective (Baker 
and Schmitz 1971). 

Food Items : During the first few weeks as larvae, the 
primary food items are small animals, such as proto- 
zoa, waterfleas (Cladocera), copepods and ostracods 
(Miller 1 960). After this initial phase when the intestine 
has had a chance to develop, there is a switch to algae, 
zooplankton, detritus, and bottom sediments contain- 
ing benthic infauna (Miller 1963, Baker and Schmitz 
1971, Lippson etal. 1979). 

Biological Interactions 

Predation : Although this species provides a forage 
base for predator fish, the rapid first year growth of the 
gizzard shad often makes it nearly invulnerable to 
predation by the fall of its first year (Jenkins 1 970, Lee 
et al. 1 980). Known estuarine predators of this species 
include spotted gar and longnose gar (Bonham 1 940, 
Darnell 1 958), and freshwater predators include large- 
mouth bass (Micropterus salmoides) (Houser and 
Netsch 1971) and white bass (Morone chrysops) 
(Netschetal. 1971). 

Factors Influencing Populations Gizzard shad popula- 
tions usually grow rapidly when introduced into new 
systems (e.g., reservoirs), possibly due to abundant 
detritus and other food sources. Where gizzard shad 
are abundant, they affect the populations, growth and 
habitat of game fish such as largemouth bass 
{Micropterus salmoides) and crappie (Pomoxis spe- 
cies) (Jenkins 1 970, Guest et al. 1 990). Where they co- 
occur with threadfin shad (Dorosoma petenense), it is 
possible that the two species compete for available 
food sources (Baker and Schmitz 1971). Winter kills 
occasionally occur in the lower Great Lakes, and when 
they do, gizzard shad provide a source of food for birds 
(Miller 1 960). Extensive die-offs may also occur in late 
summer (Mettee et al. 1996). 


150 


Gizzard shad, continued 


Personal Communications 


Mettee, Maurice F. 
Tuscaloosa, AL 

References 


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Baker, CD., and E.H. Schmitz. 1971. Food habits of 
adult gizzard and threadfin shad in two Ozark reser- 
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Fisheries Society, Washington, DC, 511 p. 

Bodola, A. 1966. Life history of the gizzard shad, 
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Houser, A., and N.F. Netsch. 1971. Estimates of 
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Jenkins, R.M. 1970. Reservoir fish management. In: 
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Jester, D.B., and B.L. Jensen. 1972. Life history and 
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Bonham, K. 1940. Food of gars in Texas. Trans. Am. 
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Chambers, G. V., and A.K. Sparks. 1959. An ecologi- 
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Darnell, R.M. 1958. Food habits of fishes and larger 
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Dunham, F. 1972. A study of commercially important 
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Fischer, W. (ed.). 1978. FAO Species Identification 
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Guest, W.C., R.W. Drenner, S.T. Threlkeld, F.D. Mar- 
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536. 

Gunter, G. 1938. Notes on invasion of fresh water by 
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Gunter, G. 1942. A list of the fishes of the mainland of 
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Jones, P.W., F.D. Martin and J.D. Hardy, Jr. 1978. 
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Juneau C.L., Jr. 1975. An inventory and study of the 
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Kelley, J.R., Jr. 1965. A taxonomic survey of the fishes 
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Lee, D.S., OR. Gilbert, OH. Hocutt, R.E. Jenkins, D.E. 
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Lippson, A.J., and R.L. Moran 1974. Manual for 
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Loftus, W.F., and J.A. Kushlan. 1987. Freshwater 
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Mettee, M.F., P.E. O'Neil, and J.M. Pierson. 1996. 
Fishes of Alabama and the Mobile Basin. Oxmoor 
House, Birmingham, AL, 820 p. 

Miller, R.R. 1960. Systematics and biology of the 
gizzard shad (Dorosoma cepedianum) and related 
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Perret.W.S. 1971. Cooperative Gulf of Mexico estua- 
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Pineda, P. H.A.K. 1975. A study of fishes of the lower 
Nueces River. M.S. thesis, Texas A&l Univ., Kingsville, 
TX, 118 p. 

Renfro, W.C. 1960. Fishes of the Aransas River, 
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Robins, C.R., R.M. Bailey, C.E. Bond, J.R. Brooker, 
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Springer, V.G. 1961. Notes on and additions to the fish 
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Springer, V.G. , and K.D. Woodburn. 1960. An ecologi- 
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bution and natural history of the fresh and brackish 
water fishes of the Ochlockonee River, Florida and 
Georgia. Bull. Tall Timbers Res. Stn. No. 20, 111 p. 

Swingle, H. A. 1971. Biology of Alabama Estuarine 
Areas - Cooperative Gulf of Mexico Estuarine Inven- 
tory. Ala. Mar. Res. Bull. 5:1-123. 

Tarver, J.W.,andL.B. Savoie. 1976. An inventory and 
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tion, Louisiana St. Univ., Baton Rouge, LA, 207 p. 


152 


Bay anchovy 


Anchoa mitchilli 
Adult 


2 cm 


(from Fischer 1978) 


Common Name: bay anchovy 

Scientific Name: Anchoa mitchilli 

Other Common Names: anchovy, anchois bai 

(French), anchoa de caleta (Spanish) (Fischer 1978) 

Classification (Robins et al. 1991) 

Phylum: Chordata 

Class: Osteichthyes 

Order: Clupeiformes 

Family: Engraulidae 

Value 

Commercial : The bay anchovy is not currently har- 
vested in the United States due to its small size, but is 
of some use as bait and in the preparation of anchovy 
paste (Hildebrand 1943, Hildebrand 1963, Daly 1970, 
Christmas and Waller 1973). It can be caught with 
beach seines and trawls (Fischer 1978). This species 
and other "coastal herrings" represent a large 
underutilized fishery resource with a potential yield of 
1 to 2 million mt (SEFSC 1 992). Anchovies are seldom 
taken as bycatch by trawl or purse seine fisheries due 
to their small size (Christmas et al. 1960). 

Recreational : The bay anchovy is indirectly important 
to recreational fisheries as a major forage item for 
many game fish (Hildebrand 1943, Christmas and 
Waller 1973). 

Indicator of Environmental Stress : Because of its im- 
portance as a forage species, this species can be 
considered an indicator of the health of an estuary 
(Shipp 1986). Studies supported by the Texas Water 
Quality Board show that the bay anchovy can be used 
to indicate poor water quality. This species can quickly 
adapt to pollution stress due to its small size and short 
food chain and become the dominant species of the 


polluted area. Its dominance in a particular area for two 
or more consecutive seasons can be indicative of 
deteriorating water quality (Bechtel and Copeland 1 970, 
Livingston 1975). 

Ecological : Bay anchovies probably constitute the great- 
est biomass of any fish in the estuarine waters of both 
the southeastern U.S. and the U.S. Gulf of Mexico 
(Reid 1 955, Perret 1 971 , Christmas and Waller 1 973, 
Perry and Boyes 1 977, Perry 1 979, Shipp 1 986). This 
species is a staple item in the diet of many predatory 
bird and fish species, and is a crucial link in the 
estuarine food web between zooplankton and higher 
trophic level predators (Hildebrand 1943, Reid 1955, 
Christmas and Waller 1973, Robinette 1983, Shipp 
1 986). Distributions of predators indicate that the bay 
anchovy is an important prey species in the weedy 
shallows as well as surface and bottom waters (Darnell 
1961). Larval bay anchovy are one of the dominant 
species of ichthyoplankton in the Gulf of Mexico during 
the summer months (Raynie and Shaw 1994). 

Range 

Overall : This species occurs from Casco Bay, Maine to 
nearTampico, Mexico (Hildebrand 1943, Hildebrand 
1963, Daly 1970, Houde 1974, Hoese and Moore 
1977). It is taken only rarely in the Yucatan, Gulf of 
Maine, and Florida Keys, and never in the West Indies 
(Hildebrand 1 943, Daly 1 970, Hoese and Moore 1 977). 
It has also been shown by morphometric methods that 
virtually every section of the coast within the range of 
the bay anchovy has a distinctive population, and that 
clinal variation over this species' range may account for 
differences in form (Hildebrand 1 943, Hildebrand 1 963, 
Leeetal. 1980). 


153 


Bay anchovy, continued 


Table 5.20. Relative abundance of bay anchovy in 
31 Gulf of Mexico estuaries (from Volume /)• 


Life stage 


Estuary 


A S J L E 


Florida Bay 


• 


m 


Ten Thousand Islands 


Caloosahatchee River 


Charlotte Harbor 


Tampa Bay 


Suwannee River 


Apalachee Bay 


• 


m 


Apalachicola Bay 


• 


m 


St. Andrew Bay 


® 


® 


Choctawhatchee Bay 


• 


m 


Pensacola Bay 


• 


o 


Perdido Bay 


® 


o 


Mobile Bay 


• 


• 


Mississippi Sound 


Lake Borgne 


Lake Pontchartrain 


m^ 


• 


Breton/Chandeleur Sounds 


® 


® 


Mississippi River 


• 


® 


Barataria Bay 


Terrebonne/Timbalier Bays 


Atchafalaya/Vermilion Bays 


Calcasieu Lake 


• 


• 


Sabine Lake 


® 


o 


Galveston Bay 


• 


• 


Brazos River 


Matagorda Bay 


_^ 


o 


San Antonio Bay 


• 


• 


Aransas Bay 


Corpus Christi Bay 


Laguna Madre 


Baffin Bay 


• 


• 


A S J L E 


Relative abundance: 

# Highly abundant 

(§) Abundant 

O Common 

V Rare 

blank Not present 


Life stage: 

A - Adults 

S - Spawning adults 

J - Juveniles 

L - Larvae 

E - Eggs 


Within Study Area : Within U.S. Gulf of Mexico estuar- 
ies, the bay anchovy occurs from the Rio Grande, 
Texas to the Florida Keys, primarily in open bays 
(Springer and Woodburn 1960, Hoese and Moore 
1977) (Table 5.20). 

Life Mode 

All life stages are pelagic, and occur throughout the 
water column (Kuntz 1913, Reid 1955, Hoese 1965, 
Houde 1974, Hoese and Moore 1977, Ward and 
Armstrong 1980). Eggs are most abundant at the 
surface; however, they are found throughout the water 
column, while larvae, juveniles, and adults are prima- 
rily nektonic (Kuntz 1 91 3, Hildebrand 1 943, Reid 1 955, 
Darnell 1 958, Darnell 1 961 , Jones et al. 1 978). Larvae 
primarily occupy the upper portion of the water column, 
while juveniles are more closely associated with deeper 
waters. Adults are pelagic and are found primarily in 
inshore waters, but they occur in offshore waters as 
well (Hildebrand 1963, Jones et al. 1978). Large 
schools form during the day in protected areas, usually 
close to shore. The bay anchovy has been observed 
to form small schools at night while feeding in the 
presence of predators (Hildebrand 1943, Arnold et al. 
1960, Daly 1970, Hoese and Moore 1977, Ward and 
Armstrong 1980). Activity is primarily nocturnal and is 
probably associated with feeding (Zimmerman 1969, 
Daly 1970). 

Habitat 

Ty pe: This is primarily a shallow estuarine and inshore 
coastal waterspecies (Gunter 1 945, Kilby 1 955, Arnold 
etal. 1960, Springerand Woodburn 1960, Swingle and 
Bland 1974, Jones et al. 1978, Sheridan 1978, Ward 
and Armstrong 1980, Sheridan 1983). The bay an- 
chovy is able to exploit a wide variety of habitats, 
including bays and bayous, sandy beaches, muddy 
coves, grassy areas along beaches, rivers and their 
mouths, and both shallow and deeper waters offshore 
(Reid 1 955, Swingle and Bland 1 974, Swift et al. 1 977, 
Jones et al. 1978, Sheridan 1978), but prefers bays 
and estuaries to shallow waters of the Gulf of Mexico 
(Gunter 1945, Kilby 1955, Springer and Woodburn 
1960, Christmas and Waller 1973). It is particularly 
abundant in primary and secondary bays, around 
shallow bay margins, islands, spoil banks, and shel- 
tered coves, and is less common in tertiary bays (Kilby 
1955, Simmons 1957, Swingle 1971, Ward and 
Armstrong 1 980). It has been reported to occur from 
fresh to hypersaline waters (Simmons 1957, Perret 

1 971 , Swingle and Bland 1 974) and from depths of 0.5 
to 20.0 m, appearing to prefer 2 to 3 m (Reid 1954, 
Renf ro 1 960, Miller 1 965, Bechtel and Copeland 1 970, 
Franks 1970, Perret 1971, Swingle 1971, Dunham 

1972, Dokken et al. 1984). This species has been 
collected in water with turbidities of 0.5 m to 0.7 m 
secchi depth (Reid 1955), and it has been suggested 


154 


Bay anchovy, continued 


that the bay anchovy is attracted to areas of high 
turbidity (Livingston 1975). 

Substrate : The bay anchovy is known to occur over 
unvegetated mud substrates (Cornelius 1984), but 
also occurs in grassy areas (Hildebrand and Cable 
1930, Reid 1954, Kilby 1955, Hildebrand 1963, 
Gallaway and Strawn 1 974). It has also been collected 
over bottoms of clay, hard sand, silty clay, clayey silt, 
silt and sand, sandy mud, and muddy sand (Reid 1 954, 
Reid 1955, Miller 1965, Franks 1970, Swingle 1971, 
Dunham 1 972, Tarver and Savoie 1 976, Dokken et al. 
1984). 

Physical/Chemical Characteristics : 
Temperature and salinity: Eggs are commonly found 
between 8 and 15% with spawning and development 
having been observed at 30.9 to 37% and from 22° to 
32°C (Kuntz 1913, Hoese 1965, Detwylerand Houde 
1 970, Dunham 1 972, Houde 1 974, Tarver and Savoie 
1976). Preferred temperatures range from 27.2° to 
27.8°C (Ward and Armstrong 1980). The larvae, 
juvenile and adult stages are considered both euryha- 
line and eurythermal. They have been collected from 
waters ranging from 0.0 to 80%o and from water tem- 
peratures ranging from 4.5° to 39.8°C (Gunter 1945, 
Reid 1954, Kilby 1955, Simmons 1957, Renfro 1960, 
Springer and Woodburn 1960, Miller 1965, Edwards 
1 967, Franks 1 970, Perret 1 971 , Swingle 1 971 , Wang 
and Raney 1971, Dunham 1972, Wagner 1973, 
Gallaway and Strawn 1974, Swingle and Bland 1974, 
Juneau 1975, Pineda 1975, Tarver and Savoie 1976, 
Swift et al. 1 977, Barrett et al. 1 978, Chung and Strawn 
1982, Cornelius 1984). Although they can occur in 
warmer temperatures, bay anchovies in Galveston 
Bay are not abundant above 33°C (Gallaway and 
Strawn 1 974). Larvae are generally collected in great- 
est abundance between 3 and 7%o (Perry and Boyes 
1977, Ward and Armstrong 1980). Adults prefer tem- 
peratures ranging from 8.1 ° to 32.2°C with one Missis- 
sippi study reporting greatest abundances between 
20° to 30°C (Perry and Boyes 1977, Ward and 
Armstrong 1 980). A possible upper lethal limit of 40°C 
was reported in one temperature study (Chung and 
Strawn 1982). 

Salinity: Salinity generally appears to have little rela- 
tionship with juvenile and adult distribution and abun- 
dance (Hoese 1 965, Christmas and Waller 1 973, Krull 
1976, Perry and Boyes 1977, Ward and Armstrong 
1 980, Cornelius 1 984). Reported salinity ranges vary 
among the different life stages and among different 
locations. In Texas, larvae have been collected at 0.5 
to 1% in Matagorda Bay while juveniles and adults 
have been collected at 1 to 32%o (Ward and Armstrong 
1 980). The reported salinity range in Alazan Bay is 1 1 
to 30%o for adults, and 1 1 to 20% o and 31 to 40%o for 


juveniles (Cornelius 1984). Gunter (1945) reports an 
overall occurrence at <5%o in Copano and Aransas 
Bays, while Simmons (1 957) reported it to be <50% o in 
the upper Laguna Madre. In Alabama, it has been 
reported from 20 to 29.9%o in Mobile and Baldwin 
counties (Swingle 1971), and 0.0 to 14.9% in Lake 
Pontchartrain, LA (Tarverand Savoie 1 976). Along the 
Mississippi coastline, occurrence was reported at 20.0 
to 25.0%o for larvae, 15 to 20%o for small juveniles, 0- 
5%o and 25-30%o for larger juveniles (Christmas and 
Waller 1973, Perry and Boyes 1977). Bay anchovies 
have been collected in freshwater rivers of Alabama, 
many miles upstream of Mobile Bay (Mettee et al. 
1996). 

Turbidity: The bay anchovy may be attracted to areas 
of high turbidity, and has been collected in water with 
a turbidities of 0.5 m to 0.7 m secchi depth (Robinette 
1983). 

Dissolved oxygen (DO): In Louisiana, the bay anchovy 
was collected in waters with a dissolved oxygen range 
of 1 .5 to 1 1 .9 ppm (Barrett 1 978). In the Chesapeake 
Bay, DO concentrations below 3 mg/l probably limit the 
viability and productivity of this species (Killam et al. 
1992). 

Movements and Migrations : Migrations are probably 
limited to seasonal inshore-offshore movements. Bay 
anchovies move into deeper waters of bays and estu- 
aries during winter, and back inshore during summer 
(Hildebrand 1943, Hildebrand 1963, Christmas and 
Waller 1973, Swingle and Bland 1974, Perry and 
Boyes 1977, Robinette 1983). Larvae appear to mi- 
grate into lower salinity nursery areas to mature, and 
then, as juveniles and adults, move to deeper, more 
saline areas (Gunter 1945, Hoese 1965, Edwards 
1967, Swingle and Bland 1974, Killam et al. 1992). 
Larvae appear on inshore nursery grounds in Missis- 
sippi waters during April and May (Perry and Boyes 
1977). Peak larval movement into a Texas tidal pass 
occurred during June in one study (Allshouse 1983). 
Immigration into nursery areas continues through Oc- 
tober and November (Perry and Boyles 1 977). During 
flood tides, larval bay anchovy may move to the middle 
of tidal passes to maximize transport into estuarine 
areas (Raynie and Shaw 1994). 

Reproduction 

Mode : This species has separate male and female 
sexes (gonochoristic). Milt and roe are broadcast, and 
fertilization is external. 

Spawning : Spawning occurs in waters less than 20 m 
deep near barrier islands, in bays and estuaries, tidal 
passes, harbors, sounds, and in the Gulf of Mexico 
where it is limited to the shallow inshore areas in bay 


155 


Bay anchovy, continued 


water masses (Hoese 1965, Bechtel and Copeland 
1970, Sabins and Truesdale 1974, Perry and Boyes 
1977, Jones et al. 1978, Ward and Armstrong 1980). 
Spawning has been observed in higher salinity por- 
tions of estuaries with ranges of 30 to 37% and <45%> 
(Bechtel and Copeland 1 970, Swingle and Bland 1 974, 
Dokken et al., 1984). Spawning by large schools 
usually occurs in the early evening, between 6 and 9 
pm, during warm water (>19°C) periods (Kuntz 1913, 
Hoese 1965, Jones et al. 1978, Ward and Armstrong 
1 980). Egg densities peak at different times depending 
on location. Based on studies of gonads and collection 
of juveniles and larvae, reported spawning seasons 
are: February to March, and June to August in the Gulf 
near Port Aransas, Texas and the latter part of March 
in Copano and Aransas Bays (Gunter 1945, Hoese 
1965, Allshouse 1983); summer months (June and 
July) in East Bay, Texas; February to October in 
Galveston Bay, Texas (Bechtel and Copeland 1970); 
spring and summer with peak spawning from March 
through October in Louisiana (Dugas 1970, Wagner 
1973, Sabins and Truesdale 1974); and February 
through October with a July peak along the Mississippi 
coastline (Edwards 1 967, Christmas and Waller 1 973, 
Perry and Boyes 1 977). Based on collection of larvae, 
the spawning season in the north-central Gulf of Mexico 
is March through September/October (Ditty pers. 
comm.). In Tampa Bay, spawning begins after water 
temperatures have reached 20°C and stops by No- 
vember (Phillips 1981). Some additional spawning is 
reported to occur throughout the year in some areas 
(Miller 1 965, Perret 1 971 , Swingle 1 971 , Wagner 1 973, 
Ward and Armstrong 1980, Dokken etal. 1984). This 
may be attributable to the Gulf's usually short and mild 
winters that sometimes allow shallow water winter 
temperatures to approach and exceed 20°C (Hoese 
1 965, Dokken et al. 1 984). In Biscayne Bay, Florida, it 
is suggested that spawning occurs all year, but is 
uncommon in December and January (Jones et al. 
1978). 

Fecundity : Data using fish from Chesapeake Bay indi- 
cate that during the peak spawning period females 
spawn a batch of 400 to 2000 eggs every four days 
(Luo and Musick 1 991 ), with the actual number directly 
related to the weight of the female (approximately 400 
eggs per g ram of wet weight female). This can conceiv- 
ably result in a female producing 30,000 to 50,000 eggs 
during the four month season in Chesapeake Bay 
(Houde pers. comm.). 

Growth and Development 

Egg Size and Embryonic Development : Eggs have a 
barely elliptical shape, and are 0.84 to 1.11 mm in 
diameter (Farooqi et al. 1 995). Average egg size tends 
to decrease with increasing salinity (Jones et al. 1 978). 
Eggs are transparent with no oil globule and the yolk is 


composed of separate masses appearing as large 
cells with an overall volume of 0.15 mm^ (Kuntz 1913, 
Hildebrand 1943, Houde 1974, Farooqi et al. 1995). 
Eggs float at or near water surface until near hatching 
and then gradually sink (Kuntz 191 3, Hildebrand 1943). 
Incubation takes approximately 24 hours at 27.8°C 
(Kuntz 1913, Farooqi et al. 1995) 

Age and Size of Larvae : Larvae are 1 .8 to 2.7 mm total 
length (TL) at hatching and weigh 1 7.6 \ig (Kuntz 1913, 
Detwyler and Houde 1970, Houde 1978, Ward and 
Armstrong 1980, Farooqi et al. 1995). The yolk sac is 
comparatively large and greatly elongated tapering to 
a point posteriorly. It is completely absorbed 1 5 to 1 8 
hours after hatching (AH). The body is elongate, 
slender, and nearly transparent with little pigmentation. 
Larvae are 2.6 to 2.8 mm TL at 12 hours AH. Develop- 
ment of mouth and gut, pigmentation of eyes, and yolk 
exhaustion are completed simultaneously at 36 hours 
after hatching at 26.2°C and 30.9%o (Kuntz 1913, 
Hildebrand 1943, Detwyler and Houde 1970). The 
critical period in which the larvae must begin to feed is 
2.5 days after hatching (Houde 1974). Size when 
feeding was initiated was 2.9 mm SL (Houde 1 978). A 
growth rate of 0.70 mm/day was reported for the fourth 
day (AH) (Detwylerand Houde 1 970) reaching a weight 
of 236.0 ug after 1 6 days (Houde 1 978). Larval survival 
in the laboratory is highest from 24 to 28°C, with faster 
growth at the higher temperatures (Houde 1974). 

Juvenile Size Range : Metamorphosis into juvenile 
form begins at 1 5.5 mm SL, and is essentially complete 
by 22.5 mm SL (Jones et al. 1 978, Ward and Armstrong 
1 980). A length of 1 8 mm TL is attained during the first 
month (AH) and a growth rate of 1 mm/month occurs 
overthe following 2 months (Edwards 1 967, Christmas 
and Waller 1 973). Juveniles mature rapidly, becoming 
sexually mature within their first year. 

Age and Size of Adults : The bay anchovy matures in 
approximately 2.5 months (Hildebrand 1 963, Jones et 
al. 1978) at 34 to 45 mm TL (Gunter 1945, Edwards 
1 967, Ward and Armstrong 1 980). Reported sizes for 
adults in the study area range from 34 to 93 mm TL 
(Gunter 1 945, Renfro 1 960, Franks 1 970, Perret 1 971 , 
Dunham 1972, Wagner 1973, Pineda 1975, Tarver 
and Savoie 1 976) with a recorded mean of 56.3 mm TL 
for males and 60.0 mm TL for females (Ward and 
Armstrong 1 980). Two and possibly three size classes 
have been observed in populations, but they are virtu- 
ally indistinguishable due to the occurrence of spawn- 
ing throughout the year (Gunter 1945, Miller 1965, 
Perret 1971, Cornelius 1984). 

Food and Feeding 

Trophic mode : Bay anchovies are primary consumers, 
feeding primarily on zooplankton in currents at night 


156 


Bay anchovy, continued 


(Reid 1955, Bechtel and Copeland 1970, Daly 1970). Personal communications 


Food Items : Young anchovies are plankton strainers. 
They consume zooplankton such as copepod nauplii 
and rotifers until a body length of approximately 7 mm 
is reached, at which time they switch to copepodites 
and copepods (Darnell 1958, Detwyler and Houde 
1970). Some detritus is also consumed, but phy- 
toplankton generally is not, which suggests that food 
straining occurs near the bottom (Darnell 1958). As 
anchovies grow in size their diet becomes increasingly 
selective, shifting from copepods to small shrimp, 
larval and juvenile fish, mysids, insect larvae, crab 
zoeae, clam larvae, cladocerans, schizopods, gastro- 
pods, copepods, isopods, malacostracans, oligocha- 
etes, polychaetes, and supplemented by detritus from 
occasional bottom feeding (Hildebrand 1943, Reid 
1954, Reid 1955, Darnell 1958, Arnold et al. 1960, 
Darnell 1961, Bechtel and Copeland 1970, Detwyler 
and Houde 1 970, Carr and Adams 1 973, Weaver and 
Halloway 1974, Sheridan 1978, Levine 1980). Gut 
analysis of anchovies 30 to 49 mm long showed the 
following diet proportions: 9% microinvertebrat.es; 58% 
zooplankton, and 33% organic detritus (Darnell 1 961 ). 
Benthic animals and sand are most frequently encoun- 
tered during the winter, suggesting more intensive 
benthic feeding at this time (Darnell 1958). 

Biological Interactions 

Predation : The small size and high abundance of this 
species makes it one of the most important forage 
species in the Gulf of Mexico (Robinette 1983). Many 
species are known to consume bay anchovies, includ- 
ing snook, gar (Lepisosteus species), red drum, sand 
seatrout, spotted seatrout, silverperch, Atlantic needle- 
fish (Strongylura marina), inshore lizardfish (Synodus 
foetens), ladyfish (Elopssaurus), blue catfish (Ictalurus 
furcatus), Atlantic croaker, southern flounder, crevalle 
jack, and cobia (Rachycentroncanadum) (Gunter 1 945, 
Reid 1955, Darnell 1958, Darnell 1961, Carr and 
Adams 1973, Sheridan 1978, Rozas and Hackney 
1 984, Killam et al. 1 992, Franks et al. 1 996). 

Factors Influencing Populations : Population density 
appears to be primarily influenced by food supply (i.e., 
zooplankton) present in the water column (Reid 1 955). 
This probably accounts for their preference for bay 
habitats and, when found in the Gulf, bay water masses 
(Hoese1965). 


Ditty, J.G. Louisiana State University, Coastal Fisher- 
ies Institute, Baton Rouge, LA. 

Houde, Edward D. University of Maryland, Chesa- 
peake Biological Laboratory, Solomons, MD. 

Peterson, Mark S. Gulf Coast Research Lab., Ocean 
Springs, MS. 

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160 


Hardhead catfish 


Ah us felis 
Adult 


5 cm 


(fromGoode 1884) 


Common Name: hardhead catfish 

Scientific name: Arius felis 

Other Common Names: sea catfish, hardhead, silver 

cat, tourist trout (Arnold et al. 1960, Benson 1982, 

Breuer 1 957, Bryan 1 971 , Christmas and Waller 1 973); 

macA7o/roncr7af(French), bagre gato (Spanish) (Fischer 

1978). 

Classification (Robins et al. 1991) 

Phylum: Chordata 

Class: Osteichthyes 

Order: Cypriniformes 

Family: Ariidae 

Value 

Commercial : The hardhead catfish is not sought by the 
commercial fishery because it has a low market value 
and becomes entangled in nets and pump hoses. It 
contributes a small portion (2-3%) to the industrial 
bottom fish fishery of Louisiana and Mississippi, which 
uses low value fish to produce pet food, fish meal, fish 
oil, and protein supplements for animal feeds. How- 
ever, it is frequently discarded due to the possibility of 
animals ingesting its spines (Haskell 1 961 , Roithmayr 
1965, Dunham 1972, Swingle 1977, Benson 1982). It 
was used briefly as a food fish during World Wars I and 
II (Gunter 1 945). Its nutritive value compares favorably 
with croaker, spot, and spotted seatrout, but attempts 
to market it as human food have failed because the 
meat is dark and often has a strong odor (Benson 
1982). 

Recreational : Hardhead catfish are frequently caught, 
but are usually discarded by anglers. They are held in 
low esteem because of their sharp venomous spines, 
undesirable flesh, and difficulty in handling and remov- 
ing them from the hook (Gunter 1945, Arnold et al. 


1960, Harris and Rose 1968, Fontenot and Rogillio 
1 970, Hoese and Moore 1 977, Swingle 1 977). Fishery 
statistics for the Gulf of Mexico showed a combined 
total recreational catch of 18,474,000 saltwater cat- 
fishes (hardhead catfish and gafftopsail catfish (Bagre 
marinus}) in 1 988 (NMFS 1 989). Although edible, this 
fish is not often consumed due to its reputation of 
feeding on any available organic matter (Gallaway and 
Strawn 1974). 

Indicator of Environmental Stress : This species has 
been used in research on the effects of sublethal 
copper exposure on marine fish (Scarfe et al. 1982, 
Steele 1 989). It has been used to study prevalence of 
pathological abnormalities as an indicator of environ- 
mental stress (Fournieetal. 1996). Bioaccumulationof 
contaminants and liver lesions in hardhead catfish 
have been found to be correlated with substrate con- 
taminant levels in Tampa Bay (McCain et al. 1996). 

Ecological : The hardhead catfish is highly abundant in 
shallow coastal waters of southeastern U.S., but is 
occasionally found in deep water (Chittenden and 
McEachron 1976). It is an opportunistic feeder, and 
can utilize diverse food sources. This may account for 
its successful adaptation to different habitats (Darnell 
1958, Hildebrand 1958, Hellier 1962, Diener et al. 
1974, Dugas 1975, Hoese and Moore 1977, Benson 
1 982). It is not a major forage species, but is important 
in estuarine ecosystems as a scavenger (Fontenot and 
Rogillio 1970, Wagner 1973). This fish is very abun- 
dant in estuarine habitats, and can compete with game 
fishes for space and food (Fontenot and Rogillio 1 970, 
Muncy and Wingo 1983). 


161 


Hardhead catfish, continued 


Table 5.21 . Relative abundance of hardhead catfish 
in 31 Gulf of Mexico estuaries (from Volume 1). 

Life stage 


Estuary 


A S J L E 


Florida Bay 


® 


® 


® 


® 


® 


Ten Thousand Islands 


o 


O 


o 


o 


o 


Caloosahatchee River 


® 


® 


® 


® 


® 


Charlotte Harbor 


® 


® 


• 


® 


® 


Tampa Bay 


o 


O 


o 


o 


o 


Suwannee River 


• 


o 


® 


o 


o 


Apalachee Bay 


® 


® 


® 


® 


® 


Apalachicola Bay 


• 


• 


• 


• 


• 


St. Andrew Bay 


• 


• 


• 


• 


• 


Choctawhatchee Bay 


® 


® 


® 


® 


® 


Pensacola Bay 


® 


® 


® 


® 


® 


Perdido Bay 


® 


o 


® 


o 


o 


Mobile Bay 


® 


® 


® 


® 


® 


Mississippi Sound 


• 


® 


® 


o 


o 


Lake Borgne 


• 


o 


® 


o 


o 


Lake Pontchartrain 


® 


o 


® 


o 


o 


Breton/Chandeleur Sounds 


o 


o 


® 


o 


o 


Mississippi River 


• 


® 


® 


® 


® 


Barataria Bay 


• 


® 


• 


® 


® 


Terrebonne/Timbalier Bays 


® 


® 


® 


® 


® 


Atchafalaya/Vermilion Bays 


® 


o 


o 


o 


o 


Calcasieu Lake 


® 


o 


® 


o 


o 


Sabine Lake 


o 


o 


o 


o 


o 


Galveston Bay 


® 


® 


® 


® 


® 


Brazos River 


o 


na 


o 


na 


na 


Matagorda Bay 


® 


® 


® 


® 


® 


San Antonio Bay 


• 


• 


• 


• 


• 


Aransas Bay 


® 


® 


® 


® 


® 


Corpus Christi Bay 


® 


® 


® 


® 


® 


Laguna Madre 


® 


® 


• 


® 


® 


Baffin Bay 


• 


• 


• 


• 


• 


A S J L E 


Relative abundance: 

% Highly abundant 
® Abundant 
O Common 
V Rare 
Dlank Not present 
na No data available 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


Range 

Overall : The range is along the Atlantic coast from 
Cape Cod, Massachusetts to Yucatan, Mexico (Jones 
et al. 1 978, Lee et al. 1 980). This species is extremely 
abundant in the shallow coastal waters of North Caro- 
lina, around Florida, and throughout the Gulf of Mexico, 
but is absent from the Caribbean (Shipp 1986). 

Within Study Area : Within U.S. Gulf of Mexico estuar- 
ies, hardhead catfish are found from the Rio Grande, 
Texas, to Florida Bay, Florida. This is one of the most 
ubiquitous fishes present in the brackish and salt 
waters of the bays and shallow waters of the northern 
Gulf of Mexico (Table 5.21) (Gunter 1945, Harris and 
Rose 1968, Cornelius 1984). 

Life Mode 

Eggs and yolk sac larvae are carried in mouths of 
males, but are demersal if dropped (Gunter 1947). 
Juveniles and adults are demersal and predominantly 
nocturnal (Darnell 1 958, Harris and Rose 1 968, Hoese 
et al. 1968, Zimmerman 1969, Diener et al. 1974, 
Dugas 1975, Steele 1984, Steele 1985, DeLancey 
1989, Sogard et al. 1989) with some diurnal activity, 
which can possibly be attributed to differences in life 
cycle stages or seasonal variation (Hoese et al. 1 968, 
Moore et al. 1 970). In areas of the Gulf of Mexico with 
pronounced tidal fluctuations, activity associated with 
high tides has been noted (Sogard et al. 1989). It is 
often found in schools (Gunter 1938, Benson 1982) 
which may be formed and maintained by specific 
sounds it produces (Tavolga 1962). 

Habitat 

Ty pe: Eggs and yolk sac larvae are carried in the 
mouths of adult males usually in shallow oligohaline to 
mesohaline waters of bays, lagoons, or Gulf inlets (Lee 
1937, Gunter 1947, Ward 1957, Zimmerman 1969, 
Bechtel and Copeland 1970, Bryan 1971). Juveniles 
are collected from fresh to euhaline salinities in waters 
0.6 to 3.0 m in depth (Miller 1965, Swingle 1971, 
Dunham 1972). They are apparently more numerous 
than adults in waters of low salinity (Gunter 1947). 
Adults are taken from fresh to hypersaline waters. 
They have been collected at depths from 0.6 to 91 .4 m, 
but principally from 4 to 7 m (Lee 1937, Gunter 1947, 
Hildebrand 1954, Simmons 1957, Hoese 1960, Miller 
1965, Perry 1970, Perret et al. 1971, Swingle 1971, 
Dunham 1972, Franks et al. 1972, Swift et al. 1977, 
Benson 1982, Cornelius 1984). They prefer warm 
waters in shallow grassy areas of bays and the Gulf 
(Lee 1937, Miles 1949, Hellier 1962, Miller 1965, 
Zimmerman 1 969, Franks et al. 1 972, Chittenden and 
McEachron 1976, Hoese and Moore 1977, Benson 
1 982, Cornelius 1 984), but occasionally enter freshwa- 
ter or brackish rivers and creeks (Swift et al. 1 977, Lee 
et al. 1980, Loftus and Kushlan 1987). 


162 


Hardhead catfish, continued 


Substrate : Juveniles and adults have mostly been 
found over bottoms of mud, oyster beds, sand, shell, 
sandy mud, silt, and sand with shell (Lee 1937, Reid 
1955, Gunter and Hall 1965, Miller 1965, Swingle 
1971). Juveniles have been reported not to use 
seagrass beds (Zimmerman 1969), although adults 
have been found in areas with seagrass and detritus 
substrates. 

Physical/Chemical Characteristics : 
Temperature - Eggs and Larvae: Eggs have been 
observed in both laboratory and field studies over a 
temperature range of 28.0° to 34.0°C (Gunter 1945, 
Ward 1 957, Bryan 1 971 , Perret et al. 1 971 , Wang and 
Raney 1971, Christmas and Waller 1973). Yolk sac 
larvae have been observed in the field from 15.0° to 
34.9°C (Gunter 1945, Christmas and Waller 1973, 
Tarver and Savoie 1976). 

Temperature - Juveniles and Adults: Both juveniles 
and adults have been observed in the field from 5.0° to 
39.0°C (Hellier 1962, Miller 1965, Perret et al. 1971, 
Swingle 1 971 , Wang and Raney 1 971 , Dunham 1 972, 
Franks et al. 1972, Christmas and Waller 1973, 
Gallaway and Strawn 1 974, Perret and Caillouet 1 974, 
Juneau 1975, Tarver and Savoie 1976, Barrett et al. 
1978, Benson 1982). The maximum acceptable tem- 
perature is probably 37.0°C, with 39.0°C being close to 
the upper lethal limit for this species (Gallaway and 
Strawn 1974). The preferred temperature range ap- 
pears to be 19.0° to 25.0°C (Benson 1982). 

Salinity - Eggs and Larvae: Eggs have been observed 
in both laboratory and field studies in salinities ranging 
from 1.8 to 36.4%o (Gunter 1945, Ward 1957, Bryan 

1971, Perret et al. 1971, Wang and Raney 1971, 
Christmas and Waller 1973). Yolk sac larvae have 
been collected from brooding males in salinities rang- 
ing from 2.0 to 36.0%o (Bryan 1 971 , Perret et al. 1 971 , 
Wang and Raney 1971, Christmas and Waller 1973, 
Cornelius 1984). 

Salinity - Juveniles and Adults: Free swimming juve- 
niles have been collected from to 56% salinity. They 
are reported to prefer <10%o (Perret etal. 1971, Wang 
and Raney 1 971 , Christmas and Waller 1 973, Cornelius 
1984). Adults are euryhaline, and are common from 
0.0 to 45% (Gunter 1 945, Gunter 1 947, Gunter 1 956, 
Simmons 1 957, Hoese 1 960, Hellier 1 962, Miller 1 965, 
Bryan 1971, Perret 1971, Swingle 1971, Dunham 

1972, Frank et al. 1972, Christmas and Waller 1973, 
Perret and Caillouet 1974, Swingle and Bland 1974, 
Juneau 1975, Tarver and Savoie 1976, Swift et al. 
1 977, Barrett et al. 1 978, Cornelius 1 984), but occur in 
salinities as high as 60%o (Simmons 1 957). They have 
been reported to show some preference for 15.0 to 
30.0% o salinities, and are increasingly less common 


below 1 5%o (Gunter 1 945, Perret et al. 1 971 , Swingle 
1 971 , Franks et al. 1 972, Christmas and Waller 1 973, 
Swingle and Bland 1974). 

Dissolved Oxygen: The hardhead catfish has been 
collected in waters with a dissolved oxygen (DO) 
content range of 2.7 to 11.1 parts per million (ppm) 
(Bryan 1971, Barrett etal. 1978). It is sometimes found 
in habitats characterized by low DO (Benson 1982). 

Movements and Migrations : The hardhead catfish gen- 
erally decreases in abundance in bays and estuaries 
along the northern Gulf of Mexico and Texas coast 
during fall and winter as it moves to deeper waters of 
the Gulf or sometimes within an estuary system to 
overwinter. It then returns to shallows during spring 
and summer (Gunter 1945, Miller 1965, Swingle 1971, 
Franks et al. 1972, Landry and Strawn 1973, Steele 
1985). Older age class fish are reported to migrate 
while many of the younger ones remain in the bays 
(Swingle 1971). Migration to the Gulf can begin as 
early as September with the lowest numbers in bay 
systems occurring from Novemberto February (Swingle 
1 971 , Wagner 1 973). Abundance increases with tem- 
perature (Wagner 1 973, Tarver and Savoie 1 976) with 
returns to the bays and estuaries beginning from March 
to April. Peak abundance is observed from April and 
May to as late as October along with a high influx of 
young-of-the-year fish (Chambers and Sparks 1959, 
Arnold et al. 1960, Hellier 1962, Hoese et al. 1968, 
Zimmerman 1969, Perret et al. 1971, Christmas and 
Waller 1 973, Wagner 1 973, Perret and Caillouet 1 974, 
Juneau 1975, Chittenden and McEachron 1976, Ju- 
neau and Pollard 1981, Sheridan 1983, Cornelius 
1984). Migration may be triggered by photoperiod 
(Steele 1984, Steele 1985). 

Reproduction 

Mode : This species has separate male and female 
sexes (gonochoristic), and fertilization occurs exter- 
nally. Fertilized eggs and post-hatch larvae are mouth- 
brooded by adult males. 

Spawning : In the Gulf of Mexico, spawning takes place 
from May to September in waters 0.6 to 1 .2 m deep. It 
occurs in shallow waters of secondary and primary 
bays, and Gulf inlets (Lee 1937, Gunter 1945, Gunter 
1 947, Reid 1 955, Ward 1 957, Kelley 1 965, Bechtel and 
Copeland 1970, Bryan 1971, Wagner 1973). Spawn- 
ing may also occur in nearshore areas of the Gulf of 
Mexico. Although no spawning has been observed in 
this area, ripe females with large ovarian eggs have 
been taken there in 21 .9 to 27.4 m depths during July 
(Hildebrand 1 954). Eight young with yolk sacs whose 
total lengths (TL) were approximately 45 mm were 
collected in the surf on Galveston Island in July (Pattillo 
pers. observ.). Furthermore, the absence of adults has 


163 


Hardhead catfish, continued 


been noted in some inshore areas during the spawning 
season (Springer and Woodburn 1960, Dugas 1970). 

Spawning females have slightly everted hemorrhagic 
genital openings (Gunter 1947), and enlarged pelvic 
fins which may serve to enhance fertilization (Lee 
1 937). Females with enlarging pelvic fins are seen as 
early as March and through July and do not totally 
disappear until after October (Gunter 1945). Motile 
sperm in males has been noted from early March until 
the middle of July (Ward 1 957). It has been suggested 
that eggs are initially deposited in sandy depressions. 
The males fertilize the eggs and then pick them up into 
their mouths to brood them (Gunter 1 947, Jones et al. 
1978). Brooding males have enlarged branchial and 
buccal cavities to accommodate eggs or larvae, and 
their mouths are hemorrhagic in appearance (Lee 
1937, Reid 1955, Zimmerman 1969). Brooding males 
are observed from May to August (Lee 1937, Gunter 
1945, Gunter 1947, Reid 1955, Breuer 1957, 
Zimmerman 1969, Dugas 1970, Bryan 1971, Christ- 
mas and Waller 1 973, Swift et al. 1 977). The numbers 
of eggs or larvae reported found in brood males range 
from 1 to 48 and do not appear to be related to the 
length of the male (Lee 1937, Gunter 1945, Gunter 
1 947, Reid 1 955, Reid 1 957). Males do not feed during 
the brooding period which lasts about 60 days (Lee 
1937, Gunter 1947, Jones et al. 1978). 

Fecundity : Females produce 1 4 to 64 mature ova each 
season, along with numerous small, nonfunctional 
eggs. The left ovary is slightly larger and typically has 
3 to 6 more eggs than the right (Lee 1 937, Gunter 1 945, 
Gunter 1947, Reid 1955, Ward 1957, Jones et al. 
1 978). Females may spawn more than once a season 
(Gunter 1945). 

Growth and Development 

Egg Size and Embryonic Development : Eggs are de- 
mersal. Ripe ovarian eggs are greenish, slightly oval 
or elliptical, and measure 12-19 mm in diameter (Lee 
1 937, Gunter 1 947, Reid 1 955, Ward 1 957, Jones et al. 
1 978). Many small nonfunctional eggs are attached to 
ripe eggs and to each other by a thin, colorless, 
adhesive film that is lost as development proceeds. 
Non-functional eggs may serve as food for males that 
fast while brooding (Gunter 1947, Ward 1957). Eggs 
reach the gastrula stage after about 29 hours, and 
hatching probably occurs in about 30 days (Ward 
1957, Jones etal. 1978). 

Age and Size of Larvae : Hatching size ranges from 29 
to 45 mm TL and occurs primarily in June (Bryan 1 971 , 
Gallaway and Strawn 1974, Cornelius 1984). The 
duration of the larval stage ranges from about 2 to 4 
weeks in the wild and up to 55 days under laboratory 
conditions (Jones et al. 1 978). Although mouth brooded 


young are considered to be in the larval stage, their fin 
ray complement is complete before yolk absorption, 
and therefore, a true larval stage is not considered to 
exist (Jones et al. 1 978). The yolk supply is used up by 
50 mm TL (Gunter 1945). 

Juvenile Size Range : Juveniles are released by male 
parents from June to August (Swingle 1 971 , Christmas 
and Waller 1973, Gallaway and Strawn 1974). The 
standard length (SL) of juveniles when released ranges 
from 33 to 58 mm (Gallaway and Strawn 1 974) and 41 
to 62 mmTL (Gunter 1945, Swingle 1971, Christmas 
and Waller 1973). Juveniles in the wild have been 
observed to grow 10 mm/month from July to October; 
however, cooler watertemperatures drastically reduce 
the growth rate during winter months (Christmas and 
Waller 1973). 

Age and Size of Adults : Minimum sizes noted for 
sexually mature adults are 1 35 mm TL and 1 26 SL for 
females, and 142 mm SL and 201 mm TL for brood 
males (Lee 1937, Gunter 1947). Maximum reported 
sizes are 635 mm TL and 330 mm SL (Reid 1955, 
Barrett et al. 1978) with average sizes of 110 mm TL 
and fork lengths (FL) of 100 to 160 mm (Perret et al. 
1 971 , Chittenden and McEachron 1 976). Adults rarely 
exceed 1.154 kg in weight (Gallaway and Strawn 
1974). The average life span is 2 to 3 years (Swingle 
1971, Chittenden and McEachron 1976). 

Food and Feeding 

Trophic mode : This species is carnivorous throughout 
its development. Both juveniles and adults are oppor- 
tunistic, nocturnal bottom feeders utilizing a wide range 
of feeding modes such as scavenging, carnivory, and 
ectoparasitism (Miles 1949, Darnell 1958, Hildebrand 
1958, Hellier 1962, Hoese 1966, Harris and Rose 
1968, Odum 1971, Diener et al. 1974, Dugas 1975, 
Benson 1982). 

Food Items : The hardhead catfish feeds primarily on 
crustaceans (shrimp and crabs), and insects. Molluscs 
are also an important diet item. This species may pass 
through three feeding stages in its development: zoop- 
lankton, especially copepods, are most important for 
individuals <100 mm TL; benthic micro-invertebrates 
are most important for individuals between 100 and 
200 mm TL; crabs and fishes gradually assume impor- 
tance in fish >200 mm TL (Darnell 1 958). Specific diet 
items that have been reported include: bottom debris 
and detritus; plant tissue, algae, polychaetes, gastro- 
pods, bivalves (Rangia cuneata and Congeria 
leucophaeta), ostracods, isopods, copepods, cirripedia, 
amphipods, mysids, penaeid shrimp including brown 
shrimp and pink shrimp, grass shrimp, blue crabs, 
xanthid (mud) crabs, insects, arachnids, menhaden, 
anchovies, silversides, mullets, juvenile hardhead cat- 


164 


Hardhead catfish, continued 


fish, various eggs and cysts, hermit crabs, nudibranchs, 
fish bones, and scales actively taken from living fish 
(Gunter 1945, Miles 1949, Reid 1955, Darnell 1958, 
Hellier 1962, Hoese 1966, Harris and Rose 1968, 
Hildebrand 1958, Dieneretal. 1974, Hoese and Moore 
1977, Swift et al. 1977, Levine 1980). In addition, 
hardhead catfish feeding in the surf zone of South 
Carolina have been found to consume retantians, mole 
crabs, and isopods (DeLancey 1989). 

Biological Interactions 

Predation : The hardhead catfish is not a major forage 
species (Fontenot and Rogillio 1970). It has been 
reported as prey for longnose gar, cobia, bull shark, 
jewf ish, ladyf ish, spotted seatrout, and red drum (Gunter 
1945, Miles 1949, Darnell 1961, Branstetter 1981). 

Factors Influencing Populations : Studies have demon- 
strated that sounds produced by the hardhead catfish 
could enable it to avoid obstructions, and probably 
predators, at close range. These sounds may also be 
used to communicate during breeding and nocturnal 
schooling (Breder 1968, Tavolga 1962, 1971, 1977). 
Nematodes have been observed to parasitize hard- 
head catfish in blister-like swellings under the skin of 
the caudal region (Gunter 1945). 

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168 


Sheepshead minnow 


Cyprinodon variegatus 
Adult 


(from Jordan 1925) 


Common Name: sheepshead minnow 

Scientific Name: Cyprinodon variegatus 

Other Common Names: Variegated minnow 

(Hildebrand 1919); sheepshead killifish (Harrington 

and Harrington 1 961 ); sheepshead pupfish (Blair et al. 

1968); broad killifish, and chubby (Breuer 1957). 

Classification (Robins et al. 1991) 

Phylum: Chordata 

Class: Osteichthyes 

Order: Atheriniformes 

Family: Cyprinodontidae 

Value 

Commercial : This fish has some commercial value as 
bait (Simpson and Gunter 1956, Perschbacher and 
Strawn 1986), but little information is available on its 
use. 

Recreational : This species' recreational value is lim- 
ited to its use as bait by anglers, and as a forage for 
game fish species. In addition, it is occasionally kept as 
an aquarium fish. 

Indicator of Environmental Stress : The sheepshead 
minnow is used extensively as a bioassay organism by 
U.S. Environmental Protection Agency (EPA) and oth- 
ers for acute, partial-chronic, and chronic bioassays in 
order to set water quality standards. Testing is prima- 
rily for effects of organochlorides and organophospho- 
rus compounds on the estuarine community, but this 
species is also useful in the evaluation of the 
hepatocarcinogenic risks of chemicals in contami- 
nated coastal waters (Schimmel et al. 1 974, Schimmel 
and Hansen 1974, Goodman et al. 1979, Karara and 
Hayton 1984, Couch and Courtney 1987, Hale 1989, 
Hutchinson and Williams 1989, Miller et al. 1990). 


Ecological : The sheepshead minnow and other 
cyprinodontids are important in the control of salt water 
mosquitoes (Hildebrand 1919, Harrington and 
Harrington 1 961 ) and also in the export of energy from 
the marsh by serving as food for birds and larger fish 
(Hildebrand 1919, Simmons 1957, Perschbacher and 
Strawn 1986). Burrowing behavior by this and other 
species of marsh fish during cold weather may ad- 
versely affect nesting success of wading birds by 
making these fish less available to avian predation 
(Frederick and Loftus 1 993). The sheepshead minnow 
is able to thrive in marginal shallow water habitats, and 
therefore utilizes areas devoid of other fish species 
(Shipp1986). 

Range 

Overall : The range for this species extends along the 
Atlantic coast, from Maine to Yucatan, Mexico, and 
throughout the West Indies to northern South America 
(Blair et al. 1 968, Hoese and Moore 1 977, Hardy 1 978, 
Leeetal. 1980). 

Within Study Area : Within U.S. Gulf of Mexico estuar- 
ies, this fish can be found from the Rio Grande, Texas, 
to Florida Bay, Florida (Table 5.22) (Odum and Caldwell 
1955, Springer and Woodburn 1960, Tabb and Man- 
ning 1 961 , Finucane 1 966, Moe et al. 1 966, Blair et al. 
1 968, Wang and Raney 1 971 , Hoese and Moore 1 977, 
Hardy 1978, Lee et al. 1980). 

Life Mode 

Eggs are demersal (Kuntz 1914, Schimmel and Hansen 
1974, Hardy 1978). Larvae, juveniles, and adults are 
markedly diurnal (Breder 1959, Ruebsamen 1972). 
They have been observed to school, especially when 
frightened (Hildebrand and Schroeder 1928, Martin 


169 


Sheepshead minnow, continued 


Table 5.22. Relative abundance of sheepshead 
minnow in 31 Gulf of Mexico estuaries (from Volume 

Life stage 


Estuary 


A S J L E 


Florida Bay 


® 


O 


® 


o 


o 


Ten Thousand Islands 


O 


O 


o 


o 


o 


Caloosahatchee River 


o 


O 


o 


o 


o 


Charlotte Harbor 


o 


O 


o 


o 


o 


Tampa Bay 


• 


® 


• 


® 


® 


Suwannee River 


• 


• 


• 


• 


• 


Apalachee Bay 


• 


• 


• 


• 


• 


Apalachicola Bay 


® 


® 


® 


® 


® 


St. Andrew Bay 


® 


® 


® 


® 


® 


Choctawhatchee Bay 


® 


® 


® 


® 


® 


Pensacola Bay 


® 


® 


® 


® 


® 


Perdido Bay 


o 


o 


o 


o 


o 


Mobile Bay 


® 


® 


® 


® 


® 


Mississippi Sound 


® 


o 


o 


o 


o 


Lake Borgne 


o 


o 


o 


o 


o 


Lake Pontchartrain 


o 


o 


o 


o 


o 


Breton/Chandeleur Sounds 


o 


o 


o 


o 


o 


Mississippi River 


® 


If) 


® 


® 


® 


Barataria Bay 


• 


® 


® 


® 


® 


TerrebonneATimbalier Bays 


o 


o 


o 


o 


o 


Atchafalaya/Vermilion Bays 


o 


o 


® 


o 


o 


Calcasieu Lake 


o 


o 


® 


o 


o 


Sabine Lake 


® 


® 


® 


® 


® 


Galveston Bay 


® 


® 


® 


® 


® 


Brazos River 


® 


® 


® 


® 


® 


Matagorda Bay 


® 


® 


® 


® 


® 


San Antonio Bay 


® 


® 


® 


® 


® 


Aransas Bay 


® 


® 


® 


® 


® 


Corpus Christi Bay 


® 


® 


® 


® 


® 


Laguna Madre 


• 


• 


• 


• 


• 


Baffin Bay 


® 


® 


• 


® 


® 


A S J L E 


Relative abundance: 

# Highly abundant 
® Abundant 
O Common 
V Rare 
blank Not present 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


1 972), and are demersal in shallow coastal and inland 
waters (Reid 1955, Harrington and Harrington 1961, 
Springer and Woodburn 1960, Tabb and Manning 
1961, Peterson 1990). 

Habitat 

Ty pe: All life stages are estuarine and are restricted to 
bays and coastal inland areas, preferring quiet, shal- 
low waters. They are found in salt marshes, sloughs, 
coves, bays, creeks, canals, and ditches (Hildebrand 
and Schroeder 1 928, Simpson and Gunter 1 956, Breuer 
1957, Gunter 1958, Gunter 1967, Strawn and Dunn 
1967, Franks 1970, Martin 1972, Swift et al. 1977, 
Loftus and Kushlan 1 987). Sheepshead minnows are 
uncommon in heavily vegetated marsh areas (Loftus 
and Kushlan 1987). Larvae often occupy the water's 
edge while larger individuals (7 mm) may stay on the 
bottom (Ward and Armstrong 1980). This fish is 
generally found in depths ranging from 0-1 .5 m (Raney 
et al. 1953, Phillips and Springer 1960). 

Substrate : All life stages occur over bottoms areas 
where vegetation is generally, but not strictly, absent. 
Bottoms can consist of rock, sand, mud, detritus mud, 
or mud with shell fragments (Reid 1 955, Simpson and 
Gunter 1956, Franks 1970, Martin 1972, Swift et al. 
1977, Loftus and Kushlan 1987), occasionally with 
turtle grass, shoal grass, or algae present (Hudson et 
al. 1970). 

Physical/Chemical Characteristics 
Temperature - Eggs: Egg development has been ob- 
served to occur at 17.4-27.5°C (Renfro 1960) and 
>26°C (Schimmel and Hansen 1974). Optimal devel- 
opment occurs at 22.8-28.9°C (Ward and Armstrong 
1980). 

Temperature - Larvae, Juveniles, and Adults: These 
life stages are all eurythermal. Their reported tempera- 
ture range in Texas is 8.8-34.9°C (Gunter 1945, 
Simmons 1 957, Strawn and Dunn 1 967, Pineda 1 975), 
5.0-33.5°C in Mississippi (Christmas and Waller 1 973; 
Franks 1970), and 7.2-43.0°C in Florida (Reid 1954, 
Odum and Caldwell 1955, Kilby 1955, Phillips and 
Springer 1 960, Harrington and Harrington 1 961 , Hudson 
et al. 1970, Wang and Raney 1971, Subrahmanyam 
and Drake 1975). The sheepshead minnow has been 
observed to be resistant to near freezing conditions, at 
least for short periods (Gunter and Hildebrand 1951, 
Simpson and Gunter 1956). Laboratory and field 
observations found that it begins burrowing into the 
substrate between 7° and 9° C possibly to escape 
predation (Loftus and Kushlan 1987, Frederick and 
Loftus 1993). 

Salinity: The sheepshead minnow is a euryhaline spe- 
cies recorded from freshwater to hypersaline condi- 


170 


Sheepshead minnow, continued 


tions in all life stages. Observations suggest a prefer- 
ence for salinities of 1 0-25.0%° and 21 .0-30.0%o, being 
less common above this range than below (Gunter 
1 945, Gunter 1 950, Reid 1 954, Kilby 1 955, Odum and 
Caldwell 1955, Phillips and Springer 1960, Tabb and 
Manning 1961, Franks 1970, Hudson et al. 1970, 
Swingle 1971, Wang and Raney 1971, Martin 1972, 
Christmas and Waller 1973, Pineda 1975, 
Subrahmanyam and Drake 1975, Swift et al. 1977, 
Cornelius 1984, Nordlie 1985). It has been collected 
from an overall salinity range of 0-142.4% o . The high 
extreme of this range is probably very close to the 
upper tolerance limit for this species (Gunter 1945, 
Simpson and Gunter 1956, Simmons 1957, Renfro 
1960, Hoese 1960, Gunter 1967, Martin 1972, Ward 
and Armstrong 1 980, Nordlie 1 985). However, it rarely 
invades salinities higher than 80%o, possibly due to the 
lack of food at such high salinities (Hildebrand 1957). 
Environmental factors experienced during growth and 
development may affect the ability of different popula- 
tions to withstand salinity variations (Martin 1968). 

Dissolved Oxygen: The sheepshead minnow appears 
to have a strong tolerance of hypoxia (Peterson 1 990). 
It has been found in Chesapeake Bay in waters with a 
dissolved oxygen (DO) content ranging from 1 to 6 
ppm, and 20 to 90% saturation (De Silva et al. 1962). 
It has also been taken from anoxic waters where the 
DO content ranged from to 0.81 ppm (Odum and 
Caldwell 1 955). "Obligate gulping" of air is believed to 
be used in order to relieve oxygen stress. 

Movements and Migrations : This species remains in 
estuaries throughout the year (Rogers and Herke 
1 985). Observed movements appear to be influenced 
by seasonal fluctuations in temperature. As tempera- 
tures begin to drop in the fall there is a general 
movement to warmer, slightly deeper waters. It has 
been noted that at this time individuals can be taken by 
trawls in these deeper waters where none were present 
during warmer months (Gunter 1945, Simpson and 
Gunter 1956, Breuer 1957, Springer and Woodburn 
1960). 

Reproduction 

Mode : This species has separate male and female 
sexes (gonochoristic), with equal (or nearly so) sex 
ratios (Hildebrand 1919, Raney et al. 1953, Warlen 
1964). Fertilization is external. 

Spawning : This species has an extended spawning 
season lasting from February to October and probably 
throughout the year in warmer waters (Kuntz 1914, 
Hildebrand 1919, Gunter 1950, Kilby 1955, Raney et 
al. 1953, Martin 1972, Ruebsamen 1972, DeVlaming 
et al. 1 978). Ripe females have been collected in water 
temperatures ranging from 1 5 to 28.5°C (Ruebsamen 


1972). Drops in salinity may initiate spawning activity 
(Martin 1 972). Spawning can occur at depths of 2.5-61 
cm in shallow arms of small bays, large tide pools, 
mangrove lagoons, roadside ditches, and pools in 
shallow, gently flowing streams over bottoms of sand, 
black silt, or mud. Males occupy territories up to 0.3-0.6 
m in diameter and may or may not construct nest pits. 
Pits, when constructed, are over sand, gravel, or soft 
mud bottoms with a detritus overlay, and are 1 0-1 5 cm 
in diameter, 2.5-3.8 cm deep, and are centrally located 
in well groomed, oval shaped territories. This territory 
is defended by the male against all but ripe females. 
Spawning may take place within or outside of the 
territories, but not usually within the nest pit. Spawning 
territories are typically situated adjacent to banks or up 
to 3 m from shore and are usually associated with 
submerged logs or rocks. The density of territories 
may approach 1 00 per 0.9 m 2 area (Raney et al. 1 953, 
Simpson and Gunter 1956, Hardy 1978, Ward and 
Armstrong 1980). 

Fecundity : Sheepshead minnows are fractional spawn- 
ers. Fecundity varies with each spawn and each 
female. Single females spawn a number of times 
during a single season at intervals of 1 -7 days with an 
average of 4 spawnings per nest entry, and deposit 1- 
3 eggs per spawning (Kuntz 1914, Hildebrand 1919, 
Hardy 1978). Spawning throughout the year is pos- 
sible in southern parts of the range (DeVlaming et al. 
1978). In one laboratory study, the number of eggs 
produced over a 28 day period per female in vitro 
ranged from 2 to 1,028 and averaged 186 (Schimmel 
and Hansen 1974). Another study reported from 2 to 
24 eggs spawned by a single female on thirty occa- 
sions from April 9 through August 1 6 with the possibility 
that the actual number may have exceeded observa- 
tions (Hildebrand 1919). The ovary from a single 
female in this study contained 1 40 oocytes with at least 
50% mature. 

Growth and Development 

Egg Size and Embryonic Development : Eggs are de- 
mersal, develop oviparously, and are adhesive or 
semi-adhesive by means of minute threads which stick 
to plants, the sides of aquaria, each other, and the 
bottom substrate. Eggs are spherical in form (1 .0-1 .73 
mm in diameter), yellowish in color, and highly translu- 
cent. The egg membrane is thick and heavy with a 
visible perivitelline space between it and the vitelline 
membrane. Small groups of minute oil globules are 
scattered over the surface of the yolk sphere that 
normally rests at the upper pole. Incubation time can 
vary from 4-1 2 days: 1 2 days at 1 7.4-25.5°C and 1 1 0%o 
salinity; 5-6 days at laboratory temperature; 5 days at 
30°C; 4-5 days at 28°C and 30% o salinity. Hatching 
typically occurs in spring and summer (Kuntz 1914, 
Hildebrand 1919, Hubbs and Drewry 1959, Renfro 


171 


Sheepshead minnow, continued 


1960, Schimmel and Hansen 1974, Hardy 1978). 

Age and Size of Larvae : Newly hatched larvae have a 
total length (TL) of 4 mm. The yolk is relatively large, 
and the dorsal and ventral fin folds are continuous. 
Larvae are slightly yellowish in color and the posterior 
half of their body is marked by lighter and darker 
vertical bands. At five days after hatching the yolk is 
almost completely absorbed and larvae are >5 mm TL. 
The general color is still yellowish with vertical bands 
slightly more conspicuous. On the sixth day, with the 
larvae averaging 8 mm in length and about 4 mg in 
weight, they begin active free swimming (Usher and 
Bengtson 1981). At 9 mm many adult characters are 
apparent. The vertical bands are present, but not fully 
developed. Individuals are considered juveniles be- 
ginning at 12 mm (Kuntz 1914, Hildebrand 1919, 
Hildebrand and Schroeder 1 928, Schimmel and Hansen 
1974). 

Juvenile Size Range : During the juvenile life stage, the 
back becomes markedly elevated, the body depth 
proportionally greater, and the caudal fin more rounded 
than in the adult. Coloration is quite characteristic, 
although the general color is lighter in the adult. Juve- 
niles reach maturity in vitro at 3 months with sex 
dichromatism and ripe females occurring at 27 mm 
(Kuntz 1914, Schimmel and Hansen 1974). A field 
study in Louisiana observed growth to be about 5 mm/ 
month from March through October (Ruebsamen 1972). 

Age and Size of Adults : Reported size averages for 
each sex in Texas are 45.0 mm TL for males, and 46.5 
mm TL for females (Simpson and Gunter 1 956). The 
largest published size is 93 mm (Gunter 1945). 

Food and Feeding 

Trophic Mode : The sheepshead minnow is a primary 
consumer, and is often termed herbivorous, 
detritivorous, and, infrequently, larvivorous and om- 
nivorous. 

Food Items : Diet principally consists of plant material, 
diatoms and other algae, detritus, amphipods, copep- 
ods, and mosquito larvae and pupae. The remains of 
insects, fish, sponge, annelid fragments, and pelecy- 
pods have also been reported. Sand and mud are also 
conspicuous stomach contents, suggesting benthic 
feeding (Hildebrand and Schroeder 1 928, Gunter 1 950, 
Simpson and Gunter 1956, Springer and Woodburn 
1960, Harrington and Harrington 1961, Martin 1970, 
Odum 1 971 , Ruebsamen 1 972, Schimmel and Hansen 
1974, Subrahmanyam and Drake 1975, Levine 1980, 
Perschbacher and Strawn 1986). 


Biological Interactions 

Predation : Known fish predators include spotted 
seatrout, Atlantic croaker, and red drum (Gunter 1 945, 
Darnell 1958). Because they often occupy shallow 
water marsh habitat, sheepshead minnows are prey 
for several species of wading birds (Frederick and 
Loftus 1993). 

Factors Influencing Populations : This species has the 
ability to tolerate a broad range of environmental 
parameters, allowing it to survive under extreme con- 
ditions in marginal shallow water habitats that may be 
devoid of other fish species (Shipp 1986). The onset 
of cooler water temperatures can initiate burrowing or 
movementto deeper, warmer waters during the fall and 
winter. 

References 

Blair, W.F., A.P. Blair, P. Brodkorb, F.R. Cagle, and 
G.A.Moore. 1968. Vertebrates of the United States, 
2nd ed. McGraw-Hill, Inc., New York, 616 p. 

Breder, CM., Jr. 1959. Studies on social groupings in 
fishes. Bull. Am. Mus. Nat. Hist. 117:394-481. 

Breuer, J. P. 1957. An ecological survey of Baffin and 
Alazan Bays, Texas. Publ. Inst. Mar. Sci., Univ. Texas 
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175 


Gulf killifish 


Fundulus grandis 
Adult 


2 cm 


(from Eddy 1969) 


Common Name: gulf killifish 

Scientific Name: Fundulus grandis 

Other Common Names: Chub, finger mullet, top 

minnow, bullminnow, mudminnow, mudfish (Gunter 

1945, Hoese and Moore 1977, Waas et al. 1983). 

Classification (Rosen 1964, Rosen and Patterson 

1969, Robins et al. 1991) 

Phylum: Chordata 

Class: Osteichthyes 

Order: Atheriniformes 

Family: Cyprinodontidae 

Value 

Commercial : This species has some commercial value 
as a live bait fish. Supplies are derived entirely from 
wild populations where they are trapped or seined. 
Fish have been reported to sell at $0.65 per dozen 
(Waas et al. 1 983), but total dollar value of this industry 
is unknown since, due to its limited size, no statistics 
are available (Simpson and Gunter 1956, Hoese and 
Moore 1977, Perschbacher and Strawn 1986, Waas 
and Strawn 1 983). Several studies have examined the 
feasibility of commercial production of gulf killifish and 
found it could be economically profitable (Trimble et al. 
1 981 , Tatum et al. 1 982, Waas et al. 1 983, MacGregor 
etal. 1983). 

Recreational : Gulf killifish are used along the Gulf 
coast, especially in Alabama, by recreational fisher- 
men who prize this species as a live bait for flounder, 
red drum, sand seatrout, and spotted seatrout (Simpson 
and Gunter 1 956, Hoese and Moore 1 977, Waas et al. 
1983, Perschbacher and Strawn 1986). 

Indicator of Environmental Stress : The gulf killifish has 
been used occasionally as an indicator organism 


(Courtney and Couch 1984). Studies by the U.S. 
Environmental Protection Agency (EPA) and others 
suggest it may be a responsive, useful estuarine spe- 
cies in research on the effects of water-soluble frac- 
tions of fuel oil, organochlorides, and carcinogens 
(Ernst and Neff 1 977, Courtney and Couch 1 984). The 
National Marine Fisheries Service (NMFS) has used 
this species to study the effects of acidified water on 
estuarine life (McFarlane and Livingston 1 983, Courtney 
and Couch 1984). Bioaccumulation of contaminants 
and liver lesions in gulf killifish have been found to be 
correlated with substrate contaminant levels in Tampa 
Bay (McCain etal. 1996). 

Ecological : The gulf killifish is important in the export of 
energy from salt marshes by serving as food for larger 
fish and piscivorous birds (Jenni 1969, Perschbacher 
and Strawn 1986), and in the control of salt marsh 
mosquito populations through predation (Harrington 
and Harrington 1961). 

Range 

Overall : Distribution is continuous from Laguna de 
Tamiahua, Veracruz, Mexico throughout the Gulf of 
Mexico and along the Atlantic coast of northeastern 
Florida up to the Mantangas River. It is also found in 
Cuba (Rivas 1948, Blair et al. 1968, Kushlan and 
Lodge 1974, Relyea 1983, Duggins et al. 1989). It is 
closely related to the mummichog (F. heteroclitus) 
(Duggins et al. 1989, Bernardi and Powers 1995), 
which occurs in estuaries of the U.S. east coast as far 
south as Indian River, Florida (Nelson et al. 1991). 

Within Study Area : Within U.S. Gulf of Mexico estuar- 
ies, the gulf killifish occurs from Florida Bay, Florida to 
the Rio Grande, Texas (Table 5.23) (Springer and 


176 


Gulf killifish, continued 


Table 5.23. Relative abundance of gulf killifish in 31 

Gulf of Mexico estuaries (Nelson et al. 1992, Van 

Hoose pers. comm.). 

Life stage 


Estuary 


A S J L E 


Florida Bay 


O 


o 


o 


o 


o 


Ten Thousand Islands 


O 


® 


® 


® 


® 


Caloosahatchee River 


O 


o 


o 


o 


o 


Charlotte Harbor 


® 


® 


® 


® 


® 


Tampa Bay 


O 


o 


o 


o 


o 


Suwannee River 


® 


® 


® 


® 


® 


Apalachee Bay 


® 


® 


® 


® 


® 


Apalachicola Bay 


o 


o 


o 


o 


o 


St. Andrew Bay 


o 


o 


o 


o 


o 


Choctawhatchee Bay 


o 


o 


o 


o 


o 


Pensacola Bay 


o 


o 


o 


o 


o 


Perdido Bay 


o 


o 


o 


o 


o 


Mobile Bay 


® 


® 


® 


® 


® 


Mississippi Sound 


® 


® 


® 
o 


® 


® 


Lake Borgne 


® 


o 


o 


o 


Lake Pontchartrain 


o 


o 


o 


o 


o 


Breton/Chandeleur Sounds 


o 


o 


o 


o 


o 


Mississippi River 


® 


® 


® 


® 


® 


Barataria Bay 


• 


• 


• 


• 


• 


Terrebonne/Timbalier Bays 


• 


• 


• 


• 


• 


AtchafalayaA/ermilion Bays 


® 


® 


® 


® 


® 


Calcasieu Lake 


o 


o 


® 


o 


o 


Sabine Lake 


® 


® 


® 


® 


® 


Galveston Bay 


® 


® 


® 


® 


® 


Brazos River 


® 


o 


® 


o 


o 


Matagorda Bay 


® 


® 


® 


® 


® 


San Antonio Bay 


® 


® 


® 


® 


® 


Aransas Bay 


® 


® 


® 


® 


® 


Corpus Christi Bay 


o 


o 


o 


o 


o 


Laguna Madre 


® 


® 


® 


® 


® 


Baffin Bay 


® 


® 


® 


® 


® 


A S J L E 


Relative abundance: 


® 
O 

blank 


Highly abundant 

Abundant 

Common 

Rare 

Not present 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


Woodburn 1 960, Powell et al. 1 972, Price and Schlueter 
1985, Comp 1985). 

Life Mode 

Eggs are demersal and adhesive (Relyea 1983). Lar- 
vae, juveniles, and adults are nektonic in shallow 
coastal waters 0.6 to 2.0 m in depth (Gunter 1 945, Reid 

1955, Springer and Woodburn 1960, Franks 1970, 
Swingle 1971). This species forms schools, with 15 to 
20 individuals typical while feeding (Relyea 1983). It 
has also been observed to congregate in large num- 
bers after dark in shallows near mangroves (Harrington 
and Harrington 1961). 

Habitat 

Type : All life stages are estuarine residents. They 
inhabit shallow waters near the shores of oyster bars, 
tidal ponds, sloughs, salt water creeks, bayous, marsh 
pools, and coastal inland ponds (Gunter 1 945, Gunter 
1950, Reid 1955, Simpson and Gunter 1956, Renfro 
1960, Gunter 1967, Wagner 1973, Hoese and Moore 
1977, Swift etal. 1977). They have been reported from 
fresh to hypersaline habitats (Simpson and Gunter 

1956, Renfro 1960, Swingle 1971). 

Substrate : All life stages occur over bottoms where 
vegetation is generally, but not strictly, absent. Bot- 
toms can consist of hard muddy sand, mud, silt, clay, 
detritus, or shell, and occasionally with seagrass or 
algae present. They are also common among man- 
grove prop roots and emergent marsh vegetation 
(Gunter 1945, Reid 1955, Simpson and Gunter 1956, 
Renfro 1 960, Springerand Woodburn 1 960, Harrington 
and Harrington 1 961 , Tabb and Manning 1 961 , Strawn 
and Dunn 1967, Franks 1970, Swingle 1971, Swift et 
al. 1977, Greeley and MacGregor 1983, Thayer et al. 
1987). 

Physical/Chemical Characteristics 

Temperature - Eggs: Spawning and egg development 

have been recorded from 4° to 33°C (Hubbs and 

Drewry 1959, Tatum et al. 1978, Waas and Strawn 

1983). 

Temperature - Larvae: Larvae have been reared in 
culture ponds at temperatures ranging from 22° to 
35.5°C (Tatum et al. 1978, Waas and Strawn 1983). 

Temperature - Juveniles and Adults: Adult and juvenile 
stage fish are eurythermal, and have been reported 
from waters ranging from 2° to 34.9°C (Gunter 1945, 
Franks 1970, Perret et al. 1971, Wang and Raney 
1 971 , Christmas and Waller 1 973, Pineda 1 975, Tatum 
et al. 1978, Courtney and Couch 1984). They have 
been able to withstand prolonged exposure to 38°C;'n 
vitro (Waas 1 982). A lethal low temperature of -1 .5°C 
has been reported by Umminger (1971). 


177 


Gulf killifish, continued 


Salinity - Eggs: Egg development has occurred from 
to 80%° (Hubbs and Drewry 1959, Tatum et al. 1978, 
Waas 1982, Perschbacher et al. 1990). The highest 
hatching percentages occur from to 35%o 
(Perschbacher et al. 1990). 

Salinity - Larvae: Best larval growth and survival occurs 
in the 5 to 40%o range (Perschbacher et al. 1990). 
Observations indicate a preference for lower salinity 
waters ranging from 5 to 1 8.3%o (Gunter 1 950, Gunter 
1967, Franks 1970, Swingle 1971, Christmas and 
Waller 1 973, May 1977, Courtney and Couch 1984). 

Salinity - Juveniles and Adults: Both adult and juvenile 
life stages are euryhaline, and have been found in 
waters with salinities of 0.0 to 76.1 %o (Gunter 1945, 
Gunter 1 950, Simmons 1 957, Reid 1 954, Hoese 1 960, 
Gunter, 1967, Franks 1970, Swingle 1971, Wang and 
Raney 1971, Christmas and Waller 1973, Wagner 
1973, Pineda 1975, Swift et al. 1977, Tatum et al. 
1978). 

Movements and Migrations : Reported movements have 
been associated with feeding. The gulf killifish moves 
onto marshes with flooding tides to feed, and returns on 
the outgoing tide to tidal streams (Harrington and 
Harrington 1961, Perschbacher and Strawn 1986, 
Perschbacher et al. 1990), and shoreline flats (Reid 
1 954). One study reports movement to deeper waters 
during cold weather (May 1977). 

Reproduction 

Mode : This species has separate male and female 
sexes (gonochoristic), and fertilization is external (Able 
and Hata 1984). 

Spawning : Spawning occurs in estuaries in shallow 
water among dense beds of marsh vegetation that are 
typically flooded only during the bi-weekly high tides 
(Simmons 1957, Harrington and Harrington 1961, 
Greeley and MacGregor 1 983). Eggs are deposited in 
clusters on submerged vegetation, plant roots, or on 
the substrate itself (Waas 1982). Spawning periods 
appear to be regulated primarily by temperature, with 
photoperiod, food availability, tides, and circadian 
mechanisms acting as indirect regulators (Tatum et al. 
1978, Waas 1982, MacGregor et al. 1983, Waas and 
Strawn 1 983, Hsiao and Meier 1 989). Spawning peaks 
have been reported in spring, summer, and fall. A shift 
in spawning season from early spring through summer 
in the northern and western Gulf to the cooler late fall 
through spring in south Florida is apparent with re- 
corded seasons in the study area being: April-Septem- 
ber in Corpus Christi Pass, Texas; March-June in 
Copano and Aransas marshes, Texas (Gunter 1945); 
April-May at Blackjack Peninsula, Texas (Gunter 1950); 
March-April and August-September in Trinity Bay, 


Texas (Waas 1982); March-September in Mississippi 
Sound, Alabama (MacGregor et al. 1 983); June-July in 
Mobile Delta, Alabama (Swingle 1 971 ); late fall through 
early spring in the Tampa Bay area (Springer and 
Woodburn 1 960); and April-September at Cedar Key, 
Florida (DeVlamingetal. 1978). Evidence also exists 
of bimodal and year round spawning in some areas 
(Gunter 1 945, Gunter 1 950, Kilby 1 955, Swingle 1 971 , 
Ruebsamen 1972, Christmas and Waller 1973, 
Subrahmanyam and Drake 1975, De Vlaming et al. 
1 978, Waas 1 982, Waas and Strawn 1 983). Spawning 
is apparently more prevalent in the evening than in the 
day (Tatum et al. 1978). 

Fecundity : Gulf killifish are fractional spawners and 
spawn many times per season (De Vlaming et al. 1 978, 
Waas 1 982, Waas and Strawn 1 983). Usually 1 to 20 
eggs are deposited per oviposition, but this species 
has been found to have the potential to produce as 
many as 1 200 eggs over a spawning season, with the 
number of eggs correlated with length of the female 
(Tatum 1978, Waas 1982, Waas and Strawn 1983). 
Frequency of spawning is unknown and so actual 
fecundity can not be determined, but one study con- 
ducted over a period of 1 65 days (March through mid- 
August) showed a daily deposition range of 0.01-1.18 
eggs for females averaging 9.6 g (Tatum et al. 1982). 
Other Fundulus species have been found to spawn 
almost daily (Waas 1982, Waas and Strawn 1983). 

Growth and Development 

Egg Size and Embryonic Development : All growth and 
development occurs within the estuary. Eggs are pale 
yellow translucent spheres with vacuoles concentrated 
at one pole. The color of fertilized eggs changes from 
yellow to gray as the embryos develop. Eggs are 
relatively large and range in size from 1 .0 to 2.1 mm in 
diameter, averaging approximately 2.0 mm (Tatum et 
al. 1978, Tatum et al. 1982, Waas 1982, Waas and 
Strawn 1983). Embryonic development is oviparous 
with egg hatching determined by incubation tempera- 
ture (Courtney and Couch 1984). Hatching has been 
observed at 9 to 1 4 days after fertilization at 26 to 31 °C 
and 30%o, 1 4 to 28 days at 1 2.5 to 33°C and 5 to 1 0%o, 
15 to 28 days at 12.5%o, and 21 days at 20°C (Hubbs 
and Drewry 1959, Ernst and Neff 1977, Tatum et al. 
1978, Tatum et al. 1982, Waas 1982, Courtney and 
Couch 1984). Moderate salinities do not appear to 
affect development and growth. Eggs may be able to 
withstand exposure to air, an adaptation to fluctuating 
water levels in coastal marshes (Loftus and Kushlan 
1987). 

Age and Size of Larvae : Little information is available 
on the age and size of gulf killifish larvae. 


178 


Gulf killifish, continued 


Juvenile Size Range : In a captive rearing study, fish 4 
to 6 weeks old had grown to an average weight of 0.1 
g in a temperature range of 1 2.5 to 33°C and salinities 
of 5 to 10%o (Tatum et al. 1978). After 52 days, these 
fish had reached a mean weight and total length of 2.0 
g (range: 0.8-7.2 g) and 56 mm (range: 40-84 mm). 
Temperatures during this period ranged from 22° to 
35.5°C, and salinity varied from 1 1 to 16%o. 

Age and Size of Adults : Field studies of gulf killifish 
show age class I fish range from 1 8 to 30 mm standard 
length (SL). Fish in class II average 68 mm SL and 
attain reproductive maturity during this time when they 
reach 40 to 50 mm total length (TL). Adults range in 
size from 40 to 141 mm TL and weigh up to 45.0 g. 
These fish survive into class III size, but rarely into 
class IV (Gunter 1945, Gunter 1950, Reid 1955, 
Simpson and Gunter 1 956, Renf ro 1 960, Springer and 
Woodburn 1960, Franks 1970, Swingle 1971, Christ- 
mas and Waller 1 973, Waas 1 982, Waas et al. 1 983). 
The gulf killifish is one of the largest species of Fundu- 
lus occurring in southern Florida coastal marshes 
(Loftus and Kushlan 1987). 

Food and Feeding 

Trophic Mode : Gulf killifish are opportunistic predators, 
but they can also feed omnivorously. Feeding is 
throughout the water column during daylight hours 
(Ruebsamen 1972, Tatum et al. 1982, Relyea 1983, 
Rozas and LaSalle 1 990). Young fish are detritivores, 
but become more carnivorous with increased age and 
size. 

Food Items : The diet of the gulf killifish varies with the 
habitat in which it is feeding (Rozas and LaSalle 1 990). 
Crustaceans and insects form a large portion of this 
fish's diet. Food items include: mosquitoes, isopods, 
amphipods, tanadaceans, pelecypods, gastropods, 
annelids, polychaetes, insects, fishes, crabs, larval 
grass shrimp, fiddler crabs, hermit crabs, detritus, 
substrate, vascular plant tissue, and some algae prob- 
ably as a consequence of amphipod grazing (Simpson 
and Gunter 1956, Springer and Woodburn 1960, 
Harrington and Harrington 1961, Odum 1971, 
Ruebsamen 1972, Subrahmanyam and Drake 1975, 
May 1977, Levine 1980, Relyea 1983, Perschbacher 
and Strawn 1986, Rozas and LaSalle 1990). 

Biological Interactions 

Predation : Predators include wading birds and larger 
piscivorous fishes (Jenni 1969, Perschbacher and 
Strawn 1986). 

Factors Influencing Populations : The incidence of para- 
sitism by Eimeria funduli (Protozoa: Eimeriidae) has 
been reported over a broad area of the range of the gulf 
killifish (Solangi and Ogle 1981). Although heavily 


infected fish can have 80 to 85% of both liver and 
pancreatic tissues replaced by E. funduli oocytes, the 
disease does not appear to cause mortality in infected 
fish maintained in the laboratory. Growth rate, how- 
ever, is considerably reduced, which could adversely 
affect the reproductive potential of local populations, 
and commercial production of this species for bait 
(Solangi and Ogle 1981). 

Personal communications 

Peterson, Mark S. Gulf Coast Research Lab., Ocean 
Springs, MS. 

Van Hoose, Mark S. Alabama Division of Marine 
Resources, Dauphin Island, AL. 

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180 


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182 


Silversides 


Menidia species 
Adult 


■yn^m?>^^l^^^^ 


^X^^^^^^Si 


2 cm 


(from Bigelow and Schroeder 1953) 


Common Name: silversides 

Scientific Name: Menidia species 

Other Common Names: inland silverside, tidewater 

silverside, Mississippi silverside, waxen silverside, 

glassy silverside, glassminnow, hardhead (Bigelow 

and Schroeder 1953, Massman 1954, Kilby 1955, 

Springer and Woodburn 1960, Hubbs et al. 1971, 

Middaugh et al. 1985, Robins et al. 1991). 

Classification (Robins et al. 1991) 

Phylum: Chordata 

Class: Osteichthyes 

Order: Perciformes 

Family: Atherinidae 

Two species of Men/'d/'acommonly occur in estuaries of 
the Gulf of Mexico: the inland silverside (M. beryllina), 
and the tidewater silverside (Menidia peninsulae) 
(Johnson 1975, Chernoff et al. 1981, Robins et al. 
1 991 ). These were not recognized as distinct species 
until fairly recently (Robins et al. 1980, Chernoff et al. 
1981). The formerly recognized inland freshwater 
species, M. audens, is now considered synonymous 
with M. beryllina (Lee et al. 1 980, Chernoff et al. 1 981 ). 
Other recognized species in the Gulf of Mexico region 
include the key silverside {M. conchorum) (Duggins et 
al. 1 977, Robins et al. 1 991 ), and Texas silverside (/W. 
clarkhubbsi) (Echelle and Mosier 1982, Robins et al. 
1 991 ). The Atlantic silverside (M. menidia) is found in 
estuaries of the U.S. east coast (Bigelow and Schroeder 
1 953, Nelson et al. 1 991 ), but not in the Gulf of Mexico 
(Leeetal. 1980). 

Menidia beryllina and M. peninsulae can be distin- 
guished by the morphology of the rearward extension 
of the swim bladder (Echelle and Echelle 1997). This 
structure is long and transparent in M. beryllina, short 


and opaque in M. peninsulae and intermediate in M. 
clarkhubbsi and hybrid individuals. These species can 
also be distinguished by the distance between the 
dorsal and anal fins relative to standard length (Chernoff 
et al. 1 981 , Middaugh and Hemmer 1 987a). 

The Menidia species were considered together in 
Volume /of this series (Nelson et al. 1 992) because of 
their ecological similarities, and because many pub- 
lished studies do not completely distinguish between 
them. In this life history summary, information on 
individual species is noted where their identity is known. 
Where species identity is uncertain, information is 
attributed to "Menidia", "Menidia species" or "silver- 
sides". 

Value 

Commercial : Silversides have little commercial value 
otherthan providing forage for commercially important 
fish, but they are reported to be delicious when properly 
cooked (Kendall 1902, Garwood 1968, Benson 1982, 
Ross pers. comm.). 

Recreational : Silversides are important forage for game 
fish, and are also sometimes used as bait (Simmons 
1957, Garwood 1968, Benson 1982, Hubbs 1982). 

Indicator : Eggs and larvae have been used to study the 
toxic effects of chlorine as a biocide (Morgan and 
Prince 1 977). Silversides are considered good indica- 
tors for oil pollution (Solangi 1 980) and have been used 
as bioassay organisms by the U.S. Environmental 
Protection Agency (EPA) (Poole 1978). 

Ecological : Silversides are among the most abundant 
nearshore surface fishes. They are secondary con- 


183 


Silversides, continued 


Table 5.24. Relative abundance of silversides 

(Menidia species) in 31 Gulf of Mexico estuaries 

(from Volume h. 

Life stage 


Estuary 


A S J L E 


Florida Bay 


• 


• 


• 


• 


• 


Ten Thousand Islands 


® 


® 


® 


® 


® 


Caloosahatchee River 


• 


• 


• 


• 


• 


Charlotte Harbor 


Tampa Bay 


• 


• 


• 


• 


• 


Suwannee River 


® 


® 


® 


® 


® 


Apalachee Bay 


• 


• 


• 


• 


• 


Apalachicola Bay 


• 


• 


• 


• 


• 


St. Andrew Bay 


® 


® 


® 


® 


® 


Choctawhatchee Bay 


® 


® 


® 


® 


® 


Pensacola Bay 


r ® 


® 


® 


® 


® 


Perdido Bay 


® 


® 


® 


® 


® 


Mobile Bay 


® 


® 


® 


® 


® 


Mississippi Sound 


• 


• 


® 


o 


Lake Borgne 


® 


® 


® 


® 


® 


Lake Pontchartrain 


® 


® 


® 


® 


® 


Breton/Chandeleur Sounds 


o 


o 


o 


o 


o 


Mississippi River 


® 


® 


® 


® 


® 


Barataria Ba} 


® 


® 


• 


® 


® 


Terrebonne/Timbalier Bays 


® 


® 


® 


® 


® 


Atchafalaya/Vermilion Bays 


® 


o 


® 


o 


o 


Calcasieu Lake 


® 


® 


® 


® 


® 


Sabine Lake 


® 


® 


® 


® 


® 


Galveston Bay 


® 


® 


® 


® 


® 


Brazos River 


® 


® 


® 


® 


® 


Matagorda Bay 


® 


® 


® 


® 


® 


San Antonio Bay 


® 


® 


® 


® 


® 


Aransas Bay 


® 


® 


® 


® 


® 


Corpus Christi Bay 


® 


® 


® 


® 


® 


Laguna Madre 


• 


• 


• 


• 


• 


Baffin Bay 


A S J L E 


Relative abundance: 

9 Highly abundant 
® Abundant 
O Common 
V Rare 
blank Not present 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


sumers, and are important forage fishes for top carni- 
vores in the nearshore area (Simmons 1957, Hellier 
1 962, Garwood 1 968, Shipp 1 979, Hubbs 1 982, Benson 
1982, Shipp 1986). They are considered useful as 
biological control agents of mosquitoes and gnats 
(Hubbs et al. 1 971 , Middaugh et al. 1 985). 

Range 

Overall : The range of Menidia beryllina extends from 
Quincy, Massachusetts to Vera Cruz, Mexico along the 
coast and in estuaries, bays and sounds, and in fresh- 
water rivers and impoundments. In inland waters, they 
are found from the Mississippi Valley to Reelfoot Lake, 
Tennessee, and the Red and Arkansas River drain- 
ages in Oklahoma. M. beryllina has been introduced 
and established in reservoirs in Texas and California 
(Tilton and White 1964, Martin and Drewry 1978, Lee 
et al. 1980, Middaugh et al. 1985). M. peninsulae 
occurs from the east coast of Florida to eastern Mexico, 
in moderate to high salinity estuarine and coastal 
waters (Johnson 1975). 

Within Study Area : Within U.S. Gulf of Mexico estuar- 
ies, Menidia beryllinaoccurs from Florida Bay, Florida 
to the Rio Grande, Texas. They are ubiquitous resi- 
dents of shallow estuarine waters (Tilton and White 
1964, Christmas and Waller 1973, Martin and Drewry 
1 978, Middaugh et al. 1 985) (Table 5.24). M. peninsulae 
has a disjunct distribution in estuaries of the Gulf of 
Mexico, from Florida to Mississippi, and Texas to 
Mexico, apparently absent from the lower salinity es- 
tuarine waters of Lousiana (Johnson 1 975, Chernoff et 
al. 1 981 , Middaugh and Hemmer 1 984, Middaugh and 
Hemmer 1987a). The unisexual M. clarkhubbsi com- 
plex has been described from estuarine waters of 
Texas (Echelle and Mosier 1982), and is reported to 
occur from Texas to Alabama (Echelle et al. 1989b). 
The key silverside, M. conchorum, is endemic to the 
Florida Keys (Duggins et al. 1977). 

Life Mode 

Menidia eggs are demersal. Larvae, juveniles, and 
adults are nektonic and pelagic, and form schools 
(Hildebrand 1922, Kilby 1955, Chambers and Sparks 
1959, Arnold et al. 1960, Martin and Drewry 1978, 
Wurtsbaugh and Li 1985). All stages have diurnal 
activity, although one Florida study reports feeding 
occurring primarily at night (Darnell 1 958, Zimmerman 
1969, Odum 1971, Ruebsamen 1972, Krull 1976, 
Middaugh et al. 1985, Wurtsbaugh and Li 1985). 

Habitat 

Type : Silversides are resident species in estuaries 
(Wagner 1973). Most specimens are typically col- 
lected in the top 30-45 cm of the water column and near 
vegetated shorelines (Kilby 1 955, Breuer 1 957, Darnell 
1958, Hoese 1965, Wilson and Hubbs 1972, Wagner 


184 


Silversides, continued 


1973, Benson 1982). Habitats include lagoons, estu- 
aries, bays, marshes, beach passes, ponds, rivers, 
canals, and lakes (Gunter 1945, Bailey et al. 1954, 
Gunter 1958, Arnold etal.1 960, SpringerandWoodburn 
1960, Hellier 1962, Tilton and White 1964, Hoese 
1965, Parker 1965, Perret et al. 1971, Wilson and 
Hubbs 1972, Christmas and Waller 1973, Wagner 
1973, Cornelius 1984, Loftus and Kushlan 1987). 
Habitat partitioning among/W. beryllina, M. peninsulae, 
and M. clarkhubbsi has been noted in a study in 
Copano Bay, Texas (Echelle and Echelle 1997). M. 
peninsulaewere found primarily in seaward bays and 
connected tidal pools with mesohaline, polyhaline, and 
euhaline salinities. M. beryllina were predominant in 
freshwater streams and bays, isolated pools, and tidal 
creeks with limnetic, oligohaline, and mesohaline sa- 
linities. Both species, their hybrids, and/W. clarkhubbsi 
co-occured in shallow bays and tidal pools with 
mesohaline salinities. 

Substrate : Little preference for bottom type has been 
demonstrated for Menidia species, with collections 
made over sand, mud, shell, clay, clay-shell, clay- 
sand, and silt-clay (Simmons 1 957, Hoese and Jones 
1 963, Swingle 1 971 , Benson 1 982). One report does 
state abundances are greatest over bottoms with a 
high sand content and low percentage of organics. 
Silversides are particularly common near inundated 
terrestrial plants and aquatic vegetation such as 
Thalassia (Hildebrand 1922, Kilby 1955, Hoese and 
Jones 1963, Zimmerman 1969, Franks 1970, Fisher 
1 973, Swingle and Bland 1 974), and are often associ- 
ated with some sort of structure such as islands, piers, 
and oyster reefs (Benson 1982). 

Physical/Chemical Characteristics : Menidia species 
are considered to be eurythermal and euryhaline 
(Gunter 1 956, Renf ro 1 960, Franks 1 970, Middaugh et 
al. 1985), but temperature and salinity are factors 
affecting their distribution (Kilby 1955, Renfro 1960, 
Springer and Woodburn 1960, Swingle 1971). In 
general, M. beryllina is considered to be most abun- 
dant at salinities <19%o, whereas M. peninsulae is 
found primarily at >15%o (Middaugh et al. 1986). 


Hubbs etal. 1971, Bengtson 1985). 

Temperature - Juveniles: Juvenile Menidia have been 
collected in the wild from 5.0° to 33°C (Garwood 1 968, 
Franks 1970, Perret et al. 1971, Pineda 1975, Bonin 
1 977). Peaks in numbers have been reported at 26.5° 
and 21.8°C (Bonin 1977). In one study in Mississippi 
Sound, temperature ranges in which different juvenile 
Menidia size classes were found are: 26.4° to 28.4°C 
for fish whose total length (TL) was 1 4 to 22 mm; 21 .0° 
to 31 .8°C for 23 to 36 mm TL; and 21 .0° to 32.5°C for 
40 to 44 mm TL (Garwood 1968). 

Temperature - Adults: Adult Menidia sampled in Gulf of 
Mexico estuaries have been found from 5.0°C to 34.9°C 
(Chambers and Sparks 1959, Renfro 1960, Franks 
1970, Perret et al. 1971, Christmas and Waller 1973, 
Perret and Caillouet 1974, Pineda 1975, Tarver and 
Savoie 1 976, Barrett et al. 1 978, Middaugh et al. 1 985) 

Salinity - Eggs: Eggs of Menidia species have been 
observed in the field at salinities ranging from 0.0 to 
31.5%o (Fisher 1973, Garwood 1968, Hubbs et al. 
1 971 ). One laboratory study of M. beryllina (reported 
as M. audens) from Lake Texoma, a freshwater reser- 
voir, noted salinity affecting temperature tolerance 
limits of eggs: no survival at 100% seawater (33%o); 
normal range of 1 7° to 33°C at 25% seawater; 1 9° to 
33° at 50% seawater; and only 22° to 31 .3°C at 75% 
seawater (Hubbs et al. 1971). In other words, M. 
beryllina eggs become more stenothermal as salinity 
increases. Middaugh et al. (1986) collected adult 
Menidia from northwest Florida, and compared the 
survival of M. beryllina and M. peninsulae embryos 
incubated at an array of salinities. M. beryllina were 
euryhaline, with 73-78% survival at 5, 1 5, and 30%o. M. 
peninsulae embryos had 90% hatch at 5%o, but only 
65% hatch at 30%o, suggesting that it is the less 
euryhaline species at this life stage. 

Salinity- Larvae: The recorded salinity range for/Wen/d/'a 
larvae is 0.0 to 30%o, with higher concentrations of 
larval M. beryllinaoccumng at 2 to 8%o (Garwood 1 968, 
Martin and Drewry 1978, Bengtson 1985). 


Temperature - Eggs: Eggs of Menidia beryllina have 
been observed to develop from 13.2° to 34.2°C 
(Hildebrand 1922, Garwood 1968, Hubbs et al. 1971, 
Fisher 1 973, Hubbs 1 982, Middaugh et al. 1 985). High 
survival was recorded from 17.0° to 33.5°C and opti- 
mum survival occurred from 20.0° to 25.0°C. Upper 
lethal limit for eggs is about 35.0°C (Hubbs et al. 1 971 ). 

Temperature - Larvae: Larvae of Menidia beryllina 
have been raised under laboratory conditions and 
collected in the field over a temperature range of 21 ° + 
1°C to 30° ± 1° (Hildebrand 1922, Garwood 1968, 


Salinity - Juveniles: Juvenile Menidia have been col- 
lected in the wild from 0.0 to 34.5%o salinity (Gunter 
1945, Gunter 1950, Garwood 1968, Franks 1970, 
Pineda 1 975, Bonin 1 977, Martin and Drewry 1 978). In 
Mississippi Sound, juvenile Menidia are reported to 
occur by size class in the following salinities: 3.3 to 
1 9.4% for fish 1 4 to 22 mm TL; 2.2 to 23.8%o for 23 to 
36 mm TL; and 2.2 to 28.3%o for 40 to 47 mm TL 
(Garwood 1968). 

Salinity - Adults: Adult Menidia are reported to be 
abundant up to 45%o (Simmons 1957), and present in 


185 


Silversides, continued 


collections made in hypersaline conditions at 120% o 
(Copeland 1 967). They have been collected in waters 
with to 120%, salinity (Gunter 1945, Gunter 1950, 
Simmons 1957, Renfro 1960, Copeland 1967, Franks 
1 970, Perret et al. 1 971 , Swingle 1 971 , Christmas and 
Waller 1973, Perret and Caillouet 1974, Swingle and 
Bland 1974, Pineda 1975, Tarver and Savoie 1976, 
Barrett et al. 1 978, Cornelius 1 984). Reported salinity 
ranges of occurrence include 5.0 to 9.9%o (Tarver and 
Savoie 1 976); 0.0 to 4.9%o and 1 5.0 to 1 9.9%o (Swingle 
1 971); 10.0 to 24.9%o(Perretetal. 1971); 21.0 to 30.0%o 
(Cornelius 1 984); and 22.5%o or higher (Franks 1 970). 
However, these historical reports of disparate salinity 
ranges are probably due to different habitat affinities 
among the now-recognized Menidia species. M. 
beryllina is considered to be the more euryhaline 
species, occurring from fresh to marine salinities, 
whereas M. peninsulae is found primarily from estua- 
rine to marine salinties (Echelle and Mosier 1982). In 
a study of Copano Bay, Texas, M. peninsulae was 
predominant in seaward bays and connected tidal 
pools (salinity range 13.5-32.5%o, mean 18.9%o). M. 
beryllinawere predominant in freshwater streams and 
bays (salinity range 0.1-2.3% o , mean 0.8% o ), isolated 
pools (salinity range 2.3-20%o, mean 7.5%o), and tidal 
creeks (salinity range 3.5-7. 8%o, mean 5.1%o). Both 
species, their hybrids, and M. clarkhubbsi co-occured 
in shallow bays and tidal pools (salinity range 6.0- 
18.5%o, mean 11.4%„) (Echelle and Echelle 1997). 

Dissolved Oxygen and pH : M. beryllina can tolerate 
dissolved oxygen (DO) concentrations as low as 1.7 
parts per million (ppm) (Middaugh et al. 1 985), but have 
also been collected at 9.5 and 1 1 .0 ppm DO (Barrett et 
. al. 1 978). Collections have been made in a pH range 
of 7.2 to 9.4 (Middaugh et al. 1985). 

Movements and Migrations : Silversides are non-mi- 
gratory estuarine residents (Benson 1982, Middaugh 
et al. 1 985). Diel inshore and offshore movements are 
probably related to predator avoidance and feeding 
(Darnell 1958, Krull 1976, Wurtsbaugh and Li 1985). 
As juveniles grow, they are reported to move into 
shallower waters (Darnell 1958). 

Reproduction 

Mode : Spawning of Menidia species is by external 
fertilization of broadcast milt and roe, and egg develop- 
ment is oviparous (Fisher 1 973). Sexes of M. beryllina 
and M. peninsulae are separate (gonochoristic), but 
sex ratios in these species may be skewed in response 
to environmental conditions. In a study near Santa 
Rosa Isiand, Florida, M. peninsulae spawned during 
cool conditions (14.1-24.2°C) February through April 
were 70-94% female, whereas those spawned during 
warm conditions later in the year were 35-60% female 
(Middaugh and Hemmer 1987b, Echelle and Echelle 


1 997). This temperature-dependent expression of sex 
may be a reproductive adaptation to favor growth of 
females during optimum conditions, and allow matura- 
tion within a year (Middaugh and Hemmer 1987b). 
Small populations of a unisexual all-female gynoge- 
netic species complex (M. clarkhubbsi) have been 
described from Texas (Echelle and Mosier 1982). 
These fish produce diploid eggs without genetic re- 
combination, and embryonic development is initiated 
by spawning with one of the bisexual Menidia species, 
without genetic contribution from the sperm. The 
resulting progeny are clones of the parental M. 
clarkhubbsi individual. This "species" may have origi- 
nated from hybrids between M. beryllina and a now- 
extinct progenitor species similar to M. peninsulae 
(Echelle and Echelle 1 997). M. beryllinaxM. peninsulae 
hybrids are known to occur in low frequency in waters 
where the two species are sympatric, with habitat 
affinities intermediate to the two parental species. 
Hermaphroditic individuals have also been reported 
(Yan1984). 

Spawning : Spawning of Menidia beryllina (reported as 
M. audens) occurs during the day in the late morning 
(Hubbs et al. 1 971 ), and takes place in Gulf of Mexico 
estuaries in spring and fall as a bimodal peak. Occa- 
sional spawning throughout the year has also been 
reported. Ripe adults usually appear by March, but 
sometimes as early as February, and are collected 
throughout the year in some areas. Seasonal peaks 
usually occur in May to June and September to Janu- 
ary (Hildebrand 1922, Gunter 1945, Gunter 1950, 
Simmons 1957, Hellier 1962, Hoese 1965, Garwood 
1968, Swingle 1971, Ruebsamen 1972, Christmas 
and Waller 1 973, Wagner 1 973, Gallaway and Strawn 
1974, Swingle and Bland 1974, Pineda 1975, Hubbs 
1982). Salinity has little effect on spawning condition 
of M. beryllina, which is probably triggered instead by 
rising temperatures or possibly changes in water levels 
(Hoese 1965, Garwood 1968, Hubbs 1982, Middaugh 
et al. 1985). Evidence of spawning was found over a 
salinity range of 3.6 to 31 .5%o and a temperature range 
of 15.0° to 32.7°C, but slowed or ceased at 30.0°C 
(Garwood 1 968, Hubbs 1 982, Middaugh 1 985). Spawn- 
ing of M. beryllina is probably most prevalent in tidal 
freshwater or brackish water in the upper parts of 
estuaries (Martin and Drewry 1978), and occurs in 
shallow waters with gently sloping bottoms having an 
abundance of rooted aquatic and/or inundated terres- 
trial plants, tree roots, and dead leaves (Hildebrand 
1922, Wilson and Hubbs 1972, Fisher 1973). It has 
also been reported in a low to medium salinity tidal pass 
in Louisiana (Sabins and Truesdale 1974). M. 
peninsulaeis primarily a nocturnal spawner, and peak 
spawning activity coincides with interruptions in cur- 
rent velocity (Middaugh and Hemmer 1 984). In a study 
near Santa Rosa Island, Florida, spawning activity of 


186 


Silversides, continued 


M. peninsulae extended from February to July, with 
peaks March through June, at temperatures 16.7 to 
30.8°C (Middaugh and Hemmer 1987a). Spawning 
activity peaked during "equatorial tides", when tidal 
height and current were at their minima, possibly an 
adaptation to enhance fertilization success. Spawning 
occurred in shallow water, 10 - 60 cm deep, and 
spawned eggs adhered to the red algae Ceramium 
byssoideumover rocky substrate (Middaugh and Hem- 
mer 1987a). 

Fecundity : Silversides are fractional spawners that 
spawn several times per season, and sometimes all 
year (Hildebrand 1922, Hellier 1962, Fisher 1973). 
Female Menidia beryllina in one study deposited 1 to 
20 eggs in a single spawning pass, and were not 
observed to repeatedly broadcast eggs. Females 
stripped of ripe eggs yielded 10 to 200 eggs per 
individual (Fisher 1 973). Fecundity is size dependent, 
with average sized females (standard length (SL) 75 
mm) producing approximately 835 eggs daily, large 
females about 2000 eggs, and small females about 
200 eggs. Over a spawning period of 91 to 1 22 days, 
an average sized M. beryllina female has the capacity 
to produce 75,985 to 101,879 eggs, a large female 
1 32,860 to 1 78,21 eggs, and a small female 45,000 to 
61 ,000 eggs (Hubbs 1 982). Spawners are usually age 
class-1 fish, but class-0 fish have been found to spawn 
occasionally (Fisher 1973, Hubbs 1982). 

Growth and Development 

Egg Size and Embryonic Development Eggs of Menidia 
beryllina are demersal with gelatinous threads that 
attach to vegetation, other objects, and to each other 
on or near bottom (Hildebrand 1 922, Martin and Drewry 
1 978). They have a clear yellowish appearance with a 
large oil globule occupying a central position and 
variously distributed smaller globules ranging from a 
few to several (Hildebrand 1922, Hubbs 1982). The 
chorion has a tuft of 4 to 9 adhesive filaments one of 
which is enlarged and much longer than the others, 
about 30 to 50 mm in total length. Eggs are not quite 
spherical when first spawned and range about 0.75 to 
1.0 mm in diameter (Hildebrand 1922, Martin and 
Drewry 1 978). Cleavage is meroblastic and equal with 
the second cleavage at right angles to the first (Martin 
and Drewry 1978). Hatching occurs in 10 days at 
27.5°C and 5 days in warmer temperatures (Hubbs et 
al. 1971, Hubbs 1982). Larvae are present through the 
spring, and in summer and fall months (Martin and 
Drewry 1978). 

Age and Size of Larvae : Menidia beryllina larvae are 
about 3.5-4.0 mm TL at hatching (Hildebrand 1922, 
Martin and Drewry 1 978). They have an oval yolk sac 
with a single oil globule in the anterior end. In a 
laboratory feeding experiment, yolk depletion and star- 


vation occurred in 3 to 4 days at 30°C, and 2 to 3 days 
at 1 5°C (Hubbs et al. 1 971 , Martin and Drewry 1 978). 
The body is elongate and slender with an extremely 
short gut and an anus about 1 /4 of way from tip of snout 
to rear of caudal finfold (Martin and Drewry 1978). 
They are highly transparent with 3 to 1 1 melanophores 
on the dorsal surface of the head, and a cluster above 
the gut and dorsal surface of the yolk. At 7.8 mm TL, 
about 15 caudal rays and 8 anal ray bases become 
visible. The first dorsal fin is rudimentary and other 
median fins have a full complement of rays tending 
toward the adult fin shape. The pelvic fins are formed. 
Larvae are aggregating by 8 to 1 mm TL, and school- 
ing by 1 1 to 1 2 mm TL. The first dorsal fin is formed by 
11 to 1 2 mm TL(Martin and Drewry 1 978). The end of 
this stage is at about 11 to 1 2 mm TL (Garwood 1 968, 
Martin and Drewry 1978). 

Juvenile Size Range : In Mississippi Sound, the size 
range for juvenile stage Menidia is about 1 2 to 49 mm 
TL (Garwood 1 968). Length-frequency data are unre- 
liable for a growth estimate, but one study of Menidia in 
Tampa Bay indicated 5-7 mm per month from June to 
November, and that early-spawned juveniles grew 
about 8 mm SL per month from June to September. 
Lengths of 75 to 85 mm SL were achieved after 1 year 
of growth (Springer and Woodburn 1960). Winter cold 
evidently inhibits growth (Martin and Drewry 1978). 

Age and Size of Adults : Silversides may reach sexual 
maturity by 45 mm TL or 33 mm SL (Hellier 1962, 
Garwood 1968, Martin and Drewry 1978). Males are 
smaller than females with average sizes of 50.9 and 
55.0 mm TL for males and 59.5 and 61 .0 mm TL for 
females being reported (Hildebrand 1 922, Gunter 1 945). 
Maturity is usually reached by 1 year, but sometimes as 
early as 5 months (Martin and Drewry 1978, Hubbs 
1982). Weight ranges from 0.1 to 7.5 g for fish 15 to 87 
mm SL with a 95 mm TL fish weighing 1 1 .4 g and a 55 
mm TL fish weighing 2.84 g (Franks 1 970, Barrett et al. 
1978). The largest reported size is 125 mm TL 
(Simmons 1 957). The life span Menidia is usually one 
year, with some survivals to 2 years (Gunter 1945, 
Martin and Drewry 1978, Hubbs 1982). Total length 
(TL) can be estimated from standard length (SL) for 
silversides by multiplying SL by 1.2 (Hubbs 1982). 

Food and Feeding 

Trophic Mode : Silversides are carnivorous, secondary 
consumers feeding mainly during daylight hours espe- 
cially in the early morning with some additional after- 
noon feeding by adults (Darnell 1 958, Middaugh et al. 
1 985, Wurtsbaugh and Li 1 985). One study of Menidia 
beryllina in Louisiana reports equal feeding intensity 
both day and night (Ruebsamen 1 972). M. peninsulae 
are reported to feed primarily during the day (Middaugh 
and Hemmer 1984). Trophic partitioning between 


187 


Silversides, continued 


Menidia species has been noted (Lee et al. 1980, 
Bengtson 1984, Bengtson 1985). 

Food Items : Various larval and adult crustaceans are 
the predominant food items of Menidia (Odum 1971, 
Levine 1980). Silversides less than 16 mm SL feed 
primarily on the larval stages of copepods and other 
crustaceans (Odum 1971). Larval M. beryllina have 
been successfully reared on/4rtem/anauplii, nutrition- 
ally similar to known natural foods such as the copepod 
Acartia (Bengtson 1985). Juveniles 15 to 42 mm SL 
are known to feed on mollusc veliger larvae. Detritus 
is a major item in small size classes, but is fairly 
common in larger ones as well, although declining in 
importance (Darnell 1958, Ruebsamen 1972, Carrand 
Adams 1 973, Diener et al. 1 974). Detritus is probably 
obtained as suspended material rather than from the 
benthos (Carr and Adams 1 973). Isopods and amphi- 
pods form the bulk of food in all size classes with 
isopods and veligers declining in fish larger than 40 to 
54 mm TL to be replaced by insects, especially chi- 
ronomid larvae, pupae and adults (Darnell 1 958, Levine 
1980). Larger fish also consume more megalops 
larvae, copepods, and mysids than smaller size classes 
(Carr and Adams 1 973). Schizopods are consumed by 
all size classes, but mainly by intermediate size fish. 
Fish form a small but significant diet item (Levine 
1 980). Fish prey include bay anchovy, gulf menhaden, 
silversides, and gulf pipefish (Syngnathus scovelll). 
Miscellaneous items consumed include sand, filamen- 
tous algae, vascular plant material, rotifers, annelids, 
ostracods, arachnids, eggs, cysts, and fish remains 
(Darnell 1958, Ruebsamen 1972, Levine 1980). 

Biological Interactions 

Predation : Silversides are important forage fishes for 
many commercial and recreational fishes and othertop 
trophic level carnivores (Simmons 1957, Garwood 
1968, Hubbs 1982). Reported predators include gar 
(Lep/sosfeL/sspecies), catfish (/cfa/urusspecies), hard- 
head catfish, silversides, spotted seatrout, red drum, 
white bass (Morone chrysops), largemouth bass 
(Micropterus salmoides), and crappie (Pomoxis spe- 
cies) (Simmons 1957, Darnell 1958, Garwood 1968, 
Hubbs et al. 1971, Diener et al. 1974, Hubbs 1982, 
Rozas and Hackney 1984, Wurtsbaugh and Li 1985). 
Near Santa Rosa Island, Florida, pinfish have -been 
reported to prey on newly-spawned eggs of M. 
peninsulae adhering to red algae (Middaugh and Hem- 
mer 1987a). 

Factors Influencing Populations : Hybridization be- 
tween Menidia peninsulae and M. menidia has been 
reported in northeastern Florida (Johnson 1975), and 
hybridization between M. beryllina and M. peninsulae 
is known to occur in Texas estuaries (Echelle and 
Echelle 1 997). The clonal lineages of the/W. clarkhubbsi 


complex may be ephemeral, because of lack of genetic 
variation and recombination, accumulation of deleteri- 
ous alleles, and inability to adapt to changing environ- 
mental conditions (Echelle and Echelle 1997). How- 
ever, this asexual life history strategy provides a short- 
term reproductive advantage, and enables utilization 
of intermediate habitats. Trophic competition and 
partitioning has been demonstrated between M. 
menidia and M. beryllina in Rhode Island estuaries. 
The later spawning time and slower growth rate of M. 
beryllina may be an adaptation to the lower zooplank- 
ton abundance later in the season (Bengtson 1984, 
Bengtson 1985). However, in situ experiments in 
Rhode Island suggest that the size-specific survival of 
M. beryllina larvae may depend more on the suite of 
predators present than on a limited zooplankton forage 
base (Gleason and Bengtson 1996). The key silver- 
side (M. conchorum) is being considered as a candi- 
date species under the federal Endangered Species 
Act because of its rare status (NMFS 1997, Jordan 
pers. comm.). 

Personal communications 

Jordan, Terry. NOAA National Marine Fisheries Ser- 
vice, Silver Spring, MD. 

Ross, Stephen T. University of Southern Mississippi, 
Hattiesburg, MS. 

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189 


Silversides, continued 


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192 


Common snook 


Centropomus undecimalis 
Adult 


10 cm 


(from Fischer 1978) 


Scientific Name: Centropomus undecimalis 

Common Name: common snook 

Other Common Names: gulf pike, salt water pike, 

linesider, snook robalo (Higgins and Lord 1 926, Hoese 

and Moore 1977, Rivas 1986); crossie blanc (French), 

robalo comun, robalo bianco (Spanish) (Fischer 1 978, 

NOAA1985). 

Classification (Robins et al. 1991) 

Phylum: Chordata 

Class: Osteichthyes 

Order: Perciformes 

Family: Centropomidae 

Value 

Commercial : The common snook is harvested through- 
out much of its range (Hildebrand 1 958, Tucker 1 986). 
In the U.S., it was caught commercially on a small scale 
in Texas and Florida at one time, but declining numbers 
led to a ban on commercial landings in Florida in 1 958, 
and to its virtual disappearance in Texas with the last 
commercially landed fish reported there in 1 961 (Higgins 
and Lord 1926, Baughman 1943, Hildebrand 1958, 
Marshall 1 958, Volpe 1 959, Tucker 1 986, Matlock and 
Osburn 1987). It is caught and sold mostly fresh in 
Mexico, Central and South America, and in the Carib- 
bean (Fischer 1 977). Harvest is by gill nets, cast nets, 
and hook and line. The common snook is also consid- 
ered a possible mariculture species (Roberts 1990). 

Recreational : This is a popular gamefish, putting up 
spectacular fights as well as being good eating 
(Baughman 1943, Marshall 1958, Volpe 1959, Martin 
and Shipp 1 971 , Ager et al. 1 976, Hoese and Moore 
1 977, Tucker et al. 1 985, Tucker 1 986). The common 
snook readily accepts natural or artificial bait on hook 
and line, and is also caught by spearing (Marshall 


1 958, Ager et al. 1 976). Population declines since the 
1930's have resulted in reduced catches by anglers 
along the Gulf coast (Hildebrand 1958, Seaman and 
Collins 1 983, Tucker 1 986, Matlock and Osburn 1 987). 
This decline has resulted in it being classified as a 
species of special concern by the state of Florida 
(Tucker 1986, Johnson 1987). The Florida Depart- 
ment of Natural Resources maintains a closed season 
on snook during both the winter and summer months, 
a bag limit, and a minimum size limit to relieve fishing 
pressure (Seaman and Collins 1983, Kunneke and 
Palik 1984, NOAA 1985). All species of Centropomus 
are covered by the Florida regulations (Taylor pers. 
comm.). In Texas, recreational catches of snook 
decreased considerably from the 1940's through the 
1960's. Catches of snook along the Texas coast 
currently represent less than 0.1% of the recreational 
landings (Matlock and Osburn 1 987). Texas maintains 
size limits and bag limits for snook (TPWD 1993). 

Indicatorof Environmental Stress : Reductions in snook 
populations may be due in part to environmental alter- 
ation and degradation, reduced freshwater discharge 
to estuaries, sewage and industrial pollution, and in- 
secticides (Marshall 1958, Killam et al. 1992). 

Ecological : The common snook is considered a high 
trophic level carnivore, preying mostly on fish (Springer 
and Woodburn 1 960, Harrington and Harrington 1 961 , 
Shafland and Koehl 1979). 

Range 

Overall : The common snook is distributed in tropical 
and subtropical waters from North Carolina to as far 
south as Rio de Janeiro, Brazil (Marshall 1958, Rivas 
1962, Lee et al. 1980, Seaman and Collins 1983). It 


193 


Common snook, continued 


Table 5.25. Relative abundance of common snook 
in 31 Gulf of Mexico estuaries (Nelson et al. 1992, 
Taylor pers.comm.). ^^ 


Estuary 


A S J L E 


Florida Bay 


O 


o 


Ten Thousand Islands 


® 


® 


® 


V 


V 


Caloosahatchee River 


O 


® 


o 


Charlotte Harbor 


® 


O 


® 


V 


V 


Tampa Bay 


® 


® 


o 


V 


V 


Suwannee River 


V 


Apalachee Bay 


V 


Apalachicola Bay 


V 


St. Andrew Bay 


V 


Choctawhatchee Bay 


V 


Pensacola Bay 


V 


Perdido Bay 


Mobile Bay 


Mississippi Sound 


Lake Borgne 


Lake Pontchartrain 


Breton/Chandeleur Sounds 


Mississippi River 


Barataria Bay 


V 


Terrebonne/Timbalier Bays 


Atchafalaya/Vermilion Bays 


Calcasieu Lake 


Sabine Lake 


Galveston Bay 


V 


V 


Brazos River 


Matagorda Bay 


V 


V 


San Antonio Bay 


Aransas Bay 


V 


V 


V 


V 


V 


Corpus Christi Bay 


V 


V 


V 


V 


V 


Laguna Madre 


V 


V 


o 


V 


V 


Baffin Bay 


A S J L E 


Relative abundance: 

Highly abundant 
® Abundant 
O Common 
V Rare 
blank Not present 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


occurs along the eastern coast of central America, 
throughout the Caribbean, along the Gulf coast from 
Mexico to Port Aransas, Texas, and along peninsular 
Florida from Pensacola Bay to the Mosquito Lagoon 
area and the St. Johns River (Table 1) (Lunz 1953, 
Marshall 1958, Yerger 1961, Linton and Rickards 
1965, Merriner et al. 1970, Martin and Shipp 1971, 
Dahlberg 1 972, Cooley 1 974, Ager et al. 1 976, Hoese 
and Moore 1 977, Tucker 1 986). Centers of abundance 
occur in the Caribbean, southwestern Gulf of Mexico, 
and mangrove belts of southern Florida (Odum 1971, 
Gilmore et al. 1 983, Tucker 1 986). Mitochondrial DNA 
analyses indicate that Caribbean stocks are distinct 
from Florida stocks (Tringali and Bert 1996). 

Within Study Area : The common snook is relatively 
common along the west coast of Florida as far north as 
the Homosassa River area (Table 5.25). It is found only 
occasionally along the northern coast of the Gulf of 
Mexico (Cooley 1 974). In Texas, it is only abundant in 
the lower Laguna Madre, and is rarely found north of 
Port Aransas (Baughman 1 943, Cooley 1 974, Matlock 
and Osburn 1987). There is one report of a single 
juvenile captured off Grand Terre Island, Louisiana 
(Guillory et al. 1985). Mitochondrial DNA analyses 
indicate that Caribbean stocks are distinct from Florida 
stocks (Tringali and Bert 1996). Mitochondrial DNA 
analyses indicate that snook from the Atlantic and Gulf 
coasts of Florida comprise distinct stocks, and may 
therefore warrant consideration as separate manage- 
ment units (Tringali and Bert 1996). 

Life Mode 

Eggs and early larvae are pelagic and planktonic (Ager 
et al. 1976, Tucker 1986). As snook mature into 
juveniles and adults they become pelagic and nektonic 
(NOAA 1 985). Juveniles and adults are usually found 
in schools (Bruger 1 981 , Tucker 1 986). All life stages 
exhibit diurnal activity. 

Habitat 

Ty pe: This fish is considered to be estuarine depen- 
dent (Tolley et al. 1 987). Eggs and larvae are found in 
the shallow open waters of river mouths, beach inlets 
and passes, and estuarine passes in polyhaline to 
euhaline salinities (Volpe 1959, Linton and Rickards 
1 965, Moe 1 972, Ager et al. 1 976, Shafland and Koehl 
1979, Lau and Shafland 1982, Tucker 1986). They 
have been raised in the laboratory in euhaline salini- 
ties, but can survive and develop in freshwater by 14 
days after hatching (Shafland and Koehl 1 979, Lau and 
Shafland 1982, Tucker 1986). Larvae probably hatch 
in shallow open waters off beaches, inlets, and passes, 
and make their way inshore to estuarine nursery grounds 
(Linton and Rickards 1965). Larvae have been col- 
lected in the summer in Naples Bay, Florida, associ- 
ated with the bottom, which may allow them to take 


194 


Common snook, continued 


advantage of two-layered circulation as the mecha- 
nism for transport into the upper reaches of estuaries 
(Tolleyetal. 1987). 

Juvenile snook inhabit neritic and estuarine areas. 
They prefer protected bodies of water, usually of small 
surface area and shallow water depth, when small 
(Springer and Woodburn 1960), and seagrass beds 
when larger (Gilmore et al. 1983). Shoreline vegeta- 
tion is also considered a possible important element as 
juveniles also occur in areas with vegetation otherthan 
seagrass (McMichael et al. 1989). They have been 
collected in ditches, tidal pools, headwaters of creeks, 
ponds, bays, and shorelines in freshwater to euhaline 
salinities in water depths from 0.3 to 1 .2 m (Lunz 1 953, 
Marshall 1958, Springer and Woodburn 1960, Tabb 
and Manning 1 961 , Gunter and Hall 1 965, Linton and 
Rickards 1 965, Merriner et al. 1 970, Martin and Shipp 
1 971 , Breuer 1 972, Dahlberg 1 972, Fore and Schmidt 
1973, Ager et al. 1976, Hoese and Moore 1977, 
McMichael et al. 1 989). In southwest Florida, Fore and 
Schmidt (1973) reported that primary nursery areas 
were brackish, shallow, warm tidal streams and dredged 
canals with slow currents, soft bottoms, and little sub- 
merged vegetation, but often with shoreline stands of 
red or white mangrove. McMichael et al. (1989) 
described a similar habitat for juvenile snook in the 
Tampa Bay area. On the Florida east coast, Gilmore 
et al. (1983) reported that juveniles with standard 
lengths (SL) that average 27.5 mm are typically found 
in freshwater tributaries. They begin to move from 
stream banks and bank vegetation to deeper water or 
salt marshes at 60 mm SL, 40 to 70 days old. Juveniles 
move from this habitat at an average size of 67 mm SL, 
showing up in seagrass beds after reaching lengths of 
1 00 to 1 50 mm SL. Their residence here is from 1 to 6 
months with most fish leaving at 300 mm SL. 

Adults are found in estuarine and neritic waters. They 
inhabit Gulf passes, channels, beaches, river mouths, 
mangrove or salt marshes, brackish estuarine waters, 
and tidal ponds, lakes, and streams (Higgins and Lord 
1 926, Marshall 1 958, Tabb and Manning 1 961 , Gunter 
and Hall 1 963, Odum 1 971 , Kushlan and Lodge 1 974, 
Ager et al. 1 976, Hoese and Moore 1 977). They have 
been reported in waters from 0.3 to 3.66 m in depth and 
in salinities ranging from fresh to euhaline (Baughman 
1943, Gunter and Hall 1963, Cooley 1974, Kushlan 
and Lodge 1974, Loftus and Kushlan 1987). In sum- 
mer, they have been reported in offshore areas such as 
coral reefs as far as 70 miles west of Key West, Florida, 
in the Dry Tortugas National Park (Schmidt pers. 
comm.). 

Substrate : Juveniles and adults have been found over 
bottoms of clay, mud, mud-sand, sand, sand with 
rocks, detritus with mud and sand, and sand with shell 


(Breuer 1957, Marshall 1958, Gunter and Hall 1963, 
Gunter and Hall 1 965, Bruger 1 981 , McMichael et al. 
1989). 

Physical/Chemical Characteristics : 
Temperature: The common snook is very sensitive to 
temperature, with detrimental effects occurring at ap- 
proximately 15°C or lower (Marshall 1958, Gilmore et 
al. 1983). 

Temperature - Eggs: Eggs have not been observed in 
the wild, but they have been successfully spawned and 
developed at 28° ± 1 ° C (Shaf land and Koehl 1 979, Lau 
and Shafland 1982, Tucker 1986). 

Temperature - Larvae: Larvae propagated in laborato- 
ries have been successfully reared at 24.6 to 32.4°C 
(Shafland and Koehl 1979, Lau and Shafland 1982, 
Tucker 1 986). Snook larvae have been collected from 
Naples Bay, Florida, in temperatures ranging from 
28.7° to 31 .4°C (Tolley et al. 1 987). In a hatchery study, 
snook larvae reared at 24°C did not survive, and 
development rates increased with incubation tempera- 
ture. Optimum yolk utilization efficiency and larval 
growth occurred at 26°C (Limouzy 1993). 

Temperature - Juveniles and Adults: Juveniles and 
adults have been collected in waters with a tempera- 
ture range of 1 4.2° to 35.6°C (Marshall 1 958, Springer 
and Woodburn 1 960, Tabb and Manning 1 961 , Gunter 
and Hall 1963, Linton and Rickards 1965, Merriner et 
al. 1970, Martin and Shipp 1971, Dahlberg 1972, 
Cooley 1974, Shafland and Foote 1983, McMichael et 
al. 1989). Temperature tolerance may differ through- 
out the common snook's range due to such parameters 
as genetic stock, salinity, size, and diet (Howells et al. 
1 990). In laboratory experiments on the effect of falling 
temperature, juveniles ceased feeding at 14.2°C, lost 
equilibrium at 12.7°C, and died at 12.5°C (Shafland 
and Foote 1 983). Other studies suggest a lower lethal 
temperature for juvenile snook of 9°C in salt water 
(19% ) and 10°C in freshwater (Howells et al. 1990). 
Abnormal behavior has been reported below 14.2°C, 
with death occurring from 9 to 17°C. The lower lethal 
limit for small juveniles has been reported as 9 to 14°C, 
while that of sub-adults and adults probably approaches 
the lower end of a 6 to 13°C range, making them 
somewhat more tolerant of colder temperatures than 
fingerlings (Marshall 1958, Springer and Woodburn 
1 960, Gunter and Hall 1 963, Shafland and Foote 1 983, 
Howells et al. 1 990). Many field studies have reported 
snook as lethargic, stunned, or killed as a result of 
winter freezes (Marshall 1958, Cooley 1974). Gunter 
(1 941 ) reported a severe winter kill of snook along the 
Texas coast due to cold weather in 1940. 


195 


Common snook, continued 


Salinity - Eggs and Larvae: Eggs and larvae have been 
raised in the laboratory in salinities from 30 to 38%o 
(Shafland and Koehl 1979, Lau and Shafland 1982, 
Tucker 1986). Both appear to prefer polyhaline to 
euhaline salinity ranges and are unable to develop in 
fresh water. Larvae at 1 4 days of development can be 
successfully transferred to fresh water and are consid- 
ered euryhalineatthis point (Ageretal. 1976, Shafland 
and Koehl 1979). Field studies show a significant 
relationship between larval size and salinity, with larger 
larvae occurring in lower salinities (Tolley et al. 1 987). 
Snook larvae have been collected from Naples Bay, 
Florida, in salinities ranging from 1 4.8 to 33.5%o (Tolley 
etal. 1987). 

Salinity - Juveniles and Adults: Both juveniles and 
adults are euryhaline, and have been reported from a 
salinity range of 0.0 to 36%o (Hildebrand 1 958, Marshall 
1958, Springer and Woodburn 1960, Tabb and Man- 
ning 1961, Tabb et al. 1962, Gunter and Hall 1963, 
Gunterand Hall 1965, Bryan 1971, Martin and Shipp 
1 971 , Dahlberg 1 972, Fore and Schmidt 1 973, Cooley 
1974, Kushlan and Lodge 1974, Gilmore et al. 1983, 
McMichael et al. 1989). Adult snook are more often 
associated with moderate to higher salinities within this 
range (Marshall 1958, Fore and Schmidt 1973, Sea- 
man and Collins 1983, Palik and Kunneke 1984). On 
the east coast of Florida, juvenile snook <50mm con- 
sistently occur at lower salinities, whereas those 
>150mm are generally found in higher salinity waters 
(Gilmore etal. 1983). Snook are relatively widespread 
in freshwater areas in Florida, and have been collected 
in Lake Okeechobee, coastal rivers, the Big Cypress 
Swamp, and at several locations in the Everglades 
(Loftus and Kushlan 1987). Physiological studies of 
juveniles indicate they can osmoregulate at salinities 
between and 45%o in a manner similar to other 
brackish water fishes (Quintero and Grier 1 985). More 
than 70% of seing-caught and 90% of trawl-caught 
specimens taken in the Little Manatee River from 1 988 
to 1991 were taken at salinities less than 5% . Maxi- 
mum numbers were taken during October and Novem- 
ber. Changes in blood osmolality and gill morphology 
of juvenile snook after acclimation at various salinities 
(0, 15, 30, and 40%>) has been studied (Quinterro and 
Torres 1993). The chloride cells within the gills ap- 
peared to be metabolically active regardless of the 
acclimation salinity. 

Dissolved Oxygen: Dissolved oxygen (DO) level may 
limit the distribution of this fish in confined or isolated 
marsh habitats (Gilmore et al. 1983). Juvenile snook 
have been collected in impounded wetland habitats 
associated with the Indian River Lagoon with DO levels 
of less than 1.0 ppm (no ref). Peterson and Gilmore 
(1991) found an ontogenetic change in a juvenile 
snook's ability to survive reduced oxygen levels which 


correlated well with the habitat shift noted by Gilmore 
et al. (1983). Small juveniles may also use aquatic 
surface respiration to utilize the well-oxygenated sur- 
face film during hypoxic events (Peterson et al. 1 991 ). 

Movements and Migrations : Snook is a relatively non- 
migratory, inshore species (Volpe 1959, Moe 1972). 
Apparently this fish has a broad inshore range and 
moves freely in this area, as conditions permit, in short 
coastwise movements (Moe 1 972, Tucker 1 986). Eggs 
and larvae are carried by currents or swim to nursery 
areas where they remain until maturity. It has been 
suggested that the optimal salinity for activity changes 
with development in juveniles from freshwater to isos- 
motic levels to match, or even determine, their gradual 
migration to higher salinities (Perez-Pinzon and Lutz 
1991). Movements from estuaries and fresh water 
tributaries to spawning areas just offshore can be 
considered a limited spawning migration (Moe 1972, 
Tucker 1986). Some southerly movements in re- 
sponse to falling water temperature have been noted 
(NOAA 1 985). Juvenile snook exhibit a habitat speci- 
ficity which changes as the fish grow older, resulting in 
localized movements. Adult habitat requirements are 
not as narrow as those of juveniles, although limited 
movement occurs throughout the life cycle (Gilmore et 
al. 1983). In a study of Tampa Bay, Florida, most 
juvenile snook were concentrated in two tributaries, the 
Alafia and Little Manatee Rivers (CES 1992). Adult 
snook were also concentrated in tributaries, except in 
the spring when they were scattered throughout 
nearshore areas of Tampa Bay. In another study of 
Little Manatee River, Florida, most juveniles were 
found along the shoreline at two marginal creek/cove 
sites (Matheson and Rydene 1993). 

Reproduction 

Mode : This species can be considered a protandric 
hermaphrodite, suggested by skewed sex ratios that 
significantly favor small males, and the absence of age 
and 1 females (Taylor and Grier 1993, Taylor pers. 
comm.). Comparisons of the chromosomes of males 
and females do not show differences in chromosomatic 
size or number (Ruiz-Carus 1993). The banding 
patterns on the chromosomes supported the hypoth- 
esis of protandric hermaphroditism. Examination of 
more than 4,100 snook gonads confirmed that snook 
undergo sex reversal (Taylor and Grier 1 993). For all 
snook <500mm and under age 4 the sex ratio was 
skewed in favor of males (6.1 M:1 .OF), whereas for fish 
>800mm and over age 7 the sex ratio favors females 
(1 .0M:3.2F). Direct evidence from pond-held juvenile 
males demonstrates that female common snook are 
derived from post-mature males (Taylor pers. comm.). 
Fertilization is external, by broadcast of milt and roe. 


196 


Common snook, continued 


Spawning : In Florida, spawning occurs from May to 
mid-November with peak spawning periods from June 
to July along the southeast and southwest coasts, and 
in August along the east central coast. These peaks 
may vary among locations. In a study of snook in 
Tampa Bay, a diel and lunar sampling protocol was 
used to determine peak periods of various reproduc- 
tive activities (Roberts etal. 1988). Thegonadosomatic 
index of adult snook and the catch per unit effort 
(CPUE) of larvae were highest during the new moon 
period in June and July. Eggs were most abundant 
during late evening and early morning hours. Some 
spawning may occur year round in the warmer parts of 
the range (Marshall 1 958, Volpe 1 959, Ager et al. 1 976, 
Moe 1 972, Tucker 1 986). In south Texas, the primary 
spawning period is June to August (MatlockandOsburn 
1987). One female with roe was reported from Corpus 
Christi, Texas in July (Baughman 1943). Snook can 
spawn repeatedly during a single season (Fore and 
Schmidt 1973, Seaman and Collins 1983). Fish ready 
to spawn congregate in schools in shallow, saline, 
open waters just offshore in such areas as river mouths, 
estuarine passes, and along open beaches in the 
vicinity of inlets. Actual spawning is most likely to occur 
in shallow nearshore waters (Marshall 1958, Volpe 
1 959, Linton and Rickards 1 965, Moe 1 972, Ager et al. 
1 976, Bruger 1 981 , Gilmore et al. 1 983). Salinities of 
>20% o are necessary to activate sperm for successful 
spawning (Ager et al. 1 976, Shafland and Koehl 1 979). 

Fecundity : Spawning females produce large numbers 
of eggs; a female with a fork length (FL) of 584 mm 
contained about 1 ,440,000 eggs (Volpe 1 959). Fecun- 
dity has been tentatively estimated at 20,412 eggs/kg 
body weight, with some fractional spawning being 
reported (Marshall 1958, Ager et al. 1976). Common 
snookcan be considered batch-synchronous, i.e., they 
can spawn once every 3 to 4 days for about 152 days 
from mid-April to mid-September in Florida waters. 
Batch fecundity is approximately 850,000 eggs, and if 
there are 38 spawning events per season, total fecun- 
dity for a 800 mm FL female could be 32,000,000 eggs 
per year (Taylor pers. comm.). 

Growth and Development 

Egg Size and Embryonic Development : Development 
is oviparous. Eggs are 0.68 to 0.73 mm in diameter, 
spherical, yellowish-white in color with transparent yolk 
material containing a single well defined oil globule that 
ranges from 0.17 to 0.30 mm in diameter. Hatching 
rates reported in laboratory experiments are 16-18 
hours at 28°C and 24 to 30 hours at 27.8° to 30.6°C. 
Fertilized eggs float in salt water with a salinity of >20%o 
(Ager et al. 1976, Lau and Shafland 1982, Tucker 
1986). 


Age and Size of Larvae : Larvae are 1 .4 to 1 .5 mm SL 
at hatching and have a large yolk sac that contains a 
large oil globule in the anterior portion, and a transpar- 
ent finfold present around most of the body (Lau and 
Shafland 1 982, Tucker 1 986). Their length increases 
to about 2.1 mm SL by 36 hours after hatching (AH) 
(Lau and Shafland 1982). At this time eyes are 
becoming pigmented, the mouth begins to develop, the 
yolk sac is absorbed, and the gut increases in diameter 
and is partitioned (Lau and Shafland 1982). Eyes and 
jaws are complete 32 to 48 hours AH and the digestive 
system is functional by 72 hours AH (Shafland and 
Koehl 1 979, Tucker 1 986). At approximately 96 hours 
AH, larvae are 2.2 to 2.3 mm SL, the oil globule is 
completely absorbed, and the swimbladder is visible 
above the gut. Notochord flexion begins from 3.6 to 3.8 
mm SL, and is usually complete by 4.5 mm. Caudal fin 
is visible by 3.2 mm SL; pelvic fin buds visible between 
5.0 to 5.5 mm SL, pelvic girdle completely ossified by 
8.6 mm SL and heavily lined with teeth (Lau and 
Shafland 1982). The larval stage ends with scale 
development at 1 3.8 to 1 6.4 mm SL, 34 days AH (Lau 
and Shafland 1982). Growth rate for larvae varies. 
Newly hatched larvae at 28°C±1 °C grow 1 .02 mm/day 
for a few hours, slowing rapidly to about 0.15 mm/day 
when about 2.4 mm SL. Growth rate then increases 
gradually with increasing size from 0.15 to 0.50 mm/ 
day in snook between 3.5 to 22.0 mm SL (Lau and 
Shafland 1 982). The osteological develpment of larval 
snook is described in detail by Potthoff and Tellock 
(1993). 

Juvenile Size Range : The minimum size described for 
juveniles is 1 3.8 mm SL (Lau and Shafland 1 982). The 
caudal skeleton is ossified by 21 .9 mm SL, and by 26.4 
mm SL melanophores begin to form along lateral line, 
darkening it and the fins. Juveniles have appearance 
of small adults at this point (Lau and Shafland 1982). 
The reported growth rate for juveniles in the wild is 0.5- 
1.2 mm/day (Fore and Schmidt 1973, Gilmore et al. 
1 983, McMichael et al. 1 989) with a reported average 
of 0.6-0.7 mm/day for the first eight months of life 
(McMichael et al. 1989). Juveniles are 163 mm FL at 
the end of their first winter, and 342 mm FL by the end 
of their second (Volpe 1959). Some juveniles mature 
by the end of their second year, but most are not mature 
until their third year when they reach a FL of 500 mm 
(Marshall 1958, Volpe 1959). 

Age and Size of Adults : Marshall (1958) reported 
minimum sizes for adults of 337 mm FL for females, 
and 338 mm FL for males. Predicted size and age for 
Florida gulf coast snook at 50% maturity are 401 mm 
FL at 1.93 years for males, and 499 mm FL at 2.64 
years for females (Taylor pers. comm.). Estimates for 
Florida east coast snook at 50% maturity are 379 mm 
FL at 2.26 years for males, and 644 mm FL at 3.68 


197 


Common snook, continued 


years for females. Volpe (1959) reported a maximum 
life span of about 7 years. However, Taylor ef al. (1 993) 
reported that males can live 13 years and attain 925 
mm TL, and females 1 9 years and 1 , 1 05 mm TL. In the 
Everglades region, 4 and 5 year old fish comprise 59% 
of the snook population. The sex ratio is approximately 
3:1, males to females (Gilmore et al. 1983). 

Food and Feeding 

Trophic Mode : The common snook is an opportunistic 
carnivore that tends to be piscivorous, with its specific 
diet varying among habitats (Seaman and Collins 
1983). The common snook is a visual predator that 
forages throughout the water column and on the bot- 
tom, often in narrow passes accompanied by strong 
currents (Springer and Woodburn 1960, Fore and 
Schmidt 1973, Seaman and Collins 1983, Manooch 
1984, NOAM 985). 

Food Items : Larvae are considered stenophagous. 
They are planktivores preying chiefly on copepods and 
their eggs and larvae. They also feed on other inver- 
tebrate eggs, crab zoea, foraminifera, algae, and plant 
tissue (Harrington and Harrington 1961). In a labora- 
tory rearing study, larvae began feeding when 2 to 3 
days old, and accepted rotifers, newly hatched Artemia, 
and copepod nauplii between 53 and 130 microns in 
size (Shafland 1977). Late postlarvae also feed on 
neonatal Gambusia (Gilmore et al. 1983, Shafland 
1 977). Juveniles become piscivorous at 25 to 30 mm 
TL with fish constituting a major portion of their diet by 
56 mm SL (Springer and Woodburn 1960, Shafland 
and Koehl 1979). Food organisms of juvenile snook 
include bay anchovy, pinfish, sailfin molly (Poecilia 
latipinna), western mosquitofish (Gambusia affinis), 
sheepshead minnow, gobies, silversides, red drum, 
killifishes, grass shrimp, plant tissue, insects, and other 
fishes. Smaller specimens have also been reported 
eating small Crustacea and zooplankton (Springer and 
Woodburn 1960, Harrington and Harrington 1961, 
Bryan 1971, Fore and Schmidt 1973, Gilmore et al. 
1983). Field studies of juvenile snook in Tampa Bay 
suggest that feeding occurs during daytime hours 
(McMichael et al. 1 989). Adults consume mostly fish, 
crabs, and shrimp, but crayfish, and some plant tissue 
are also utilized (Marshall 1958, Fore and Schmidt 
1973). Fish constitute the most important component 
with the following reported from diet studies: menha- 
den, mojarras, mullet, pinfish and other sparids, an- 
chovies, pigfish, sailfin and other mollys, western 
mosquitofish and other Gambusia species (Marshall 
1 958, Bryan 1 971 , Odum 1 971 ). Crabs found in adult 
snook stomachs are mostly from the family Portunidae 
and include blue crab (Callinectes sapidus), C. ornatus, 
Portunus gibbesii, and P. sayi. Mud crabs (Xanthidae) 
and hermit crabs (Paguridae) are also part of the 
common snook's diet (Fore and Schmidt 1973). 


Biological Interactions 

Predation : It is during the larval and juvenile stages that 
the common snook is vulnerable to predation by other 
piscivorous species (Seaman and Collins 1983). 

Factors Influencing Populations : Habitat requirements 
and temperature are probably the most important 
factors determining the range of snook in U.S. waters 
(Cooley 1974, Ager et al. 1976, Hoese and Moore 
1977). The preferred habitats, mangrove and salt 
marshes, are not extensive in the northwestern Gulf of 
Mexico which, along with the need for relatively warm 
temperatures, probably accounts for the relative scar- 
city of this species. This habitat is similar to that of the 
tarpon, Megalops atlanticus, which, like the snook, is 
declining in numbers, giving support to the hypotheses 
of habitat destruction and/or environmental change as 
factors in their decline (Marshall 1958, Rivas 1962, 
Odum 1971, Cooley 1974, Hoese and Moore 1977, 
Peterson and Gilmore 1991). Interaction with other 
species include habitat overlapping and parasitism. 
Possible competition may exist between snook and 
associated fish such as tarpon, ladyfish, spotted 
seatrout, silver perch, and bank sea bass (Linton and 
Rickards 1965). An unidentified nematode has been 
reported parasitizing the mesentery and stomach wall 
of snook, but apparently with no ill effects (Marshall 
1958). Other reported parasites are Philometra 
centropomi in the nasal mucosa and Prosthenhystera 
obesa in the gall bladder (Seaman and Collins 1983). 
Snook have also been identified as a host for 
Lymphocystisvirus. Larval recruitment and/or juvenile 
survival may be enhanced by increased upland runoff 
or marsh flooding (Tilmant et al. 1 989). The presence 
of juveniles in low salinity areas may be a survival 
adaptation to exploit areas that are largely free of 
piscine predators (Fore and Schmidt 1 973). The Texas 
Parks and Wildlife Department, in cooperation with 
Texas A&M University and the University of Texas, has 
been experimenting with hatchery propagation of snook 
as a means to stock Texas bays (Vega pers. comm.). 
Studies of hatchery rearing of snook have also been 
conducted in Florida (Mote 1993). 


198 


Common snook, continued 


Personal communications 

Peterson, Mark S. Gulf Coast Research Lab., Ocean 
Springs, MS. 


Rubec, Peter J. 
Petersburg, FL. 


Florida Marine Resarch Institute, St. 


Schmidt, Thomas W. South Florida Research Center, 
Everglades National Park, Homestead, FL. 

Taylor, Ronald G. Florida Marine Resarch Institute, St. 
Petersburg, FL. 

Vega, Robert. Texas Parks and Wildlife Department, 
Corpus Christi, TX. 

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201 


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202 


Pomatomus saltatrix 
Adult 


25 cm 


(from Goode 1884) 


Common Name: bluefish 

Scientific Name: Pomatomus saltatrix 

Other Common Names: blue, tailor, snapper, elf, 

fatback, snap mackerel, skipjack, snapping mackerel, 

horse mackerel, greenfish, skip mackerel, chopper, 

Hatteras blue (Wilk 1 977); fasserga/(French), anchova 

de banco (Spanish) (Fischer 1978, NOAA 1985). 

Classification (Robins et al. 1991) 

Phylum: Chordata 

Class: Osteichthyes 

Order: Perciformes 

Family: Pomatomidae 

Value 

Commercial : In the Gulf of Mexico, the bluefish is 
considered an incidental commercial species, with 
most catches occurring in coastal waters (Lund 1 961 , 
Barger et al. 1 978, Benson 1 982). In the Gulf of Mexico 
during 1992, approximately 134.3 mt of bluefish were 
harvested with over 85 per cent coming from Florida 
(Newlin 1993). It was once common enough to support 
a small fishery in east Texas waters, but has not been 
of commercial interest there since the 1930's (Gunter 
1945, Hoese 1958, Newlin 1993). In Alabama, it is a 
relatively minor component of that state's commercial 
fishery, contributing only 7.7 mt in 1 992 (Swingle 1 971 , 
Newlin 1993). Louisiana landed 12.2 mt and Missis- 
sippi landings were too small to be reported (Newlin 
1 993). Haul seines, gill nets, and hook and line are the 
primary types of gear used. In Florida, bluefish is 
generally not the targeted species, but is used to 
supplement catches of other species (GMFMC 1 981 ). 
Harvest is limited to fish over 10 inches, and catches 
are largely by trammel nets in waters off the Gulf 
beaches. In recent years, incidental catch in shrimp 
trawls have made up 25% of the Florida harvest. 


Catches are made by pound nets, gill nets, purse 
seines, long haul seines, beach seines, and hook and 
line here and in other areas of the range of this fish 
(Walford et al. 1 978, GMFMC 1 981 ). The market price 
is generally low, with the average price per pound to 
fishermen only $0.27 in 1992 (Newlin 1993), but they 
can supplement the income of commercial fishermen 
when more desirable species are unavailable (Manooch 
1 984). Bluefish are usually marketed fresh due to poor 
freezing quality. 

Recreational : This is an important game species in 
both U.S. and Mexican waters. Its recreational impor- 
tance far outweighs its commercial value, especially on 
the Atlantic seaboard (Hildebrand 1957, Lund 1961, 
Swingle 1977, Barger et al. 1978, Benson 1982). Its 
voracity makes it an exciting game fish and it is also an 
excellent food fish when eaten fresh (Hoese and Moore 
1977). Fishery information for the Gulf of Mexico 
showed a total catch of 501,000 bluefish in 1992 
(NMFS 1 993). Most of the recreational catch occurs in 
coastal waters within 3 miles of shore. Angling meth- 
ods include surf casting; float fishing from piers, docks, 
bridges, and jetties; and trolling, casting, live bait 
fishing, and chumming from boats (Walford et al. 
1978). 

Indicator of Environmental Stress : Bluefish 
bioaccumulate contaminants such as polychlorinated 
biphenyls (PCB) into various adipose tissues from the 
water column and through the marine food chain 
(Sanders and Haynes 1988, Eldridge and Meaburn 
1992). Studies by the National Marine Fisheries Ser- 
vice (NMFS), the Food and Drug Administration (FDA), 
and Environmental Protection Agency (EPA) have 
found concentrations of PCB in large bluefish (>500 


203 


Bluefish, continued 


Table 5.26. Relative abundance of bluefish in 
Gulf of Mexico estuaries (from Volume /). 

Life stage 


31 


Estuary 


A S J L E 


Florida Bay 


O 


V 


Ten Thousand Islands 


O 


V 


Caloosahatchee River 


Charlotte Harbor 


O 


o 


Tampa Bay 


o 


V 


Suwannee River 


o 


o 


Apalachee Bay 


o 


o 


Apalachicola Bay 


o 


o 


St. Andrew Bay 


® 


o 


Choctawhatchee Bay 


® 


o 


Pensacola Bay 


o 


o 


Perdido Bay 


o 


o 


Mobile Bay 


o 


o 


Mississippi Sound 


o 


o 


Lake Borgne 


Lake Pontchartrain 


Breton/Chandeleur Sounds 


V 


Mississippi River 


V 


V 


Barataria Ba} 


o 


Terrebonne/Timbalier Bays 


V 


Atchafalaya/Vermilion Bays 


V 


Calcasieu Lake 


V 


Sabine Lake 


V 


Galveston Bay 


o 


Brazos River 


o 


Matagorda Bay 


V 


San Antonio Bay 


V 


Aransas Bay 


V 


V 


Corpus Christi Bay 


V 


V 


Laguna Madre 


Baffin Bay 


A S J L E 


Relative abundance: 

O Highly abundant 
® Abundant 
O Common 
V Rare 
blank Not present 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


mm FL) that exceed the limit of 2 ug/g set by the FDA. 
This has prompted investigation to determine if states 
with bluefish fisheries need to control the consumption 
of large individuals by recreational and subsistence 
fishermen that regularly eat these fish, and how to 
minimize human exposure by regulating the bluefish 
harvest (Sanders and Haynes 1988, Eldridge and 
Meaburn 1992). 

Ecological : The bluefish is a pelagic marine predator, 
and is primarily a visual feeder (Olla et al. 1970, Olla 
and Studholme 1972). The bluefish is probably in 
competition with other pelagic predators such as striped 
bass (Morone saxatilis), Spanish mackerel 
(Scomberomorous maculatus), king mackerel (S. cav- 
alla), seatrout and weakfish (Cynoscion species), and 
little tunny (Euthynnus alletteratus). 

Range 

Overall : The bluefish occurs in temperate coastal wa- 
ters of the Atlantic and Indian Oceans, and is one of the 
most widespread of the U.S. coastal and estuarine 
fishes (Fischer 1978). Along the U.S. east coast, 
bluefish occur from Cape Cod to Florida (Lund 1961, 
Wilk 1 977). It is occasionally found as far north as Nova 
Scotia, and occurs throughout the Gulf of Mexico from 
Florida to Mexico, but are absent from Central America. 
Along the Atlantic coast of South America, bluefish 
occur from Argentina to Colombia. It is also found off 
Cuba, Bermuda, and the Azores, in the eastern Atlantic 
off the Canary Islands, and from Portugal to Senegal. 
Its range includes the Mediterranean and Black Seas 
as well. It is found off Africa from Angola to South 
Africa. Distribution in the Indian Ocean includes the 
East coast of southern Africa, Madagascar, Malay 
Peninsula, Tasmania, and southern and western Aus- 
tralia where it is reported abundant off southern 
Queensland and New South Wales. There is a single 
report in the eastern Pacific off the coast of Chile (Lund 
1 961 ). Based on the seasonal and spatial distribution 
of bluefish larvae, it has been hypothesized that two 
spawning populations exist on the U.S. east coast, one 
spawning in the spring south of Cape Hatteras, and 
one in the summer in the Mid-Atlantic bight (Kendall 
and Walford 1979). 

Within Study Area : Within U.S. Gulf of Mexico estuar- 
ies, this species occurs from Florida Bay, Florida to the 
Rio Grande, Texas (Table 5.26) (Lund 1961, Wilk 
1 977). It is less abundant overall in the Gulf of Mexico 
than along the Atlantic coast (Walford et al. 1978). 
Bluefish occur in coastal waters off of Texas, Louisiana 
(Hoese and Moore 1977), Mississippi, Alabama, and 
the west coast of Florida (Hardy 1978, GMFMC 1981 , 
Manooch 1984, NOAA 1985). Larval bluefish in the 
northern Gulf of Mexico are reported to occur primarily 
between 88° and 93° longitude, and to be relatively 


204 


Bluefish, continued 


uncommon in the eastern Gulf off of the Florida coast 
(Ditty and Shaw 1995). Recreational catch data sug- 
gest that bluefish are more common off of Louisiana 
and Texas, and less common along the Florida Gulf 
coast (Ditty and Shaw 1995). 

Life Mode 

Both eggs and larvae are pelagic and planktonic 
(Lippson and Moran 1974, Norcross et al. 1977). 
Juveniles and adults are pelagic and nektonic. This is 
a migratory species in which both large juveniles and 
adults school, but usually separately. Adults are diur- 
nal, and are active all daylight hours (Pullen 1962, 
Parker 1965, Olla et al. 1970, Olla and Studholme 
1972, Hardy 1978, Bargeret al. 1978, Benson 1982). 
Swimming speed increases at dawn and decreases 
during the late afternoon and evening (Walford et al. 
1978). 

Habitat 

Ty pe: This species inhabits temperate and warm tem- 
perate zones, generally in continental shelf waters 
(Wilk 1977). Eggs and larvae are found in continental 
shelf waters, usually over depths <1 00m. Larvae move 
inshore sometime during theirfirst growing season and 
are occasionally found in the mouth of bays. They were 
collected from water depths ranging from 34 to 183 m 
in one study, with all but one captured in waters >49 m 
deep (Moe 1972, Lippson and Moran 1974, Norcross 
et al. 1974, Barger et al. 1978, Benson 1982). Eggs 
and larvae are found in euhaline (marine) salinities 
(Barger et al. 1978, Benson 1982). Juveniles have 
been reported from both inshore and offshore areas in 
clear and turbid waters. Inshore collections include 
such habitats as along ocean beaches, lagoons, 
sounds, bays, barrier island passes, estuaries, and 
bayous. 

Juveniles are known to enter estuaries, and may 
remain there for several months at a time on the U.S. 
east coast (Juanes et al. 1993, McBride et al. 1993). 
Movement into these areas may benefit survival and 
growth due to shelter and food resources (Gunter 
1945, Arnold et al. 1960, Pullen 1962, Zimmerman 
1969, Perret et al. 1971, Franks et al. 1972, Norcross 
et al. 1 974, Hardy 1 978, Benson 1 982). Early juveniles 
(1 4.0-1 6.5 mm) can be found as far as 96 km offshore. 
Juveniles are usually found above the thermocline, 
with a reported depth range of 1 .1 to 26 m deep (Clark 
et al. 1969, Zimmerman 1969, Franks et al. 1972, 
Norcross etal. 1974, Hardy 1978). Juveniles have also 
been collected considerable distances up rivers in New 
England (Norcross et al. 1 974, Hardy 1 978). Salinities 
from which juveniles are reported range from fresh to 
euhaline (Gunter 1945, Pullen 1962, Parker 1965, 
Perret et al. 1 971 , Franks et al. 1 972, Hardy 1 978). 


Adults have been captured in nearshore areas of 
barrier islands and their passes, and along island 
beaches on the Gulf side, but are not common in low- 
salinity estuarine areas. Adults may move into or near 
estuaries to feed (Simmons 1 957, Franks et al. 1 972, 
Swingle 1977, Benson 1982). They prefer shallow 
water, near dropoffs from shoal and banks (Shipp 
1 986). However, they may occur in water as deep as 
100 m (Lund 1961, Franks et al. 1972, Hardy 1978), 
and during the spawning season, they have been 
reported up to 1 48 km offshore in the Mid-Atlantic Bight 
(Norcross et al. 1974). In Texas, they are sometimes 
found in association with schools of gulf menhaden 
(Breuer 1949). 

Substrate : Juveniles have been found over bottoms of 
shell and sandy shell with hard packed mud (Pullen 
1962, Zimmerman 1969). Bottom types for all life 
stages are probably many and varied due to the pelagic 
and wide ranging nature of this species. 

Physical/Chemical Characteristics : 
Temperature - Eggs: In one laboratory study, eggs 
fertilized in vitro were successfully incubated in a 
temperature range of 18 to 22.2°C, with an average 
temperature of 20.0°C until hatching (Deuel et al. 
1966). Eggs in the wild occur from 18 to 26.3°C 
(Norcross et al. 1974). 

Temperature - Larvae: In one study of 1 8 specimens, 
larval bluefish were reported in the Gulf of Mexico over 
a temperature range of 23.2 to 26.4°C (Barger et al. 
1 978, Benson 1 982). Ditty and Shaw (1 995) collected 
70 larval bluefish in the northern Gulf of Mexico at a 
mean temperature of 24.6°C, with a range of 22.4 to 
26.9°C. Minimum temperature has been suggested as 
21 °C (Hardy 1978). 

Temperature - Juveniles: Juveniles have been re- 
corded in temperatures from 1 4.8 to 31 .2°C in the Gulf 
of Mexico (Gunter 1945, Pullen 1962, Perret et al. 

1971, Wang and Raney 1971, Franks et al. 1972, 
Hardy 1978). Water temperatures below 10°C are 
considered lethal for this life stage (Lund and Maltezos 
1 970), but these temperatures generally don't occur in 
the Gulf of Mexico. 

Temperature - Adults: The temperature range recorded 
for adults is 1 8-21 .0°C (Deuel et al. 1 966, Franks et al. 

1972, Norcross et al. 1974). Swimming speed is 
significantly affected by temperature with stressful 
behavior noted below 1 1 .9°C and above 29.8°C (Olla 
and Studholme 1971). Adults can survive tempera- 
tures as low as 7.5°C temporarily (Lund and Maltezos 
1970). 


205 


Bluefish, continued 


Salinity - Eggs: In one laboratory study, eggs fertilized 
in vitro were successfully incubated in a salinity of 
32.5%o until hatching (Deuel et al. 1966). Eggs in the 
wild occur from 26.6 to 34.9%o, but are found most often 
in 30%o or greater (Norcross et al. 1974). 

Salinity - Larvae: In one study of 1 8 specimens, larval 
bluefish were reported in the Gulf of Mexico over a 
salinity range of 35.7 to 36.6%o (Barger et al. 1978). 
Ditty and Shaw (1 995) collected 70 larval bluefish in the 
northern Gulf of Mexico at a mean salinity of 33.0%o, 
with a range of 26.7 to 36.3%o. They have been 
collected in salinities as high as 38%o in the Atlantic 
Ocean (Kendall and Walford 1979). 

Salinity - Juveniles: Juveniles have been recorded 
over a salinity range of 8.0 to 36.2%> in the Gulf of 
Mexico (Gunter 1 945, Pullen 1 962, Perret et al. 1 971 , 
Wang and Raney 1971, Franks et al. 1972, Hardy 
1978). 

Salinity - Adults: Salinity preference for adults seems to 
be 26.6 to 34.9%<= (Benson 1982), but they exhibit an 
overall range of 7.0-36.5%o, with only rare occurrences 
above 35%o (Simmons 1 957, Deuel et al. 1 966, Franks 
etal. 1972, Hardy 1978). 

Movements and Migrations : Larval bluefish in the 
northern Gulf of Mexico are reported to reach peak 
abundance in April, and November-December (Ditty et 
al. 1988). Young of the year bluefish move inshore 
sometime during their first growing season, and some 
are found in estuaries and their tributaries (Norcross et 
al. 1 974, Hardy 1 978, Benson 1 982). Age class fish 
arrive in Texas coastal waters during late November 
when they are 48-56 mm standard length (SL) (Hoese 
1 965), and some evidently enter bay systems (Gunter 
1945, Pullen 1962, Perret et al. 1971, Benson 1982). 
Adults are caught off the Texas coast primarily from 
April to September, with peaks in July and August, and 
appear to be entirely absent during December and 
January (Springer and Pirson 1959). Adults move 
seasonally in groups loosely collected into aggregates 
that can be 6 to 8 km long (Hardy 1 978). They generally 
move north in spring and summer, and south in fall and 
winter (Moe 1 972, Wilk 1 977). In the Gulf of Mexico, 
they remain offshore during much of the year, moving 
inshore during the summer in Louisiana, late summer 
and fall in Mississippi, and fall in Florida and the 
northwestern Gulf. Florida bluefish remain inshore 
until spring, with large numbers still found off southern 
Florida in March and some present throughout the year 
(Springer and Woodburn 1960, Deuel et al. 1966, 
Perry 1970, Hoese 1977). Seasonal migrations ap- 
pear to be linked to water temperature and possibly 
photoperiod (Lund and Maltezos 1970, Olla and 
Studholme 1971). In the Atlantic, fall migration ap- 


pears to be triggered when temperatures fall to 13 to 
1 5°C. In this area, fall migration is believed to go in two 
directions (Lund and Maltezos 1970): juveniles are 
essentially shore fish and move southward along the 
coast staying with the warmer water and will enter inner 
bays, whereas adults are pelagic and move offshore to 
find warmer water in which to overwinter (Lund and 
Maltezos 1970). Movements between offshore and 
inshore waters are irregular and may be a response to 
wind induced changes in water temperature (Reid 
1954, Lund and Maltezos 1970). Migrating bluefish 
have been reported to enter public beach waters and 
nip at swimmers (de Sylva 1976, IGFA 1991). 

Reproduction 

Mode : This species has separate male and female 
sexes (gonochoristic), but hermaphroditism has not 
been examined. Fertilization is external by broadcast 
of milt and roe, and no accessory organs are present 
(Wilk 1977). 

Spawning : The bluefish is an offshore ocean spawner 
(Lippson and Moran 1 974). Gulf of Mexico populations 
appear to spawn over the continental shelf, as they do 
in the Atlantic off the eastern U.S. (Moe 1 972, Lippson 
and Moran 1974, Norcross et al. 1974, Barger et al. 
1978). The spawning period varies depending on 
location. Spawning in the northern Gulf of Mexico may 
be bimodal, occurring in both spring and fall. Fall 
spawning occurs from late September through early 
November (Hildebrand 1957, Barger et al. 1978, 
Finucane et al. 1980). Spring spawning is known to 
occur in waters off the Louisiana coast (Barger et al. 
1978). Spawning locations may be associated with 
hydrologically dynamic areas, such as the estuarine/ 
oceanic frontal zone of the Mississippi River plume 
(Ditty and Shaw 1995). It has been inferred, but not 
consistently demonstrated, that such frontal zones 
offer a nutritional advantage to larval fish. In the 
Atlantic on the U.S. east coast, spawning is reported in 
the spring 55 to 148 km offshore in salinities of 25.6 to 
32.5%o, and water temperatures of 1 4 to 25.6°C (Deuel 
et al. 1 966, Norcross et al. 1 974, Hardy 1 978). In this 
area, optimal temperature and salinity for spawning 
were 25.6°C and 31 %«, and little spawning was re- 
ported at 18°C and 31.7%o, and 20.5°C and 26.6%o. 
The majority of spawning in the Chesapeake Bay area 
is reported to occur at temperatures above 22°C and 
surface salinities of 31 %o or greater (Deuel et al. 1 966, 
Norcross et al. 1974). 

Fecundity : The number of eggs produced is a function 
of size and age (Wilk 1977). In Atlantic waters of the 
U.S. east coast, a 528 mm female contained about 
900,000 maturing eggs while a 585 mm female con- 
tained about 1,100,000 eggs. 


206 


Bluefish, continued 


Growth and Development 

Egg Size and Embryonic Development : Fertilized eggs 
are 0.90-1 .20 mm in diameter, with a single oil globule 
present 0.22-0.30 mm in diameter (Deuel et al. 1966, 
Lippson and Moran 1 974). The egg capsule is thin, but 
tough, and is transparent and colorless. Yolk is a pale 
amber and the oil globule is a deeper amber. Perivi- 
telline space is about one sixth the egg radius. Devel- 
opment is oviparous and cell division proceeds rapidly. 
Regular movements are first noticed about 37 hours 
after fertilization (AF) with mass hatching occurring 
between 44 to 46 hours AF at 18.5 to 22.2°C, and 46 
to 48 hours AF at 18.0 to 22.2° (Deuel et al. 1966, 
Lippson and Moran 1974, Norcross et al. 1974). Egg 
incubation time at 25° C has been estimated at 30 to 36 
hours (Ditty and Shaw 1995). 

Age and Size of Larvae : Newly hatched larvae are 2.0- 
2.4 mm total length (TL) and grow to 2.9 mm TL during 
their first day. The yolk sac is absorbed by about 4 mm 
TL. Incipient fin rays are evident by 6 mm TL, and 
countable by 8 mm TL. Fin development is complete 
by 1 3 to 1 4 mm TL marking the end of the larval stage 
(Deuel et al. 1 966, Lippson and Moran 1 974, Norcross 
etal. 1974). 

Juvenile Size Range : The minimum length of this stage 
is about 1 4 mm SL (Lippson and Moran 1 974, Norcross 
et al. 1974). Maturity occurs during the second year 
when fish are about 300 to 350 mm fork length (FL) 
(Deuel et al. 1966). A 200 mm TL female with nearly 
mature eggs was reported from Mexican waters 
(Hildebrand 1957). Testes mature slightly earlier than 
ovaries in fish of similar size (Wilk 1977). 

Age and Size of Adults : In the Gulf of Mexico, adult 
bluefish have been estimated up to 8 years old, and up 
to 767 mm FL (Barger 1 990), based on otolith analysis. 
Initial growth in the Gulf of Mexico is considered to be 
rapid. Barger (1990) provides VonBertalanffy growth 
parameters for Gulf of Mexico and southeast U.S. 
bluefish. On the U.S. east coast, bluefish up to 9 years 
old have been aged through scale analyses, but larger 
and presumably older fish have been reported that 
may be as old as 14 years (Wilk 1977). Sizes for 
different year classes range as follows; 230 mm FL at 
1 + year; 400 mm FL at 2+ years; 490 mm FL at 3+ years 
(1 .81 6 kg); 580 mm FL at 4+ years (3.1 78 kg); 640 mm 
FL at 5+ years (4.086 kg); 690 mm FL at 6+ years 
(4.540 kg); and 71 mm FL at 7+ years (5.448 kg) (Wilk 
1977). A size of about 860 mm FL and 8.455 kg is 
suggested for fish reaching 14 years of age (Wilk 
1977), and a fish caught in North Carolina waters 
weighed 14.40 kg (IGFA 1991). 


Food and Feeding 

Trophic Mode : The bluefish is a voracious, pelagic, 
marine predator that visually feeds on a variety of 
fishes and invertebrates throughout the water column 
(Olla et al. 1970, Olla and Studholme 1972, Benson 
1982). It has earned nicknames such as "marine 
piranah" and "chopper" because fish will move in large 
schools through shoals of bait fish in a feeding frenzy 
(IGFA 1991). Schools of bluefish can be located at a 
distance by hovering seagulls that are eating forage 
fish driven to the surface by feeding bluefish (Olla et al. 
1970). During these feeding frenzies, bluefish are 
known to even strand themselves on shore while in 
pursuit of prey that have fled inshore (IGFA 1 991 ). 

Food Items : Larval and early juvenile bluefish feed 
mostly on copepods, and gradually shift to fish and 
crab larvae (Marks and Conover 1 993). Copepods are 
the most common prey type in fish <60 mm TL. Crab 
larvae are initially consumed by bluefish < 40 mm TL, 
while the onset of piscivory occurs in the 30-70 mm TL 
size range. As bluefish grow, they tend to consume 
increasingly larger teleost prey. The shift in food items 
corresponds to the period of inshore migration, making 
the change in diet coincident with a habitat shift (Marks 
and Conover 1 993). The prey of adult bluefish include 
annelid worms, mysids, shrimps, crabs, lobsters, squid, 
lampreys, small sharks, eels, herrings, anchovies, 
killifishes, silversides, halfbeaks, bluefish, pipefish, 
sciaenids, jacks, flatfish, searobins, mackerels, mul- 
lets, cods, sea bass, porgies, wrasses, puffers, butter- 
fish, sand lances, cusk-eels, lizardfish, and eelpouts 
(Miles 1949, Richards 1976, Benson 1982). Bluefish 
feeding activities drive prey species near the waters 
surface, where they are vulnerable to predation by 
piscivorous birds (Safina 1990a, Safina 1990b). 

Biological Interactions 

Predation : Only such large predators as sharks, tunas, 
swordfish, and wahoo pose threats to these fast swim- 
mers (Medved and Marshall 1981). 

Factors Influencing Populations : Fin rot has been 
noted as a disease to which this species is particularly 
vulnerable. Known parasites include isopods, copep- 
ods, cestodes, trematodes, nematodes, and protozo- 
ans (Wilk 1977). 


207 


Bluefish, continued 


Personal communications 

Ditty, James G. Louisiana State Univ., Baton Rouge, 
LA. 

McBride, Richard S. Florida Marine Research Inst., St. 
Petersburg, FL. 

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210 


Caranx crysos 
Adult 


10 cm 


(from Goode 1884) 


Common Name: blue runner 

Scientific Name: Caranx crysos 

Other Common Names: jager boca, bau, deep water 

cavaly (McKenney et. al. 1958); carangue coubal 

(French), cojinuda negra (Spanish) (Fischer 1978, 

NOAA1985). 

Classification (Robins et al. 1991) 

Phylum: Chordata 

Class: Osteichthyes 

Order: Perciformes 

Family: Carangidae 

Value 

Commercial : The blue runner is one of the most com- 
mercially important species of the jacks, but stocks still 
remain relatively unexploited (Heald 1970, Goodwin 
and Johnson 1 986). Annual landings of blue runner in 
the northeast Gulf of Mexico have been reported as 
approximately 600 metric tons (Heald 1970). Beach 
and haul seines are the primary gear used to catch blue 
runner, and catches occur off the coasts of Louisiana 
and Florida (Heald 1970). Large incidental catches 
occur during commercial red drum purse seining op- 
erations off of Gulf of Mexico barrier islands (Overstreet 
1 983). This species has traditionally been used as bait, 
but has gained popularity as a fresh or frozen food fish, 
with small amounts being exported to the Caribbean 
area (Shaw and Drullinger 1990). In Puerto Rico, 
Trinidad, and the West Indies, blue runner is an impor- 
tant food fish (McKenney et. al. 1 958), and is marketed 
either fresh or salted (Shaw and Drullinger 1990). 
Recruitment to the fishery occurs at age III (NOAA 
1985, Goodwin and Johnson 1986). 


Recreational : Blue runner is fished recreationally, pri- 
marily in the late spring and summer, in coastal areas 
from jetties and small boats (McKenney et al. 1958, 
Sutherland 1 977, Shipp 1 986). An estimated 1 ,079,000 
were caught by anglers in the Gulf of Mexico during 
1991 (Van Voorheesetal. 1992). It is used extensively 
as bait along the southeast coast of the United States 
(McKenney et al. 1958, NOAA 1985), especially for 
larger reef fishes such as amberjacks, and fordeep sea 
fishing forsailfish (McKenney et al. 1958). 

Indicator of Environmental Stress : The blue runner is 
not typically used in studies of environmental stress. 

Ecological : The blue runner is a carnivorous species, 
feeding throughout the water column (NOAA 1985). 

Range 

Overall : This fish is widely distributed in the western 
Atlantic Ocean from Nova Scotia to Brazil, and through- 
out the Gulf of Mexico (McKenney et al. 1 958, Fischer 
1978, Johnson 1978, Goodwin and Johnson 1986). It 
also occurs in the Caribbean, the West Indies, and 
Bermuda. The areas of greatest abundance of blue 
runner are the tropical waters along the southeast 
coast of the United States along the western side of the 
Gulf Stream and between the Florida current and the 
shore, throughout the West Indies, and seasonally 
throughout the Gulf of Mexico (McKenney et al. 1 958, 
Allison 1961, Johnson 1978, Goodwin and Johnson 
1986). It is particularly common along the lower east 
coast of Florida (MacKenney et al. 1958). 

Within Study Area : Blue runner occur seasonally from 
Tampa Bay, Florida to the Rio Grande, Texas (Goodwin 
and Finucane 1985, Goodwin and Johnson 1986, 


211 


Blue runner, continued 


Table 5.27. Relative abundance of blue runner in 31 
Gulf of Mexico estuaries (from Volume /)• 

Life stage 


Estuary 


A S J L E 


Florida Bay 


V 


V 


Ten Thousand Islands 


o 


o 


Caloosahatchee River 


Charlotte Harbor 


o 


o 


Tampa Bay 


o 


o 


Suwannee River 


o 


o 


Apalachee Bay 


o 


o 


Apalachicola Bay 


o 


o 


St. Andrew Bay 


® 


o 


Choctawhatchee Bay 


o 


o 


Pensacola Bay 


o 


o 


Perdido Bay 


o 


o 


Mobile Bay 


o 


o 


Mississippi Sound 


o 


® 


® 


® 


® 


Lake Borgne 


Lake Pontchartrain 


Breton/Chandeleur Sounds 


Mississippi River 


Barataria Bay 


o 


Terrebonne/Timbalier Bays 


V 


Atchafalaya/Vermilion Bays 


Calcasieu Lake 


Sabine Lake 


Galveston Bay 


V 


V 


Brazos River 


Matagorda Bay 


San Antonio Bay 


Aransas Bay 


Corpus Christi Bay 


Laguna Madre 


Baffin Bay 


A S J L E 


Relative abundance: 

Highly abundant 
® Abundant 
O Common 
V Rare 
blank Not present 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


Adams pers. comm., Nelson et al. 1 992). Within U.S. 
estuaries of the Gulf of Mexico, the blue runner ap- 
pears to be most common along the west coast of 
Florida (Table 5.27) (Heald 1970, Fischer 1978), and 
not generally common in estuaries west of the Missis- 
sippi River (Shaw and Drullinger 1990, Adams pers. 
comm., Cambell pers. comm., Rice pers. comm.). 
However, larval data suggest that blue runner are 
common in coastal marine waters west of the Missis- 
sippi River (Ditty pers. comm.) 

Life Mode 

This is a pelagic, fast-swimming species (Goodwin and 
Johnson 1 986). Early life stages are planktonic. Late 
juveniles form small schools in and at the edges of the 
Florida Current (McKenney et. al. 1958). Adults usu- 
ally form schools, although larger individuals will re- 
main solitary (Nichols 1938, Goodwin and Finucane 
1985). 

Habitat 

Type : The blue runner is neritic and oceanic inhabiting 
primarily tropical and warm waters surrounding conti- 
nents or large islands (McKenney et. al. 1 958, Goodwin 
and Johnson 1986). In the Atlantic Ocean off the 
southeastern U.S., larvae and juveniles inhabit off- 
shore waters in association with the Gulf Stream (Berry 
1 959). The larvae of blue runner are present in the Gulf 
Stream from May through November and are in great- 
est abundance from mid-June to mid-August (Fable et 
al. 1 981 , Shaw and Drullinger 1 990). Larvae are found 
in the Gulf of Mexico from April through August (Ditty et 
al. 1 988), and the greatest numbers occur in the central 
region, where they are found in waters over the conti- 
nental shelf (Shaw and Drullinger 1990). Juveniles 
occur over deep water, but are usually present in the 
upper 100 m of the water column (McKenney et al. 
1958). However, they have been known to occur in 
depths of 1 80 m or greater (Johnson 1 978). Individuals 
greaterthan 1 00 mm SL inhabit the shelf and nearshore 
waters of the Atlantic coast, and peak in abundance 
during June and July (Berry 1 959, Dooley 1 972, Johnson 
1978, Goodwin and Johnson 1986). Early juveniles 
are associated with floating objects such as sargas- 
sum seaweed or jellyfish, and acquire a cryptic colora- 
tion during this period (Nichols 1 938, Lindall et al. 1 973, 
Johnson 1978, NOAA 1985, Shipp 1986). 

Substrate : Because this species is pelagic, it occurs 
over a wide variety of substrates (NOAA 1985). 

Physical/Chemical Characteristics 
Temperature: Recently hatched larvae (<2.5 mm SL) 
occur in water surface temperatures of 28.8°-30.1° C 
(Shaw and Drullinger 1990), while larvae of all sizes 
occur in thermal habitats of 20.4-32°C (Johnson 1 978, 
Shaw and Drullinger 1990). Juveniles are found at 


212 


Blue runner, continued 


20.4°-29.4°C (Johnson 1978). Adults inhabit areas 
where the temperature ranges from 20.0-30.8°C. 

Salinity: The blue runner inhabits polyhaline to euhaline 
areas depending on life stage. Offshore spawning 
suggests that eggs occupy areas of marine salinities. 
Newly hatched larvae occur in salinities of 25.0-36.2% o 
(Shaw and Drullinger 1990). Larvae occupy salinities 
ranging from 24.8-37.7%o, with most larvae found be- 
low 33%o (Shaw and Drullinger 1990). Juveniles are 
taken in 35.2-36.0% o , and adults inhabit areas ranging 
from 26.0 to 36.2%o (Johnson 1978). 

Migrations and Movements : In the Caribbean Sea and 
Atlantic Ocean, larval and early juvenile blue runner 
are carried to the Florida coast and then northward by 
the Antilles Current and Gulf Stream, respectively. 
Juveniles 80-140 mm in length may migrate to inshore 
waters of the Atlantic coast or move eastward with the 
currents (Berry 1 959, Dooley 1 972). Adults and juve- 
niles favor the northern Gulf of Mexico during warm 
months (Berry 1959). Adults and larger fish migrate 
southward or move offshore during colder months 
(Decemberto June) (Berry 1 959, Johnson 1 978, NOAA 
1985). Adults probably migrate offshore during the 
spawning season to reproduce (Goodwin and Finucane 
1985). 

Reproduction 

Mode : This species has separate male and female 
sexes (gonochoristic). Fertilization is external, by 
broadcast of milt and roe. 

Spawning : Based on the collection of larvae in the Gulf 
of Mexico, spawning occurs from January to August in 
offshore waters, but some evidence indicates spawn- 
ing may occur throughout the year in some areas of the 
Gulf (Goodwin and Finucane 1985). Along the south- 
east Atlantic coast of the United States, spawning 
occurs from early April to early September (Berry 
1959). The greatest period of activity occurs during 
June, July, and August (Goodwin and Finucane 1 985). 
Larvae are most abundant in the Gulf Stream mid-June 
to mid-August (McKenney et al. 1958, Berry 1959, 
Johnson 1978, Ditty et al. 1988), but are captured 
throughout the year in some areas of the Gulf (Goodwin 
and Finucane 1985). Spawning location, based on 
occurrence of larvae, is offshore and occurs in water 
depths >40m (Ditty pers. comm., Shaw and Drullinger 
1990). 

Fecundity : Reported fecundity varies from 41 ,000 ova 
in a 288 g fish to 1,546,000 ova in a 1,076 g fish. 
Goodwin and Finucane (1985) have developed curvi- 
linear equations to estimate fecundity. 


Growth and Development 

Egg Size and Embryonic Development : Little informa- 
tion is available on blue runner eggs, but the closely 
related Caranx mate has clear, spherical, pelagic eggs 
with a yolk diameter of 0.66±0.02 mm (Shaw and 
Drullinger 1990). 

Age and Size of Larvae : Blue runner larvae are not well 
known, but the larvae of the closely related Caranx 
mate range 1 .32 to 1 .70 mm SL when they hatch, and 
average length is 1.46 mm SL (Shaw and Drullinger 
1990). 

Juvenile Size Range : Transformation to the juvenile 
stage occurs around 12 mm (Ditty pers. comm.). The 
most noticeable changes in the structural development 
of a blue runner occur in two stages. The first stage 
happens between 8-12 mm and the second between 
45-60 mm (McKenney et. al. 1958). Blue runner is a 
fast growing species. Approximately 75% of their 
maximum size is attained by age 3 to 4 years (Johnson 
1978, Goodwin and Johnson 1986). 

Age and Size of Adults : Males mature by a length of 
225 mm SL, but females do not mature until approxi- 
mately 247 mm SL. The largest recorded blue runner 
is 711 mm FL (Johnson 1978, Goodwin and Johnson 
1986). Estimates of maximum weight approach 2.73 
kg. The blue runner is a moderately long-lived species, 
with a possible life span of up to 1 1 years. Goodwin and 
Johnson (1 986) have developed a growth equation for 
this species. 

Food and Feeding 

Trophic Mode : The blue runner is a carnivorous preda- 
tor, feeding on fish, crustaceans, and other inverte- 
brates (McKenney et al. 1958, NOAA 1985). Larval 
and early juveniles are carnivorous planktivores ca- 
pable of foraging throughout the water column. 

Food Items : 

Larvae forage almost entirely on cyclopoid copepods. 
Juveniles also feed on calanoid copepods. At lengths 
greater than 1 0.0 mm, juvenile blue runner eat amphi- 
pods, larval fish, decapod larvae, ostracods, and fish 
eggs; however, copepods remain the main diet con- 
stituent (McKenney et al. 1958, Dooley 1972). Adults 
feed throughout the water column on fishes, crusta- 
ceans, and other invertebrates (NOAA 1985). 

Biological Interactions 

Predation : Juveniles are evidently preyed on by sur- 
face-feeding shore birds such as terns (McKenney et 
al. 1958). 


213 


Blue runner, continued 


Factors Influencing Populations : Schools of carangid 
fish have been found in association with schools of red 
drum (Overstreet 1983). Commercial fishermen use 
this knowledge to set nets for drum, and catch blue 
runner as well. 

Personal communications 

Adams, Daniel R. Copano Causeway State Park, 
Rockport, TX. 

Cambell, Page. Texas Parks and Wildlife Dept., 
Brownsville, TX. 


Goodwin, J.M., IV, and J.H. Finucane. 1985. Repro- 
ductive biology of blue runner (Caranxcrysos) from the 
eastern Gulf of Mexico. Northeast Gulf Sci. 7(2): 139- 
146. 

Goodwin, J.M., IV, and A.G. Johnson. 1986. Age, 
growth, and mortality of blue runner, Caranx crysos 
from the northern Gulf of Mexico. Northeast Gulf Sci. 
8(2):107-114. 

Heald, E.J. 1970. Fishery resources Atlas II. West 
coast of Florida to Texas. Univ. Miami, Sea Grant 
Tech. Bull. No. 4, 174 p. 


Ditty, James G. Louisiana State Univ., Baton Rouge, 
LA. 

Rice, Ken. Texas Parks and Wildlife Dept., Brownsville, 
TX. 

References 

Allison, D.T. 1961. List of Fishes from St. Andrew Bay 
System and Adjacent Gulf of Mexico. Unpublished 
manuscript. Fla. St. Univ., Tallahassee, FL. 

Berry, F.H. 1959. Young 'crevalle jacks' (Caranx 
species) off the southeastern Atlantic coast of the 
United States. Fish. Bull., U.S. 59(1 52):41 7-532. 

Ditty, J.G., G.G. Zieske, and R.F. Shaw. 1988. Sea- 
sonality and depth distribution of larval fishes in the 
northern Gulf of Mexico above 26°00' N. Fish. Bull., 
U.S. 86(4):81 1-823. 

Dooley, J.K. 1972. Fishes associated with the pelagic 
sargassum complex, with a discussion of the sargas- 
sum community. Contrib. Mar. Sci. 16:1-32. 

Fable, W.A., Jr., H.A. Brusher, L. Trent, and J. Finnegan, 
Jr. 1981. Possible temperature effects on charter boat 
catches of king mackerel and other coastal pelagic 
species in northwest Florida. Mar. Fish. Rev. 43:21-26. 

Fischer, W. (ed.). 1978. FAO Species Identification 
Sheets for Fishery Purposes, Western Central Atlantic 
(Fishing Area 31), Vol. II. Food and Agriculture Orga- 
nization of the United Nations, Rome. 

Goode, G.B. 1884. The fisheries and fishing industry 
of the United States. Sec. I, Natural history of useful 
aquatic animals. U.S. Comm. Fish, Washington, DC, 
895 p., 277 pi. 


Johnson, G.D. 1978. Development of fishes of the 
Mid-Atlantic Bight: An atlas of egg, larval, and juvenile 
stages, Vol. IV, Carangidae through Ephippidae. U.S. 
Fish Wildl. Serv. Biol. Rep. FWS/OBS-78/12, 314 p. 

Lindall, W.N., Jr., J.R. Hall, W.A. Fable, Jr., and LA. 
Collins. 1973. A survey of fishes and commercial 
invertebrates of the nearshore and estuarine zone 
between Cape Romano and Cape Sable, Florida. 
NOAA NMFS, Natl. Tech. Info. Serv., Springfield, VA, 
62 p. 

McKenney, T.W., E.C. Alexander, and G.L. Voss. 
1 958. Early development and larval distribution of the 
Carangid fish, Caranx crysos (Mitchill). Bull. Mar. Sci. 
Gulf Caribb. 8(2): 167-200. 

Nelson, D.M., M.E. Monaco, CD. Williams, T.E. Czapla, 
M.E. Pattillo, L. Coston-Clements, L.R. Settle, and E.A. 
Irlandi. 1992. Distribution and abundance of fishes 
and invertebrates in Gulf of Mexico estuaries, Vol. I: 
Data summaries. ELMR Rep. No. 10. NOAA/NOS 
SEA Division, Rockville, MD, 273 p. 

Nichols, J.T. 1938. Notes on Carangin fishes. IV. On 
Caranxcrysos (Mitchill). Am. Mus. Novitates. 1014:1- 
4. 

National Oceanic Atmospheric Administration (NOAA). 
1985. Gulf of Mexico Coastal and Ocean Zones 
Strategic Assessment: Data Atlas. NOAA NOS Strate- 
gic Assessment Branch, Rockville, MD. 

Overstreet, R.M. 1 983. Aspects of the biology of the 
red drum, Sciaenops ocellatus, in Mississippi. Gulf 
Res. Rep., Supp. No. 1, p. 45-68. 

Robins, OR., R.M. Bailey, C.E. Bond, J.R. Brooker, 
E.A. Lachner, R.N. Lea, and W.B.Scott. 1991. Com- 
mon and scientific names of fishes from the United 
States and Canada, Fifth Edition. Am. Fish. Soc. Spec. 
Pub. No. 20. American Fisheries Society, Bethesda, 
MD, 183 p. 


214 


Blue runner, continued 


Shaw, R.F., and D.L. Drullinger. 1990. Early-life 
history profiles, seasonal abundance, and distribution 
of four species of carangid larvae off Louisiana, 1 982- 
1983. NOAA Tech. Rep. NMFS 89, 37 p. 

Shipp, R.L. 1986. Guide to fishes of the Gulf of Mexico. 
Dauphin Island Sea Lab, Dauphin Island, AL, 256 p. 

Sutherland, D.F. 1977. Catch and catch rates of fishes 
caught by anglers in the St. Andrew Bay System, 
Florida, and adjacent coastal waters, 1973. NOAA 
Tech. Rep. NMFS SSRF-708, 9 p. 

Van Voorhees, D.A., J.F. Witzig, M.F. Osborn, M.C. 
Holliday, and R.J. Essig. 1992. Marine recreational 
fishery statistics survey, Atlantic and gulf coasts, 1 990- 
1991. Current Fisheries Statistics No. 9204. NOAA 
NMFS Fish. Stat. Div., Silver Spring, MD, 275 p. 


215 


Crevalle jack 


Caranx hippos 
Adult 


10 cm 


(from Goode 1884) 


Common Name: crevalle jack 

Scientific Name: Caranx hippos 

Other Common Names: jack, common jack, yellowtail 

jack, hardtail jack, amber jack, crevalle, jack crevalle, 

runner, Jenny Lind, rudder fish (Hildebrand and 

Schroeder 1928, Reid 1955, Springer and Woodburn 

1960, Gunter and Hall 1963, Gunter and Hall 1965); 

carangue crevalle (French), jure! comun (Spanish) 

(Fischer 1978, NOAA 1985). 

Classification (Robins et al. 1991) 

Phylum: Chordata 

Class: Osteichthyes 

Order: Perciformes 

Family: Carangidae 

Value 

Commercial : The meat of this fish is generally consid- 
ered to be medium quality, and is therefore not particu- 
larly sought by commercial fishermen. The commer- 
cial fishery in the U.S. portion of the Gulf of Mexico is 
primarily in western Florida, where they are caught 
mostly by haul seine and gillnet, but also by purse 
seine, handline, and trolling. In Venezuela, it is caught 
mainly by purse seines, handlines, "mandingas," and 
traps. If is commonly found in Panama markets where 
it is esteemed as a food fish and brings a good price 
(Benson 1 982, Hildebrand and Schroeder 1 928, Fischer 
1978, Johnson et al. 1985). 

Recreational : An estimated 1,725,000 crevalle jacks 
were caught by recreational fishermen in the Gulf of 
Mexico during 1991 (Van Voorhees et al. 1992). The 
crevalle jack is known for its hard fighting ability and 
many anglers enjoy this challenging fish, but it is 
regarded as a nuisance by some since it takes consid- 
erable time to land on light tackle (Tabb and Manning 


1 961 , Hoese and Moore 1 977, Benson 1 982). Despite 
general opinion, it can be very good when properly 
prepared and cooked (Johnson et al. 1 985). This is the 
most common of the large carangid fishes caught by 
recreational fisherman on the west coast of Florida 
(Reid 1954). 

Indicator of Environmental Stress : The crevalle jack is 
not typically used in studies of environmental stress. 

Ecological : This is a large, pelagic carnivore that preys 
mainly on other fish (Hildebrand and Schroeder 1 928, 
Breuer 1949, Perret et al. 1971, Swingle and Bland 
1974). 

Range 

Overall : The range for this species includes the west- 
ern Atlantic from Nova Scotia to Uruguay, and tropical 
and temperate waters around the world, primarily in 
shallow continental waters. There is one record only 
from the Bahamas and a few from the West Indies, 
where it is probably uncommon. It is relatively more 
common in the northern part of its range (Hildebrand 
and Schroeder 1928, Bigelow and Schroeder 1953, 
Berry 1959, Hoese and Moore 1977, Fischer 1978, 
Johnson 1978). 

Within Study Area : This jack is present throughout the 
Gulf of Mexico. It is common in Texas and Louisiana 
waters and parts of the west coast of Florida (Hoese 
and Moore 1977, Fischer 1978) (Table 5.28). 

Life Mode 

This is a large pelagic fish common in offshore waters. 
It is most active during the day in the upper water 
column. Both adults and juveniles are schooling, but 


216 


Crevalle jack, continued 


Table 5.28. Relative abundance of crevalle jack 
31 Gulf of Mexico estuaries (from Volume /). 

Life stage 


;in 


Estuary 


A S J L E 


Florida Bay 


® 


® 


Ten Thousand Islands 


O 


O 


Caloosahatchee River 


O 


O 


Charlotte Harbor 


® 


o 


Tampa Bay 


® 


® 


Suwannee River 


o 


o 


Apalachee Bay 


o 


o 


Apalachicola Bay 


o 


o 


St. Andrew Bay 


o 


o 


Choctawhatchee Bay 


o 


o 


Pensacola Bay 


o 


o 


Perdido Bay 


o 


o 


Mobile Bay 


o 


o 


Mississippi Sound 


o 


O 


o 


o 


o 


Lake Borgne 


o 


Lake Pontchartrain 


o 


Breton/Chandeleur Sounds 


o 


o 


Mississippi River 


o 


Barataria Bay 


o 


o 


Terrebonne/Timbalier Bays 


V 


o 


Atchafalaya/Vermilion Bays 


o 


Calcasieu Lake 


o 


Sabine Lake 


V 


V 


Galveston Bay 


V 


o 


Brazos River 


o 


Matagorda Bay 


o 


o 


San Antonio Bay 


o 


o 


Aransas Bay 


o 


o 


Corpus Christi Bay 


o 


o 


Laguna Madre 


o 


® 


Baffin Bay 


o 


o 


A S J L E 


Relative abundance: 

9 Highly abundant 
® Abundant 
O Common 
V Rare 
blank Not present 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


some large adults are solitary (Arnold et al. 1960, 
Springer and Woodburn 1960, Perret et al. 1971, 
Swingle 1971, Christmas and Waller 1973, Swingle 
and Bland 1974, Benson 1982). 

Habitat 

Ty pe: Eggs and larvae are pelagic and offshore in 
marine salinities, and may be associated with offshore 
currents (Berry 1959, Benson 1982). Larvae are 
present in the Gulf of Mexico March through Novem- 
ber, reaching peak abundance June through August 
(Ditty et al. 1 988). Juveniles probably migrate inshore 
during the early juvenile stage (about 21 mm), and are 
frequently associated with floating debris and sargas- 
sum weed. Crevalle jack selectively inhabit inshore 
waters during the later part of the juvenile stage, 
usually in shallow, brackish areas and occasionally 
entering fresh water. Juveniles are found in bays, gulf 
passes, sounds, estuaries, brackish lakes and ponds, 
canals, and rivers, in salinities ranging from fresh to 
hypersaline (Hildebrand and Schroeder 1928, Gunter 
1945, Reid 1955, Simmons 1957, Darnell 1958, Berry 

1959, Arnold et al. 1960, Springer and Woodburn 

1 960, Tabb and Manning 1 961 , Gunter and Hall 1 963, 
Hoese 1 965, Kelley 1 965, Bechtel and Copeland 1 970, 
Franks 1 970, Perret et al. 1 971 , Swingle 1 971 , Dahlberg 

1 972, Christmas and Waller 1 973, Swingle and Bland 
1 974, Barret et al. 1 978, Lee et al. 1 980, Benson 1 982, 
Shipp 1986). 

Adults are pelagic and are associated with waters of 
the continental shelf and continental islands (Berry 
1 959). They are found in a wide range of depths from 
shallow inshore to oceanic waters (Benson 1 982), and 
in salinities ranging from fresh to hypersaline (Johnson 
1978). Collections have also been made in brackish 
estuarine waters, upstream in coastal rivers, and com- 
monly in shallow flats (Johnson 1978, Adams pers. 
comm.). In Texas, they occur in the nearshore area 
from February or March through October and some- 
times November, with variable peaks in abundance 
(Springer and Pirson 1958). Larger adults remain 
offshore and are seldom taken in bays and other 
inshore waters (Gunter 1945, Christmas and Waller 

1973, Lindall et al. 1973, Benson 1982). 

Substrate : Since this is a pelagic schooling fish, it is not 
associated with a particular bottom type, but it has 
been recorded from bottoms of mud, sand, shelly sand, 
and hard packed bottoms with a mud and algae film 
(Reid 1955, Gunter and Hall 1963, Benson 1982). 

Physical/Chemical Characteristics 

Temperature - Larvae: Larvae have been recorded 

from water temperatures of 20.0 to 29.0°C (Johnson 

1978). 


217 


Crevalle jack, continued 


Temperature - Juveniles and Adults: Juveniles and 
adults have been collected over a temperature range 
of 1 5.0 to 38.0°C (Gunter 1 945, Gunter and Hall 1 963, 
Franks 1 970, Roessler 1 970, Perret et al. 1 971 , Wang 
and Raney 1971, Christmas and Waller 1973, Perret 
and Caillouet 1974, Juneau 1975, Tarver and Savoie 
1 976, Barret et al. 1 978). The lower lethal temperature 
limit for juveniles is around 7.4-1 0.0°C (Hoff 1971, 
Gilmore et al. 1978). Their apparent preference is 
25.0-29.9°C (Perret et al. 1971). Adults are most 
common in temperatures of 18 to 33.6°C (Gunter 
1945, Johnson 1978). 

Salinity - Larvae: Larvae have been recorded in salini- 
ties of 35.2 to 36.7%o (Johnson 1978). 

Salinity - Juveniles and Adults: Both adults and juve- 
niles are considered euryhaline and have been found 
in waters with salinities ranging from 0.0 to 60.0%o 
(Gunter 1 942, Gunter 1 945, Reid 1 955, Gunter 1 956, 
Simmons 1 957, Gunter and Hall 1 963, Gunter and Hall 
1 965, Dugas 1 970, Franks 1 970, Roessler 1 970, Perret 
et al. 1971, Swingle 1971, Wang and Raney 1971, 
Dahlberg 1972, Christmas and Waller 1973, Perret 
and Caillouet 1974, Swingle and Bland 1974, Juneau 
1 975, Tarver and Savoie 1 976, Barrett et al. 1 978). In 
one study, fish 30 to 285 mm in total length (TL) were 
mostly caught in salinities above 30.0%o (Gunter 1 945). 
In another study, the majority of fish ranging from 20 to 
180 mm TL with an average size of 60 mm TL were 
collected from 1 0.0 to 1 9.9%, (Perret et al. 1 971 ). 

Dissolved Oxygen: Juveniles have been collected in 
waters with a dissolved oxygen (DO) range of 4.0 to 7.5 
parts per million (ppm) (Barrett et al. 1978). 

Movements and Migrations : Little is known about move- 
ments and migrations of this species, but they probably 
involve a complex pattern of spawning and develop- 
mental migrations, and temperature induced move- 
ments. Adults migrate offshore to spawn, but a con- 
certed migration is improbable due to the extended 
spawning season (Gunter 1945, Berry 1959, Moe 
1972, Johnson 1978, NOAA 1985). Larvae are asso- 
ciated with the northern movements of the Gulf Stream 
(Berry 1959). Early juveniles, 21-55 mm standard 
length (SL), migrate inshore. Juveniles enter bays and 
estuaries from the Gulf when the water temperature is 
above 20.0°C, and they have reached 90 to 285 mm TL 
in size (Gunter 1945, Benson 1982). They probably 
migrate south or move into warmer, offshore waters 
during colder months (Berry 1959). In Florida, the 
crevalle jack has been observed in shallow water at all 
times of the year except during winter months (Reid 
1 954). Juveniles and adults have been recorded along 
the Atlantic coast and in the Gulf of Mexico from April 
through November. However, they are most common 


in coastal waters of the Gulf from June to October 
(Joseph 1 952, Joseph and Yerger 1 956, Bass and Hitt 
1978). 

Reproduction 

Mode : This species has separate male and female 
sexes (gonochoristic). Fertilization is external, by 
broadcast of milt and roe. 

Spawning : Spawning evidently occurs over the outer 
shelf in oceanic waters greaterthan 40 m in depth (Ditty 
pers. comm.), and probably to the south of the Florida 
Straits (Berry 1 959, Hoese 1 965, Fahay 1 975, Benson 
1 982). The spawning season in the western Atlantic is 
thought to be March to September (Berry 1959). 

Fecundity : Actual fecundity is unknown. In one study, 
the ovaries of a 520 mm TL female with well developed 
eggs were 1 1 by 60 mm (Beebe and Tee- Van 1 928). 

Growth and Development 

Egg Size and Embryonic Development , and Age and 
Size of Larvae : The actual spawning locations of 
crevalle jack are not well known, and little is known 
about the development of eggs and larvae (Berry 1 959, 
Johnson 1978). 

Juvenile Size Range : Metamorphosis to the juvenile 
stage occurs around 12 mm SL (Ditty pers. comm.). 
The growth rate is reported to increase after juveniles 
reach a length of 50 mm (Nichols 1937, Johnson 
1 978). Age and size at sexual maturity remain uncer- 
tain. Males with developed testes have been collected 
when 540 to 690 mm SL in size (Berry 1 959), and a 406 
mm SL female was recorded as having well developed 
eggs (Beebe and Tee-Van 1928). 

Age and Size of Adults : Specific maximum sizes forthis 
species are uncertain. Lengths of 1010 mm TL and 
weights up to 25 kg have been documented, but 
unsubstantiated reports have recorded fish measuring 
more than 1 50 cm TL and weighing 32 kg (Berry 1 959, 
Fischer 1 978, Shipp 1 986). Adult females are typically 
larger than males of a given age (Berry 1959). 

Food and Feeding 

Trophic Mode : This species is a diurnal carnivore, 
apparently preying on small schooling fish of the coastal 
zone (Hildebrand and Schroeder 1928, Saloman and 
Naughton 1984). 

Food Items : This species has been observed in Florida 
feeding wildly along shorelines on larval fishes consist- 
ing mostly of ladyfish, anchovies, and cyprinodonts 
(Tabb and Manning 1961). Small jacks have been 
found to prey mostly on a variety of clupeids, while 
medium size fish usually ate clupeids and spa rids, and 


218 


Crevalle jack, continued 


large fish consumed various clupeids, carangids, and 
sparids (Saloman and Naughton 1984). Large fish 
appear to be more opportunistic than smaller ones, but 
food availability seems to a major factor in determining 
diet since it changes between sizes, seasons, areas, 
and years. Gulf menhaden is a favorite food (Breuer 
1949, Swingle and Bland 1974) as well as scaled 
sardine, anchovies, Spanish sardine, Atlantic bumper, 
pinfish, halfbeaks, crevalle jacks, and Atlantic 
cutlassfish. After fish, crustaceans such as penaeid 
shrimp or portunid crabs are the second most impor- 
tant prey item depending on area. In addition, numer- 
ous other fish are consumed as well as squid, bivalves, 
gastropods, echinoderms, sea grasses, algae, sand, 
and wood (Darnell 1958, Odum 1971, Benson 1982, 
Saloman and Naughton 1984). 

Biological Interactions 

Predation : Known predators include larger, fast swim- 
ming predators such as great barracuda and blackfin 
tuna (Berry 1959). 

Factors Influencing Populations : Parasites observed 
on this species include: Nematodes- Ascaris sp.; Ces- 
todes- Tetrarhyncus bisculatus; Trematodes- Disto- 
mum appendiculatum, D. tenue, Gasterostomum 
arcuatum, and G. gracilescens (Linton 1904). 

Personal communications 

Adams, Daniel R. Copano Causeway State Park, 
Rockport, TX. 

Ditty, James G. Louisiana State Univ., Baton Rouge, 
LA. 

References 

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Observations on fishes and other biota of East Lagoon, 
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Beebe, W.S., and J. Tee-Van. 1928. The fishes of 
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Benson, N.G. (ed.). 1982. Life history requirements of 
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Berry, F.H. 1959. Young jack crevalles (Caranx 
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Bigelow, H.B., and W.C. Schroeder. 1953. Fishes of 
the Gulf of Maine. Fish. Bull., U.S. 53:1-577. 

Breuer, J. P. 1949. A report on the effects of Port Arthur 
menhaden fishery on food and game fish for the period 
of June 6 to September 9, 1 949, inclusive. Tex. Game 
Fish Comm. Mar. Lab., Rockport, TX, 1949:84-93. 

Christmas, J.Y., and R.S. Waller. 1973. Estuarine 
vertebrates, Mississippi. In Christmas, J.Y., (ed.), 
Cooperative Gulf of Mexico estuarine inventory and 
study, Mississippi, p. 320-434. Gulf Coast Research 
Laboratory, Ocean Springs, MS. 

Dahlberg, M.D. 1972. An ecological study of Georgia 
fishes. Fish. Bull., U.S. 70:323-353. 

Darnell, R.M. 1958. Food habits of fishes and larger 
invertebrates of Lake Pontchartrain, Louisiana, an 
estuarine community. Publ. Inst. Mar. Sci., Univ. 
Texas 5:353-416. 

Ditty, J.G., G.G. Zieske, and R.F. Shaw. 1988. Sea- 
sonality and depth distribution of larval fishes in the 
northern Gulf of Mexico above 26°00' N. Fish. Bull., 
U.S. 86(4):81 1-823. 

Dugas, R.J. 1970 An ecological survey of Vermilion 
Bay, 1968-1969. M.S. thesis, Univ. Southwestern 
Louisiana, Lafayette, LA, 108 p. 


Bass, D.G., and V.G.Hitt. 1978. Sport fishery ecology 
of the Escambia River, Florida. Northwest Streams 
Research Project, Fla. Game Freshwater Fish Comm., 
Tallahassee, FL. 

Barrett, B.B., J.L. Merrell, T.P. Morrison, M.C. Gillespie, 
E.J. Ralph, and J.F. Burdon. 1978. A study of 
Louisiana's major estuaries and adjacent offshore 
waters. Louis. Dept. Wildl. Fish., Tech. Bull. No. 27, 
197 p. 


Fahay, M.P. 1975. An annotated list of larval and 
juvenile fishes captured with surface-towed meter net 
in the south Atlantic Bight during four RV Dolphin 
cruises between May 1 967 and February 1 968. NOAA 
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Fischer, W. (ed.). 1978. FAO Species Identification 
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nization of the United Nations, Rome. 


Bechtel, T.J., and B.J. Copeland. 1970. Fish species 
diversity indices as indicators of pollution in Galveston 
Bay, Texas. Contrib. Mar. Sci. 15:103-132. 


219 


Crevalle jack, continued 


Franks, J. S. 1970. An investigation of the fish popu- 
lation within the inland waters of Horn Island, Missis- 
sippi, a barrier island in the northern Gulf of Mexico. 
Gulf Res. Rep. 3(1):3-104. 

Gilmore, R.G., L.H. Bullock, and F.H. Berry. 1978. 
Hypothermal mortality in marine fishes of south-central 
Florida, January, 1 977. Northeast Gulf Sci. 2(2):77-97. 

Goode, G.B. 1884. The fisheries and fishing industry 
of the United States. Sec. I, Natural history of useful 
aquatic animals. U.S. Comm. Fish, Washington, DC, 
895 p., 277 pi. 

Gunter, G. 1942. A list of the fishes of the mainland of 
North and Middle America recorded from both fresh- 
water and sea water. Am. Midi. Nat. 28(2):305-326. 

Gunter, G. 1945. Studies on marine fishes of Texas. 
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Gunter, G. 1956. A revised list of euryhaline fishes of 
North and middle America. Am. Midi. Nat. 56:345-354. 

Gunter, G., and G.E. Hall. 1963. Biological investiga- 
tions of the St. Lucie estuary (Florida) in connection 
with Lake Okeechobee discharges through the St. 
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Gunter, G., and G.E. Hall. 1965. A biological investi- 
gation of the Caloosahatchee estuary of Florida. Gulf 
Res. Rep. 2(1):1-64. 

Hildebrand, S.F., and W.C. Schroeder. 1928. Fishes 
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220 


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221 


Florida pompano 


Trachinotus carolinus 
Adult 


8 cm 


(from Goode 1884) 


Common Name: Florida pompano 
Scientific Name: Trachinotus carolinus 
Other Common Names: pompano, common pom- 
pano, Atlantic pompano, sunfish, pampano amarillo 
(Spanish), pompaneau sole (French) (Hildebrand and 
Schroeder 1928, Gunter 1945, Arnold et al. 1960, 
Gunterand Hall 1 965, Hoese 1 965, Parker 1 965, Berry 
and Iversen 1967, Fischer 1978, Benson 1982, NOAA 
1985). 

Classification (Robins et al. 1991) 
Phylum: Chordata 
Class: Osteichthyes 
Order: Perciformes 
Family: Carangidae 

Value 

Commercial : This fish is highly desired due to its 
excellent flavor and high market value. Although 
catches are not large and are often unpredictable, the 
Florida pompano supports an important fishery along 
the South Atlantic and Gulf of Mexico coasts, with 
Florida the leading producer. Most fish caught in 
Florida are landed during winter on the west coast from 
Monroe County to Charlotte County, primarily south of 
Cape Romano. Commercially harvested fish enterthe 
market at total lengths (TL) of 250-360 mm and 0.5-0.7 
kg. They were historically harvested mostly by tram- 
mel nets, but with the advent of nylon monofilament 
most are now taken by gill nets (Hildebrand and 
Schroeder 1928, Gunter 1945, Fields 1962, Berry and 
Iversen 1967, Finucane 1969a, Iversen and Berry 
1 969, Bellinger and Avault 1 970). 

Recreational : Florida pompano are a favorite fish among 
anglers due to their high quality as a food fish and their 
fighting ability on light tackle. An estimated 269,000 


fish were caught by anglers during 1991 in the Gulf of 
Mexico (Van Voorhees et al. 1992). Pompano are 
usually caught by bottom fishing offshore, or by casting 
from shore or boat (Gunter 1945, Berry and Iversen 
1967, Iversen and Berry 1969, Bellinger and Avault 
1970). 

Indicator of Environmental Stress : Florida pompano 
are not typically used in studies of environmental 
stress. 

Ecological : The Florida pompano is found in coastal 
and estuarine waters, where it is a generalized carni- 
vore feeding primarily on benthic prey. Juveniles can 
be a dominant species of the surf zone (Gunter 1958, 
Bellinger and Avault 1971, Benson 1982). 

Range 

Overall : The Florida pompano is found in the coastal 
waters from Cape Cod, Massachusetts to southeast- 
ern Brazil. It is widely distributed but uncommon 
among islands of the West Indies, being most abun- 
dant along continental waters. It is also uncommon 
north of Cape Hatteras, and the highest abundance 
occurs along the Florida coast (Hildebrand and 
Schroeder 1 928, Fields 1 962, Berry and Iversen 1 967, 
Iversen and Berry 1969, Gilbert 1986, Shipp 1986). 

Within Study Area : This species occurs throughout the 
Gulf of Mexico, but is most abundant along the west 
coast of Florida from Florida Bay to Charlotte Harbor 
(Table 5.29) (Hoese and Moore1977, Fischer 1978, 
Gilbert 1986). In the western Gulf of Mexico, it is 
apparently more common south of the Rio Grande, in 
Mexico, than in Texas (Hildebrand 1954). 


222 


Florida pompano, continued 


Table 5.29. Relative abundance of Florida pompano 
in 31 Gulf of Mexico estuaries (Nelson et al. 1992). 


Life 


stage 


Estuary 


A S J L E 


Florida Bay 


• 


® 


Ten Thousand Islands 


o 


O 


Caloosahatchee River 


V 


V 


Charlotte Harbor 


® 


® 


Tampa Bay 


o 


o 


Suwannee River 


V 


V 


Apalachee Bay 


o 


o 


Apalachicola Bay 


V 


V 


St. Andrew Bay 


o 


o 


Choctawhatchee Bay 


o 


o 


Pensacola Bay 


V 


o 


Perdido Bay 


o 


Mobile Bay 


o 


V 


V 


V 


Mississippi Sound 


V 


o 


® 


o 


o 


Lake Borgne 


Lake Pontchartrain 


BretorVChandeleur Sounds 


o 


o 


o 


o 


o 


Mississippi River 


o 


Barataria Bay 


o 


Terrebonne/Timbalier Bays 


V 


o 


Atchafalaya/Vermilion Bays 


V 


Calcasieu Lake 


o 


Sabine Lake 


Galveston Bay 


o 


Brazos River 


Matagorda Bay 


o 


San Antonio Bay 


o 


o 


Aransas Bay 


V 


o 


Corpus Christi Bay 


V 


o 


Laguna Madre 


o 


® 


Baffin Bay 


V 


V 


A S J L E 


Relative abundance: 

# Highly abundant 

® Abundant 

O Common 

V Rare 

blank Not present 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


Life Mode 

Pompano are a dominant species of exposed sandy 
beach habitats. All stages are pelagic and nektonic, 
with diurnal feeding behavior (Finucane 1969b, 
Armitage and Alevizon 1980, Modde and Ross 1981, 
Benson 1982). Juveniles and adults show schooling 
behavior (Benson 1982, Christmas and Waller 1973, 
Simmons 1957). 

Habitat 

Type : Eggs and larvae are pelagic in offshore waters. 
Larvae have been collected in depths of 5.5 m and as 
far as 24.2 km offshore in marine waters (Fields 1 962, 
Finucane 1969a, Fahay 1975, Johnson 1978). The 
optimum habitat for juveniles is shallow water, low 
energy, marine surf zones along open beaches with 
gradual slopes; however, they are also reported from 
marshes and bays (Gunter 1 945, Gunter 1 958, Springer 
and Woodburn 1960, Gunter and Hall 1965, Hoese 
1965, Iversen and Berry 1969, Bellinger and Avault 
1971, Swingle 1971, Dahlberg 1972, Armitage and 
Alevizon 1980, Modde 1980, Modde and Ross 1981). 
They are collected in salinities ranging from mesohaline 
to euhaline, but appear to prefer polyhaline and higher 
salinities (Gunter 1 945, Springer and Woodburn 1 960, 
Gunter and Hall 1965, Finucane 1968, Bellinger and 
Avault 1970, Swingle 1971, Christmas and Waller 
1973, Johnson 1978). Adults are abundant around 
inlets and along sandy beaches of barrier islands, and 
around oil platforms and artificial reefs. They tend to be 
more characteristic of marine waters in turbid rather 
than clear areas, although they are collected occasion- 
ally from bay waters. The recorded salinities for sites 
where adults have been collected range from 
mesohaline to euhaline, but captive fish have been 
adapted to fresh water. Adults may be found in shallow 
waters, but are also found in waters somewhat deeper 
than juveniles with fish over 200 mm TL being collected 
from depths of 33 to 40 m (Hildebrand 1954, Parker 
1 965, Finucane 1 969a, Johnson 1 978, Benson 1 982). 

Substrate : The Florida pompano is typically found over 
sandy bottoms with little or no rooted vegetation. They 
are also reported from bottoms of broken shell debris, 
and silt and mud (Bellinger and Avault 1971, Modde 
1980, Modde and Ross 1981). 

Physical/Chemical Characteristics : 

Temperature - Eggs and Larvae: Eggs in laboratory 

conditions developed up to middle and late gastrula- 

tion at temperatures from 23.0 to 25.0° (Finucane 

1969b). 

Temperature - Juveniles and Adults: Juveniles have 
been taken from 10.0° to 34.9°C and (Gunter 1945, 
Springer and Woodburn 1 960, Gunter and Hall 1 963, 
Gunter and Hall 1 965, Finucane 1 969a, Bellinger and 


223 


Florida pompano, continued 


Avault 1 970, Perret et al. 1 971 , Christmas and Waller 
1 973), and adults from a temperature range of 17.0° to 
31 .7°C (Finucane 1 969a, Johnson 1 978). The majority 
of fish collected are from a temperature range of 28.0 
to 31 .7°C (Finucane 1 969a). Temperature appears to 
strongly affect the presence and behavior of this spe- 
cies. Experimental work has shown the need for stable 
temperatures for maximum growth, with the ideal tem- 
perature being 25.0°C or above (Finucane 1969b). 
Feeding is reduced below 18.0°C, and ceases at 
1 3.0°C. Activity is also greatly reduced at this tempera- 
ture (Finucane 1968). Physiological shock becomes 
evident at about 12.0°C with partial to complete kills 
occurring from 10.0° to 15.5°C (Berry and Iversen 
1967, Moe et al. 1968). All fish have an upper lethal 
limit of about 38.0°C, although small juveniles have 
been observed in tide pools at temperatures above 
46.0°C (Moe et al. 1968). 


Gulf of Mexico, larvae are present May through August 
(Ditty et al. 1988) as they move with currents. Young 
pompano arrive in the surf zone as juveniles, at a size 
of approximately 1 to 1 5 mm TL (Bellinger and Avault 
1 970, Bellinger and Avault 1 971 , Christmas and Waller 
1973, Finucane 1969a, Gunter 1945, Hoese 1965, 
Moe et al. 1968, Perret et al. 1971, Modde 1980, 
Modde and Ross 1 981 ). Juveniles leave the surf zone 
when 75 to 150 mm TL for deeper water and move 
south along the coast, probably in response to colder 
winter temperatures (Bellinger and Avault 1 970, Berry 
and Iversen 1967, Fields 1962, Gunter 1945, Iversen 
and Berry 1969, Swingle 1971). 

Reproduction 

Mode : This species has separate male and female 
sexes (gonochoristic). Fertilization is external, by 
broadcast of milt and roe. 


Salinity - Eggs and Larvae: Under laboratory condi- 
tions, eggs developed up to middle and late gastrula- 
tion at salinities of 31 .2 to 37.71%o (Finucane 1969b). 

Salinity - Juveniles: Juveniles have been reported from 
salinities ranging from 9.3 to 36.7% , with a preference 
shown for 20%o and higher (Gunter 1 945, Springer and 
Woodburn 1960, Gunter and Hall 1963, Gunter and 
Hall 1965, Finucane 1968, Finucane 1969a, Bellinger 
and Avault 1970, Perret et al. 1971, Swingle 1971, 
Christmas and Waller 1973). One collection from 
Laguna Madre, Texas reported large schools at 45 to 
50%o (Simmons 1967). Fish in laboratory conditions 
were able to tolerate salinities down to 1 .27%o (Moe et 
al. 1968). 

Salinity - Adults: Adults occur in salinities from 32.1 to 
35.6%o. They do not normally enter water less than 
32%o, although fish in captivity were acclimated to 
1 .27%o (Moe et al. 1 968, Johnson 1 978). 

Dissolved Oxygen: This species has been collected 
from a dissolved oxygen (DO) range of 3.43 to 5.64 
parts per million (ppm), but is adversely affected below 
4 ppm with death occurring at about 2.5 ppm (Finucane 
1969a, Moeetal. 1968). 

pH: Experiments with pH showed physiological shock 
at 1 1 .9 and 3.9 on either end of the scale, and death 
occurring at 12.4 and 3.7 (Moe et al. 1968) 

Movements and Migrations 

The Florida pompano apparently undergoes extensive 
migrations, but patterns of movement are not clearly 
known. Spawning apparently takes place in offshore 
waters in early spring to late summer in the Gulf Stream 
or in locations where transport of eggs and larvae are 
influenced by current (Fields 1 962, Moe 1 972). In the 


Spawning : Spawning has not been directly observed. 
Specific spawning areas are unknown, but they are 
probably offshore (Fields 1962, Berry and Iversen 

1967, Finucane 1969a, Sabins and Truesdale 1974, 
Fahay 1975, Gilbert 1986), and spawning may occur 
over an extended period of time. It may begin as early 
as February and peak from April to June followed by 
lesser spawnings in summer and early fall (July-Octo- 
ber). Spawning throughout the year is possible in the 
tropical Gulf of Mexico and the Caribbean Sea (Gunter 
1 945, Gunter 1 958, Berry and Iversen 1 967, Finucane 
1 969a, Iversen and Berry 1 969, Christmas and Waller 
1973, Sabins and Truesdale 1974). 

Fecundity : Maturity probably occurs after one year with 
spawning unlikely until the second year (Finucane 

1968, Moe et al. 1968). At least four different egg 
development stages are present in adult females indi- 
cating multiple spawning (Finucane 1968) with an 
average size female containing 4 to 8 hundred thou- 
sand eggs (Finucane 1968, Moe et al. 1968, Finucane 
1969a). 

Growth and Development 

Egg Size and Embryonic Development : Mature unfer- 
tilized eggs are round, symmetrical, and average 0.7 
mm in diameter. They possess a large yolk with a 
narrow perivitelline space occupying 10 to 15% of the 
egg volume. One oil globule is evident, and the surface 
of the egg is smooth (Finucane 1968,1969a). Fertil- 
ized eggs are spherical with a single, large oil globule, 
partially segmented yolk mass, narrow perivitelline 
space, and a sculptured membrane. Average diam- 
eter of the oil globule and egg is 0.29 mm, and 0.92 mm 
respectively. Eggs are almost colorless and have an 
irregularly segmented light yellow yolk. The oil globule 
is nearly spherical and is dark yellow in a position at the 
top of the egg. No chromatophores are present 


224 


Florida pompano, continued 


(Finucane 1 969b). Eggs incubated at 23°-25°C under 
laboratory conditions reached blastula stage 10-12 
hours after fertilization; mid to late gastrulation re- 
quired 20-22 hours. Eggs did not survive past that 
stage (Finucane 1969b). 

Age and Size of Larvae : In the month it takes larvae to 
reach coastal beaches after being spawned, larvae 
increase in size from 3 to 1 2 mm SL or longer (Finucane 
1969a). 

Juvenile Size Range : The juvenile stage begins when 
fish reach a standard length (SL) of about 7.0 mm and 
larger. At 7.0 mm SL dorsal and anal spines are 
prominent and soft rays evident. At 150 mm SL, all but 
dentary teeth disappear; and by about 1 70 mm SL the 
dentary teeth are not evident (Fields 1962). Daily 
growth rates range from 0.5 mm/day for fish in the surf 
zone to 1.3 mm/day for hatchery reared specimens 
(Bellinger and Avault 1970, Johnson 1978). Rates of 
25 to 42 mm for monthly growth under optimal condi- 
tions has been noted with 255 to 356 mm TL possible 
for first year growth (Finucane 1 968, 1 969a, Moe et al. 
1968, Bellinger and Avault 1970). A weight gain of 18 
g/month was reported for hatchery reared fish and 
weights of 454 to 567 g were considered possible as a 
first year weight for fish in mariculture (Finucane 1 968, 
1969b). 

Age and Size of Adults : Wild fish probably first spawn 
in their second year, but in hatchery culture it may be 
possible to spawn them in less than 2 years (Finucane 
1 968, Moe et al. 1 968). Ripe fish taken in Florida were 
275 to 380 mm TL and weighed 456 to 1 1 40 g (Finucane 
1 968). Other Florida studies reported ripe females with 
fork lengths (FL) of 255 and 356 mm, and females with 
developing oocytes were 273 to 400 mm FL and 
weighed 468 to 596 g. Ripe males were collected with 
a length range of 225 to 230 mm FL (Finucane 1968, 
1969a, Moeetal. 1968). The maximum size forthisfish 
is about 450 mm TL (Hoese and Moore 1 977). Florida 
pompano probably live 3 or 4 years under natural 
conditions (Berry and Iversen 1967). 

Food and Feeding 

Trophic Mode : Florida pompano are a generalized 
carnivore that feed primarily during the day on infaunal 
bottom bivalves (Finucane 1 969a, Bellinger and Avault 
1971, Armitage and Alevizon 1980, Benson 1982). 
Adults have large, well developed pharyngeal plates 
which allow them to feed on hard-shelled prey items 
such as bivalves and crabs (Bellinger and Avault 
1971). Smaller pompano are opportunistic feeders, 
apparently preying on those organisms that are most 
available at the time and utilizing the surf to help 
uncover food. As juvenile pompano grow in size, they 
undergo a shift towards hard-shelled prey items 


(Bellinger and Avault 1971). 


Food Items : Smallest size classes feed primarily on 
benthic and pelagic invertebrates, frequently eating 
polychaetes, amphipods, gastropod larvae, insects, 
and some calanoid copepods. The frequency of these 
items decrease as the fish grows (Hildebrand and 
Schroeder 1928, Berry and Iversen 1967, Bellinger 
and Avault 1 971 ). Fish 1 to 25 mm TL were found to 
have eaten polychaetes, amphipods, gastropod lar- 
vae, mysids, brachuran megalops, and dipteran lar- 
vae. When 26 to 50 mm TL they ate fewer polychaetes 
and amphipods, and ate a wider variety of organisms, 
but still fed heavily on gastropod larvae, post larval 
shrimp, clams, and brachuran megalops. Fish 76 to 
125 mm TL fed most frequently on small clams espe- 
cially Donax variablis and Hippa species. Larger 
juveniles have also been reported to feed on crab 
larvae, barnacles, cumacea, and fish eggs and larvae 
(Springer and Woodburn 1960, Fields 1962, McFarland 
1963, Berry and Iversen 1967, Finucane 1969a, 
Bellinger and Avault 1971, Modde and Ross 1981). 
Prey of fish 200 to 275 mm SL were primarily bivalves 
such as Tellina, Donax variablis, and Brachiodon 
exustus (Finucane 1 968, Armitage and Alevizon 1 980). 
Although not major prey items, larger pompano have 
been reported to eat shrimp, crabs, and fish (Gunter 
1945, Gunter 1958, Miles 1949). 

Biological Interactions 

Predation : No studies have identified Florida pompano 
as a regular item in the diet of other fishes or higher 
vertebrates (Gilbert 1986). Juveniles are probably 
preyed on by larger fish and birds that forage along the 
beaches. 

Factors Influencing Populations : Several parasites have 
been reported for this species including protozoans, 
nematodes encysted in the viscera or in the body 
cavity, cestodes encysted in mesentary and on vis- 
cera, trematodes, isopods in the mouth, gill area, and 
various body parts and fins, and copepods on the skin 
(Linton 1904, Finucane 1968). However, infestations 
do not appear to be heavy, and there is no evidence 
that parasites or diseases are a threat to this species in 
its natural habitat (Gilbert 1986). 

References 

Armitage, T.M., and W.S. Alevizon. 1980. The diet of 
the Florida pompano (Trachinotus carolinus) along the 
east coast of central Florida. Fla. Sci. 43(1): 19-26. 

Arnold, E.L., Jr., R.S. Wheeler, and K.N. Baxter. 1 960. 
Observations on fishes and other biota of East Lagoon, 
Galveston Island. U.S. Fish Wildl. Serv., Spec. Sci. 
Rep. Fish. No. 344, 30 p. 


225 


Florida pompano, continued 


Bellinger, J.W., and J.W. Avault, Jr. 1970. Seasonal 
occurrence, growth, and length-weight relationship ot 
juvenile pompano, Trachinotus carolinus in Louisiana. 
Trans. Am. Fish. Soc. 99(2):353-358. 

Bellinger, J.W., and J.W. Avault, Jr. 1971 Food habits 
of juvenile pompano, Trachinotus carolinus, in Louisi- 
ana. Trans. Am. Fish. Soc. 100(3):486-494. 

Benson, N.G., (ed.). 1982. Life history requirements 
of selected finfish and shellfish in Mississippi Sound 
and adjacent areas. U.S. Fish Wild). Serv. Biol. Rep., 
FWS/OBS-81/51,97p. 

Berry, F., and E.S. Iversen. 1967. Pompano: Biology 
fisheries and farming potential. Proc. Gulf Caribb. 
Fish. Inst. 19:116-128. 

Christmas, J.Y., and R.S. Waller. 1973. Estuarine 
vertebrates, Mississippi. In Christmas, J.Y., (ed.), 
Cooperative Gulf of Mexico estuarine inventory and 
study Mississippi, p. 320-434. Gulf Coast Research 
Laboratory, Ocean Springs, MS. 

Dahlberg, M.D. 1972. An ecological study of Georgia 
fishes. Fish. Bull., U.S. 70:323-353. 


Finucane, J.H. 1969b. Faunal production report. Rept. 
Bur. Comm. Fish. Biol. Lab., St. Petersburg Beach, 
Fla., Fiscal Year 1 969. U.S. Bur. Comm. Fish. Circ. No. 
342, p. 11-18. 

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227 


Gray snapper 


Lutjanus griseus 
Adult 


8 cm 


(from Fischer 1 978) 


Common Name: gray snapper 
Scientific Name: Lutjanus griseus 
Other Common Names: mangrove snapper, mango 
snapper, black snapper (Shipp 1 986); Pensacola snap- 
per (Goode 1884); ivaneau sardear/se(French), pargo 
prieto (Spanish) (Fischer 1978, NOAA 1985). 
Classification (Robins et al. 1991) 
Phylum: Chordata 
Class: Osteichthyes 
Order: Perciformes 
Family: Lutjanidae 

Value 

Commercial : The commercial fishery for gray snapper 
is used as a seasonal supplement to other fisheries. 
Hook and line, long line, and fish traps are the main 
fishing methods, but boat seines and gill nets are also 
used. The main fishing grounds are continental and 
island shelf waters, especially in the vicinity of Cuba, 
south Florida, Laguna Madre, and Venezuela (Starck 
and Schroeder 1971, Fischer 1978, Bortone and Wil- 
liams 1986, Grimes 1987). In U.S. federal waters of the 
Gulf of Mexico, a 12 inch minimum size limit applies 
(GMFMC 1 996a). This species is marketed mostly as 
a fresh product and is considered an excellent food fish 
(Fischer 1978). 

Recreational : The gray snapper is common in Florida 
and supports an important sport fishery with 3 and 4 
year old fish making up most of the inshore harvest 
(Rutherford et al. 1989b). The most common angling 
method is hook and line with cut bait, but in southern 
Florida they are also caught by fish traps and spear 
guns (Bortone and Williams 1986). The largest land- 
ings occur in Florida where, in 1986, approximately 
1 ,540,000 fish were landed recreationally (Starck and 


Schroeder 1971, NMFS 1987). Greatest catches 
occur in late summer. In U.S. federal waters of the Gulf 
of Mexico, a 12 inch minimum size limit and daily bag 
limit have been established (GMFMC 1996b). 

Indicator of Environmental Stress : This species is not 
typically used in studies of environmental stress. 

Ecological : The gray snapper is a general carnivore. 
Adults and particularly juveniles are associated with 
estuarine areas. Along with other snappers, this spe- 
cies is an important component of marine, nearshore 
reef, or reef-like biotopes (Bortone and Williams 1 986). 

Range 

Overall : The gray snapper is found in the western 
Atlantic, tropical and subtropical marine and estuarine 
waters of Florida, the West Indies, Bermuda, the Baha- 
mas, and the shelf waters of the Gulf of Mexico. 
Occasionally juveniles are found as far north as Cape 
Cod, Massachusetts and as far south as Rio de Janeiro, 
Brazil (Croker 1962, Starck and Schroeder 1971, 
Fischer 1978, NOAA 1985). 

Within Study Area : This species is distributed through- 
out the Gulf of Mexico. It is common along the entire 
Florida west coast increasing in abundance south- 
ward, and is the most common species of snapper in 
Florida Bay and adjacent estuaries (Tabb and Manning 
1 961 ). It is less common along the central and western 
Gulf coast (Starck and Schroeder 1971, Hoese and 
Moore 1 977, Shipp 1 986). The relative abundance of 
gray snapper in 31 Gulf of Mexico estuaries is depicted 
in Table 5.30 (Nelson et al. 1992, Comyns pers. 
comm., VanHoose pers. comm.). 


228 


Gray snapper, continued 


Table 5.30. Relative abundance of gray snapper in 
31 Gulf of Mexico estuaries (from Volume t}. 


Life 


stage 


Estuary 


A S J L E 


Florida Bay 


• 


Ten Thousand Islands 


O 


Caloosahatchee River 


V 


Charlotte Harbor 


O 


o 


Tampa Bay 


o 


Suwannee River 


O 


o 


Apalachee Bay 


O 


o 


Apalachicola Bay 


V 


V 


St. Andrew Bay 


o 


o 


Choctawhatchee Bay 


o 


o 


Pensacola Bay 


® 


o 


Perdido Bay 


o 


Mobile Bay 


V 


o 


Mississippi Sound 


V 


o 


Lake Borgne 


Lake Pontchartrain 


Breton/Chandeleur Sounds 


o 


Mississippi River 


Barataria Bay 


o 


Terrebonne/Timbalier Bays 


V 


AtchafalayaA/ermilion Bays 


Calcasieu Lake 


V 


Sabine Lake 


Galveston Bay 


V 


Brazos River 


Matagorda Bay 


V 


V 


San Antonio Bay 


V 


Aransas Bay 


V 


V 


Corpus Christi Bay 


V 


V 


Laguna Madre 


V 


o 


Baffin Bay 


V 


V 


A S J L E 


Relative abundance: 

Highly abundant 

® Abundant 

O Common 

V Rare 

blank Not present 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


Life Mode 

Eggs can be considered pelagic and non-adhesive, 
and occur in offshore waters (Thresher 1984, Shaffer 
pers. comm.). Larvae whose total length (TL) is under 
1 mm are planktonic and occur offshore (Bortone and 
Williams 1 986). Juveniles are pelagic and non-school- 
ing in early stages; larger juveniles are weak schoolers 
(Starck 1971, Hardy 1978). Adults are pelagic and 
demersal, and are often in schools diurnally, dispers- 
ing by night and moving to inshore grass beds (Croker 
1 962, Starck and Schroeder 1 971 , Hardy 1 978, NMFS 
1987, Sogardetal. 1989). 

Habitat 

Type : Eggs are marine, neritic, and demersal (Starck 
and Schroeder 1 971 ). Larvae are marine, neritic, and 
planktonic. Their range is not reported, but they are 
known to occur in offshore shelf waters and near coral 
reefs. Larvae of Lutjanus species are known to be 
present in the Gulf of Mexico April through November, 
with an abundance peak June through August (Ditty et 
al. 1988). Gray snapper pre-juveniles begin to move 
into estuarine habitats and have been collected in 
grass beds (Starck and Schroeder 1971, Richards et 
al. 1984, Hardy 1978). Juveniles are estuarine, river- 
ine and marine, and are found in estuaries, channels, 
bayous, ponds, coastal marshes, mangrove swamps, 
and freshwater creeks. Older juveniles may move to 
offshore habitats with adults and can occur as far out 
as 1 4 km. Juveniles occupy inshore grassy areas until 
they reach lengths of 80 mm (Croker 1962, Starck 
1971). They are sometimes associated with areas of 
swift tidal flow, and, less frequently, will occupy areas 
around ledges, pilings, jetties, rocks, coral hedges, 
grass, orgorgonian coral patches (Starckand Schroeder 
1 971 ; Hardy 1 978). In Florida Bay, they prefer habitats 
where seagrass density and species diversity is high 
(Chester and Thayer 1 990). Adults are marine, estua- 
rine, and riverine. They occur offshore up to 32 km near 
coral reefs, rock shelves and similar structures, and 
inshore near ledges of channels and around artificial 
structures, and in estuaries, mangrove swamps and 
lagoons. They have also been reported in coastal plain 
freshwater drainage canals, creeks and rivers, and 
even from some coastal freshwater lakes. This spe- 
cies has been reported from depths ranging from to 
180 m with smaller snapper generally inhabiting shal- 
lower water than larger snapper (Lee et al. 1980, 
Bortone and Williams 1 986, Loftus and Kushlan 1 987, 
Chester and Thayer 1990). 

Substrate : Eggs are typically found in proximity to 
offshore reefs (Starck and Schroeder 1 971 , Rutherford 
et al. 1983, Powell et al. 1987). Powell et al. (1987) 
noted pre-flexion larvae "candidates" over offshore 
reefs. Lutjanidae larvae have been reported in shelf 
waters from Florida to Texas. Postflexion larvae and 


229 


Gray snapper, continued 


juveniles (15-35 mm) are present in shallow basins 
with Thalassia present adjacent to mud banks, and 
postlarval juveniles have been found over dense (1000- 
4000 shoots/m 2 ) seagrass beds of Halodule wrightii 
and Syringodium filiforme. Juveniles are recorded 
from Thalassia grass flats; soft marl bottoms, marl 
sands, fine marl mud with shell and rock outcrops, and 
detritus; seagrass meadows and mangrove roots; 
seagrass meadows near jetties and pilings (Tabb and 
Manning 1 961 , Rutherford et al. 1 983, Rutherford et al. 
1989a). Adults typically occur around hard bottoms, 
natural and artificial, but also soft bottoms; wharves, 
pilings, rocky areas; sand, rubble, rock with supporting 
alcyonarians, sponges and Thalassia; coral reefs, rock 
outcrops, shipwrecks; sandy grass beds, coral reefs, 
sandy, muddy and rocky bottoms (Springer and 
Woodburn 1960, Starck and Davis 1966, Starck and 
Schroeder 1 971 , Manooch and Matheson 1 984). It is 
also suggested that the preferred substrate is mud. 
They are occasionally found in areas of alcyonarian or 
algal growths. In one study, specimens between 110 
and 275 mm were recorded in areas of mud to shelly- 
sand bottoms (Lindall et al. 1973). 


are considered to be generally non-migratory, and tend 
to remain in areas in which they have become estab- 
lished. A mark-recapture study in Florida, however, 
found movement to the southwest as the individuals 
grew, with a mean travel distance of 1 8.3 km (Bryant et 
al. 1989). Some movements are noted in connection 
with feeding, environmental conditions, and seasonal 
spawning. Mature fish migrate to offshore reefs during 
the summer to spawn. Most return to the inshore and 
estuarine habitats, however, some remain near the 
reefs (Starck and Schroeder 1 971 ). Adults that inhabit 
reefs move off into surrounding waters to feed at night 
(Starck and Davis 1966, Moe 1972). 

Reproduction 

Mode : The gray snapper has separate male and fe- 
male sexes (gonochoristic), but exhibits no apparent 
external dimorphism. Sex ratio is reported as equal 
(Croker 1 962, Starck and Schroeder 1 971 , Rutherford 
et al. 1 983). Eggs and milt are broadcast into the water 
column, and fertilization is external, with no indication 
of nest building or egg guarding (Starck and Schroeder 
1971, Grimes 1987). 


Physical/Chemical Characteristics : 
Temperature: Eggs are found in the marine seawater 
zone in the vicinity of offshore reefs (Starck and 
Schroeder 1971). Larvae have been recorded occur- 
ring in ranges of 1 5.6 to 27.2°C (Hardy 1 978) and 26 to 
28°C in vitro (Richards and Saksena 1980). Juveniles 
are found in temperature ranges of 17.2° to 36.0°C 
(Hardy 1978); 16 to 31 °C (Tabb and Manning 1961); 
and 12.8° to 31.7°C (Rutherford et al. 1989a). Adults 
occur in water temperatures from 13.4° to 32.5°C 
(Springer and Woodburn 1960, Wang and Raney 
1 971 ), and their lower lethal limit is 1 1 °-1 4°C (Starck 
and Schroeder 1971). Increased mortalities accom- 
pany sudden temperature drops (Starck 1971). 

Salinity: Eggs have been hatched in vitro in a salinity 
range from 32 to 36%o (Richards and Saksena 1980). 
Larvae and juveniles are euryhaline. Juveniles have 
been observed in salinities ranging from to 66.6%o 
(Tabb and Manning 1 961 , Bortone and Williams 1 986, 
Rutherford et al. 1 983, Rutherford et al. 1 989a). Adults 
are euryhaline and have been found in salinities rang- 
ing from to 47.7%o (Hardy 1978, Wang and Raney 
1971). 

Migrations and Movements : Newly hatched larvae are 
planktonic, but develop rapidly and make their way to 
the inshore nursery areas at about 1 mm (Starck and 
Schroeder 1 971 , Chester and Thayer 1 990). By about 
80 mm, early juveniles move to deeper estuarine 
habitats, but have been observed moving out of an 
area in response to extreme temperatures (Starck and 
Schroeder 1971, Chester and Thayer 1990). Adults 


Spawning : The gray snapper is a summer spawner, 
typically from June through August, but is also reported 
to spawn in September in the Florida Keys (Starck and 
Schroeder 1971, Grimes 1987). Spawning occurs 
offshore in the Gulf of Mexico around reefs or shoals. 
Evidence indicates batch spawning occurs at night 
near full moons throughout the reproductive cycle 
(Starck and Schroeder 1971, Grimes 1987). The 
spawning season may be protracted over a long period 
(Druzhinin 1970). 

Fecundity : Since gray snapper are multiple spawners, 
batch fecundity and spawning frequency must be esti- 
mated in order to describe overall fecundity. Collins 
(pers. comm.) has estimated batch fecundity of 20 gray 
snapper from northwest Florida. These fish were 
captured in the summer months of 1993-1995, and 
ranged from 333 to 641 mm TL. Batch fecundity 
estimates ranged from 29,000 to 1 ,256,000 hydrated 
oocytes. Estimates of spawning frequency for gray 
snapper have not yet been completed (Collins pers. 
comm.). In other studies, a 315 mm female produced 
590,000 eggs (Starck 1 971 , Hardy 1 978), while a 354 
mm standard length (SL) fish produced 548,000,000 
(Grimes 1987). One gram of ovarian tissue has been 
reported to contain 1 25,000 eggs (Starck and Schroeder 
1971). 

Growth and Development 

Egg Size and Embryonic Development : Eggs are ovipa- 
rous, non-adhesive, ranging 0.04-0.06 mm in diam- 
eter, and contain a single central oil globule (Starck and 
Schroeder 1 971 , Grimes 1 987). These demersal eggs 


230 


Gray snapper, continued 


develop rapidly and hatch in about 1 8 hours in ambient 
seawater (Grimes 1 987). Eggs hatch in the vicinity of 
offshore reets. 

Age and Size of Larvae : Larval development takes 
place offshore near spawning sites (Richards et al. 
1984, Kelly et al. 1986, Powell et al. 1987). Newly 
hatched larvae absorb their yolk sac within 45 hours 
(Grimes 1987). Richards and Saksena (1980) gave 
growth rates of continually fed larvae as 2.7-2.8 mm 
notocord length (NL) (4 days), 3.0-3.1 mm NL (5 days), 
3.4 mm NL (7 days), 4.1-4.2 mm NL (9 days), 6.2 mm 
SL (15 days), 9.6-12.5 mm SL (26 days) and 15.4 mm 
SL (36 days). The flexion stage occurs at about 4.2 mm 
SL, and post-flexion at 6.2 mm SL. Larvae are sparsely 
pigmented. 

Juvenile Size Range : The juvenile stage begins at 12 
mm SL. They are heavily pigmented and can be 
identified by a full complement of meristic characters 
(Richards and Saksena 1 980). Springerand Woodburn 
(1960) reported mean lengths of Age Class fish for 
periods of September, November and December 1 957 
as 33 mm, 42.6 mm and 51.7 mm respectively. The 
following year they assigned lengths to Age Class 
fish for October (1 8.2 mm), November (25.3 mm) and 
December (34 mm). Croker (1962) determined mean 
fork lengths (FL) using back calculations for age classes 

I through VII as Class I - 81 mm, Class 11-180 mm, 
Class III - 241 mm, Class IV - 295 mm, Class V - 352 
mm, Class VI - 431 mm, and Class VII - 456 mm. 
Different results were obtained in another study, par- 
ticularly in the later age classes: Class I - 79 mm, Class 

II - 143 mm, Class III - 199 mm, Class IV - 255 mm, 
Class V - 293 mm, Class VI - 334 mm, Class VII - 381 
mm, Class VIII - 438 mm, and Class IX - 478 mm 
(Starck and schroeder 1 971 ). Growth rates of 1 26 + 2 
mm for the first year and 48-62 mm/year for fish one to 
fouryears of age have been reported (Rutherford et al. 
1983). 

Age and Size of Adults : Using sectioned otoliths, 
Manooch and Matheson (1984) calculated TL for fish 
up to 19 years of age. Their results were similar to 
those of Croker (1962). A length of 772 mm was 
determined for 1 9 year old fish. The oldest specimen 
they observed was a 775 mm fish, 21 years old. Starck 
and Schroeder (1 971 ) suggest a maximum weight for 
the gray snapper at around 8 kg but stated that fish over 
3.6 kg were rare. Maturity is reached at about 200 mm 
TL, probably during the third year (Starck and Schroeder 
1971). In one study, the smallest female observed 
spawning was 195 mm SL and the smallest ripe male 
was 185 mm SL (Starck and Schroeder 1971, Hardy 
1978). Johnson et al. (1994) collected adult gray 
snapper from Gulf of Mexico commercial and recre- 
ational fisheries, with a length range of 236 to 764 mm 


TL, and an estimated age range of one to 25 years. 
Von Bertalanffy growth parameters have been derived 
for this species (Johnson et al. 1994). 

Food and Feeding 

Trophic Mode : The gray snapper is an opportunistic 
carnivore at all life stages. 

Food Items : Richards and Saksena (1980) fed zoop- 
lankton in the 73-110 u.m range in vitro to newly 
hatched gray snapper larvae. Copepods and amphi- 
pods are important food items of fish at 10-20 mm 
(Starck and Schroeder 1971). Juveniles are diurnal 
feeders that primarily prey on crustaceans, but they 
also consume fish, molluscs and polychaetes. Very 
small juveniles (10-20 mm TL) forage primarily on 
amphipods. Penaeid shrimp dominate the diet of 
larger juveniles, but a variety of crabs (blue crab, spider 
crab, mud crabs, and fiddler crabs) are also eaten 
(Rutherford et al. 1983). Grassbeds appear to be the 
most important feeding habitat for juveniles and adults 
(Starck 1971, Harrigan et al. 1989, Hettler 1989). 
Adults are typically nocturnal predators, consuming 
fish, shrimp, and crabs. Fish eaten are largely grunts 
(Haemulon species), but also include killifishes, pipe- 
fish (Syngnathusspec\es), gulf toadfish (Opsanusbeta), 
gobies, seahorses (Hippocampus species), and silver 
jenny (Eucinostomus quia). Algae and marine plants 
are commonly found, possibly consumed incidentally 
during routine feeding. Proportions of prey species 
consumed varies within and among habitats (Rivas 
1 949, Reid 1 954, Springer and Woodburn 1 960, Tabb 
and Manning 1 961 , Starck and Davis 1 966, Starck and 
Schroeder 1 971 , Rutherford et al. 1 983, Harrigan et al. 
1989, Hettler 1989). 

Biological Interactions 

Predation : Little information on predation of gray snap- 
per is available, but other carnivorous fishes probably 
prey on larvae and juveniles. 

Factors Influencing Populations : Abundance and dis- 
tribution of juveniles appears to be influenced by den- 
sity and species composition of seagrass (Chester and 
Thayer 1990). 


231 


Gray snapper, continued 


Personal communications 

Collins, L. Alan. NOAA National Marine Fisheries 
Service, Panama City, FL. 

Comyns, Bruce H. Gulf Coast Research Lab., Ocean 
Springs, MS. 

Shaffer, Rosalie N. NOAA National Marine Fisheries 
Service, Panama City, FL. 

Van Hoose, Mark S. Alabama Division of Marine 
Resources, Dauphin Island, AL. 

References 

Bortone, S.A., and J.L. Williams. 1986. Species 
profiles: life histories and environmental requirements 
of coastal fishes and invertebrates (South Florida): 
Gray, Lane, Mutton, and Yellowtail snappers. U.S. 
Fish Wildl. Serv. Biol. Rep. USFWS/TR-82(11.52). 

Bryant, H.E., M.R. Dewey, N.A. Funicelli, G.M. Ludwig, 
D.A. Meineke, and L.J. Mengal. 1989. Movement of 
five selected sports species of fish in Everglades 
National Park. Bull. Mar. Sci. 44:515. 

Chester, A.J., and G.W. Thayer. 1 990. Distribution of 
spotted seatrout ( Cynoscion nebulosus) and gray snap- 
per (Lutjanus griseus) juveniles in seagrass habitats of 
western Florida Bay. Bull. Mar. Sci. 46:345-357. 

Croker, R.A. 1960. A contribution to the life history of 
the gray (mangrove) snapper, Lutjanus griseus 
(Linnaeus). M.S. thesis, Univ. of Miami, Coral Gables, 
FL, 93 p. 

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232 


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233 


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234 


Sheepshead 


Archosargus probatocephalus 
Adult 


(from Goode 1884) 


Common Name: sheepshead 
Scientific Name: Archosargus probatocephalus 
Other Common Names: Sheepshead bream, sheep- 
shead porgie, convict fish (Jennings 1985); rondeau 
mouton (French), sargo chopa (Spanish) (Fischer 
1978). 

Classification (Robins et al. 1991) 
Phylum: Chordata 
Class: Osteichthyes 
Order: Perciformes 
Family: Sparidae 

There are three subspecies of sheepshead along the 
western Atlantic seaboard. A. p. probatocephalus is 
the more northern race ranging from Nova Scotia to 
Cedar Key, Florida. A. p. oviceps limited to the Gulf of 
Mexico ranging from St. Marks, Florida to Campeche 
Bank, Mexico. A. p. aries is the southern form ranging 
from Belize to Brazil (Jennings 1985). 

Value 

Commercial : Traditionally, the sheepshead has had 
some commercial value for food, but its acceptance as 
a food fish varies among coastal localities (Jennings 
1985, Beckman et al. 1991). Commercial interest in 
this species has, however, increased markedly since 
1981 as regulation of fisheries for other more popular 
food fish has increased (Render and Wilson 1992, 
GSMFC 1 992). It is taken commercially by seines and 
incidentally by offshore shrimp trawlers, but is some- 
times caught intentionally during the spawning season 
when it is most abundant (Benson 1982, Jennings 
1985). It has a low retail value, and most incidental 
trawl catches are probably discarded. 


Recreational : The sheepshead supports a moderate 
sport fishery in most months (Benson 1982, Beckman 
etal. 1991). It is a common fish in inshore waters, often 
caught on fiddler crab or barnacle bait (Hoese and 
Moore 1977). Fishery information for the Gulf of 
Mexico showed a total catch of 4,054,000 sheepshead 
in 1992 (NMFS 1993). It is frequently discarded 
because the dorsal spines make cleaning difficult. 

Indicator of Environmental Stress : The sheepshead is 
not typically used in studies of environmental stress. 

Ecological : Sheepshead juveniles and adults are com- 
mon demersal predators. Predation by this species 
may be important in controlling the ecological structure 
of sessile invertebrate and motile epifauna communi- 
ties (Sedberry 1987). 

Range 

Overall : Sheepshead range from Nova Scotia to Florida, 
and the Gulf of Mexico in continental waters. It is found 
from Honduras to Rio de Janeiro, but is absent from 
islands of the Caribbean Sea (Fischer 1978, Johnson 
1978, Shipp 1988). It is common south of Cape 
Hatteras. 

Within Study Area : A. probatocephalus has been di- 
vided into three subspecies, with A. p. oviceps occur- 
ring through the Gulf of Mexico from St. Marks, Florida 
to Campeche Bank Mexico (Caldwell 1965, Fischer 
1978, Lee et al. 1980) (Table 5.31). Greatest abun- 
dance in the Gulf of Mexico probably occurs off of 
southwest Florida (Shipp 1988). 


235 


Sheepshead, continued 


Table 5.31 . Relative abundance of sheepshead in 
31 Gulf of Mexico estuaries (from Volume /)• 

Life stage 


Estuary 


A S J L E 


Florida Bay 


O 


V 


o 


o 


Ten Thousand Islands 


O 


V 


o 


Caloosahatchee River 


V 


V 


V 


Charlotte Harbor 


V 


V 


V 


Tampa Bay 


o 


V 


o 


o 


V 


Suwannee River 


o 


o 


o 


Apalachee Bay 


V 


V 


V 


Apalachicola Bay 


o 


o 


o 


St. Andrew Bay 


o 


V 


o 


o 


V 


Choctawhatchee Bay 


o 


o 


o 


Pensacola Bay 


o 


o 


o 


Perdido Bay 


® 


o 


o 


Mobile Bay 


® 


® 


o 


Mississippi Sound 


o 


o 


o 


o 


o 


Lake Borgne 


o 


® 


Lake Pontchartrain 


o 


o 


Breton/Chandeleur Sounds 


o 


o 


Mississippi River 


o 


o 


Barataria Bay 


® 


o 


Terrebonne/Timbalier Bays 


® 


® 


Atchafalaya/Vermilion Bays 


o 


o 


Calcasieu Lake 


V 


o 


Sabine Lake 


o 


o 


Galveston Bay 


o 


o 


Brazos River 


o 


o 


Matagorda Bay 


® 


® 


San Antonio Bay 


® 


o 


Aransas Bay 


o 


o 


o 


o 


o 


Corpus Christi Bay 


o 


o 


o 


o 


o 


Laguna Madre 


o 


® 


Baffin Bay 


o 


V 


o 


V 


V 


A S J L E 


Relative abundance: 

% Highly abundant 
® Abundant 
O Common 
V Rare 
blank Not present 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


Life Mode 

Eggs are buoyant, and spawning typically occurs over 
the inner continental shelf. Larvae are pelagic. Juve- 
niles and adults are demersal omnivores, and prefer 
"live hard-bottomed areas." This fish does not school, 
but may form feeding aggregations (Johnson 1978, 
Lee et al. 1980, Sedberry 1987). 

Habitat 

Type : Eggs are typically marine, in coastal waters of 
the inner continental shelf. Larvae are known to be 
present in the Gulf of Mexico January through May, 
with peak abundance February through April (Ditty 
1986, Ditty et al. 1988). Larvae are pelagic as they 
move into estuaries, then become estuarine-depen- 
dent and associated with seagrass beds. The pelagic 
stage probably lasts until larvae are about 30 to 40 
days old when metamorphosis into juveniles occurs. 
After metamorphosis, juveniles "settle out," becoming 
substrate-oriented, then move to nearshore reefs as 
they mature (Sedberry 1987, Parsons and Peters 
1989). Both juveniles and adults are demersal. Adults 
occur in nearshore waters over "live bottom" areas. 

Substrate : Juveniles are usually associated with grass 
beds until they are around 50 mm, then they move into 
the more typical adult habitats (McClane 1 964, Dugas 

1970, Lee et al. 1980, Juneau and Pollard 1981). 
Adults occur around oyster beds, shallow muddy bot- 
toms, Spartina marshes, piers and rocks, and jetties. 
They can also be found in some abundance in bare 
sand surf zones feeding on infaunal bivalves and 
crustaceans (Shipp 1988). 

Physical/Chemical Characteristics 
Temperature: Optimal growth in captivity has been 
reported at around 25°C (Tucker 1989). Juveniles 
have been collected in temperatures ranging from 8.0 
to 29.6° C (Wang and Raney 1971, Pineda 1975, 
Jennings 1985). Temperature tolerance in adults 
ranges from 5° (Christmas and Waller 1973, Perret et 
al. 1971) to 35.1° C (Roessler 1970). 

Salinity: The sheepshead is euryhaline (Gunter 1956) 
with collection sites ranging in salinities from to 45%o 
(Simmons 1 957, Kelly 1 965, Dugas 1 970, Perret et al. 

1971, Wang and Raney 1971, Dunham 1972, Perret 
and Caillouet 1974, Juneau 1975, Tarver and Savoie 
1 976, Benson 1 982). Larvae have been collected from 
5.0 to 24.9%o (Christmas and Waller 1 973). Juveniles 
and adults are found in salinities from nearly fresh 
(0.26%o) to 43.8%o (Herald and Strickland 1 948, Gunter 
and Hall 1965, Lee et al. 1980, Loftus and Kushlan 
1987). 


236 


Sheepshead, continued 


Dissolved Oxygen: 

Minimum dissolved oxygen (DO) tolerances for this 
species are not well known, but kills have been re- 
ported in semi-open and closed canals in coastal 
Louisiana where severe oxygen depletion occurred 
(Adkins and Bowman 1976). 

Movements and Migrations : This is not considered a 
true migratory species (Jennings 1985), but one tag- 
ging study showed a maximum traveled distance of 
109 km prior to the spawning season (Bryant et al. 
1 989). Adults move to offshore waters in the spring and 
return to bays after spawning. The sheepshead re- 
mains in nearshore waters during warm seasons and 
moves out of the estuaries during periods of low 
temperatures (Gunter 1945, Dugas 1970, Jennings 
1985, Bryant et al. 1989). 

Reproduction 

Mode : This species has separate male and female 
sexes (gonochoristic). Fertilization is external, by 
broadcast of milt and roe into the water column. 

Spawning : Spawning probably occurs offshore 
(Springer and Woodburn 1960), from February through 
April (Hildebrand and Cable 1938, Springer and 
Woodburn 1960, Christmas and Waller 1973, Render 
and Wilson 1993). The reported peak occurs during 
the months of March and April (Beckman et al. 1991). 

Fecundity : Fecundity appears to vary between fish 
from the inshore area, and older, larger fish that are 
caught offshore (Render and Wilson 1993). Fish 
caught offshore had an average fecundity of 87,000 
eggs/batch and ranged from 14,000 to 250,000 eggs/ 
batch. The average fecundity of fish from the inshore 
area was 11,000 eggs/batch, and ranged 1,100 to 
40,000 eggs/batch. Frequency of spawning was esti- 
mated to be every 1 to 20 days. 

Growth and Development 

Egg Size and Embryonic Development : Eggs are ap- 
proximately 0.8 mm diameter, and are buoyant. Hatch- 
ing occurs in about 40 hours at 24-25°C (Johnson 
1978, Tucker 1989). 

Age and Size of Larvae : Larvae are about 2.0 mm 
when they hatch, and by 5 mm, they have absorbed the 
yolk sac. Transition to the juvenile stage begins at 
about 1 1 to 1 2 mm (Mook 1 977). 

Juvenile Size Range : Juveniles attain adult pigmenta- 
tion patterns by approximately 25 to 30 mm (Johnson 
1 978). Growth is rapid up to 6 to 8 years of age, after 
which it levels off (Beckman et al. 1 991 ). 


Age and Size of Adults : Sexual maturity is reported to 
occur in most individuals by age 2 (Beckman et al. 
1 991 , Render and Wilson 1 993). All males are usually 
mature by age 3, and all females by age 4. The 
sheepshead is one of the largest members of its family 
(Shipp 1988). It can grow up to 610 mm (Hoese and 
Moore 1 977), and the record size in Louisiana is 9.6 kg. 
Females exhibit a faster growth rate and achieve larger 
maximum sizes than males. This is a long-lived spe- 
cies with a life span of at least 20 years. Von Bertalanffy 
growth equations have been developed for both sexes 
(Beckman et al. 1991). 

Food and Feeding 

Trophic Mode : Little information is available regarding 
the role of sheepshead in the trophic dynamics of 
estuaries (Jennings 1985). Larvae are carnivorous. 
Juveniles and adults are omnivores, but adults in 
offshore environments function more as sessile animal 
feeders, while juveniles feed primarily on plant material 
in inshore habitats (Sedberry 1987). 

Food Items : Hildebrand and Cable (1938) found that 
ostracods were the primary food for fishes less than 30 
mm. Benson (1982) summarizes the diet of sheeps- 
head as: larvae consuming primarily zooplankton, ju- 
veniles consuming zooplankton as well as polychaetes 
and chironomid larvae; large juveniles and adults eat 
blue crab, young oysters, clams, crustaceans and 
small fish. Juveniles and adults are basically omnivo- 
rous feeding on plant material as well as crustaceans, 
molluscs and small fishes (primarily young Atlantic 
croaker) (Gunter 1945, Darnell 1961, Tabb and Man- 
ning 1 961 , Kelly 1 965, Levine 1 980, Odum et al. 1 982, 
Overstreet and Heard 1 982, Shipp 1 988). In one study, 
smaller adults (<350 mm SL) were found to consume 
mostly bryozoans, while larger fish (>350 mm SL), that 
also fed heavily on bryozoans, included more bivalves, 
echinoderms, and ascidians in their diet. Both size 
groups consumed barnacles and decapods in lesser 
amounts. Foraminiferans, cnidarians, polychaetes, 
gastropods, and small arthropods were also eaten. 
Algae may be important in the diet of sheepshead in 
inshore habitats (Ogburn 1984), but plant material 
becomes less important in the diet of adults as they 
move offshore (Sedberry 1987). 

Biological Interactions 

Predation: Little information is available regarding pre- 
dation of sheepshead, but it seems likely that larvae 
and juveniles could be utilized as a food source by 
predatory fishes. 


237 


Sheepshead, continued 


Factors Influencing Populations : The sheepshead is 
host to ciliates, nematodes, trematodes, and isopods, 
none of which are known to endanger populations of 
the species (Jennings 1985). Adkins and Bowman 
(1976) found oxygen depletion in a semi-open and 
closed canals in Louisiana to result in death of this 
species. The sheepshead is frequently found associ- 
ated with black drum (Wang and Raney 1971). 


Dunham, F. 1972. A study of commercially important 
estuarine dependent industrial fishes. Louis. Wildl. 
Fish. Comm., Tech. Bull. No. 4, 63 p. 

Fischer, W. (ed.). 1978. FAO Species Identification 
Sheets for Fishery Purposes, Western Central Atlantic 
(Fishing Area 31), Vol. V. Food and Agriculture Orga- 
nization of the United Nations, Rome. 


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240 


Lagodon rhomboides 
Adult 


5 cm 


(fromGoode 1884) 


Common Name: pinfish 

Scientific Name: Lagodon rhomboides 

Other Common Names: bream, pin perch, sand perch, 

sailor's choice, butterfish; sarselema (French); poisson 

beurre (Cajun French); sargo selema, chopa espina 

(Spanish) (Fischer 1978, Muncy 1984). 

Classification (Robins et al. 1991) 

Phylum: Chordata 

Class: Osteichthyes 

Order: Perciformes 

Family: Sparidae 

Value 

Commercial : The pinfish is included in the unclassified 
or industrial fish categories in commercial catch statis- 
tics (Fischer 1 978, Muncy 1 984). It is a potential source 
of fish meal, and has value as a forage fish for many 
commercial fish species (Muncy 1 984). It also contrib- 
utes a small part to the industrial groundfish fishery of 
the northern Gulf of Mexico (Roithmayr 1965). Pinfish 
are caught mainly with trawls, but also with gill nets, 
trammel nets, beach seines, traps, and on hook and 
line (Fischer 1978). Commercially caught fish are 
marketed for food are mostly sold as fresh product. 

Recreational : Pinfish are often caught while fishing for 
other species (Muncy 1984). Although it is excellent 
eating, the pinfish is not widely consumed due to its 
relatively small size (Fischer 1978). It is often sought 
by young anglers (Shipp 1986). Recreational fishery 
information for the Gulf of Mexico (except Texas) 
showed an estimated total catch of 8,674,000 pinfish in 
1992 (O'Bannon 1994). 

Indicator of Environmental Stress : Pinfish have been 
used extensively in bioassay experiments on the toxic- 


ity of hydrocarbons (Finucane 1969, Parrish, et al. 
1 975, Schimmel et al. 1 977) and physiological experi- 
ments studying the effects of hydrocarbons and envi- 
ronmental conditions on fish (Cameron 1 969b, Cameron 
1 970, Kloth 1 970, Kjelson and Johnson 1 976, Lee et al. 
1980). 

Ecological : The pinfish is an estuarine dependent 
species. It is often so abundant and predaceous that 
it is believed to alter the composition of estuarine 
epifaunal communities (Orth and Heck 1980, Coen et 
al. 1 981 , Stoner 1 980, Stoner 1 982, Muncy 1 984). This 
fish is numerically dominant in the shallow, subtidal 
seagrass communities in the Gulf of Mexico, and its 
predation on amphipod communities probably limits 
amphipod abundance in these areas. In addition, the 
consumption of plants and detritus by pinfish is impor- 
tant in the export of organic materials in estuaries. 

Range 

Overall : The pinfish occurs in coastal waters from as far 
north as Cape Cod, Massachusetts, through the Gulf of 
Mexico and the north coast of Cuba, to the Yucatan 
peninsula. It is rare north of Maryland and most 
common south of Cape Hatteras, North Carolina through 
to the northern Gulf of Mexico (Fischer 1 978, Lee et al. 
1980, Muncy 1984). Fitzsimons and Parker (1985) 
have demonstrated no karyotypic differences among 
sampling locations, suggesting a single population for 
the southeast and Gulf coasts. 

Within Study Area : The pinfish is abundant throughout 
the Gulf of Mexico, except in the very turbid brackish 
waters of Louisiana west of the mouth of the Missis- 
sippi River (Table 5.32) (Hoese and Moore 1977). 


241 


Pinfish, continued 


Table 5.32. Relative abundance of pinfish in 31 G 
of Mexico estuaries (from Volume /). 

Life stage 


ulf 


Estuary 


A S J L E 


Florida Bay 


• 


• 


V 


Ten Thousand Islands 


• 


® 


® 


Caloosahatchee River 


o 


• 


Charlotte Harbor 


• 


• 


• 


Tampa Bay 


• 


• 


o 


Suwannee River 


• 


• 


o 


Apalachee Bay 


® 


® 


o 


Apalachicola Bay 


® 


® 


o 


St. Andrew Bay 


• 


• 


® 


Choctawhatchee Bay 


o 


® 


• 


Pensacola Bay 


® 


• 


® 


Perdido Bay 


o 


® 


o 


Mobile Bay 


® 


® 


® 


Mississippi Sound 


• 


• 


® 


Lake Borgne 


® 


® 


Lake Pontchartrain 


o 


® 


Breton/Chandeleur Sounds 


o 


Mississippi River 


o 


Barataria Bay 


® 


Terrebonne/Timbalier Bays 


® 


Atchafalaya/Vermilion Bays 


o 


Calcasieu Lake 


o 


o 


Sabine Lake 


o 


Galveston Bay 


® 


Brazos River 


® 


Matagorda Bay 


® 


• 


San Antonio Bay 


o 


® 


Aransas Bay 


® 


® 


Corpus Christi Bay 


® 


® 


Laguna Madre 


® 


• 


Baffin Bay 


o 


® 


- 


A S J L E 


Relative abundance: 

Highly abundant 
® Abundant 
O Common 
V Rare 
blank Not present 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


Life Mode 

Eggs that are fertile are semi-buoyant. Although little 
is known about spawning areas and egg distributions, 
they are assumed to be planktonic and offshore, based 
on indirect evidence of their larval distributions (Sabins 
and Truesdale 1974, Darcy 1985). The pinfish is 
typically non-schooling, although compact aggrega- 
tions have been reported (Kloth 1970). Pinfish have a 
primarily diurnal pattern of activity, but some nocturnal 
activity has been observed (Sogard et al. 1989). 

Habitat 

Ty pe: Eggs are marine and neritic. Larvae are marine 
and estuarine. Larval pinfish are known to occur in the 
Gulf of Mexico October through April, with peak abun- 
dance Decemberthrough February (Ditty 1 986, Ditty et 
al. 1 988). Juveniles are marine, estuarine and riverine. 
Juveniles are common over areas of seagrass, where 
activity appears to be associated with high tides (Fischer 
1978, Sogard et al. 1989). Adults are marine to 
riverine, preferring protected waters and depths of 30 
to 50 m in the Gulf (Franks et al. 1972, Chittenden and 
MacEachran 1976), but they have been collected in 
waters as deep as 92 m (Perry 1 970). Adults probably 
prefer euhaline (marine) salinities (Wang and Raney 
1971). 

Substrate : The pinfish is most abundant over veg- 
etated shallow flats, preferred mainly by juveniles, but 
also occurs occasionally in other areas that offer some 
degree of cover such as rocky bottoms, jetties, pilings, 
and in mangrove areas (Reid 1954, Gunter and Hall 
1965, Hansen 1970, Fischer 1978, Lee et al. 1980, 
Coenetal. 1981). 

Physical/Chemical Characteristics : 
Temperature: Pinfish are eurythermal, tolerating tem- 
peratures from 3.4° to 37.5° C (Pineda 1 975, Roessler 
1970, Lee et al. 1980). Water temperature has been 
suggested as a major factor in the control of emigration 
to offshore spawning sites. Extremely high and low 
temperatures cause pinfish to leave shallow areas for 
nearby deeper waters seasonally, and even daily 
(Cameron 1969a). Increased water temperatures in- 
crease the amount of erythrocytes and hemoglobin of 
pinfish (Cameron 1970, Houston 1973). Tolerance to 
cold temperatures is strongly influenced by acclimation 
temperature, and this has led to ambiguous measures 
of low lethal temperatures in the past (Bennett and 
Judd 1 992). In a recent study, juveniles were found to 
have a Critical Thermal Minimum (CTMin) of 3.4° C. 

Salinity: Pinfish are euryhaline, tolerating salinities 
from to 43.8%o in the Gulf of Mexico (Roessler 1 970, 
Pineda 1 975, Lee et al. 1 980). Vegetation rather than 
salinity is thought to have a greater affect on the 
distribution of pinfish (Weinstein 1979). However, 


242 


Pinfish, continued 


heavy rains reducing salinity to 4%o have been reported 
to decrease the abundance of juvenile pinfish in a 
shallow seagrass bed (Cameron 1969b). In addition, 
Subrahmanyam and Coultas (1980) positively corre- 
lated salinity and pinfish abundance. Adult pinfish 
apparently prefer higher salinity waters and stay mostly 
in the Gulf or close to Gulf passes (Wang and Raney 
1971). 

Dissolved Oxygen (DO): The oxygen-carrying capac- 
ity of pinfish blood is related to environmental condi- 
tions, increasing with lower dissolved oxygen, higher 
salinities, and increased activity (Cameron 1 970). The 
incipient lethal level for this species is a DO content of 
about 1.1 mg/l (Cameron 1969a). 

Migrations and Movements : Larvae begin to move into 
estuaries from the marine environment when they 
reach a total length (TL) of 11 mm (Johnson 1978). 
Juveniles migrate up into the estuaries during spring 
and summer. Juveniles rarely leave the protected 
areas of vegetated flats except at night when they 
move into the nearby sand flats (Stoner 1979). In 
addition, when water temperatures exceed 32°C in the 
flats they move to the cooler, deeper waters of chan- 
nels. Juveniles and adults migrate out of the estuaries 
in the fall to their spawning grounds in the mostly 
deeper Gulf waters (Gunter 1945, Perry 1970). Here 
they aggregate in size groups. Gunter (1 945) reported 
that some juveniles remain inshore, while Perry (1 970) 
found a stable adult population remaining offshore in 
deep (73-91 m) Gulf waters. 

Reproduction 

Mode : This species has separate male and female 
sexes (gonochoristic). Fertilization is external, by 
broadcast of milt and roe into the water column (Cody 
and Bortone 1992). 

Spawning : Spawning location is probably related to 
water depth and temperature (Johnson 1978). Most 
studies in the northern Gulf of Mexico indicate that 
spawning takes place in the fall and winter (Gunter 
1 945, Reid 1 954, Caldwell 1 957, Christmas and Waller 
1 973, Sabins and Truesdale 1 974, Kjelson and Johnson 
1 976, Johnson 1 978, Lee et al. 1 980, Cody and Bortone 
1992). 

Fecundity : In one study, a 157 mm TL female from 
Florida collected in November contained an estimated 
90,000 eggs (Caldwell 1957). In another study, eight 
pinfish, with standard lengths (SL) ranging from 1 1 1 to 
152 mm, spawned an estimated 7,700 to 39,200 (av- 
eraging from 21,600) eggs (Hansen 1970). A pro- 
tracted spawning period is considered likely for this 
species based on gonadosomatic indices (Cody and 
Bortone 1992). 


Growth and Development 

Egg Size and Embryonic Development : The diameter 
of pinfish eggs is reported to range from 0.90 to 0.93 
mm (Schimmel 1977) and 0.99 to 1.05 (Cardeilhac 
1976). 

Age and Size of Larvae : When observed in a laboratory 
study, larvae hatched after 48 hours when incubated at 
1 8°C, and were 2.3 mm TL (Cardeilhac 1 976, Johnson 
1 978). The yolk sac, visible for 24 hours after hatching, 
was completely absorbed when the larvae reached 2.7 
mm TL. Larval development is complete when indi- 
viduals reach 12.0 mm SL (Zieske 1989). Zieske 
(1989) thoroughly describes pinfish larvae and early 
juveniles. 

Juvenile Size Range : Juveniles range in size from 15 
mm TL (12 mm SL) to 100 mm TL or more (Hansen 
1970, Zieske 1989). 

Age and Size of Adults : The majority of pinfish become 
sexually mature from 80 to 1 00 mm TL (Hansen 1 970, 
Johnson 1 978). This usually occurs during the spawn- 
ing migration or at the offshore spawning grounds 
(Hansen 1970). Adults average growth increments of 
80 mm SL after the first year, 50 mm SL after the 
second, and 45 mm SL after the third (Caldwell 1 957). 
Most adults are greater than 110 mm TL in size. 

Food and Feeding 

Trophic Mode : Pinfish are voracious predators as 
juveniles and subadults (Carr and Adams 1 973, Stoner 
1979). Adults are reported to be omnivorous (Stoner 
1980). 

Food Items : Juveniles feed primarily on shrimps, mysids, 
and amphipods (Carr and Adams 1 973, Stoner 1 979, 
Levine 1980, Schmidt 1993). The diet of adults is 
similar to juveniles, but has a large component of plant 
material (Stoner 1980). Weinstein et al. (1982) have 
reported cellulose digestive activity. Other reported 
food items are: fish eggs, insect larvae, decapod crabs, 
bivalve molluscs, and polychaetes (Levine 1980, 
Schmidt 1993). 

Biological Interactions 

Predation : Pinfish are an important forage item for 
many fish species (Darcy 1 985). Known piscine preda- 
tors include alligator gar (Lepisosteus spatula), \ongnose 
gar (Lepisosteus osseus), ladyfish (Elops saurus), 
spotted seatrout, red drum, bighead searobin (Prionotus 
tribulus), southern flounder, and gulf flounder (Gunter 
1945, Kemp 1949, Darnell 1958, Diener et al. 1974, 
Muncy 1984, Rozas and Hackney 1984). Pinfish are 
also preyed on by bottle-nosed dolphin (Tursiops 
truncatus) (Kemp 1949). 


243 


Pinfish, continued 


Factors Influencing P opu lations: Large numbers of 
pinfish have died during episodic winter events when 
water temperatures have dropped to approximately 
4°C (Gunter 1941, Muncy 1984). 

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245 


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284. 


246 


Silver perch 


Bairdiella chrysoura 
Adult 


5 cm 


(from Goode 1884) 


Common Name: silver perch 

Scientific Name: Bairdiella chrysoura 

Other Common Names: butterfish (Springer and 

Woodburn 1960); yellowtail (Gunter 1945); silver 

croaker, mamselle blanche (French), and corvineta 

blanca (Spanish) (Fischer 1978). 

Classification (Robins et al. 1991) 

Phylum: Chordata 

Class: Osteichthyes 

Order: Perciformes 

Family: Sciaenidae 

Value 

Commercial : Catches of silver perch are mostly inci- 
dental in fisheries for more important commercial spe- 
cies. The principal gear used is pound nets, seines, 
and bottom trawls. Separate statistics are not reported 
for this species. Occasionally, large individuals are 
marketed fresh for human consumption (Fischer 1 978, 
Manooch 1984). 

Recreational : Silver perch are caught on hook and line 
by anglers, but are not specifically sought. Catches are 
usually incidental, and often discarded due to small 
size (Fischer 1978, Manooch 1984, Shipp 1986). Sil- 
ver perch are sometimes used as bait by recreational 
fishermen (Fischer 1978, Manooch 1984). Its silvery 
color makes it an attractive bait, but it is uncommon in 
large numbers for capture. An estimated 305,000 
silver perch were caught in Gulf of Mexico waters 
(excluding Texas) during 1991 by recreational fisher- 
men (Van Voorhees et al. 1992). 

Indicator of Environmental Stress : Hansen and Wilson 
(1970) recorded concentrations of DDT and its me- 
tabolites from 0.02 to 1 .26 in 0-class fish from Florida's 


Pensacola estuary. 

Ecological : The silver perch is primarily a benthic 
carnivore that consumes a diet consisting mostly of 
crustaceans (Killametal. 1992). It can be an abundant 
species in estuaries (Sheridan et al. 1 984), and there- 
fore play a key role in the ecology of a system. Because 
of its abundance, it is likely to be the prey of numerous 
piscivorous fish species (Killam et al. 1992). 

Range 

Overall : The silver perch occurs in coastal waters of the 
western Atlantic from the Gulf of Maine off of Massa- 
chusetts to southern Florida and through the northern 
Gulf of Mexico (Lee et al. 1 980, Shipp 1 986). 

Within Study Area : In the Gulf of Mexico, the silver 
perch ranges from south Florida into Mexico near the 
Rio Grande River (Lee et al. 1980, Shipp 1986). It is 
common in northern Gulf of Mexico estuaries, and less 
so to the south (Shipp 1986) (Table 5.33). 

Life Mode 

Eggs are pelagic and buoyant, larvae are pelagic to 
demersal, and both juveniles and adults are demersal 
(Johnson 1978, Ditty and Shaw 1994). Spawning 
occurs in the evening (Kuntz 1914). Activity is primarily 
nocturnal, and is affected by tidal cycles (Sogard et al. 
1989). 

Habitat 

Type : Silver perch are estuarine-dependent, and the 
majority of spawning occurs in estuaries (Ditty pers. 
comm.). Eggs may be estuarine to marine depending 
on where spawning occurs (Johnson 1 978), and larvae 
are pelagic (Ditty and Shaw 1 994). Juveniles are found 


247 


Silver perch, continued 


Table 5.33. Relative abundance of silver perch ir 
Gulf of Mexico estuaries (from Volume 1). 

Life stage 


131 


Estuary 


A S J L E 


Florida Bay 


O 


O 


® 


o 


o 


Ten Thousand Islands 


O 


® 


® 


® 


® 


Caloosahatchee River 


® 


® 


® 


® 


® 


Charlotte Harbor 


® 


• 


® 


• 


• 


Tampa Bay 


f> 


• 


® 


® 


® 


Suwannee River 


® 


® 


o 


1*1 


® 


Apalachee Bay 


o 


o 


o 


o 


o 


Apalachicola Bay 


® 


1*1 


® 


® 


® 


St. Andrew Bay 


® 


® 


® 


® 


® 


Choctawhatchee Bay 


o 


o 


o 


o 


o 


Pensacola Bay 


o 


o 


o 


o 


o 


Perdido Bay 


o 


o 


o 


o 


o 


Mobile Bay 


o 


o 


o 


o 


o 


Mississippi Sound 


• 


o 


• 


o 


o 


Lake Borgne 


• 


o 


• 


o 


o 


Lake Pontchartrain 


o 


o 


Breton/Chandeleur Sounds 


o 


o 


Mississippi River 


o 


o 


Barataria Bay 


® 


® 


® 


1*1 


® 


Terrebonne/Timbalier Bays 


o 


o 


® 


o 


o 


Atchafalaya/Vermilion Bays 


o 


Calcasieu Lake 


o 


Sabine Lake 


o 


V 


Galveston Bay 


"cP 


o 


o 


o 


o 


Brazos River 


o 


o 


o 


o 


o 


Matagorda Bay 


o 


o 


o 


o 


o 


San Antonio Bay 


o 


o 


o 


o 


o 


Aransas Bay 


o 


o 


o 


o 


o 


Corpus Christi Bay 


o 


o 


o 


o 


o 


Laguna Madre 


o 


o 


® 


o 


o 


Baffin Bay 


® 


1*1 


If) 


® 


® 


A S J L E 


Relative abundance: 

Highly abundant 
® Abundant 
O Common 
V Rare 
blank Not present 


Life stage: 

A - Adults 
S - Spawning 
J - Juveniles 
L - Larvae 
E - Eggs 


mostly in estuaries (Lee et al. 1980). They occur in a 
wide variety of habitats, including backwater areas, 
tidal tributaries, and over bare bottom areas but show 
a preference for shallow vegetated seagrass regions 
(Killam et al. 1992). They also can be found in 
abundance around other structured habitats such as 
rocks and seawalls. Adults, although most common in 
bays and quiet lagoons (De Sylva 1965), can also 
occur in sandy unvegetated habitats in shallow 
nearshore waters of the Gulf of Mexico at depths up to 
1 8 m (Gunter 1 945, Miller 1 964, Killam et al. 1 992). All 
life stages appear to prefer polyhaline to euhaline 
salinities (Killam et al. 1 992). Hoese and Moore (1 977) 
report that the silver perch is more common in higher 
salinity bays. 

Substrate : Adults are found over mud and sand bot- 
toms (Robins and Tabb 1965). Juveniles are found 
along shore zone rivers in ditches, in lower portions of 
marsh creeks over mud and sand bottoms (Thomas 
1971), and often over heavy detritus (Hildebrand and 
Cable 1 930). They usually occur in grass beds (Hoese 
and Moore 1977, Lee et al. 1980). 

Physical/Chemical Characteristics : 
Temperature: This is a eurythermal species that is very 
tolerant of the warm water conditions that are typical of 
estuaries (Killam et al. 1 992). Ripe individuals or eggs 
have been collected at 19.4 to 28°C (Johnson 1978). 
Larvae have been taken in temperatures from 1 6.4° to 
31.8°C (Jannke 1971). Juveniles are taken in tem- 
peratures from 4.8° (Thomas 1971) up to 32.5°C 
(Springer and Woodburn 1960, Wang and Raney 
1 971 ). Adults have been taken at temperatures from 
1 0° to 34.5°C (Roessler 1 970, Darovec 1 983). Upper 
lethal limits determined for fish 20 to 200 mm were 
LD50 at 34° to 37°C after 3 hours, and LD1 00 at 37° to 
40°C after 30 minutes (Killam et al. 1992). 

Salinity: The silver perch is a euryhaline species (Killam 
et al. 1992). Ripe individuals or eggs have been 
collected at 1 4.3 to 26%o (Johnson 1 978). Larvae have 
been taken in salinities from <1 to 37.4%o, although 
most occurred at salinities >10% o (Lippson and Moran 
1974, Killam et al. 1992). Juveniles are taken in 
salinities from (Thomas 1971, Wang and Raney 
1971, Lee etal. 1980) to 35.5%o(Springerand Woodburn 
1960; Wang and Raney 1971, Wagner 1973). They 
are most abundant at salinities >20%o (Killam et al. 
1992). Adults have been found in salinities ranging 
from to 48%o (Gunter 1945; De Sylva 1965; Wagner 
1 973, Darovec 1 983), but appear to prefer those parts 
of the estuary characterized by moderate to high 
salinities (Killam et al. 1992). 

Movements and Migrations : Adults move to deeper 
bay waters and offshore in the winter, and return to 


248 


Silver perch, continued 


coastal lagoons in the spring to spawn (Gunter 1945, 
Miller 1964, De Sylva 1965). Juveniles move into the 
shallow inner bays (Gunter 1945), and then, as they 
grow, move back to deeper bay and offshore water, 
especially during winter months (Killam et al. 1992). 

Reproduction 

Mode : This species has separate male and female 
sexes (gonochoristic). Fertilization is external, by 
broadcast of milt and roe into the water column 

Spawning : As with most of the drums, sounds pro- 
duced by specialized muscles inserted at the swim 
bladder wall are believed to have a purpose in the 
spawning activity. Spawning probably occurs in the 
deeper waters of primary bays and passes (Hildebrand 
and Cable 1 930, Gunter 1 945, Springerand Woodburn 
1 960, Thomas 1 971 , Sabins and Truesdale 1 974, Mok 
and Gilmore 1983), but may also occur offshore to 
some extent since eggs have been collected there 
(Hildebrand and Cable 1930, Wang and Raney 1971, 
Christmas and Waller 1973). The reported season is 
May to September in northern Florida (Reid 1 954) with 
similar times in Texas and Louisiana (Gunter 1945, 
Wagner 1973, Sabins and Truesdale 1974). Some 
year-round spawning appears to occur in the estuaries 
of southern Florida (Killam et al. 1992). Spawning 
peaks may occur in spring and late summer, but may 
vary with location (Christmas and Waller 1973, Lee et 
al. 1 980). Based on the presence of larval silver perch 
in the northern Gulf of Mexico, it can be inferred that 
spawning occurs March through October, with peak 
from April to August (Ditty et al. 1988). 

Fecundity : A Florida study examined 1 1 females rang- 
ing in size and weight from 1 39.3 to 1 77.4 mm SL and 
55.3 to 123.8 g, respectively, and determined their 
mean fecundity to be 90,407 eggs (Schmidt 1993). 

Growth and Development 

Egg Size and Embryonic Development : Reported egg 
sizes range from 0.59 to 0.88 mm total diameter (mean 
0.69-0.83 mm). They are buoyant, transparent, and 
possess one relatively large oil globule (Kuntz 1914, 
Joseph et al. 1 964, Ditty and Shaw 1 988). Embryonic 
development is oviparous. 

Age and Size of Larvae : Yolk sac larvae hatch at 1 .5- 
1 .9 mm TL (Welsh and Breder 1 923). Ditty and Shaw 
(1 994) report incubation times of 1 8 hours at 27°C, and 
40-50 hours at 20°C. Two days after hatching the yolk 
sac is completely absorbed when larvae measure 2.5 
to 2.8 mm TL (Kuntz 1914, Welsh and Breder 1923). 

Juvenile Size Range : The juvenile stage is attained at 
a total length (TL) of about 10 - 12 mm (Kuntz 1914, 
Ditty and Shaw 1 994). By 1 5 mm, their fin rays are fully 


developed, and their body is lightly pigmented except 
in the thoracic region (Wang and Kernehan 1 979). By 
30 mm SL, juveniles essentially have the form of an 
adult (Johnson 1978). Juveniles have growth rates 
around 15 mm/month from May to November 
(Hildebrand and Cable 1930, Christmas and Waller 
1973). 

Age and Size of Adults : The silver perch reaches 
sexual maturity during its first year in the warmer, more 
southern parts of its range (Schmidt 1 993). In northern 
areas of its range where water temperatures are cooler 
for longer periods of time, growth is slower and maturity 
may not occur until the second year (Hildebrand and 
Cable 1 930, Welsh and Breder 1 923). A study in south 
Florida found maturity in both males and females 
occurred at about 95 mm SL (Schmidt 1993). Maxi- 
mum size seldom exceeds 240 mm TL (Welsh and 
Breder 1 923). This fish may live up to 6 years (Welsh 
and Breder 1923, Lee et al. 1980). 

Food and Feeding 

Trophic Mode : The silver perch is primarily a benthic 
carnivore, feeding mostly on c