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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. Nelson3 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

TMfWTOf

'Current address: U.S. Army Corps of Engineers, Galveston TX 77553.
2Current 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

Ten Thousand Islands, FL

T M

Caloosahatchee River, FL

T M

Charlotte Harbor, FL

T M

Tampa Bay, FL

T M

Suwannee River, FL

T M

Apalachee Bay, FL

T M

Apalachicola Bay, FL

T M

St. Andrew Bay, FL

T M

Choctawhatchee Bay, FL

T M

Pensacola Bay, FL

T M

Perdido Bay, FL/AL

T M

Mobile Bay, AL

T M

Mississippi Sound, MS/AL/LA

T M

Lake Borgne, LA

T M

Lake Pontchartrain, LA

* M

Breton/Chandeleur Sounds, LA

* M

Mississippi River, LA

T M

Barataria Bay, LA

T M

Terrebonne/Timbalier Bays, LA

T M

Atchafalaya/Vermilion Bays, LA

T M

Calcasieu Lake, LA

T M

Sabine Lake, LA/TX

T M

Galveston Bay, TX

T M

Brazos River, TX

T M

Matagorda Bay, TX

T M

San Antonio Bay, TX

* M

Aransas Bay, TX

* M

Corpus Christi Bay, TX

* M

Laguna Madre, TX

* *

Baffin Bay, TX

* *

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

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

Tidal fresh
0.0 - 0.5 ppt

Adults

Spawning

Juveniles

Larvae

Eggs

Mixing
0.5 - 25.0 ppt

Adults

Spawning

Juveniles

Larvae

Eggs

Seawater
>25.0 ppt

Adults

Spawning

Juveniles

Larvae

Eggs

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

Type: 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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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.

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.

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

Bay scallop, continued

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

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

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 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 0 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).

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 0 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

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

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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Bay scallop, continued

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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

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

Caloosahatchee River

Charlotte Harbor

Tampa Bay

Suwannee River

lit

Apalachee Bay

Apalachicola Bay

St. Andrew Bay

Choctawhatchee Bay

_Qj

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 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

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

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%0 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).

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).

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

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).

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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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

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

Apalachicola Bay

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

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

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

Type: 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

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 0 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 0 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

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),
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Atlantic rangia, continued

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Atlantic rangia, continued

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Settle, and L. Coston-Clements. 1991. Distribution
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Div., Rockville, MD, 177 p.

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Mar. Sci. 17:9-13.

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from fall-out in a clam Rangia cuneata Gray. Nature
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Rangia cuneata Gray. Chesapeake Sci. 9:99-102.

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670503, CFSTI.

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

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

Caloosahatchee River

Charlotte Harbor

Tampa Bay

•

Suwannee River

Apalachee Bay

Apalachicola Bay

St. Andrew Bay

Choctawhatchee Bay

Pensacola Bay

Perdido Bay

~o\

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 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,

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%0 (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

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

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,

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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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,

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

Ten Thousand Islands

Caloosahatchee River

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

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

Baffin Bay

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).

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 0 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.

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 0 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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Bay squid, continued

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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.

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.

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)

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

Ten Thousand Islands

Caloosahatchee River

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

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

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.).

Brown shrimp, continued

Habitat

Type: 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%0, and have good growth at 2 to 40%o. Juvenile
brown shrimp are distributed over 0 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

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 0 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

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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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

Pink shrimp, continued

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

Life

1 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

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 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

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

Type: 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).

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

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 0 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.).

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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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).

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

Apalachee Bay

•

Apalachicola Bay

•

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 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.

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

Type: 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%0. 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

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).

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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White shrimp, continued

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NOAA Tech. Memo. NMFS-SEFC-250, 68 p.

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).

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

Ten Thousand Islands

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

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

Baffin Bay

A S J L E

Relative abundance:

Highly abundant
Abundant
Common
Rare

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%0, with
optimum development occurring at 20° to 27°C and 1 7
to 27%0 (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

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 0 to 55%o
(freshwater to hypersaline), but are most common in
oligohaline to euhaline salinities of 2 to 36%0 (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

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).

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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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-

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

Ten Thousand Islands

Caloosahatchee River

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

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

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).

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).

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).

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.

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.

References

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Spiny lobster, continued

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Spiny lobster, continued

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714.

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.

Blue crab, continued

Table 5. 1 1 . Relative abundance of blue crab in
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

r®

Suwannee River

•

Apalachee Bay

•

Apalachicola Bay

•

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

•

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 M J L E

Relative abundance: L

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

ife stage:

- Adults

1 - Mating

- Juveniles

- Larvae (zoeae anc
megalopae)

■Eggs

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

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-

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
0 parts per million (ppm) DO (32°C and 15%o salinity)
and 4.3 hours at 0 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%oand 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 0 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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107

Stone crab

Menippe species

Adult

V.^'!^^ "'■* ' ^-l. J J

Vx^^skL

HllfcMl. 1 n11*

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

(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

Ten Thousand Islands

Caloosahatchee River

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

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

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

Apalachee Bay

Apalachicola Bay

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:

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%0 (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 0 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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117

Bull shark

Carcharhinus leucas

Adult

-^ir****?^'

"•' -'' /l^^y-^ ..'rjyl^.W', -r. ,t7.:

<^ [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

Ten Thousand Islands

Caloosahatchee River

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

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 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

Type: 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 0 cm/year for 6 to 1 0
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.

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

Ten Thousand Islands

Caloosahatchee River

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

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
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 0 to 43 years, and
females at 0 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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128

Tarpon, continued

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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

Apalachee Bay

Apalachicola Bay

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 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

Type: 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 0 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

Ten Thousand Islands

Caloosahatchee River

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

•

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:

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 0 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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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

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

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%0 (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.

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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

Apalachee Bay

Apalachicola Bay

St. Andrew Bay

Choctawhatchee Bay

Pensacola Bay

Perdido Bay

Mobile Bay

If)

Mississippi Sound

Lake Borgne

•

Lake Pontchartrain

Breton/Chandeleur Sounds

Mississippi Rivet

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:

0 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

Geological Survey of Alabama,

Baker, CD., and E.H. Schmitz. 1971. Food habits of
adult gizzard and threadfin shad in two Ozark reser-
voirs. In Hall, G.E. (ed.), Reservoir Fisheries and
Limnology, p. 3-11. Spec. Pub. No. 8, American
Fisheries Society, Washington, DC, 511 p.

Bodola, A. 1966. Life history of the gizzard shad,
Dorosoma cepedianum (Le Sueur) in western Lake
Erie. Fish. Bull., U.S. 65:391-425.

Houser, A., and N.F. Netsch. 1971. Estimates of
young-of -year shad production in Beaver Reservoir. In
Hall, G.E. (ed.), Reservoir Fisheries and Limnology, p.
359-370. Spec. Pub. No. 8, American Fisheries Soci-
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Jenkins, R.M. 1970. Reservoir fish management. In:
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America, p. 173-182. Spec. Pub. No. 7, American
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Jester, D.B., and B.L. Jensen. 1972. Life history and
ecology of the gizzard shad, Dorosoma cepedianum
(Le Sueur) with reference to Elephant Butte Lake.
Univ. New Mexico, Agric. Exp. Sta. Res. Rep. No. 28,
56 p.

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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bays. Publ. Inst. Mar. Sci., Univ. Texas 6:213-250.

Darnell, R.M. 1958. Food habits of fishes and larger
invertebrates of Lake Pontchartrain, Louisiana, an
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Dunham, F. 1972. A study of commercially important
estuarine-dependent industrial fishes. Louis. Wildl.
Fish. Comm. Tech. Bull. No. 4, 68 p.

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.

Guest, W.C., R.W. Drenner, S.T. Threlkeld, F.D. Mar-
tin, and J. D. Smith. 1990. Effects of gizzard shad and
threadfin shad on zooplankton and young-of-year white
crappie production. Trans. Am. Fish. Soc. 119:529-
536.

Gunter, G. 1938. Notes on invasion of fresh water by
fishes of the Gulf of Mexico, with special reference to
the Mississippi-Atchafalaya River System. Copeia
1938:68-72.

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.
Publ. Inst. Mar. Sci., Univ. Texas 1(1):1-190.

Jones, P.W., F.D. Martin and J.D. Hardy, Jr. 1978.
Development of Fishes from the Mid-Atlantic Bight: an
Atlas of Egg, Larval and Juvenile Stages, Vol. 1,
Acipenseridae through Ictaluridae. U.S. Fish Wildl.
Serv. Biol. Rep. FWS/OBS-78/1 2.

Juneau C.L., Jr. 1975. An inventory and study of the
Vermilion Bay-Atchafalaya Bay Complex. Louis. Wildl.
Fish. Comm. Tech. Bull. No. 13, p. 21-74.

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., Shreveport, LA, 133 p.

Lee, D.S., OR. Gilbert, OH. Hocutt, R.E. Jenkins, D.E.
McAllister, J.R. Stauffer, Jr. 1980. Atlas of North
American freshwater fishes. North Carolina St. Mus.
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Lippson, A.J., and R.L. Moran 1974. Manual for
identification of early developmental stages of fishes of
the Potomac River estuary. Martin Marietta Corp.
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Lippson, A.J., M.S. Haire, A.F. Holland, F. Jacobs, J.
Jenson, R.L. Moran-Johnson, T.T. Polgar, And W.A.
Richkus. 1979. Environmental Atlas of the Potomac
Estuary. Martin Marietta Corp. Environmental Ctr.,
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Plant Siting Program, 280 p., 9 maps.

Loftus, W.F., and J.A. Kushlan. 1987. Freshwater
fishes of southern Florida. Bull. Fla. St. Mus. Biol. Sci.
31:147-344.

Manooch, III, OS. 1984. Fisherman's guide: fishes of
the southeastern United States. North Carolina St.
Mus. Nat. Hist., Raleigh, NO, 362 p.

151

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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
species. Fish. Bull., U.S. 60:371-392.

Miller, R.R. 1963. Gizzard shads, threadfin shad. In:
Fishes of the Western North Atlantic. Memoir 1 , Part 3,
p. 443-451. Sears Found. Mar. Res., Yale Univ., New
Haven, CT.

Nash, C.B. 1950. Associations between fish species
in tributaries and shore waters of western Lake Erie.
Ecology 31:561 -566.

Netsch, N.F., G.M. Kersh, Jr., A. Houser, and R.V.
Kilambi. 1971. Distribution of young gizzard and
threadfin shad in Beaver Reservoir. In Hall, G.E. (ed.),
Reservoir Fisheries and Limnology, p. 95-105. Spec.
Pub. No. 8, American Fisheries Society, Washington,
DC, 511 p.

Perret.W.S. 1971. Cooperative Gulf of Mexico estua-
rine inventory and study, Louisiana, In: Cooperative
Gulf of Mexico estuarine inventory and study, Louisi-
ana; Phase I, Area description, and Phase IV, Biology.
Louis. Wildl. Fish. Comm., NewOrleans, LA, p. 29-105.

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,
Texas with respect to salinities before and after a
drought. Tex. J. Sci. 8:83-91.

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. American Fisheries Society, Bethesda, MD,
183 p.

Springer, V.G. 1961. Notes on and additions to the fish
fauna of the Tampa Bay area in Florida. Copeia 4:480-
482.

Springer, V.G. , and K.D. Woodburn. 1960. An ecologi-
cal study of the fishes of the Tampa Bay area. Prof.
Papers Ser. No. 1 , Fla. St. Board Conserv., St. Peters-
burg, FL, 104 p.

Swift, C, R.W. Yerger, and P.R. Parrish. 1 977. 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.

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
study of the Lake Pontchartrain-Lake Maurepas estua-
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No. 19, 159 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

•

Ten Thousand Islands

Caloosahatchee River

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

•

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 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

Type: 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%0 with spawning and development
having been observed at 30.9 to 37%0 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%0 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%0 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%0 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 0 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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Ala. Mar. Res. Bull. 5:1-123.

Swingle, H.A., and D.G. Bland. 1974. A study of the
fishes of the coastal watercourses of Alabama. Ala.
Mar. Res. Bull. 10:22-102.

Tarver, J.W.,andL.B.Savoie. 1976. An inventory and
study of the Lake Pontchartrain-Lake Maurepas estua-
rine complex. Louis. Wildl. Fish. Comm. Tech. Bull.
No. 19, 159 p.

Wagner, P.R. 1973. Seasonal biomass, abundance,
and distribution of estuarine dependent fishes in the
Caminada Bay System of Louisiana. Ph.D. disserta-
tion, Louis. St. Univ., Baton Rouge, LA, 207 p.

Wang, J.C.S., and E.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.

Ward, G.H., and N.E. Armstrong. 1980. Matagorda
bay, Texas: its hydrography, ecology and fishery re-
sources. U.S. Fish Wildl. Serv. Biol. Rep. FWS/OBS-
81/52, 217 p.

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

Caloosahatchee River

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

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
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

Type: 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 0 to 56%0 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%0 (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

Ten Thousand Islands

Caloosahatchee River

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

Breton/Chandeleur Sounds

Mississippi River

If)

Barataria Bay

•

TerrebonneATimbalier 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

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

Type: 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 0 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 m2 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

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Sheepshead minnow, continued

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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

Ten Thousand Islands

Caloosahatchee River

Charlotte Harbor

Tampa Bay

Suwannee River

Apalachee Bay

Apalachicola Bay

St. Andrew Bay

Choctawhatchee Bay

Pensacola Bay

Perdido Bay

Mobile Bay

Mississippi Sound

®
o

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

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 0
to 80%° (Hubbs and Drewry 1959, Tatum et al. 1978,
Waas 1982, Perschbacher et al. 1990). The highest
hatching percentages occur from 0 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 0 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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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

•

Lake Borgne

Lake Pontchartrain

Breton/Chandeleur Sounds

Mississippi River

Barataria Ba}

•

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:

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%0 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 0 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 0 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 0 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 0 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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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

Ten Thousand Islands

Caloosahatchee River

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

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:

0 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

Type: 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%0) 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 0 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%0. 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
0 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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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

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

Perdido Bay

Mobile Bay

Mississippi Sound

Lake Borgne

Lake Pontchartrain

Breton/Chandeleur Sounds

Mississippi River

Barataria Ba}

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:

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

Type: 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 0 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 0 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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209

Bluefish, continued

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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

Ten Thousand Islands

Caloosahatchee River

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

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:

0 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.

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

Caloosahatchee River

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

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:

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

Type: 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 0 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.

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220

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P-

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

Caloosahatchee River

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

BretorVChandeleur 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

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 0 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%0, 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 0 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
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Berry, F., and E.S. Iversen. 1967. Pompano: Biology
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Christmas, J.Y., and R.S. Waller. 1973. Estuarine
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Gilbert, C. 1986. Species profiles: life histories and
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Gunter, G. 1958. Population studies of the shallow
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DeLancey, L.B. 1989. Trophic relationship in the surf
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Ditty, J.G., G.G. Zieske, and R.F. Shaw. 1988. Sea-
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U.S. 86(4):81 1-823.

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):189-307.

Gunter, G., and G.E. Hall 1965. A biological investiga-
tion of the Caloosahatchee estuary of Florida. Gulf
Res. Rep. 2(1):1-64.

Fields, H.M. 1962. Pompanos (Trachinotus spp.) of
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313, p. 11-15.

Finucane, J.H. 1969a. Ecology of the pompano
(Trachinotus carolinus) and the permit (Trachinotus
falcutus) in Florida. Trans. Am. Fish. Soc. 98(3):478-
486.

Hildebrand, H.H. 1954. A study of the fauna of the
brown shrimp (Penaeus aztecus Ives) grounds in the
western Gulf of Mexico. Publ. Inst. Mar. Sci., Univ.
Texas 3(2): 1-366.

Hildebrand, S.F., and W.C. Schroeder. 1928. Fishes
of Chesapeake Bay. Bull. U.S. Bur. Fish. 43:1-366.

Hoese, H.D. 1965. Spawning of marine fishes in Port
Aransas, Texas area as determined by the distribution
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Hoese, H.D., and R.H.Moore. 1977. FishesoftheGulf
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TX, 327 p.

Iversen, E.S. , and F.H. Berry. 1969. Fish mariculture:
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Florida pompano, continued

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.

Linton, E. 1904. Parasites of fishes of Beaufort, North
Carolina. Bull. U.S. Bur. Fish. 24:321-427.

McFarland, W.N. 1963. Seasonal change in the
number and the biomass of fishes from the surf at
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Texas 9:91-111.

Miles, D.W. 1949. A study of the food habits of the
fishes of the Aransas Bay area. M.S. thesis, Univ.
Houston, Houston, TX, 70 p.

Modde, T. 1980. Growth and residency of juvenile
fishes within a surf zone habitat in the Gulf of Mexico.
Gulf Res. Rep. 6(4):377-385.

Modde, T., and ST. Ross. 1981. Seasonality of fishes
occupying a surf zone habitat in the northern Gulf of
Mexico. Fish. Bull., U.S. 78(4):91 1-922.

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Florida fishes. Fla. Dept. Nat. Res. Tech. Ser., No. 69,
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Moe, M.A., Jr., R.H. Lewis, and R.M. Ingle. 1968.
Pompano mariculture: Preliminary data and basic con-
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E.A. Lachner, R.N. Lea, and W.B.Scott. 1991. Com-
mon and scientific names of fishes from the United
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Pub. No. 20. American Fisheries Society, Bethesda,
MD. 183 p.

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.

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Dauphin Island Sea Lab, Dauphin Island, AL, 256 p.

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upper Laguna Madre of Texas. Publ. Inst. Mar. Sci.,
Univ. Texas 4(2): 156-200.

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cal study of the fishes of the Tampa Bay area. Fla.
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of the Galveston Bay System, Texas. Publ. Inst. Mar.
Sci., Univ. Texas 10:201-220.

Perret, W.S., W.R. Latapie, J.F. Pollard, W.R. Mock,
G.B. Adkins, W.J. Gaidry, and C.J. White. 1971.
Fishes and invertebrates collected in trawl and seine
samples in Louisiana estuaries In Cooperative Gulf of
Mexico Estuarine Inventory and Study, Louisiana, p.
41 -1 05. Louis. Wildl. Fish. Comm., New Orleans, LA.

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

Caloosahatchee River

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

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

Baffin Bay

A S J L E

Relative abundance:

0 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 0 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 0 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/m2) 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 0 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 0 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 0 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 0 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 0
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

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Chester, A.J., and G.W. Thayer. 1 990. Distribution of
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Croker, R.A. 1960. A contribution to the life history of
the gray (mangrove) snapper, Lutjanus griseus
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Croker, R.A. 1962. Growth of the gray snapper,
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Mote Marine Lab., Sarasota, FL, 64 p.

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

Ten Thousand Islands

Caloosahatchee River

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

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

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 0 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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Benson, N.G., (ed.) 1982. Life history requirements of
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Bryant, H.E., M.R. Dewey, N.A. Funicelli, G.M. Ludwig,
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Caldwell, D.K. 1965. Systematics and variation in the
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Christmas, J.Y., and R.S. Waller. 1973. Estuarine
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Ditty, J. G. 1986. Ichthyoplankton in neritic waters of
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Ditty, J.G., G.G. Zieske, and R.F. Shaw. 1988. Sea-
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Juneau, C.L. 1975. An inventory and study of the
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Lee, D.S., C.R. Gilbert, C.H. Hocutt, R.E. Jenkins, D.E.
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867 p.

Levine, S.J. 1980. Gut contents of forty-four Lake
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Loftus, W.F., and J.A. Kushlan. 1987. Freshwater
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Odum, W.E., C.C. Mclvor, and T.J. Smith, III. 1982.
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algae in the diet of sheepshead, Archosargus
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biology of sheepshead in the northern Gulf of Mexico.
Trans. Amer. Fish. Soc. 121:757-764.

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Archosargus probatocephalus, in offshore reef habi-
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Gulf Sci. 9:29-37.

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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

•

Ten Thousand Islands

•

Caloosahatchee River

•

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

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:

0 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

Type: 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 0 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 Populations: Large numbers of
pinfish have died during episodic winter events when
water temperatures have dropped to approximately
4°C (Gunter 1941, Muncy 1984).

References

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Cameron, J.N. 1969a. Seasonal changes in the
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Cameron, J.N. 1970. The influence of environmental
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Cardeilhac, P.T. 1976. Induced maturation and devel-
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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

Ten Thousand Islands

Caloosahatchee River

Charlotte Harbor

•

Tampa Bay

•

Suwannee River

1*1

Apalachee Bay

Apalachicola Bay

1*1

St. Andrew Bay

Choctawhatchee Bay

Pensacola Bay

Perdido Bay

Mobile Bay

Mississippi Sound

•

Lake Borgne

•

Lake Pontchartrain

Breton/Chandeleur Sounds

Mississippi River

Barataria Bay

1*1

Terrebonne/Timbalier Bays

Atchafalaya/Vermilion Bays

Calcasieu Lake

Sabine Lake

Galveston Bay

"cP

Brazos River

Matagorda Bay

San Antonio Bay

Aransas Bay

Corpus Christi Bay

Laguna Madre

Baffin Bay

1*1

If)

A S J L E

Relative abundance:

0 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 0 (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 0 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 crustaceans, and to a
lesser degree, polychaetes and nematodes (Darnell
1958, Springer and Woodburn 1960, Diener et al.
1974, Gosselink 1984, Killam et al. 1992, Schmidt
1993).

Food Items: Diet varies seasonally and with develop-
ment (Schmidt 1993). Larvae and small juveniles
consume mostly zooplankton (copepod and fish lar-
vae) (Hildebrand and Cable 1 930, Darnell 1 958). Small
juveniles (7 to 20 mm TL) consume invertebrates such
as copepods, ostracods, cladocera, schizopods, am-
phipods, mysids, and annelids. At 50 to 80 mm TL, they
feed increasingly on annelids, larger crustaceans (such
as shrimp), molluscs, chironomidae larvae. Larger
juveniles and adults also consume small fishes (pin-
fish, anchovies, gobies, silver perch) and crabs, in
addition to these other food items (Darnell 1958,
Springer and Woodburn 1960, Diener et al. 1974,
Levine 1980, Gosselink 1984, Killam et al. 1992,
Schmidt 1 993). Largerfish tend to have a more diverse
diet (Schmidt 1993).

Biological Interactions

Predation: Little information is available concerning
predation on this species, but considering its abun-
dance, it is a likely prey item for numerous species of
piscivorous fish (Killam et al. 1992). Reported preda-
tors include spotted seatrout and king mackerel
(Scomberomorus cavalla) (Kemp 1949, Darnell 1958,
Killam etal. 1992).

Factors Influencing Populations: Distribution and abun-
dance may be influenced by a variety of water quality

249

Silver perch, continued

and structural habitat parameters (Killam et al. 1992).
All life stages appear to be more abundant in moderate
to high salinities. High mortalities can occur during
extreme low water temperatures induced by seasonal
cold fronts. The dietary habits of silver perch are
especially similar to juvenile spotted seatrout of com-
parable size (Darnell 1958), which may result in com-
petition between the two species.

Personal communications

Ditty, James G. Louisiana State Univ., Baton Rouge,
LA.

Fischer, W. (ed.). 1978. FAO Species Identification
Sheets for Fishery Purposes, Western Central Atlantic
(Fishing Area 31), Vol. IV. Food and Agriculture
Organization 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.

Gosselink, J.G. 1984. The ecology of delta marshes
of coastal Louisiana: a community profile. U.S. Fish
Wildl. Serv. Biol. Rep. FWS/OBS-84/09, 134 p.

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251

Sand seatrout

Cynoscion arenarius
Adult

8 cm

(from Fischer 1978)

Common Name: sand seatrout

Scientific Name: Cynoscion arenarius

Other Common Names: white trout (Benson 1982,

Sutter and Mcllwain 1987); sand trout (Hoese and

Moore 1977); sand weakfish,acoupacfesa£>/e(French),

corvinata de arena (Spanish) (Fischer 1978, NOAA

1985).

Classification (Robins et al. 1991)

Phylum: Chordata

Class: Osteichthyes

Order: Perciformes

Family: Sciaenidae

Value

Commercial: The sand seatrout is one of the most
abundant fishes in estuarine and nearshore waters of
the Gulf of Mexico (Gunter 1 945, Christmas and Waller
1973). It is one of the most important species caught
in the industrial bottomfish and foodfish fisheries of the
northern Gulf of Mexico (Roithmayr 1965, Sheridan et
al. 1 984, Sutter and Mcllwain 1 987, Ditty et al. 1 991 ),
and is a major component of bycatch in shrimp trawls.
It consistently ranks among the top five most abundant
species in demersal fish surveys. Sand seatrout
{Cynoscion arenarius) and silver seatrout (Cynoscion
nothus) landings are grouped together as' "white
seatrout" in statistics reported by the National Marine
Fisheries Service (NMFS) (NMFS 1993). The two
species are difficult to distinguish from one another and
they overlap somewhat in distribution. The Gulf region
reported landings of 1 31 .5 mt of white seatrout valued
at $154,000 in 1992 (NMFS 1993). Alabama and
Louisiana Gulf landings in 1 992 were 265,000 pounds
valued at $1 46,000. Based on 1 992, the Louisiana and
Alabama white seatrout fishery contributed almost
95% of the western and central Gulf region's white

seatrout landings (Newlin 1 993). The majority of these
landings are believed to be attributable to silver seatrout
(Shipp 1986). The bulk of the groundfish harvest
comes from the deeper nearshore waters of the Gulf of
Mexico.

Recreational: The sand seatrout is highly prized by
recreational fishermen. The National Marine Fisheries
Service (NMFS) estimates that the recreational catch
was 3,243,000 sand seatrout in the Gulf of Mexico
during 1 992 (NMFS 1 993). The Gulf recreational catch
accounted for about 99% of the U.S. sand seatrout
recreational landings (NMFS 1 993). NMFS estimated
the following catches by fishing method in 1 992: char-
terboats-44,000; private/rental boats-2,21 4,000; shore
fisherman-986,000 (NMFS 1993). Shrimp are the
preferred bait for this fish. Sand seatrout are also taken
in recreational shrimp trawls.

Indicator: Sand seatrout are not typically used in stud-
ies of environmental stress.

Ecological: The sand seatrout serves as an important
link between estuarine and marine food webs. It
provides a direct link in the food chain between the
primary consumers and the top predators. The sand
seatrout feeds mostly on shrimp (penaeids), bay an-
chovies (Anchoa mitchilli), and Gulf menhaden
(Brevoortia patronus) (Moffet et al. 1979, Overstreet
and Heard 1982). Juvenile sand seatrout may be an
important food item in the diets of piscivorous sport and
food fish. However, the larger sand seatrouts' piscivo-
rous, predacious habits possibly place them in compe-
tition with other predators that target similar prey spe-
cies.

252

Sand seatrout, continued

Table 5.34. Relative abundance of sand seatrout 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

•

Apalachicola Bay

•

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 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

Range

Overall: The range of the sand seatrout is limited to the
coastal and shelf waters of the Gulf of Mexico, extend-
ing from Florida Bay to the Bay of Campeche. It is
considered rare in the Bay of Campeche reef areas,
and in the lower mangrove areas of the lower west
coast of Florida (Fischer 1978, NOAA 1985, Shipp
1986).

Within Study Area: The sand seatrout is common in
estuarine and nearshore waters of the Gulf of Mexico,
with the exception of the lower mangrove areas of the
lower west coast of Florida (Shipp 1 986) (Table 5.34).

Life Mode

The sand seatrout is estuarine-dependent, and spends
most of its life in the estuaries and nearshore waters of
the Gulf of Mexico. Eggs are pelagic and buoyant
(Johnson 1978). Larvae are pelagic. Juveniles and
adults are estuarine and demersal (Benson 1 982, Ditty
and Shaw 1 994). This is a schooling fish, often forming
groups with spotted seatrout (Cynoscion nebulosu$.
Its activity patterns tend to be diurnal (Vetter 1977).

Habitat

Type: The sand seatrout is truly estuarine dependent,
but can be found in environments ranging from marine
to estuarine. Larvae have been collected in inshore to
midshelf waters in depths ranging from 5 to 70 m, with
most occurring between 1 0-25 m (Cowan 1 985, Cowan
and Shaw 1988, Cowan et al. 1989). Shlossman and
Chittenden (1981) report spring spawned larvae use
estuarine marsh habitat, while late summer spawned
larvae utilize the inshore gulf waters as nurseries.
Larvae appearto have some surface orientation (Cowan
1985, Cowan and Shaw 1988), but become increas-
ingly demersal with size (Ditty et al. 1 991 ). Adults and
juveniles prefer nearshore and inshore areas and are
rarely taken in waters deeper than 55 m (Miller 1964,
Kelley 1 965. Warren and Sutter 1 982), but adults have
been caught offshore as deep as 1 10 m. According to
Shipp (1986) "this fine food fish abounds in areas
around passes and channels." Aggregations of 0.5 to
1 .0 kg sand seatrout are known to occur in deep holes
and over oyster reefs during the summer in estuaries.
Gallaway and Strawn (1974) stated that oyster reefs
and water depths greater than 1 m were preferred by
adults. Larger sand seatrout (1.5 kg) are known to
aggregate around offshore oil rigs (Shipp 1986).

Substrate: Juveniles prefer muddy bottoms, while adults
are found over most bottom types in estuaries and
nearshore Gulf areas. Larvae and juveniles prefer
grass beds and marsh areas, with soft organic bottoms
(Conner and Truesdale 1972, Benson 1982).

253

Sand seatrout, continued

Physical/Chemical Characteristics:
Temperature: The sand seatrout is apparently sensi-
tive to temperature extremes, and temperature ap-
pears to affect distribution more than does salinity
(Trent et al. 1969, Vetter 1982).

Temperature - Eggs: Eggs have been collected in
water temperatures from 24.5° to 29°C (Holt et al.
1988).

Temperature - Larvae and Juveniles: Spawning oc-
curs only above 20°C, and larvae are only found at
these temperatures (Ditty pers. comm.). Most juve-
niles are found at temperatures above 1 0°C; however,
they have been reported from 5° to 36.9°C (Gunter
1945, Wang and Raney 1971, Christmas and Waller
1973, Warren and Sutter 1982, Cowan and Shaw
1988, Cowan et al. 1989). Copeland and Bechtel
(1974) reported optimum catches in temperatures of
20° to 35°C. Some have been caught in temperatures
as high as 40°C (Gallaway and Strawn 1974).

Temperature - Adults: Adults prefer temperatures of
12° to 36°C (Miller 1964, Vetter 1977, Benson 1982)
(Simmons 1957).

Salinity - Eggs: Eggs have been collected in salinities
from 27 to 37%o (Holt et al. 1988).

Salinity - Larvae and Juveniles: Larvae mostly occur
from 14° to 21 °C in water salinities of 15 to 36%o
(Cowan 1985, Cowan and Shaw 1988, Cowan et al.
1989). Small sand seatrout have been reported in
salinities from 0 to 34.5%o (Wang and Raney 1971,
Christmas and Waller 1973, Wagner 1973, Warren
and Sutter 1982). In Mississippi Sound, best catches
for fish with total lengths (TL) of 20 to 90 mm were
reported in salinities <15%°; fish of 90 to 220 mm TL
were caught in salinities >1 5%o at 25 to 30° C (Warren
and Sutter 1982).

Salinity - Adults: Adults have been caught in salinities
as high as 45%o (Simmons 1957).

Dissolved Oxygen: Sand seatrout avoid water with
dissolved oxygen (DO) less than 4.6 to 5.0 mg/l (Benson
1982).

Movements and Migrations: Shlossman and Chittenden
(1 981 ) noted that the inshore movement of young sand
seatrout coincided with periods of rising sea level in the
northern Gulf of Mexico due to surface currents and
prevailing onshore winds. Larvae spawned in the
northwestern Gulf of Mexico appear to be carried
inshore from spawning grounds by longshore currents
(Cowan and Shaw 1 988). Larvae migrate into shallow
areas of the upper estuaries and apparently prefer

small bayous, shallow marshes, and channels during
their early development (Ditty et al. 1 991 ). Larvae and
early juveniles (<30 mm SL) first appear in estuaries in
April and occur throughout the summer and early fall,
but with distinct peaks during April-May and Septem-
ber-October (Swingle 1 971 , Franks et al. 1 972, Warren
and Sutter 1982, Ditty et al. 1991). Catch data indi-
cates that they move into the low salinity waters (less
than 15%o). A migration from bay waters to offshore
breeding grounds usually occurs in late fall or winter
(Springer and Woodburn 1960, Warren and Sutter
1 982) or with a decrease in temperature (Gunter 1 938,
1945, Kelley 1965, Perry 1970, Wagner 1973, Vetter
1 977, Warren and Sutter 1 982, Vetter 1 982, Ditty et al.
1 991 ). Most have left the estuaries by December, but
some remain all winter. The sand seatrout will also
move to deeper water to avoid extremes in tempera-
ture (Vetter 1982). Adults move back into higher
salinity (>15%o) areas of estuaries after spawning
(Benson 1982). Recruitment of juveniles into estuaries
occurs from spring through the fall (Gunter 1945,
Christmas and Waller 1 973, Warren and Sutter 1 981 ).

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: Sand seatrout adults first spawn at age 12
months (Ditty et al. 1991). Spawning has been re-
ported from March through September (Wagner 1 973,
Shlossman and Chittenden 1981, Warren and Sutter
1982) with limited spawning possible as early as De-
cember (Cowan et al. 1 989) or January (Cowan 1 985,
Cowan and Shaw 1 988, Ditty et al. 1 991 ). Based on the
presence of larval sand seatrout in the northern Gulf of
Mexico, it can be inferred that spawning occurs Febru-
ary through October, with peaks in March-April and
July-August (Ditty 1 986, Ditty et al. 1 988). Shlossman
and Chittenden (1981) identified two spawning peaks
for sand seatrout in Texas Gulf waters. The first peak
occurred from early March to May (spring) and the
second occurred during August to September (late
summer). Other studies indicate a broad period of
spawning during spring and late summer (Franks et al.
1 972, Gallaway and Strawn 1 974, Moffett et al. 1 979).
Spawning usually occurs during the early evening
hours (Shipp 1986, Ditty et al. 1991). Perry (1970)
suggests sand seatrout spawn throughout the winter in
deep water (73-91 m) based on catches of females in
February and March with roe leaking from their anal
pore. Sand seatrout spawn in the higher salinity
estuarine and nearshore Gulf waters (Sutter and
Mcllwain 1987). Most spawning appears to occur in
the shallow Gulf primarily in waters between 7 to 1 5 m
in depth (Cowan 1985), but can occur in depths up to
91 m and as far as 175 km from shore (Perry 1970,

254

Sand seatrout, continued

Sheridan et al. 1984, Cowan and Shaw 1988);
Shlossman (1 980) suggested spawning occurs in 1 4 to
40 m depths. Sheridan et al. (1984) collected the
following percentages of ripe and mature sand seatrout
in the northern Gulf: 9-17 m deep (14%); 18-36 m
(15%); 37-55m (24%); 56-73 m (38%); 79-91 m (21%).
Shlossman and Chittenden (1981) used length-fre-
quencies gradients to identify Texas spawning areas/
depths to be from 7 to 22 m. Sheridan et al. (1984)
speculates that the difference between Texas and the
northern Gulf may be due to variations in the depths of
the spawning grounds. Spawning appears to take
place initially in midshelf to offshore waters and move
shoreward as the season progresses (Ditty et al.
1991). Spawning location is probably determined by
salinity and intensity of spawning by water tempera-
ture.

Fecundity: Sheridan et al. (1984) estimated the mean
fecundity for sand seatrout (1 40 mm-278 mm SL) to be
1 00,990 ova with a range from 28,000 to 423,000 ova.
They also developed equations to estimate individual
fecundity.

Growth and Development

Egg Size and Embryonic Development: Sand seatrout
eggs are 0.67-0.90 mm in diameter (Holt et al. 1988,
Ditty and Shaw 1994). They develop oviparously and
hatch within one day of being fertilized (Shipp 1 986). At
25° to 27°C eggs begin to hatch 16 to 22 hours after
spawning (Holt et al. 1988). Other characteristics of
sand seatrout eggs have not been fully described
(Powles1981).

Age and Size of Larvae: Geographical location and
time of the year appear to have an influence on the rate
of larval growth (Ditty et al. 1991). Larvae spawned
early in the season have faster growth than those
spawned in the late summer.

Juvenile Size Range: Transformation to the juvenile
stage occurs at a length of 1 0 - 1 2 mm (Ditty and Shaw
1 994). Recruitment of juveniles into estuaries occurs
from spring through the fall (Gunter 1945, Christmas
and Waller 1973, Warren and Sutter 1981). Their
estimated growth rate is 5.8 mm/week (Warren 1981).
Fish spawned in the spring reach 160 to 190 mm TL
after six months and 220 to 280 mm after one year.
Those spawned in late summer range from 1 20 to 1 50
mm TL after 6 months, and 21 0 to 250 mm TL after one
year (Shlossman and Chittenden 1981). Monthly
increases in total length of sand seatrout are greatest
during the warm water temperatures from May to
October (35 mm TL/month) and slowest in winter (5-10
mm TL/month) when waters are cooler (Shlossman
and Chittenden 1 981 ). Growth rates in the central and
eastern Gulf range from 9.3 to 27.7 mm SL/month, and

5-10 to 35 mm TL/month in the western Gulf.

Age and Size of Adults: In one study, the smallest
maturing male was 129 mm SL and the smallest
maturing female was 140 mm SL (Sheridan et al.
1 984). Sand seatrout generally mature at 1 40-1 80 mm
total length (TL) as they approach age I in the Gulf
waters of Texas (Shlossman and Chittenden 1981).
Maximum life span for this species is estimated to be 3
years, with maximum lengths of 590 mm TL reported
by Trent and Pristas (1977). Few sand seatrout
exceed a maximum of 300 mm TL although trawl-
caught fish up to about 500 mm TL have been reported
(Ditty etal. 1991).

Food and Feeding

Trophic Mode: The sand seatrout is a generalized
predator that feeds primarily in daylight hours on live
and dead organisms (Vetter 1977). Its food habits
show that it is an opportunistic carnivore whose diet
changes with age (Ditty et al. 1 991 ).

Food Items: Age, habitat, abundance of suitable prey
and its availability in different geographic locations
influences the diet of the sand seatrout (Ditty et al.
1991). Mysids and calanoid copepods are the main
diet items of sand seatrout less than 40 mm SL (Sheridan

1979, Sheridan and Livingston 1979, Levine 1980).
Fish are the predominant food item of all larger sand
seatrout, with the bay anchovy being the most fre-
quently consumed prey (Moffet et al. 1979, Levine

1980, Overstreet and Heard 1982, Sheridan et al.
1984). Mysidaceans were eaten more often in lower
salinity areas, whereas fish were heavily consumed
near passes of the estuaries. Sand seatrout from 45 to
159 mm SL in Texas were found to have stomach
contents of 38% crustaceans, and 30% fish (Moffett et
al. 1979). Sand seatrout from 160 to 375 mm SL in
Texas contained 46% fish (mostly bay anchovies), 1 0%
crustaceans, and 1 % polychaetes. Sand seatrout from
Mississippi Sound had 3% stomatopods, 53% penaeid
shrimp, 7% caridean shrimp, and 55% fish (mostly bay
anchovies and Gulf menhaden) (Overstreet and Heard
1982) Fish from Lake Pontchartrain, Louisiana had
95% crustaceans, 4.7% fish, and a small percentage of
molluscs (Levine 1980). Other studies have found
intraspecific cannibalism and a seasonal shift in food
habits with more crustaceans consumed during the fall
and winter than during other months (Ditty et al. 1 991 ).
In addition, piscine prey is more abundant in the diet of
sand seatrout inshore than those offshore (Ditty et al.
1991).

Biological Interactions

Predation: Although predator information on this spe-
cies is unavailable, it seems likely that larvae and
juveniles may serve as minor prey items for other

255

Sand seatrout, continued

fishes.

Factors Influencing Populations: "Ecological separa-
tion" among life stages has been suggested by Springer
and Woodburn (1960), with juveniles occurring in the
bays and adults staying primarily offshore. The sand
seatrout forms a major segment of the finfish bycatch
discarded by the U.S. shrimp fleet (Ditty et al. 1991).
Fishery pressure will also continue to increase as a
result of management of the more popular and ex-
ploited species (Cowan et al. 1989, Ditty et al. 1991).
The comparison of length-weight relationships sug-
gests that distinct populations off Texas and the Loui-
siana-Mississippi coasts might exist.

Ditty, J. G. 1986. Ichthyoplankton in neritic waters of
the northern Gulf of Mexico off Louisiana: Composi-
tion, relative abundance, and seasonality. Fish. Bull.,
U.S. 84(4):935-946.

Ditty, J.G., M. Bourgeois, R. Kasprzak, and M. Konikoff .
1991. Life history and ecology of sand seatrout
Cynoscion arenarius Ginsburg, in the northern Gulf of
Mexico: a review. Northeast Gulf Sci. 12:35-47.

Ditty, J. G., and R.F.Shaw. 1994. Preliminary guide to
the identification of the early life history stages of
sciaenid fishes from the western central Atlantic. NOAA
Tech. Memo. NMFS-SEFSC-349.

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257

Sand seatrout, continued

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258

Spotted seatrout

Cynoscion nebulosus
Adult

8 cm

(fromGoode 1884)

Common Name: spotted seatrout

Scientific Name: Cynoscion nebulosus

Other Common Names: spotted weakfish, spotted

squeteague, speckles, speckled trout, salmon trout,

simon trout (Hildebrand and Schroeder 1 972); acoupa

pintade (French), con/inata pintada (Spanish) (Fischer

1978, NOAA 1985).

Classification (Robins et al. 1991)

Phylum: Chordata

Class: Osteichthyes

Order: Perciformes

Family: Sciaenidae

Value

Commercial: Commercial landings of spotted seatrout
occur throughout the year along the Gulf of Mexico.
Fresh catch is sold in local markets. During 1992,
703.1 mt of spotted seatrout were landed in the Gulf
(Newlin 1993). Louisiana harvested over 61% (431.4
mt) of the total landings followed by Florida (257.2 mt)
and Mississippi (14.5 mt). A decline in landings has
been reported for Gulf coast states in recent years,
possibly due to over-fishing and habitat destruction
(Heffernan and Kemp 1 982). These reported declines
resulted in closure of the Alabama and Texas commer-
cial fishery, and an annual harvest quota of 454 mt
(GSMFC 1993). Runaround gill nets, trammel nets,
pound nets, seines, and longlines are the common
gear used, and occasionally bottom trawls are used.
However, the commercial fishery in Florida is now
strictly hook-and-line because of a recent net ban
(DeVries pers. comm.). Many spotted seatrout are
caught incidentally while fishing for other inshore fishes
(Fischer 1978, Lassuy 1983, Perret et al. 1980).

Recreational: The spotted seatrout is one of the spe-
cies most often sought by anglers, and the sport catch
is substantially greater than the commercial harvest
(Tabb and Manning 1961, Van Voorhees et al. 1992,
NMFS 1993). Fishery information for the Gulf of
Mexico (except Texas) showed a total catch of
18,188,000 spotted seatrout in 1992 (NMFS 1993).
Seatrout are taken on light to heavy spinning tackle
from shorelines, piers and boats in beach Gulf waters,
inshore estuarine bays, sounds, bayous, and tidal
streams (Lassuy 1 983, Perret et al. 1 980). Regulations
for recreational fishing of this species vary among the
Gulf states (GSMFC 1993).

Indicator of Environmental Stress: Bryan (1 971 ) found
levels of DDT in the ovaries and eggs to be 4.77 and
2.93 parts per million, respectively, and considered
these concentrations to affect the reproductive capac-
ity of spotted seatrout in the lower Laguna Madre.
However, Butler ( 1 969) indicates that successful spawn-
ing can occur with concentrations as high as 8 parts per
million in the ovaries. The presence of PCB levels
below the maximum permissible level in food fish has
been verified in spotted seatrout from the Gulf of
Mexico (Killam et al. 1 992). Experiments with sublethal
concentrations of fuel oil (0.00-1 .00 ppm) found an
increase in the occurrence of larvae with unpigmented
eyes, and a decrease in total body length and distance
needed to initiate avoidance responses (Johnson et al.
1 979). The effect of chlorine concentrations in seawa-
ter has been tested on eggs and larvae and found to
cause increased mortality (Johnson et al. 1977).

Ecological: The spotted seatrout is a top trophic level
carnivore within coastal and estuarine ecosystems,
and probably plays a significant role as a predator in

259

Spotted seatrout, continued

Table 5.35. Relative abundance of spotted seatrout
in 31 Gulf of Mexico estuaries (from Volume /).

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

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 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

the structure of estuarine communities (Lassuy 1983,
Killametal. 1992).

Range

Overall: The spotted seatrout is found in coastal waters
from Cape Cod, Massachusetts to Carmen Island in
the Bay of Campeche, Mexico. It is most abundant
from Florida to Texas (Fischer 1978, Lee et al. 1980,
Lassuy 1983, Mercer 1984, NOAA 1985).

Within Study Area: The spotted seatrout is found from
Key West, Florida to the Rio Grande, Texas. Areas of
abundance occur around eastern Louisiana, south
Texas, Mississippi, Alabama, and along the west coast
of southern Florida (Tabb and Manning 1961, Hoese
and Moore 1 977, Lee et al. 1 980, Lassuy 1 983, Johnson
and Seaman 1986) (Table 5.35).

Life Mode

Eggs are pelagic (>30%o) or demersal (25%o) depend-
ing on salinity; initially, larvae are pelagic and become
demersal after 4 to 7 days. Juveniles and adults are
demersal, completing their entire life cycle in inshore
waters (Ditty and Shaw 1994). Large juveniles and
adults form small schools. This species possesses a
definite diel pattern of metabolic activity, with increased
activity occurring at night (Pearson 1929, Wagner
1973, Vetter 1977),

Habitat

Type: This species is estuarine-dependent, and it
completes its entire life cycle in inshore waters (Wagner
1 973). Seasonal abundance appears to be associated
with estuarine zones, with different estuarine habitats
utilized by different life history stages (Helser et al.
1993). Eggs are found from marine to estuarine
environments, are buoyant or demersal depending on
salinity, and are generally associated with grass beds
at or near barrier island passes. They are also found
in areas with fine to medium texture detritus devoid of
vegetation (Sabins and Truesdale 1974). Larvae are
demersal in deep channels with shell rubble, or in
bottom vegetation (Tabb 1966). Juveniles in Florida
have been reported from a water depth range of 0.5 to
2.2 m (Rutherford et al. 1 989a). Seagrass appears to
be a critical habitat for juveniles and adults, but back-
waters (bayous, tidal creeks, slow flowing rivers),
marshes, and other areas without extensive seagrass
beds can contain substantial numbers of juveniles as
well (Van Hoose 1987, McMichael and Peters 1989,
Killam et al. 1992). Juveniles and adults have been
found in the seagrasses Thalassia testudinum,
Syringodium filiforme, and Halodule wrightii, and abun-
dance and distribution of juveniles may be influenced
by biomass, shoot density, and species composition of
seagrass beds (Hettler 1989, Killam et al. 1992). The
preferred habitat in Louisiana is along relatively shal-

260

Spotted seatrout, continued

low marsh edges of small, saline water bodies in
Spartina altemiflora dominated areas (Peterson 1 986,
McMichael and Peters 1989, Chester and Thayer
1990). Individuals have also been found around oil
drilling platforms in the nearshore area (Stanley and
Wilson 1990). Juveniles and adults can occur in a
variety of estuarine habitats including seagrass beds,
mangrove-lined depressions, and in relatively deep
basins, tidal river mouths, channels and canals (Mok
and Gilmore 1983, Van Hoose 1987, Thayer et al.
1988, Chester and Thayer 1990, Killam et al. 1992).
Juveniles remain in submerged vegetation during sum-
mer, but may move to deeper water during the winter
months when water temperatures drop. Adults also
occur in the surf zones of barrier islands, particularly in
fall months (Perry 1970).

Substrate: The substrate for larvae is highly variable.
Vetter (1977) states larvae are dependent on grass
beds, while Benson (1982) indicates that the deep
channels near grass beds may serve as their initial
habitat ratherthan algae and muddy sand (Tabb 1 961 ),
prior to movement into the grass bed as juveniles. In
Louisiana, where inshore salinities can be fairly low
due to the influence of the Mississippi River, nursery
habitat is probably higher salinity lower bays and the
nearshore Gulf of Mexico (Herke et al. 1984). Juve-
niles and adults are generally associated with
seagrasses, particularly Halodule and Thalassia, but
they are also common over sand, sand-mud, or me-
dium to soft, mud-detritus substrates, shallow muddy
areas, oil platforms and shell reefs (Benson 1982,
Peterson 1986, Rutherford et al. 1989a, McMichael
and Peters 1 989, Chester and Thayer 1 990, Killam et
al. 1992).

Physical/Chemical Characteristics:
Temperature: Spotted seatrout appear to have a high
capacity for metabolic compensation for dealing with
the wide extremes in temperature that occur in the
estuarine habitats that they exploit on a year-round
basis (Vetter 1982).

Temperature - Eggs: Eggs and yolk sac larvae have an
optimal temperature of 28°C, but have been hatched
experimentally at 32°C (Taniguchi 1980, Gray and
Colura 1 988). However, complete survival is expected
between 23. 1 ° and 32.7°. Eggs incubated at 20°C had
a lower mean hatch rate (Gray and Colura 1988).

Temperature - Larvae and Juveniles: Larvae and juve-
niles have been collected in temperatures of 5° to 36°C
(Wang and Raney 1971, Perret et al. 1980, Benson
1 982, Rutherford et al. 1 989a, Killam et al. 1 992); their
preferred temperatures range from 20° to 30°C (Arnold
etal. 1976).

Temperature - Adults: Adults prefer temperatures from
15° to 27°C, and may move seaward if estuarine
temperatures become extreme (Mahood 1974).
Simmons (1957) reported active feeding and move-
ment between 4° to 33°C with gradual acclimation;
however, sudden drops in temperature can result in
mass mortality (Gunter 1 941 , Moore 1 976). Tempera-
tures for spawning range from 20° to 30°C (Benson
1982).

Salinity - Eggs: The highest hatch rates for experimen-
tally incubated eggs have been reported to occur at 1 5
to 25%0 and 1 9 to 38%o at 28°C (Shepard 1986, Gray
and Colura 1988), and it is suspected that in lower
salinities in the wild, survival may be reduced (Tabb
1966). The optimum salinity for eggs has been re-
ported to be 28.1%o (Killam et al. 1992). These eggs
had a significantly lower hatch rate at 5%o and all eggs
died at any temperature when the salinity was 45%o.
Eggs at 5%° would also sink to the bottom, which would
probably increase mortality in the wild. A critical
minimum (0%o) and a critical maximum (50%o) has been
determined that corresponds to 0% embryo survival at
28°C (Shepard 1986). Salinity acclimation of parents
may also affect salinity tolerance of eggs (Gray and
Colura 1988).

Salinity - Larvae: Spotted seatrout larvae are consid-
ered the most euryhaline of all sciaenid larvae (Killam
et al. 1 992). They have been collected in Florida from
8.0 to 40.0%o (Rutherford et al. 1989a, Killam et al.
1992) and optimal salinity has been reported to range
from 20 to 35%o in hatchery conditions (Arnold et al.
1976, Killam etal. 1992).

Salinity - Juveniles: Juveniles seem to prefer mesohaline
and polyhaline waters where salinities range from 8 to
25%o (Peterson 1986). They have been collected in
waters with salinities ranging from 0 to 48%o (Gunter
1 945, Wang and Raney 1 971 , Wagner 1 973, Peterson
1 986, Rutherford et al. 1 989a, Killam et al. 1 992).

Salinity - Adults: Adults are considered euryhaline and
have been collected over a salinity range of 0.2 to 75%o
(Simmons 1957, Perret et al. 1971, Mercer 1984,
Killam et al. 1992). Juveniles and adults appear to
prefer moderate salinities (Wagner 1973). Optimum
salinities, as judged by swimming performance, oc-
curred at salinities of 20 to 25%° (for fish with a total
length (TL) of 174-438 mm), but were reduced above
and below these salinities (Wakeman and Wohlschlag
1 977). They are rarely collected below 1 0%o or above
45%o in south Texas waters.

Dissolved Oxygen: Fish kills of spotted seatrout that
were due to low dissolved oxygen (DO) concentrations
have been reported in Mississippi (Etzold and Christ-

261

Spotted seatrout, continued

mas 1979).

Turbidity: Spotted seatrout appear to prefer areas of
low turbidity (Pearson 1 929). Increased mortality due
to hurricane-induced high turbidity levels has been
reported from Louisiana (Perret et al. 1980).

Movements and Migrations: In Alabama, early juve-
niles move into tidal rivers in late fall to overwinter (Van
Hoose 1987). Adult seatrout migrate very little with
most movements occurring seasonally in association
with thermal and salinity tolerances, and with spawning
activities (Tabb 1966, Bryant et al. 1989, Helser et al.
1993). Large individuals often seek cooler deeper
water during the summer, and deeper, warmer waters
of bays or the nearshore Gulf of Mexico during the
winter (Pearson 1929, Gunter 1945). Several studies
indicate that spotted seatrout are estuary-specific,
particularly in Florida, with very little movement occur-
ring between estuaries (Killam et al. 1992). This is
further substantiated by the existence of independent
populations of this species in different estuaries (Iversen
and Tabb 1962, Weinstein and Yerger 1976). In
Texas, although evidence suggests that sub-popula-
tions in bay systems mingle very little, mixing of differ-
ent groups may occur during the spawning season
which may be the reason for the low degree of variabil-
ity between major bays in this state (King and Pate
1992, Baker and Matlock 1993).

Reproduction

Mode: Spotted seatrout have separate male and fe-
male sexes (gonochoristic). Fertilization is external, by
broadcast of milt and roe into the water column, and
development is oviparous.

Spawning: Sound produced by specialized muscles
inserted at the swim bladder wall may have a purpose
in spawning activities (Mok and Gilmore 1983). The
spawning season is protracted and varies throughout
the Gulf of Mexico. It can begin as early as February
and continue until October (Pearson 1929, Gunter
1945, Herke et al. 1984, Van Hoose 1987, McMichael
and Peters 1989), but generally runs from March to
October (Hein and Shepard 1 980). Saucier and Baltz
(1 993) reported that spotted seatrout form "drumming"
aggregations in estuarine waters of Louisiana from
late May to early October, at salinities from 7to 27%o,
and temperatures from 24.5 to 33.5°C, from 6pm to
midnight, and that spawning sites were primarily lo-
cated in deep, moving water in passes between barrier
islands. Based on the presence of larval spotted
seatrout in the northern Gulf of Mexico, it can be
inferred that spawning occurs February through Octo-
ber, with a peak from April through August (Ditty et al.
1988). Spawning may occur throughout the year in
southern Florida and Mexican waters (Tabb 1961,

Tabb and Manning 1961, NOAA 1985). Spawning
occurs at dusk with the peak activity periods usually in
late April-June and August-September, and is prob-
ably related to water temperature and increasing or
decreasing photoperiods (Tabb and Manning 1961,
Hein and Shepard 1980, Perret et al. 1980, Wade
1981, Van Hoose 1987, Brown-Peterson et al. 1988,
McMichael and Peters 1989, Chester and Thayer
1 990). The recorded temperature range for spawning
is 24 to 30°C, with 23°C suggested as the minimum
temperature forsuccessful spawning (Brown-Peterson
et al. 1988). A Florida study recorded surface water
temperatures of 1 5.5 to 31 °C during spawning months
(McMichael and Peters 1989). In Florida, spawning is
essentially completed by the time temperatures rise to
28.3°C (Tabb 1966, Johnson 1978). Spawning prob-
ably occurs in moderate to high salinities (Powell et al.
1989). The surface salinity during spawning months
can range from 18.5 to 36%0 (McMichael and Peters
1989), and peak spawning occurs between 30 and
35%0 (Tabb 1966). No spawning has been observed
above 45%o (Simmons 1 957). Spawning occurs prima-
rily within coastal bays, estuaries, and lagoons, usually
in shallow grassy areas, or near passes, and in deeper
holes or channels with the eggs drifting into the grassy
areas (Welsh and Breder 1923, Pearson 1929, Guest
and Gunter 1958, Tabb 1966, Etzold and Christmas
1979, Mok and Gilmore 1983, McMichael and Peters
1989, Powell et al. 1989, Chester and Thayer 1990).
Spawning probably occurs in water that is 3 to 4.6 m
deep. Spawning may also occur in tidal passes, areas
of little or no vegetation, and, in Louisiana, the higher
salinity waters of lower bays and the nearshore Gulf of
Mexico (Sabins and Truesdale 1974, Allshouse 1983,
Herke et al. 1 984, Helser et al. 1 993).

Fecundity: Spotted seatrout are multiple spawners and
their fecundity is difficult to estimate (Brown-Peterson
et al. 1 988). Estimates of fecundity range from a mean
of 14,000 from 283 mmTL l-year class females to 1.1
million eggs for IV-year class averaging 504 mm TL
(Sundararaj and Suttkus 1962). Recent evidence
suggests that these fecundity estimates may be low
and that actual annual fecundity may average greater
than 10 million eggs. Spawning frequency appears to
be high and is estimated to occur every 3.6 days, but
this frequency is probably not sustained throughout the
entire spawning season (Brown-Peterson et al. 1 988).

Growth and Development

Egg Size and Embryonic Development: Eggs are spheri-
cal, usually with one oil droplet. Their diameter ranges
from 0.7 to 0.85 mm, and hatching occurs 16 to 20
hours after fertilization at 25°C (Fable et al. 1978).
Incubation times of 21 hours at 23°C and 15 hours at
27°C have also been reported (Ditty and Shaw 1994).

262

Spotted seatrout, continued

Age and Size of Larvae: In one laboratory study, larvae
grew from a standard length (SL) of 1 .5 mm at hatching
to 4.5 mm SL in 15 days at about 25°C (Fable et al.
1978). Peebles and Tolley (1988) report growth rates
for larval spotted seatrout in south Florida to be ap-
proximately 0.4 mm/day. Larval stage sizes range
from about 1 .8 to 1 0-1 2 mm TL (Johnson 1 978).

Juvenile Size Range: Transformation to the juvenile
stage occurs at a length of 1 0 - 1 2 mm (Ditty and Shaw
1994). Juveniles range from 10-1 2 to 180-200 mmTL
(Johnson 1978). Juvenile growth rates during the fall
are about 1 3 to 1 8 mm/month (McMichael and Peters
1 989). Along the Gulf coast of Florida, spotted seatrout
have been reported to reach 30 1 -337 mm TL at the end
of their first year, but growth slows after age I (Murphy
and Taylor 1994). Hatchery-reared juveniles have
been reported to reach 160 mm TL in 100 days (Van
Hoose 1 987). Size at maturity varies among estuaries
(Mercer 1984). Spotted seatrout mature between one
and three years of age with males tending to mature at
smaller sizes than females.

Age and Size of Adults: Maturity and spawning may
first occur at 2 years of age (Pearson 1929), but they
can occur at the end of their first year (Lassuy 1983).
Males mature as early as theirfirstyearand females by
the end of the second year (Klima and Tabb 1959).
Some females mature as early as 271 mm SL in Texas,
and they are generally all mature by 300 mm SL
(Brown-Peterson et al. 1 988). Males are much smaller
than females at maturity with all fish 200 mm SL and
longer being mature. In a northwest Florida study, 50%
of females 200-220 mm FL and 90% of females 220-
240 mm FL were mature, all of which were age I
(DeVries et al. 1995). Seventy of 73 males, all age I,
were found to be mature. There is some variation in
growth rate of spotted seatrout throughout its range
(Benson 1982), and this variation may be due to
ecological rather than genetic factors (Murphy and
Taylor 1 994). In Florida, estimated maximum ages are
6 to 8 years for females and 5 to 9 years for males
(Murphy and Taylor 1994). Adults up to 15 years old
have also been reported (Mercer 1984).

Food and Feeding

Trophic Mode: The spotted seatrout is an opportunis-
tic, visual carnivore that feeds near the surface and in
mid-water depths. It feeds mainly in seagrass areas,
and relies almost solely on free swimming organisms
for food (Darnell 1958, Stewart 1961, Vetter 1977).

Food Items: The diet of the spotted seatrout changes
as it grows and with the seasonal abundance of food
items (Pearson 1929, Gunter 1945). Larvae feed
primarily on zooplankton, especially copepods, and
switch to mostly benthic invertebrates as small juve-

niles. Juveniles have been found to consume: plank-
tonic schizopods, mysids, copepods, isopods, amphi-
pods, gastropods, bivalves, caridean and penaeid
shrimp, and fish (Stewart 1 961 , Hettler 1 989, McMichael
and Peters 1989). Juveniles <30 mm SL consume
amphipods, mysids and carideans in equal proportions
(Hettler 1989). The single most important food for
juveniles >30 mm SL was shrimp. Fish increase in
dietary occurrence as juveniles reach 50 mm SL and
larger, and can comprise almost 90% of the volume in
individuals 105-120 mm SL. Fish species consumed
include: bay anchovy, gulf menhaden, shad (Dorosoma
sp.), silversides (Menidia sp.), striped mullet, sheeps-
head minnow, rainwater killifish (Lucania parva), gulf
toadfish (Opsanus beta), inshore lizardfish(Synodus
foetens), pipefish (Syngnathus sp.), pinfish, pigfish
(Orthopristeschrysopterus), silverjenny (Eucinostomus
gula), gray snapper, unidentified snappers (Lutjanus
sp.), hardhead silverside (Atherinomorus stipes),
goldspotted killifish (Floridichthys carpio), code goby
{Gobiosoma robustum), naked goby (G. bosci), clown
goby (Microgobiusgulosus), Atlantic croaker, and spot-
ted seatrout. Young adults prey on a variety of inver-
tebrates and fish, changing almost exclusively to fish
as large adults (Gunter 1945, Darnell 1958, Seagle
1969, Danker 1979, Levine 1980, Hettler 1989,
McMichael and Peters 1989). Some marine vegeta-
tion and shell fragments have been noted that were
probably picked up while capturing prey (Tabb and
Manning 1 961 ). The diets of larger juveniles and adults
are skewed to the consumption of shrimp in the warmer
months and fish in the cooler months when shrimp are
not as available (Pearson 1929, Gunter 1945). Varia-
tions in food habits indicates that geographical location
and type of estuary influences available prey, and that
spotted seatrout stomach contents reflect this avail-
ability (Hettler 1989).

Biological Interactions

Predation: Known predators of juvenile spotted seatrout
include alligator gar (Lepisosteus spatula), striped
bass (Morone saxatilis), ladyfish (Elops saurus), tar-
pon, bluefish, silver perch, Atlantic croaker, snook,
yellow bass (Morone mississippiensis), spotted
seatrout, barracuda (Sphyraena barracuda), Spanish
mackerel, and king mackerel (Scomberomorus cav-
alla) (Miles 1 949, Darnell 1 958, Benson 1 982, Killam et
al. 1992).

Factors Influencing Populations: Species that may
possibly compete with spotted seatrout for habitat and
food include hardhead cattish, grouper (Mycteroperca
sp.), silver perch, red drum, spot, and Atlantic croaker
(Killam et al. 1992). Distribution and abundance of
juvenile spotted seatrout in Florida Bay appears to be
influenced by the biomass, shoot density, and species
composition of the seagrass community (Shipp 1986,

263

Spotted seatrout, continued

Chester and Thayer 1 990, Killam et al. 1 992). Losses
in seagrass beds and other key habitat areas have
been linked with declining seatrout populations. Over-
fishing may also be contributing to this decline (Shipp
1986). Periods of low rainfall and high salinity may
lower recruitment of young fish into the population
(Rutherford et al. 1989b). Catastrophic mortalities
have been attributed to severe cold, hurricanes, high
turbidity, excessive fresh water, red tide, and super-
saturated dissolved oxygen conditions (Gunter 1941,
Gunter and Hildebrand 1 951 , Springer and Woodburn
1960, Renfro 1963, Perret et al. 1980, Killam et al.
1992). In Louisiana, the use of weirs in canals may
impede migration of young-of-the-year fish into the
marsh areas of impounded water bodies or the move-
ment of fish trying to escape environmental extremes
(Herke et al. 1984). Larger adults are frequently
infected with pleurocerci of the tapeworm
Poecilancistrium robustrum (spaghetti worm) (Lorio
and Perret 1 978). Fish with these worms are frequently
discarded although they do not affect the taste of the
fish, nor are they infectious to humans.

Personal communications

DeVries, Douglas A. NOAA National Marine Fisheries
Service, Panama City, FL.

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268

Leiostomus xanthurus
Adult

5 cm

(from Goode 1884)

Common Name: spot

Scientific Name: Leiostomus xanthurus

Other Common Names: Flat croaker, yellowtail; golden

croaker during spawning season (Hoese and Moore

1 977); goody, roach, and post croaker (Benson 1 982),

spot croaker, tambour croca (French), and verrugata

croca (Spanish) (Fischer 1978, NOAA 1985).

Classification (Robins et al. 1991)

Phylum: Chordata

Class: Osteichthyes

Order: Perciformes

Family: Sciaenidae

Value

Commercial: Most of the commercial foodfish harvest
of spot comes from the Chesapeake Bay and south-
east U.S. Atlantic coast. Larger fish are marketed
mainly as fresh product, but due to the small size of this
species it is more frequently used by pet food proces-
sors. In the Gulf of Mexico, it contributes to the
commercial bottomfish industry of Louisiana and Mis-
sissippi which uses it for fish meal and oil as well as pet
food (Fischer 1978, Shipp 1986, Hales and Van Den
Avyle 1989). Approximately 1 to 2 mt are harvested
each year in the Gulf of Mexico, mostly for this purpose.
It is taken primarily by otter trawl, but also by gill nets,
haul seines, and pound nets (Mercer 1989).

Recreational: This species is less likely than other
sciaenids to be taken by hook and line due to its dietary
habits; however, some recreational fishing for spot
does occur on the Atlantic coast (Hales and Van Den
Avyle 1 989). It readily takes the proper bait and can be
caught near bridges, piers, and wharves, and is also
caught frequently in the smaller trawls used by
sportnetters in lower bay and nearshore areas (Shipp

1986, Hales and Van Den Avyle 1989). Fishery infor-
mation for the Gulf of Mexico (excluding Texas) showed
a total recreational catch of 825,000 spot in 1993
(O'Bannon 1994).

Indicator of Environmental Stress: This species is a
bottom feeder which often accumulates contaminants
and is a target species for NOAA's National Status and
Trends Program and other environmental monitoring
studies (NOAA 1987a, NOAA 1987b, Killam et al.
1992). It is used for monitoring many pesticides,
herbicides, heavy metals, chlorinated hydrocarbons,
and chlorination byproducts (Hales and Van Den Avyle
1 989, Heitmuller and Clark 1 989, Mercer 1 989, Killam
et al. 1992). The spot can be a common inhabitant in
environmentally stressed estuaries due to its tolerance
of a wide range of environmental conditions (Killam et
al. 1992).

Ecological: The spot is a dominant species in bottom
habitats of nearshore and inshore areas of the northern
Gulf of Mexico (Shipp 1986, Killam et al. 1992). It is
considered to be a major regulator of benthic inverte-
brate species and important in the structure and func-
tion of estuarine ecosystems (Phillips et al. 1989,
Killam et al. 1992).

Range

Overall: The spot is found along the coasts of the
western Atlantic Ocean and the Gulf of Mexico, ranging
from the Gulf of Maine to the Bay of Campeche, Mexico
in coastal shelf waters in depths up to 205 m (Bigelow
and Schroeder 1953, Springer and Bullis 1956, NOAA
1985). It is most abundant from Chesapeake Bay to
the Carolinas, and is uncommon in the Florida Keys
(Fischer 1978, Wang and Kernehan 1979).

269

Spot, continued

Table 5.36. Relative abundance of spot in 31 Gulf of

Mexico estuaries (Nelson et al. 1992, VanHoose

pers. comm.).

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

•

Perdido Bay

Mobile Bay

•

Mississippi Sound

•

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

•

Baffin Bay

•

A S J L E

Relative abundance:

0 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

Within Study Area: The spot is found throughout coastal
shelf areas of the U.S. Gulf of Mexico from Florida Bay
to the Rio Grande River. It is common in both bays and
open Gulf areas except at the extremities of its range
(Hoese and Moore 1977, Shipp 1986) (Table 5.36).

Life Mode

Eggs and early larvae are planktonic and pelagic.
Juveniles and adults are demersal in estuarine and
coastal waters (Ditty and Shaw 1994).

Habitat

Type: The spot utilizes several habitat types through-
out its life cycle. Larvae are found in the marine
environment, and have been collected in the northern
Gulf of Mexico on the continental shelf up to the 40 m
isobath, or 130 km offshore. They occur at all depths,
but are found primarily in the upper 30 m of the water
column (Sogard etal. 1987, Cowan and Shaw 1988).
Larvae are transported inshore into estuarine nursery
areas where postlarval and juvenile spot are found.
Younger juveniles are often found in the shallow head
waters of tidal creeks, and sometimes in seagrass
beds, while older juveniles move to deeper, more
saline areas of estuaries (Wang and Kernehan 1979,
Mercer 1 989, Hales and Van Den Avyle 1 989). Adults
migrate seasonally between estuarine and coastal
waters, with movement offshore occurring in the fall
(Hales and Van Den Avyle 1989).

Substrate: Adults are taken most frequently over mud
and sand bottoms in inside waters and offshore waters
to at least 132 m (Dawson 1958, Music 1974, Huish
and Geaghan 1987). They are also found over mud,
sand, and sandy shell bottom. Juveniles are found
primarily in nursery areas with mud and detritus bot-
toms (Mercer 1989).

Physical/Chemical Characteristics:
Temperature - Eggs and Larvae: Lab-spawned eggs
successfully developed at 20°C (Powell and Gordy
1 980). In waters in or nearthe Gulf Stream, larvae less
than 15 days old have been collected only in water
above 1 9.3°C (Warlen and Chester 1 985). Spot below
20.0 mm SL have been found below 20°C in Missis-
sippi Sound with the majority taken at temperatures
from 7° to 15°C (Warren and Sutter 1982). Larvae
have been collected at 5° to 1 9.3°C, and juveniles at 4°
to 35°C and (Wang and Raney 1971, Wagner 1973,
Pineda 1975, Cowan and Shaw 1988, Hales and Van
Den Avyle 1989). The upper incipient lethal tempera-
ture for post larval and small juvenile spot has been
estimated at 35.2°C (Mercer 1989), and the critical
thermal maximum for juvenile spot acclimated at 15°C
was31.0°C.

270

Spot, continued

Temperature - Juveniles

and Adults: Spot tolerate temperatures from 1 .2° to
36.7°C; however, extended periods of low tempera-
tures have resulted in dead or stunned fish. Death due
to temperature is a function of size, acclimation and
rate of temperature drop (Benson 1 982). Juvenile spot
are reportedly more tolerant of cold than adults. Large
numbers of adults are found between 25° to 30°C
(Warren and Sutter 1982).

Salinity - Eggs and Larvae: Laboratory spawned eggs
have developed at 30 to 35%o (Powell and Gordy
1980). Larvae have been collected in the field from 6
to 36%o, and appear capable of tolerating a wide range
of estuarine salinities (Warlen and Chester 1 985, Cowan
and Shaw 1988, Killam et al. 1992). They have been
reared successfully in the laboratory at 30 to 35%o.

Salinity - Juveniles and Adults: Spot is a euryhaline
species. Juveniles have been found from 0 to 36.2%o
(Kelley 1965, Wang and Raney 1971, Wagner 1973,
Pineda 1975, Lee et al. 1980, Benson 1982). They
occur in greater numbers at salinities above 1 0%o, and
are less abundant in freshwater areas (Killam et al.
1992). Adults seem to prefer a more polyhaline envi-
ronment than juveniles. Although they have been
found from 0 to 60%o (Hildebrand and Cable 1930,
Thomas 1 971 , Powell and Gordy 1 980), large numbers
occur most often from 1 5%oto 30%<= (Warren and Sutter
1982).

Dissolved Oxygen: This species is very tolerant of low
dissolved oxygen (DO) conditions and has been found
in waters with DO less than 2 parts per million (ppm)
(Killam etal. 1992). It is most common in waters where
the DO exceeds 4 ppm. For juvenile spot acclimated
to 28° C, 1 and 96 hour LC50s were determined to be
0.43 and 0.60 ppm respectively.

Migrations and Movements: Adults migrate seasonally
between estuarine and coastal waters. They enter
bays and sounds in spring and move offshore in fall and
winter to spawn (Hildebrand and Schroeder 1928,
Pearson 1929, Hildebrand and Cable 1930, Gunter
1945, Dawson 1958, Kelley 1965, Perry 1970, Franks
et al. 1972, LeBlanc et al. 1991) and avoid cold tem-
peratures (Christmas and Waller 1973, Huish and
Geaghan 1987). Post-spawning fish have been col-
lected in nearshore waters, and it is possible that adults
remain offshore after spawning although few are taken
in these areas by bottom trawling (Gunter 1 945, Dawson
1958, Hales and Van Den Avyle 1989). Larvae are
probably carried by longshore currents or by direct
across-shelf transport into nearshore waters, and into
estuarine areas by tidal flow (Cowan and Shaw 1988,
Mercer 1989). Immigration into estuaries of post-
larvae begins in December and continues through May

(Joseph 1972, Warren and Sutter 1982, Cowan and
Shaw 1988, Mercer 1989). A pattern of recruitment
along the sandy shorelines and seagrass beds of
Tampa Bay have been observed for postlarvae less
than 20 mm SL (Killam et al. 1992). These protected
regions appear extremely beneficial in promoting the
rapid growth of postlarvae. Juveniles move up into low
salinity headwater areas and may ascend brackish
water to fresh water during the spring and summer
(Hildebrand and Cable 1930). Older fish tend to seek
out deep, higher salinity waters in bays, and begin to
emigrate from estuaries in May or June, becoming
absent by late fall (Nelson 1 967, Parker 1 971 , Warren
and Sutter 1 982). Emigration occurs when they reach
total lengths (TL) of about 60 (Townsend 1956) to 88
mm, or after about 8-9 months (Kilby 1955, Wagner
1973, Killam et al. 1992), and may be a response to
seasonal temperature declines (Sheridan 1 979). Some
adults may not migrate back to inshore waters, but
remain in deep waters (50-91 m) in the Gulf (Perry
1970).

Reproduction

Mode: This species has separate male and female
sexes (gonochoristic). Fertilization is external, by
broadcast of milt and roe into the water column, and the
degree of fertilization is determined by the density of
spawning individuals (Killam et al. 1992). Egg devel-
opment is oviparous.

Spawning: Spawning occurs from late fall to early
spring offshore in moderately deep water over the
continental shelf (Townsend 1956, Dawson 1958,
Nelson 1967, Wang and Raney 1971, Sabins and
Truesdale 1 974, Allshouse 1 983, Mercer 1 989, Killam
et al. 1992) with possibly some activity near beaches
and passes (Pearson 1 929, Music 1 974). Spawning in
the Gulf waters off Louisiana occurs from near midshelf
(about 65 km) out to 1 75 km from the coast (Cowan and
Shaw 1988), although spawning activity appears to
decrease in the offshore direction (Sogard et al. 1 987).
Spawning seasons in the Gulf of Mexico are: from
October through March or April in the Tampa Bay
region of Florida (Killam et al. 1992); in the northern
Gulf off Alabama, probably from December to at least
late February (Nelson 1 967); in Louisiana waters from
Novemberthrough March (Cowan and Shaw 1 988); off
Texas late November to April, with peaks from Decem-
berto February (Pearson 1 929, Allshouse 1 983). Based
on the presence of larval spot in the northern Gulf of
Mexico, it can be inferred that spawning occurs Octo-
ber through April, with a peak from December through
January (Ditty 1 986, Ditty et al. 1 988). Sheridan et al.
(1 984) suggested a late fall peak for fish in the northern
Gulf, but no winter samples were taken. Spot held in a
laboratory only spawned at temperatures between
17.5 to 25.0° C.

271

Spot, continued

Fecundity: Fecundity ranges from 20,900 eggs in a
female with a standard length (SL) of 136 mm to
51 4,400 eggs in a 1 78 mm SL female (Sheridan et al.
1984). The spot appears to be a fractional spawner
capable of several spawning events during a single
season (Killam et al. 1992).

Growth and Development

Egg Size and Embryonic Development: Egg sizes
range from 0.72 to 0.87 mm (Lippson and Moran 1 974,
Johnson 1978, Ditty and Shaw 1994).

Age and Size of Larvae: Larvae hatch in about 48
hours at 20°C at a size of 1 .6 to 1 .7 mm SL (Ditty and
Shaw 1 994). Fruge and Truesdale (1 978) collected 86
larval spot in coastal waters of Louisiana, ranging in
size from 1 .6 to 1 0.7 mm SL. Larvae can grow from 1 .6
mm SL to 17-19 mm in 90 days (Warlen and Chester
1985). In North Carolina's Cape Fear River estuary,
daily growth rates for larvae are 0.14 to 0.16 mm/day
(Weinstein and Walters 1 981 ). Increases in the rate of
daily growth have been demonstrated when high den-
sities of microzooplankton are present, particularly
when larvae and food are concentrated in waters that
are hydrographically discontinuous (Govonietal. 1985).

Juvenile Size Range: Transformation to the juvenile
stage occurs at about 1 5 mm TL (Ditty and Shaw 1 994).
Growth rate varies with location, environmental factors
(Johnson 1978), and possibly age (Warren 1981).
Juveniles from the Gulf of Mexico grow at about 7-1 8.6
mm/month (Parker 1971, Ruebsamen 1972, Warren
1981, Warren and Sutter 1982). Spot grow rapidly in
their first year growing as much as 90 to 140 mm TL.
.Growth is slower during the second year, proceeding at
only 5.5 mm/month.

Age and Size of Adults: Maturation occurs at the end of
the second year or early in the third year on the Atlantic
coast. In the Gulf of Mexico, some spot mature at age
I; males at 123 mm SL and females at 127 mm SL
(Sheridan et al. 1984). Spot are one of the smallest
members of the drum family (Shipp 1 986). In the Gulf
of Mexico it can grow up to 250 mm TL (Hoese and
Moore 1977), although it can reach up to 340 mm SL
in the northern parts of its range (Johnson 1978).
There is a pronounced sexual dimorphism in growth
rate with females growing more rapidly. Females also
become proportionally more abundant in the popula-
tion at a later age, and live longer than males. Overall,
this is a short-lived species that rarely attains a maxi-
mum age of 5 years, but usually only lives 2 to 3 years
(Hales and Van Den Avyle 1989, Mercer 1989).

Food and Feeding

Trophic Mode: The spot can be both an opportunistic
generalist or a selective predator depending on its

developmental stage and food availability (Hales and
Van Den Avyle 1989, Killam et al. 1992). Larval and
postlarval spot are size-selective planktivores
(Livingston 1984, Mercer 1989, Govoni and Chester
1 990). Juveniles and adults are nocturnal, opportunis-
tic bottom feeders utilizing infaunal and epibenthic
invertebrates (Hales and Van Den Avyle 1989, Killam
et al. 1992). Feeding by juveniles appears to tidally
influenced, with most feeding occuring in marsh inter-
tidal zones during high tide when they can presumably
take advantage of the greater concentration of prey
items that occur there (Archambault and Feller 1 991 ,
Killam et al. 1 992). Prey items within 2 to 3 mm of the
substrate surface are most susceptible to feeding
activities by juvenile spot. Adults feed on benthic fauna
by scooping and straining sediments through their gill
rakers to remove prey items and spitting out unwanted
material (Killam et al. 1992).

Food Items: Food habits of the spot change with its
growth and development (Currin et al. 1984). Larvae
feed on zooplankton such as tintinnids, fish and inver-
tebrate eggs, bivalve veligers, copepod nauplii, and
postlarvae feed predominantly on copepods (Livingston
1 984, Mercer 1 989, Govoni and Chester 1 990). Feed-
ing appears to be influenced by visibility, size, and
motility of potential prey items (Govoni et al. 1985,
Govoni and Chester 1 990). Juveniles feed primarily on
crustaceans (especially copepods), molluscs, nema-
todes, and polychaete worms (Ruebsamen 1972,
Sheridan 1979, Levine 1980, Livingston 1984). In a
portion of Florida's Apalachicola Bay complex, the diet
of spot fell into two feeding patterns (Sheridan 1979).
Food items from shallow, low salinity, nearshore areas
consisted mostly of insect larvae, bivalves, and detri-
tus, while in deeper, higher salinity areas, it was
primarily polychaetes and harpacticoid copepods.
Adults most frequently consume polychaetes, amphi-
pods, bivalve and gastropod molluscs, cumaceans,
nematodes, mysids, and copepods (Hales and Van
Den Avyle 1989). Although some studies show that
spot will forage regardless of substrate type, evidence
suggests that muddy substrates are preferred over
sandy ones (Killam et al. 1992). The ability of spot to
sieve coarser sediment through their gill rakers may be
a limiting factor.

Biological Interactions

Predation: A study in the Cape Fear River estuary in
North Carolina found that silversides (Menidia sp.) and
killifish (Fundulus sp.) prey on larval and early juvenile
stage spot (Weinstein and Walters 1981). Other re-
ported piscine predators of spot from the U.S. Atlantic
coast include sand bar shark, silky shark, longnose
gar, striped bass, bluef ish, different species of seatrout,
king mackerel, and flounders (Dawson 1958, DeVane
1 978, Medved and Marshall 1 981 , Rozas and Hackney

272

Spot, continued

1984, Hales and Van Den Avyle 1989, Mercer 1989,
Killam et al. 1992). Wading birds such as the clapper
rail also utilize this species as food (Heard 1982).

Factors Influencing Populations: Results in a study
from the Mississippi Sound area suggest that inshore
shrimping activities have a pronounced effect on the
abundance of this and other species of groundfish
(Warren 1981). The principal causes of mortality in
juvenile spot include predation and low winter tem-
peratures during early recruitment events (Killam et al.
1 992). Predation in higher salinity waters may also be
a limiting factor in juvenile spot production (Currin et al.
1 984). Although spot may be able to survive in waters
of low DO, many of the prey items are not able to
tolerate such conditons (Killam et al. 1992). Low DO
may therefore indirectly influence the distribution pat-
terns of spot, that will move to areas with abundant food
resources. Spot and Atlantic croaker may compete for
the same food resources, but it is not known to what
extent this competition affects their abundance and
distribution.

Personal communications

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

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fluctuations in the fish fauna of the Charlotte Harbor
Estuary, Florida. Charlotte Harbor Estuarine Studies,
Mote Marine Lab., Sarasota, FL, 64 p.

Warlen, S.M., and A.J. Chester. 1985. Age, growth
and distribution of larval spot, Leiostomus xanthurus,
off North Carolina. Fish. Bull., U.S. 83:587-599.

Warren, J. R. 1981. Population analysis of the ground-
fish on the traditional shrimping grounds in Mississippi
Sound before and after the opening of the shrimp
season, 1 979. M.S. thesis, Univ. S. Miss., Hattiesburg,
MS, 113 p.

Warren, J.R., and F.C. Sutter. 1982. Industrial
bottomfish monitoring and assessment. In: Mcllwain,
T.D., Fishery monitoring and assessment completion
report, Chapt. II - Section 1 . Project No. 2-296-R, Gulf
Coast Res. Lab. Ocean Springs, MS, p. 11-1 -i - 11-1-69.

Weinstein, M.P., and M.P. Walters. 1981. Growth,
survival and production in young-of-year populations
of Leiostomus xanthurus Lacepede residing in tidal
creeks. Estuaries 4:185-197.

276

Atlantic croaker

Micropogonias undulatus
Adult

5 cm

(from Goode 1884)

Common Name: Atlantic croaker

Scientific Name: Micropogonias undulatus

Other Common Names: Croaker, crocus, hardhead,

king billy; tambour bresilien (French); la corbina,

corvinon brasilieno , and gorrubata (Spanish) (Fischer

1978, Lassuy 1983, NOAA 1985).

Classification (Robins et al. 1991)

Phylum: Chordata

Class: Osteichthyes

Order: Perciformes

Family: Sciaenidae

Value

Commercial: A commercial fishery for this species has
existed in the Atlantic Ocean since the late 1880's
(NOAA 1993). In the Gulf of Mexico, the Atlantic
croaker is the most important species of industrial
bottomfish, representing about 76% of the total land-
ings (Warren and Sutter 1982, NOAA 1985, NOAA
1993). The major harvesting areas are located be-
tween Mobile Bay, Alabama and Calcasieu Lake,
Louisiana. The Gulf fishery for croaker began expand-
ing in 1967 with the decline in landings from the
Chesapeake Bay and the discovery of large stocks
around the mouth of the Mississippi River. About 44 mt
of croaker estimated at $48 thousand were taken by
commercial fishermen in the Gulf (Newlin 1 993). More
than 43 mt were caught within 5 km of the coast.
Landings by state for 1992 were: Florida - 6.8 mt;
Alabama - 8.6 mt; Louisiana - 25.4 mt; and Texas - 3.1 8
mt (Newlin 1993). Major methods of harvest include
pound nets, haul seines, otter trawls, and gill nets with
some additional catches made by trammel and fyke
nets (Mercer 1989). It is considered an excellent
foodfish, and is exported to foreign countries where it
is a preferred species (Fischer 1977, Shipp 1986). It

occasionally appears in domestic markets where it is
usually marketed fresh (Fischer 1978).

Recreational: Atlantic croaker also contributes signifi-
cantly to the sportfish fishery in the eastern Gulf of
Mexico (Warren and Sutter 1 982). While not a particu-
larly popular game fish, it is still caught by many
fishermen. Large "bull croakers" are particularly sought
for around oil rigs west of the Mississippi delta in
Louisiana waters (NOAA 1985). The United States
marine recreational catch was about 3,293 million
croakers in 1 993 for the Gulf of Mexico (except Texas) ,
the majority being caught in nearshore waters
(O'Bannon 1994).

Indicator of Environmental Stress: This species is a
bottom feeder which often accumulates contaminants
and is a target species for NOAA's National Status and
Trends Program (NOAA 1987). The effects of heavy
metals and PCB's on Atlantic croaker reproduction
(Thomas 1 989, Thomas 1 990), the effects of sublethal
copper exposure (Scarfe et al. 1982), and of lead on
glutathione levels (Juedes 1 985) have also been stud-
ied.

Ecological: Because of its high abundance, Atlantic
croaker is an important predator of benthic inverte-
brates (Lassuy 1983).

Range

Overall: The Atlantic croaker occurs in coastal waters
of the western Atlantic, from the Gulf of Maine to
southern Florida and along the Greater Antilles. It is
rare around the Florida Keys. In the Gulf of Mexico, it
is found from southern Florida to central Mexico. It may
also occur in the southern Gulf and the lesser Antilles

277

Atlantic croaker, continued

Table 5.37. Relative abundance of Atlantic croaker
in 31 Gulf of Mexico estuaries (from Volume /).

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

•

Perdido Bay

_q^

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 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

down to Argentina, but is may be confused with a
similar species, Micropogonias furnieri (Chao and
Musick 1977, Hoese and Moore 1977, Fischer 1978).

Within Study Area: The Atlantic croaker occurs from
Florida Bay to the Rio Grande River in Texas. It is
considered one of the most common bottom-dwelling,
estuarine fish in the northern Gulf of Mexico (Table
5.37) (White and Chittenden 1976, Hoese and Moore
1977).

Life Mode

Atlantic croaker are estuarine-dependent. Eggs are
pelagic and buoyant (Ditty and Shaw 1 994), and early
larvae are pelagic and planktonic. Early larvae are
found on the mid- to outer continental shelf, but be-
come generally uniform throughout the shelf. Later
stages become more demersal and occur in more
inshore to estuarine areas. Juveniles become still
more demersal and move into tidal creeks. Adults are
demersal and move between estuarine and oceanic
waters (Lassuy 1983, Cowan 1985, Cowan and Shaw
1988).

Habitat

Type: Adults are estuarine to marine, and have been
collected from depths of 1 to 90 m. They appear to be
most abundant in mesohaline and polyhaline salinities,
and are rare below 10%o (Christmas and Waller 1973,
Wagner 1 973). Juveniles are estuarine to riverine and
prefer fresh to mesohaline salinities (Parker 1971).
Eggs and early larvae are marine, and later larvae are
marine to estuarine. Recently spawned larvae have
been collected at depths ranging from 15 to 115 m,
although most occur in the upper 30 m, about 20 to 200
km from shore (Cowan 1985, Sogard et al. 1987,
Cowan and Shaw 1988). Most small larvae were
collected near midshelf about 65-1 25 km from shore in
euhaline salinities. Fish three years old tend to domi-
nate estuaries in North Carolina while those >3 years
old are found mostly offshore (Ross 1988).

Substrate: Practically all sizes of croaker beyond the
larval stage are associated with soft bottoms (Lassuy
1983). Juveniles occur over mud-sand in shallow es-
tuarine and tidal creek areas, i.e., fine unconsolidated
substrates. Adults are associated with mud-sand,
oyster reefs, shell and live bottoms in deeper waters.

Physical/Chemical Characteristics:
Temperature - Eggs and Larvae: While eggs and newly
hatched larvae are found at 18-25°C, larger and older
larvae can be found at progressively decreasing tem-
peratures. Larvae have been found in temperatures as
low as 1 0°C in the Gulf of Mexico (Cowan 1 985, Cowan
and Shaw 1 988), but in the Chesapeake Bay area, they
are found from 0° to 24° C (Ward and Armstrong 1 980).

278

Atlantic croaker, continued

Temperature - Juveniles and Adults: The Atlantic
croaker has been collected from 0.4° to 35.5°C in the
Gulf of Mexico (Miller 1 964, Parker 1 971 , Warren and
Sutter 1 982). Juveniles are generally more tolerant of
low temperatures (0.4°-38°C) than adults (5°-35.5°C)
(Parker 1971, Wagner 1973, Pineda 1975, Rogers
1 979, Ward and Armstrong 1 980, Benson 1 982). Pref-
erred temperatures for juveniles range from 6° to 20° C,
and they grow well between 12.8° and 28.4° C. In
Mississippi waters, adults were found in highest num-
bers at <30° C (Christmas and Waller 1 973). They are
rarely found below 10° C in Texas waters (Parker
1971). Lethal minimum and maximum temperatures
are 0.6° and 38° C for juveniles and 3.3° and 36° C for
adults (Parker 1971, Ward and Armstrong 1980).

Salinity - Eggs and Larvae: Eggs and larvae are found
in euhaline waters. In the Gulf of Mexico, larvae have
been found in salinities ranging from 1 5 to 36%o (Cowan
1 985, Cowan and Shaw 1 988), but in the Chesapeake
Bay area, they are found from <1 to 21 %o (Ward and
Armstrong 1980).

Salinity - Juveniles and Adults: Atlantic croaker are
euryhaline, having been collected from 0 to 40%o and
rarely at 75%o (Simmons 1 957, Parker 1 971 , Wang and
Raney 1 971 , Warren and Sutter 1 982, Darovec 1 983,
Lassuy 1983). Juvenile croaker have been taken in
salinities of 0.0 to 36.7%o (Miller 1964, Parker 1971,
Wagner 1 973, Rogers 1 979). In Texas and Louisiana
bays, they have been found to be most abundant at
<1 5%o (Gunter 1 945, Wang and Raney 1 971 , Wagner
1973, Ward and Armstrong 1980), but they appear to
be relatively abundant from 10%o to 20%o in Alabama
and Mississippi (Swingle 1971, Etzold and Christmas
1979). Juveniles are reportedly more tolerant of low
salinities than adults (Gunter 1975). Adults are col-
lected in waters with salinities that range from 0 to 70%o
(Simmons 1957, Ward and Armstrong 1980). In Mis-
sissippi, adults were most abundant in waters with
salinities of 15 to 19.9%o (Christmas and Waller 1973,
Ward and Armstrong 1980).

Dissolved Oxygen (DO): Dissolved oxygen (DO) re-
quirements are not well known, but the presence of this
species in poorly oxygenated canals indicates a toler-
ance for low DO (Lassuy 1983). Juveniles are found in
waters with a dissolved oxygen content of 5.7 to 8.6
parts per million (ppm) (Hoese et al. 1 968). Captures
at DO concentrations from 1 through 13 ppm have
been reported with most occurring between 8 and 13
ppm (Marotz 1984).

Turbidity: Densities of Atlantic croaker have been
noted as more abundant in areas of high waterturbidity
possibly as the result of increased food availability and
predator protection due to lower visibility (Lassuy 1 983).

Migrations and Movements: Adults have seasonal
inshore and offshore migrations, although some ap-
pear to remain in offshore waters (55 to 1 1 8 m) all year
(Perry 1970). Adults move up bays and estuaries in
spring, randomly in summer, and seaward and south-
erly in fall. Larvae are carried by longshore currents
into nearshore areas where tidal flow transports them
into estuarine areas (Cowan and Shaw 1 988). Larval
recruitment into estuaries occurs from October to May,
peaking between November and February (Wagner
1973, Marotz 1984). As they mature into juveniles,
they move up into headwater areas. After spending 6-
8 months in the estuary, offshore emigration begins in
late March or early April at about 50 mm standard
length (SL) or larger and continues until November
(Kelley 1 965, Perry 1 970, Wagner 1 973, Yakupzack et
al. 1977, Rogers 1979, Marotz 1984). Emigration is
probably governed by cues from fluctuations in envi-
ronmental conditions in the nursery area (e.g. tides,
temperature, salinity, day length, etc.), and is not just a
function of fish size (Clairain 1974, Yakupzack et al.
1977).

Reproduction

Mode: This species has separate male and female
sexes (gonochoristic). Fertilization is external, by
broadcast of milt and roe into the water column, and
development is oviparous.

Spawning: Spawning in the Gulf of Mexico has been
reported from September through May, with a peak in
October, specifically around mid-October, and possi-
bly November (Sabins and Truesdale 1 974, White and
Chittenden 1 976, Allshouse 1 983, Marotz 1 984). Based
on the presence of larval croaker in the northern Gulf
of Mexico, it can be inferred that spawning occurs
September through April, with a peak from October
through January (Ditty 1 986, Ditty et al. 1 988). Based
on larval growth information, the spawning season off
western Louisiana is probably limited to November-
January, with very little spawning occurring after Janu-
ary (Cowan 1988). Most spawning probably takes
place in the nearshore Gulf of Mexico near island
passes (Sabins and Truesdale 1974, Lassuy 1983,
Sogardetal. 1987).

Fecundity: Sheridan et al. (1 984) found fecundities for
Gulf of Mexico fish ranged from 27,000 eggs for 136
mm SL to 1 ,075,000 for a 31 8 mm SL specimen. Fish
collected from Cape Hatteras, North Carolina north-
ward were reported to have a fecundity range of
100,800 to 1,742,000 for fish 196 to 390 mm total
length (TL) (Morse 1980).

Growth and Development

Egg Size and Embryonic Development: Eggs are spheri-
cal, and sizes range from 0.49 to 0.58 mm (Wang and

279

Atlantic croaker, continued

Kernehan 1979).

Age and Size of Larvae: Larvae upon hatching are 1 .3
to 2.0 mm TL (Wang and Kernehan 1 979). Incubation
time is 29-32 hours at 23°C and 26-30 hours at 25°C.
Fruge and Truesdale (1 978) collected 1 03 larval croaker
in coastal waters of Louisiana, ranging in size from 1 .7
to 10.5 mm SL. Cowan (1988) determined growth for
40-80 day larvae to be approximately 0. 1 9 mm/day. In
Texas, young-of-the-year appear from November to
January at 1 0-50 mm TL. Larval stage is complete by
approximately 1 0 mm TL when the full complement of
spines and soft rays in the dorsal and anal fins are
reached (Johnson 1978).

Juvenile Size of Larvae: Transformation to the juvenile
stage occurs at a length of approximately 1 2 mm (Ditty
and Shaw 1 994). Juveniles may range in size from 1 1
to 140 mm TL (Johnson 1978, White and Chittenden
1976). One study from western Louisiana estimates
juvenile growth rate at 0.47 mm/day or 1 4.2 mm/month
(Arnoldi et al. 1973), while other estimates from the
Mississippi Sound area are 3.1 mm/week (Warren
1981) and 13.0 mm/month (Warren and Sutter 1982).

Age and Size of Adults: Maturity in fish sampled from
Texas and Louisiana areas was reached after the first
year of growth when individuals reached 140 to 170
mm TL (White and Chittenden 1 976). Most adults live
up to 3 years with some living 4 to 5 years, but rarely
longer (Etzold and Christmas 1979, Lassuy 1983). In
North Carolina, fish older than 3 years were found
offshore, but were rare in estuaries (Ross 1988). The
oldest fish recovered there were estimated to be 7
years old. The predicted TLs for year classes are:

1 76.6 mm for age 1 ; 261 .5 mm at age 2; 331 .0 mm at
age 3; 388.0 mm at age 4; 434.5 mm at age 5; and

472.7 mm at age 6 (Ross 1 988). The largest reported
specimen was 668 mm TL (Rivas and Roithmayr
1 970). Ross (1 988) has derived Van Bertalanffy growth
models for this species.

Food and Feeding

Trophic mode: Larvae and early juveniles are carni-
vores, feeding on zooplankton in the water column
(Lassuy 1983). Older juveniles and adults are oppor-
tunistic bottom feeding carnivores that prey on poly-
chaetes, molluscs, crustaceans, and fish. Juveniles
feed by forcefully diving into the substrate, digging as
they feed. Adults feed similarly to juveniles, but are
capable of taking larger invertebrates and some fishes.
Atlantic croaker can, therefore, feed on a secondary or
higher trophic level. Feeding is by sight, olfaction, and
touch (Mercer 1989).

Food Items: Young of the year fish are reported to
consume polychaete worms, copepods, and mysids,

while older fish principally feed on crustaceans (sto-
matopods, shrimps and crabs), molluscs (gastropods
and bivalves), and fish (Levine 1980, Darovec 1983,
Sheridan et al. 1984, Mercer 1989). Early juveniles
(15-30 mm) feed on zooplankton, switching to benthic
mode as they become older and begin consuming
infaunal and epifaunal organisms sorted from bottom
debris (Mercer 1989). Food items include molluscs
(common rangia, Macoma mitchilli, Congeria
leucophaeta, Probythinella protera, Texadina
sphinctosoma), isopods, amphipods, insects, fish
(mostly bay anchovy), and detritus (Levine 1980).

Biological Interactions

Predation: Predators of Atlantic croaker are larger
piscivorous species such as striped bass, southern
flounder, bull shark, blue catfish, yellow bass, spotted
seatrout, Atlantic croaker, red drum, sheepshead, blue-
fish, and weakfish (Levine 1980, Mercer 1989).

Factors Influencing Populations: White and Chittenden
(1976) show some habitat segregation by life stage,
with smaller (<200 mm TL), younger individuals (age 0)
occupying the bays and muddy bottoms, while the
larger (>200 mm TL), older individuals (age l+) are
more localized around oyster reefs. Hoese et al.
(1968) noted that faster growing individuals tend to
leave Texas bays before the slower growing individu-
als, resulting in a bay population of smaller than aver-
age sized fish. Warren and Sutter (1983) noted that
abundance in Mississippi Sound drops dramatically in
July and that these drops may be due to shrimping
which begins in June. Shrimping activities may be
having an effect on the population of this species.
Atlantic croaker comprise an estimated 50% of the fish
discarded as bycatch and destroyed during the brown
shrimp season, and 18% of those during the white
shrimp season (Rogers 1979). The average bycatch
from 1 972 to 1 989 was estimated as 7.5 billion croaker
(NOAA 1993). This species is considered overex-
ploited in the southeastern U.S.

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SG-76-205, 54 p.

Yakupzack, P.M., W.H. Herke, and W.G. Perry. 1 977.
Emigration of juvenile Atlantic croakers, Micropogon
undulatus, from a semi-impounded marsh in south-
western Louisiana. Trans. Am. Fish. Soc. 106(6):538-
544.

Thomas, P. 1989. Effects of Aroclor 1254 and cad-
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503.

Thomas, P. 1990. Teleost model for studying the
effects of chemicals on female reproductive endocrine
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Wagner, P. R. 1973. Seasonal biomass, abundance,
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Wang, J.C.S., and R.J. Kernehan. 1979. Fishes of the
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Hattiesburg, MS, 113 p.

283

Black drum

Pogonias cromis
Adult

10 cm

(from Goode 1884)

Common Name: black drum

Scientific Name: Pogonias cromis

Other Common Names: sea drum, gray drum, oyster

cracker, drum fish, striped drum, puppy drum, butterfly

drum (Sutter et al. 1986); grand tambour (French),

tambor,corvinon negro (Spanish) (Fischer 1 978, NOAA

1985).

Classification (Robins et al. 1991)

Phylum: Chordata

Class: Osteichthyes

Order: Perciformes

Family: Sciaenidae

Value

Commercial: Black drum are commercially harvested
primarily in inshore state territorial waters, using a wide
variety of gear and vessels between states and regions
(NOAA 1 985, Sutter et al. 1 986, Geaghan and Garson
1993, Leardetal. 1993). Fishing effort occurs through-
out the year, but is especially high during the spring and
summer. Gear used includes trammel nets, gill nets,
purse seines, haul seines, trot lines, hand lines, and
trawls (trawled fish are usually bycatch). The majority
of commercial catch in the U.S. occurs in the Gulf of
Mexico. In estuarine waters, most of the fish caught are
relatively young (< 4 yrs.), while older fish (>4 yrs.) are
harvested mainly in nearshore waters of the Gulf.
Landings in the states along the Gulf from 1 950 to 1 976
comprised 84% of the total harvest in the U.S., with
Texas providing as much as 71 % of this total (Silverman
1 979, Leard et al. 1 993). Black drum in the Gulf were
relatively underutilized prior to the late 1 970's because
their flesh was considered to be poor quality, particu-
larly in the largerfish (bull drum). In addition, a marine
cestode (the pleurocercoid stage), commonly called
the "spaghetti worm" infects the flesh in larger fish

making it less marketable, although it poses no human
health threat (Simmons and Breuer 1 962). Smallerf ish
(0.5-1.5 kg) called "butterfly drum" were therefore
considered to be more valuable in the fishery. It sold
mostly as fresh product in local fish markets (Fischer
1 978). The increased market for large red drum for the
Cajun dish "blackened redfish" in the late 1970's and
early 1 980's led to expansion of the black drum fishery
(Leard et al. 1 993, Geaghan and Garson 1 993). Over-
fishing caused restrictions or bans on the red drum
commercial fishery in the Gulf coast states and in
federal waters (1986), but the high market demand
made black drum a suitable substitute, resulting in
greater fishing effort for this species. Commercial
landings for the Gulf of Mexico reached a peak of 4,800
mt in 1987, and were 964 mt in 1991 (Fitzhugh et al.
1993, Leardetal. 1993).

Recreational: The recreational fishery is very seasonal
with most effort occurring during the spring and sum-
mer (Hostettler 1982, NOAA 1985). The recreational
catch for black drum was much greater than the com-
mercial landing until the previously mentioned expan-
sion of the commercial fishery (Sutter et al. 1986).
However, this is not a preferred recreational species,
and therefore, receives little directed effort by anglers
(Leard et al. 1993). Texas probably has the largest
directed recreational fishery for this species in the U.S.
Gulf of Mexico, although its popularity is still low when
compared to other species. An estimated 583,000
black drum were caught in 1991 for the central and
eastern Gulf of Mexico region by recreational fisher-
man, making up over 64% of the reported catch for the
combined Atlantic and Gulf regions (Van Voorhees et
al. 1 992). Over 93 percent of this was from Louisiana
and Florida. Fishing gear, methods, and seasons vary

284

Black drum, continued

Table 5.38. Relative abundance of black drum in 31
Gulf of Mexico estuaries (from Volume /)•

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

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 S J L E

Relative abundance:

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

Life stage:

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

from state to state (Leard et al. 1993). In Texas, the
most successful baits used by anglers are crabs
(Callinectes sp.), shrimp (Penaeus sp.), and sea lice
(Squilla empusa) (Hostettler 1 982), but cut fish are also
used (Simmons and Breurer 1 962. Most catches are
made with rod and reels equipped with bottom rigs.
Angling regulations vary among the Gulf states (GSMFC
1993). Black drum have been experimentally hybrid-
ized with red drum to develop a potential hybrid gamef ish
(NMFS1983).

Indicator of Environmental Stress: The black drum is
not typically used in studies of environmental stress.

Ecological: This is a demersal species that feeds
mainly on benthic organisms, primarily bivalve mol-
luscs (Sutter et al. 1986). This species is known to
consume large numbers of oysters on seed reefs and
oyster "grow-out" leases in Louisiana and Mississippi
(Benson 1982, Dugas 1986).

Range

Overall: The black drum ranges from Massachusetts to
Argentina. It is common from Chesapeake Bay to
Florida, and in the Gulf of Mexico. It occurs along the
southern coasts of the Greater Antilles and all of the
Lesser Antilles, but is rare, and the South American
shelf from Guyana to Brazil. It is apparently absent in
the southern Gulf, and mainland Central America
(Hoese and Moore 1977, Fischer 1978, Shipp 1986,
Sutter etal. 1986).

Within Study Area: The black drum is common in the
northern portion of the Gulf of Mexico from Florida Bay,
Florida to the Rio Grande, Texas. It is relatively
abundant along the coasts of Louisiana, near the
Mississippi Riverdelta, and Texas (Table 5.38) (Benson
1982, Shipp 1986, Sutter et al. 1986, Nieland and
Wilson 1993).

Life Mode

The black drum is an estuarine-dependent species
(Benson 1982). Spawning occurs primarily in nearshore
waters and estuarine passes (Ditty pers. comm.). Eggs
are pelagic and buoyant (Joseph et al. 1 964, Ditty and
Shaw 1994). Larvae are pelagic, and are transported
by tidal currents through passes to estuarine waters.
Juveniles prefer shallow, nutrient rich, turbid waters,
such as tidal creeks and channels, but they have also
been found in fresh water habitats (Gunter 1942,
Gunter 1956, Sutter 1986). Adults are demersal
throughout the estuaries and bays of the northern Gulf
(Simmons and Breuer 1962, Cornelius 1984). At
maturity there is constant movement in search of food,
and feeding fish will typically travel in large schools
(Richards 1973, Bryant et al. 1989).

285

Black drum, continued

Habitat

Type: Eggs are marine to estuarine. Larvae are
marine, occurring over the inner continental shelf
(Cowan 1985, Peters and McMichael 1990), to estua-
rine. Juveniles are marine to riverine. Adults are
marine to estuarine occurring primarily in inshore neretic
waters just outside the ocean littoral zone and in
estuaries (Richards 1 973). Juveniles and young adults
prefer estuarine habitats, but older adults (>4 yrs.)
move to nearshore Gulf waters (Sutter et al.1986,
Leardetal. 1993).

Substrate: Black drum juveniles prefer unvegetated
muddy bottoms in marsh habitats. Adults are found
over unvegetated sand, mud and oyster/worm reefs
(Pearson 1929, Mok and Gilmore 1983, Cornelius
1 984, Peters and McMichael 1 990). Adult black drum
have been collected over heavily vegetated seagrass
beds during summer fish kill events in Florida Bay
(Schmidt 1993).

Physical/Chemical Characteristics:
Temperature - Eggs and Larvae: Eggs and larvae
successfully develop at 1 8° to 20°C (Garza et al. 1 978,
Johnson 1 978). Larvae have been collected at over a
temperature range of 1 1 ° to 22°C (Cowan 1 985, Peters
and McMichael 1990).

Temperature - Juveniles and Adults: Adults and juve-
niles are eurythermal. They have been found in water
temperatures ranging from 3° to 35°C (Wang and
Raney 1971, Mcllwain 1978). Sharp decreases in
water temperature cause movements to deeper water,
and mass mortalities result when conditions remain
adverse for long periods of time (Cowan 1985).

Salinity - Eggs and Larvae: Laboratory spawned eggs
hatched successfully at 8.8 to 34.0%o, with highest
survival occurring at 23 to 34%o (Garza et al. 1978).
Larvae have been collected at 0 to 36%o (Cowan 1 985,
Peters and McMichael 1990).

Salinity - Juveniles and Adults: Adults and juveniles are
euryhaline (Gunter 1942, Gunter 1956). They are
found from 0 to 80%o and are common at 9 to 26%o
(Simmons and Breuer 1 962, Mcllwain 1 978). In hyper-
saline waters at the upper end of this salinity range,'f ish
can be blinded and have body lesions (Simmons and
Breurer 1962). In Florida, juveniles 16 to 90 mm SL
occur most often in low to moderate salinities while
large juveniles are mainly found in moderate to high
salinities (Peters and McMichael 1990).

Migrations and Movements

Larvae and small young move into upper estuarine
areas and tidal creeks to low salinity nursery areas
during flood tides (Wang and Kernehan 1979). Juve-

niles move out of creeks and secondary bays at about
100 mm SL (Peters and McMichael 1990). As they
reach 1 50-200 mm SL they move into the open waters
of river mouths, bays, passes, and the nearshore Gulf.
Mature individuals often remain in bays until nearly ripe
before migrating to passes to spawn. After spawning,
they quickly return to their preferred bay habitat
(Simmons and Breuer 1 962). In fish less than 4 years
old, there is little interbay and bay-Gulf movement
throughout the year (Osburn and Matlock 1 984). There
is little intra-bay movement except for the spawning
migration, and during adverse conditions such as
temperature extremes and/or insufficient food. Black
drum move constantly in their search for food, and
these movements within a bay system can be consid-
erable if food is not abundant (Simmons and Breuer
1962, Osburn and Matlock 1984, Bryant et al. 1989).

Reproduction

Mode: This species has separate male and female
sexes (gonochoristic). Mature adults are known to
form spawning aggregations. Fertilization is external,
by broadcast of milt and roe into the water column.
Development is oviparous.

Spawning: Black drum exhibit group-synchronous
maturation of oocytes and multiple, or batch spawning
(Peters and McMichael 1990, Nieland and Wilson
1993). Mature fish spawn near passes, in open bays
and channels, and nearshore waters of the northern
Gulf of Mexico (Simmons and Breuer 1962, Mok and
Gilmore 1983, Peters and McMichael 1990, Fitzhugh
et al. 1993, Ditty pers. comm.). Depth of spawning
appears to be around 20 to 27 m (Ross et al. 1983,
Cody et al. 1 985). Ripe individuals are usually present
from November until May. Peak spawning occurs from
January to mid-April with a secondary peak sometimes
reported in Texas during early fall (Pearson 1929,
Simmons and Breuer 1 962, Allshouse 1 983, Cornelius
1 984, Murphy and Taylor 1 989, Peters and McMichael
1990, Nieland and Wilson 1993). Saucier and Baltz
(1993) reported that black drum form "drumming" ag-
gregations in estuarine waters of Louisiana from
January to April, at salinities from 10 to 27%o, and
temperatures from 1 5 to 24°C, from 6pm to 1 0pm, and
that spawning sites were primarily located in deep,
moving water in passes between barrier islands. Based
on the presence of larval black drum in the northern
Gulf of Mexico, it can be inferred that spawning occurs
December through May, with a peak from February
through April (Ditty etal. 1988). Spawning peaks occur
during the period of rising water temperatures in the
spring (Peters and McMichael 1990). Tides may also
influence the amount of spawning activity or successful
recruitment. Laboratory spawning has been achieved
at 21 °C and 28-31 %0 (Garza et al. 1977).

286

Black drum, continued

Fecundity: In one study, average fecundity of 451
females was 1,090,000 eggs (Cornelius 1984). In
Louisiana, the estimated mean annual egg production
during three breeding seasons ranged from 31.05 to
41.69 million eggs (Nieland and Wilson 1993). Esti-
mated annual egg production by a 6.1 kg female could
be as high as 32 million eggs (Fitzhugh et al. 1 993), and
the maximum observed was 67.33 million in an 1 1 .51
kg female (age 19, 855 mm FL) (Nieland and Wilson
1 993). Spawning may occur as often as every 3 or 4
days during the breeding season, with an average
clutch size of 1 .6 million eggs over 20 spawns (Fitzhugh
et al. 1 993, Nieland and Wilson 1 993). Batch fecundity
increases with age and size, and no evidence of
spawning senescence has been observed.

Growth and Development

Egg Size and Embryonic Development: Reported egg
sizes are from 0.8 to 1 .1 mm in diameter, with a mean
of 0.9 mm (Ditty and Shaw 1994). Eggs have been
reported to hatch in 24 hours at 20°C (Joseph et al.
1964, Johnson 1978, Wang and Kernehan 1979).

Age and Size of Larvae: Larvae are 1 .9 to 2.4 mm TL
at hatching (Joseph et al. 1 964, Johnson 1 978) and are
as large as 9.2 mm SL before becoming juveniles
(Peters and McMichael 1990). Larval growth rates
range from 0.2 mm/day to 0.9 mm/day.

Age and Size of Adults: In Texas waters, Simmons and
Breuer (1 962) reported adults growing to 400-430 mm
SL by the end of the third year; beyond that tag returns
indicate a growth of 25 to 50 mm/year (Simmons and
Breuer 1962, Matlock 1990). There is a sharp de-
crease in growth rate at 4-5 years that may reflect a
reallocation of energy from growth to reproduction,
because black drum mature at approximately this age
(Beckman et al. 1990). This is a relatively long-lived
species. Based on size, some individuals may live as
long as 35 years (Benson 1982), while otolith studies
indicate some individuals may live up to 43 years in
Louisiana (Beckman et al. 1990) and 58 years in
Florida (Murphy and Taylor 1 989). Black drum are the
largest sciaenids in the southeastern United States
(Peters and McMichael 1 990), and they grow to be the
largest members of the family Sciaenidae (Fitzhugh et
al. 1 993). The average maximum total length typically
reached in Texas appears to be approximately 1 000 to
1200 mm (Matlock 1990). The largest recorded adult
weighed 66.3 kg (Cave 1 974). The average maximum
TL for black drum in the Gulf of Mexico appears to be
smallerthan that occurring in the colder waters north of
Cape Hatteras. This may be due to zoogeographic
variation in black drum population dynamics (Beckman
et al. 1 990, Matlock 1 990). Beckman et al. (1 990) have
developed Von Bertalanffy growth equations for this
species.

Juvenile Size Range: Transformation to the juvenile
stage occurs at a total length of approximately 12 mm
(Ditty and Shaw 1 994). By 1 5 mm TL, juveniles attain
a general adult body shape (Johnson 1 978). Juveniles
growing from 35 to 150 mm SL average 0.9 mm/day,
and reach 1 40-1 80 mm standard length (SL) at the end
of the first year; 21 0-250 mm SL at 1 .5 years; and 290-
330 mm SL in two years (Simmons and Breuer 1962,
Peters and McMichael 1990). Ages and sizes at
maturity are similar for most U.S. locations with the
exception of Texas (Leard et al. 1993). In Texas,
studies indicate females reach maturity at 275-320 mm
total length (TL) when at the end of their second year
(Pearson 1929, Simmons and Breuer 1962). Florida
studies found males mature at sizes beginning at 450-
499 mm TL at age 4 or 5 years (Murphy and Taylor
1 989). Florida females mature when older and slightly
longer during their fifth or sixth year and between 650-
699 mm TL (Murphy and Taylor 1989). In Louisiana,
males and females are first mature at 600-640 mm FL
and most are age 5 or older (Fitzhugh et al. 1993,
Nieland and Wilson 1993). All males and females
studied whose lengths were greater than 640 mm FL
and 690 mm respectively were mature. The minimum
lengths for mature males and females were 552 mm FL
(age 3) and 628 mm FL (age 5), respectively.

Foods and Feeding

Trophic Mode: All free swimming life stages are car-
nivorous. Larvae feed on zooplankton in the water
column, while juveniles and adults are benthic feeders.
In shallow depths, their tails will stick out of the water at
times (flagging) while they feed in a vertical position
(Pearson 1929, Leard et al. 1993). Bottom feeding is
aided by the presence of a sensitive chin barbel for
finding food, and powerful pharyngeal teeth for crush-
ing molluscs and crabs (Simmons and Breuer 1962).

Food Items: The major food organism groups in order
of importanceare molluscs (mostly bivalves), arthropods
(mostly decapod crustaceans), annelids, and fish
(Dugas 1 986, Leard et al. 1 993). Some sand and plant
material have also been found that were probably
ingested incidentally while feeding. Larvae feed on
zooplankton with copepods being the primary prey
item found in stomachs (Peters and McMichael 1 990).
The numeric and volumetric importance of copepods
declines with increasing fish size. They are rarely
found in 30-60 mm black drum and are not evident in
any fish >60 mm SL. Juveniles and adults feed on
benthic organisms. Small juveniles eat soft foods such
as small fish, polychaetes, bivalve siphon tops, and
crustaceans (Pearson 1929, Simmons and Breuer
1962, Martin 1979, Peters and McMichael 1990). In
larger juveniles, bivalve and gastropod molluscs are

287

Black drum, continued

the predominant food items (Peters and McMichael
1 990) . The consumption of soft food decreases as size
increases, shifting to the main adult diet of molluscs
and crabs (Dugas 1 986, Peters and McMichael 1 990).
This change in feeding habits occurs as the pharyngeal
teeth become developed and the black drum can start
consuming hard-bodied prey (Peters and McMichael
1 990). Large juveniles (>200 mm SL) with well-devel-
oped pharyngeal teeth have diets similar to adults.
Martin (1979) reported that black drum >300 mm TL
favored bivalve molluscs, with Mulinia lateralis most
frequently encountered. Dugas (1986) found black
drum >700 mm SL prey on oysters approximately 75
mm in length. Another study observed that drum <900
mm TL consumed oysters 25-75 mm in length while
drum >900 mm TL consumed oysters 25-1 1 5 in length
(Cave 1978). Other prey items include: common
rangia, hard clam, Ensis minor, tellin clams, xanthid
crabs, insects, mysids, amphipods, barnacles, iso-
pods, penaeid shrimp, mud shrimp, hermit crabs, blue
crab, polychaetes, bay anchovy, Atlantic spadefish,
gobies, and Atlantic croaker (Cave 1978, Benson
1982, Dugas 1986, Peters and McMichael 1990).

Biological Interactions

Predation: Little information is available that describes
specific predators of black drum; however, it is likely
that larvae and juveniles are utilized as a food source
by larger predator species during their life cycle (Leard
et al. 1 993). Potential predators include various drums
(Sciaenidae), jacks (Carangidae), and mackerels
(Scombridae) as well as sharks. Filter feeding fish
such as anchovies are potential predators of black
drum eggs and larvae.

Factors Influencing Populations: Rapid and extreme
fluctuations in temperature may cause mortalities;
however, the most limiting habitat requirements ap-
pear to be amount of estuarine habitat and the accom-
panying availability of food (Leard et al. 1 993). Interac-
tion with other species have not been well studied
(Sutter et al. 1 986). Some competition may exist with
red drum and other bottom feeders for benthic re-
sources. Fishing pressure on the black drum has
increased since the mid-1980s in the northern Gulf of
Mexico, with the reductions of harvest of the red drum
(Beckman et al. 1990). The long life span of this
species implies an extremely low natural mortality rate
which probably means little surplus production is avail-
able for commercial fishery yield (Murphy and Taylor
1989). This would tend to make this species a poor
candidate for an intensive or even moderate fishery.
The normal feeding habits of this species may have a
detrimental effect on the spawning and nursery grounds
of spotted seatrout, red drum, and juvenile penaeid
shrimp by the destruction of seagrass beds (Cave
1978).

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Commission, Ocean Springs, MS, 154 p.

Martin, J. H. 1979. A study of the feeding habits of the
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104 p.

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black drum, Pogonias cromis (Osteichthyes:
Sciaenidae), off Texas. Northeast Gulf Sci. 1 1 (2):1 71 -
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Mcllwain, T.D. 1978. An analysis of recreational
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(Sciaenidae). Bull. Inst. Zool., Academia Sinica
22(2):157-186.

Murphy, M.D., and R.G. Taylor. 1989. Reproduction
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in The Southeast Region, 1 992. NOAA Tech. Memo.
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289

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290

Sciaenops ocellatus
Adult

20 cm

(from Goode 1884)

Common Name: red drum
Scientific Name: Sciaenops ocellatus
Other Common Names: red fish, red bass, channel
bass, drum, branded drum, school drum, spotted bass,
spottail (Welsh and Breder 1 924, Pearson 1 928, Yokel
1 966, Bryan 1 971 , Hoese and Moore 1 977, Overstreet
and Heard 1 978, Benson 1 982, Daniels and Robinson
1 986, WRGF 1 991 ); tambour rouge (French), corvinon
ocelado (Spanish), corvina (Spanish) (Fischer 1978,
NOAA 1985). Smaller fish (<2.27 kg) are called rat
reds or puppy drum while larger fish (>2.27 kg) are
referred to as bull reds (Welsh and Breder 1924,
Breuer 1 957, Yokel 1 966, Christmas and Waller 1 973).
Classification (Robins et al. 1991)
Phylum: Chordata
Class: Osteichthyes
Order: Perciformes
Family: Sciaenidae

Value

Commercial: The red drum is highly prized as a food
fish throughout its range and was probably the most
important sciaenid commercially before harvest was
virtually banned. Although some commercial fishery
exists on the Atlantic coast, the main industry existed
along the northern Gulf of Mexico in Texas, Louisiana,
and Florida (Boothby and Avault 1971, Bass and
Avault 1975, Hoese and Moore 1977, Matlock et al.
1977, Perret et al. 1980, Benson 1982, Vetter et al.
1983). Commercially harvested fish are mainly cap-
tured by netting using both gill and trammel nets, and
also by trotlines (Matlock et al. 1 977, Adkins et al. 1 979,
Heffernan and Kemp 1980, Matlock 1980). Fish in the
Gulf of Mexico are also caught by hand lines, beach
seines in the surf, and shrimp trawls in the intertidal
zone. Harvest occurs mainly during fall (October

through December) and spring (March through June),
and usually in estuaries (Matlock 1980). Landings
declined for Gulf coast states during the 1970's and
1980's probably due to over-fishing and habitat de-
struction (Heffernan and Kemp 1982, Swingle et al.
1984). These reported declines resulted in closure of
the Texas commercial fishery in 1981, closure of the
Alabama commercial fisheries, and restriction of the
harvest in Louisiana, Mississippi, and Florida. Com-
mercial landings for 1985 were: Alabama 1,292 mt;
Mississippi 12 mt; and Louisiana 1,334 mt (NMFS
1986). A fishery management plan developed under
emergency rule by the National Marine Fisheries Ser-
vice (NMFS) was implemented for federal waters in
1 986 (Swingle pers. comm., NMFS 1 986, Shipp 1 986).
Regulation was needed due to uncontrolled harvest by
the purse seine industry off the Louisiana coast that
was supplying red drum to the market for the popular
Cajun dish "blackened redfish." Harvest was prohib-
ited in federal waters off of Texas and Florida, and in
1 990, this ban was extended to include the entire Gulf
of Mexico (GMFMC 1996a). Surveys indicate that
spawning stocks in these waters should be restored in
the future, depending on the effectiveness of escape-
ment measures enacted to protect age classes I through
IV.

Recreational: Anglers revere this species as both a
game and food fish. Its fighting ability on light tackle
and delectable flavor has probably made this fish the
most important recreational species of sciaenid in the
Gulf of Mexico. It is especially esteemed for the table
in the south, but in the northern part of its range its
principal interest to sportsmen isasagamefishforsurf
fishing (Welsh and Breder 1924, Arnold et al. 1960,
Boothby and Avault 1971, Bass and Avault 1975,

291

Red drum, continued

Table 5.39. Relative abundance of red drum in
Gulf of Mexico estuaries (from Volume /).

Life stage

Estuary

A S J L E

Florida Bay

Ten Thousand Islands

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

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:

O 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

Hoese and Moore 1977, Adkins et al. 1979, Matlock
1 980, Perret et al. 1 980, Overstreet 1 983). All of these
characteristics make this species one of the seven
most sought gamefish in the Gulf of Mexico (Van
Voorheesetal. 1992). Fishery information for the Gulf
of Mexico during 1991 showed a total recreational
catch of over 5,549,000 fish weighing a total of 729.4
mt, with the majority caught in nearshore or inshore
waters (Van Voorhees et al. 1992). The most sought
after fish are those less than 2.2 kg. Larger fish are
unpopular due to presence of parasites in the flesh and
the belief that they have a poor flavor (Boothby and
Avault 1971, Adkins et al. 1979, Benson 1982). The
primary angling method is by hook and line in surf,
island passes, and estuaries especially during sea-
sonal runs in the spring and fall (Franks 1 970, Boothby
and Avault 1 971 , Matlock 1 980, Benson 1 982). Other
fishing methods include drift fishing, jigging, casting, or
slow trolling (WRGF 1991). Angling regulations vary
among the Gulf states (GSMFC 1993). Increased
recreational harvest in federal waters of the U.S. Exclu-
sive Economic Zone (EEZ) has made careful manage-
ment necessary throughout the range of red drum. As
a result, no sport harvest is now allowed in federal
waters of the Gulf of Mexico, and any red drum caught
must be released unharmed (GMFMC 1996b). Red
drum have been experimentally hybridized with black
drum to develop a potential hybrid gamefish (NMFS
1983).

Indicator of Environmental Stress This species is not
typically used as an indicator organism, but a case of
metal poisoning has been reported among large (7-18
kg) red drum in Florida (Cardeilhac et al. 1981).

Ecological: This is a marine, littoral, crepuscular preda-
tor that indiscriminately feeds either on the bottom or in
the water column usually in shallow water (Pearson
1928, Gunter 1945, Simmons and Breuer 1962,
Zimmerman 1969, Boothby and Avault 1971, Ward
and Armstrong 1980, Benson 1982, Holt et al. 1983).

Range

Overall: The red drum occurs in the western Atlantic
from the Gulf of Maine off Massachusetts to Key West,
Florida, and in the Gulf of Mexico from Florida to
Tuxpan, Mexico (Welsh and Breder 1924, Simmons
and Breuer 1 962, Yokel 1 966, Lux 1 969, Boothby and
Avault 1971, Hoese and Moore 1977, Lee et al. 1980,
Matlock 1980, Ward and Armstrong 1980, Holt et al.
1983, Overstreet 1983, Matlock 1987). Since 1950,
populations of red drum have virtually disappeared in
waters north of Chesapeake Bay, and New Jersey is
now probably the northern limit of this species. Centers
of abundance exist in the waters of North Carolina, and
the Gulf of Mexico (Yokel 1966, Matlock 1980, Ward
and Armstrong 1980).

292

Red drum, continued

Within Study Area: Within U.S. Gulf of Mexico estuar-
ies, the red drum occurs from the Rio Grande, Texas,
to Florida Bay, Florida (Table 5.39) (Welsh and Breder
1 924, Simmons and Breuer 1 962, Yokel 1 966, Boothby
and Avault 1971, Hoese and Moore 1977, Matlock
1980, Ward and Armstrong 1980, Holt et al. 1983,
Overstreet 1983, NOAA 1985, Matlock 1987). The
species is most abundant in waters of Texas and
Louisiana (Ward and Armstrong 1980). It is also
abundant in Mississippi, but this may be due to the
benefits of the extensive estuaries present in nearby
Louisiana (Yokel 1966).

Life Mode

Red drum are estuarine-dependent. Eggs, larvae, and
early juveniles are planktonic and pelagic (Breuer
1 957, Ward and Armstrong 1 980, Peters and McMichael
1987). Juveniles and adults are pelagic and nektonic
(Gunter 1945, Breuer 1957, Ward and Armstrong
1980, Holt et al. 1981a, Osburn et al. 1982, Benson
1982, Peters and McMichael 1987). Juveniles are
often found in schools, but adults are largely solitary
when living in shallow water (Pearson 1928, Breuer
1 957, Simmons and Breuer 1 962, Christmas and Waller
1973, Adkins et al. 1979, Benson 1982, Osburn et al.
1982, Overstreet 1983, Peters and McMichael 1987).
Some schools in the Gulf of Mexico are associated with
schools of black drum, tarpon, blue runner, little tunny
(Euthynnusalletteratus), and Florida pompano, at least
when near shore, although the red drum does not
randomly mix with schools of other species. Large
schools can contain 150,000 to 200,000 individuals
and first appear about April and disappear offshore
from September to October. Schools are often more
dispersed during summer than in spring or autumn
(Perretetal. 1980, Overstreet 1983). Activity seems to
be equally divided between night and day (Zimmerman
1969, Benson 1982, Minello and Zimmerman 1983,
Peters and McMichael 1987).

Habitat

Type:

Eggs: Eggs are spawned in nearshore and inshore
waters close to barrier island passes and channels.
After hatching, larvae and post-larvae are carried by
tidal currents into the shallow inside waters of bays and
estuaries (Pearson 1 928, Yokel 1 966, Heffernan 1 973,
Holt etal. 1981a, Benson 1982, Peters and McMichael
1 987, Johnson and Funicelli 1 991 ). Eggs from hatch-
ery spawns develop best in polyhaline to euhaline
waters (Arnold et al. 1979, Holt et al. 1983).

Larvae: Larvae move through the passes and tend to
seek shallow, slack water along the sides of the chan-
nels to avoid being carried offshore during periods of
ebbtide (King 1971). As larvae enter estuarine waters,
they seek grassy quiet coves, tidal flats, and lagoons

where the vegetation protects them from predators and
currents, and where they can avoid rough waters until
they are strong enough to swim actively (Pearson
1928, Simmons and Breuer 1962, Yokel 1966, Perret
et al. 1 980, Ward and Armstrong 1 980, Holt et al. 1 983,
Overstreet 1 983). Early larvae are found in mesohaline
to euhaline waters, and older larvae and post larvae
are euryhaline (Yokel 1966, Perret et al. 1980, Ward
and Armstrong 1980, Crocker et al. 1981, Holt et al.
1 981 a, Overstreet 1 983, Vetter et al. 1 983, Peters and
McMichael 1987).

Juveniles: Juveniles are euryhaline (Gunter 1942,
Gunter 1956, Simmons 1957, Simmons and Breuer
1962, Yokel 1966, Perret et al. 1980, Crocker et al.
1981, Holt et al. 1981a, Benson 1982, Crocker et al.
1983, Daniels and Robinson 1986, Peters and
McMichael 1 987). They are found in a wide variety of
habitats perhaps due to their movements from bay
shores to quiet backwater areas as they grow and
begin to disperse through the bay (Peters and
McMichael 1987). They prefer shallow, protected,
open waters of estuaries, coves, and secondary bays
with depths up to 3.05 m, but may also be found near
the mouths of tidal passes. Juveniles have also been
reported from shallow shorelines, tidal pools, marsh
habitats, depressions in marshy areas, boat basins,
bayous, flats, channels, reefs, back bays, around is-
lands, in rivers and neartheir mouths, and occasionally
the surf along the Gulf of Mexico in the spring following
hatching. Older juveniles tend to move into slightly
deeper, more open waters and into primary bays
(Pearson 1928, Reid 1955, Simmons 1957, Breuer
1957, Simmons and Breuer 1962, Yokel 1966,
Zimmerman 1 969, Swingle 1 971 , Christmas and Waller
1973, Perret et al. 1980, Ward and Armstrong 1980,
Crocker et al. 1981, Holt et al. 1981a, Pafford 1981,
Benson 1982, Osburn et al. 1982, Overstreet 1983,
Peterson 1986, Loftus and Kushlan 1987, Peters and
McMichael 1987, Van Hoose 1987).

Adults: Adults are also euryhaline (Gunter 1 942, Gunter
1956, Simmons and Breuer 1962, Holt et al. 1981a,
Crockeret al. 1 981 , Benson 1 982, Daniels and Robinson
1986). They are occasionally found in shallow bays,
but tend to spend more time in marine habitats after
their first spawning. They are typically found in the Gulf
of Mexico in littoral and shallow nearshore waters off
beaches (Perret et al. 1980, Ward and Armstrong
1980, Pafford 1981, Benson 1982, Overstreet 1983,
Ross et al. 1983). Adults are often caught in more
offshore waters as far as 25 km from shore in depths up
to 40 m, and are commonly reported from depths of 40
to 70 m. They are occasionally caught on Gulf reefs
(Lux 1969, Heffernan 1973, Benson 1982, Overstreet
1983, Ross etal. 1983).

293

Red drum, continued

Substrate: Newly hatched larvae are found in the Gulf
surf over pure sand bottoms. After entering bays and
estuaries, they occur over substrates of mud, sand, or
sandy mud bottoms as well as in and among patchy
sea grass meadows, but prefer muddy bottoms. Small
juveniles seem to prefer medium soft mud to firm sandy
substrates (Peterson 1986). Small fish are probably
more successful at capturing prey in the less dense
vegetation areas, while living in areas of greater sea
grass density probably helps them to avoid predation
(Pearson 1928, Simmons and Breuer 1962, Yokel
1966, Perret et al. 1980, Ward and Armstrong 1980,
Benson 1 982, Holt et al. 1 983, Overstreet 1 983). They
are normally associated with such sea grasses as
Halodule beaudettes, Ruppia maritima, and Thalassia
testudinum (Zimmerman 1969, Perret et al. 1980).
Large juveniles and adults are common over muddy,
sandy, or oyster reef bottoms with little or no sea grass
(Yokel 1966, Lee et al. 1980, Perret et al. 1980).

Physical/Chemical Characteristics:
Temperature: Tolerance of environmental conditions
changes with age, life history stage, season, and
geography (Crocker etal. 1981). No major difference
between thermal tolerances appears to exist between
populations of red drum from the Gulf of Mexico and
mid-Atlantic coast (Ward et al. 1993).

Temperature - Eggs and Larvae: Eggs and newly
hatched larvae tend to be stenothermal while 10 day
and older larvae are more eurythermal (Crocker et al.
1981). Eggs and larvae from captive spawns have
developed over a temperature range of 20° to 30°C
with optimal survival at 25°C. Highertemperatures (30
and 35°C) are associated with poor survival of yolk sac
larvae (Holt et al. 1981a, Overstreet 1983, Lee et al.
1984). Larvae and post-larvae have been collected in
the wild from 1 8.3° to 31 .0°C (Yokel 1 966, Perret et al.
1 980, Peters and McMichael 1 987, Van Hoose 1 987).

Temperature - Juveniles: Juveniles are eurythermal,
and are found in waters ranging in temperature from
2.0° to 34.9°C (Gunter 1945, Simmons and Breuer
1962, Yokel 1966, Franks 1970, Perret et al. 1971,
Wang and Raney 1971, Christmas and Waller 1973,
Pineda 1975, Tarver and Savoie 1976, Bonin 1977,
Barret et al. 1 978, Adkins et al. 1 979, Perret et al. 1 980,
Holt et al. 1981a, Daniels and Robinson 1986, Peters
and McMichael 1987). They appear to prefer tempera-
tures ranging from 10° to 30° (Ward and Armstrong
1980). Juveniles in heated discharge waters have
survived up to 35°C, but at 39°C some died, apparently
from handling stress (Overstreet 1983). Large num-
bers have been killed in sudden severe cold spells, but
normally fish will move into deeper waters during
periods of extreme temperatures (Simmons and Breuer
1962, Adkins et al. 1979). In a laboratory study, fish

ceased feeding between 7° to 9°C and death generally
occurred when temperatures fell to 4°C or lower for
several days (Miranda and Sonski 1985).

Temperature - Adults: Adults are also eurythermal, and
have been collected over a temperature range from
2.0° to 33°C (Simmons and Breuer 1 962, Yokel 1 966,
Juneau 1 975, Perret et al. 1 980, Ward and Armstrong
1 980, Daniels and Robinson 1 986). Adults are consid-
ered more susceptible to the effects of winter cold
waves than smaller fish (Yokel 1966), and they nor-
mally move into deeper waters for refuge (Simmons
and Breuer 1962).

Salinity: All life stages are sensitive to high salinities
when combined with high temperatures, but suscepti-
bility is influenced by the size of the fish (Simmons
1957).

Salinity - Eggs and Larvae: Eggs and larvae in particu-
lar are sensitive to environmental conditions (Overstreet
1 983). Eggs from hatchery spawns develop success-
fully into feeding larvae at salinities of 10 to 40%o in a
temperature of 25°C. Below 10%° the hatch rate is
poor, and below 25%0eggs sink resulting in losses from
fungal infection, crowding, and low oxygen (Vetter et
al. 1983). High salinities coupled with high tempera-
tures were associated with poor yolk sac larvae sur-
vival (Holt et al. 1 981 a). The best salinities reported for
24 hour survival and hatch are 30%o at 25°C and 34 to
36.5%« at 23° to 26°C (Neff et al. 1982, Overstreet
1 983, Lee et al. 1 984). Eggs have been collected in the
field from 21 °C to 23°C in a salinity range of 29 to 32%0
(Johnson and Funicelli 1991). Larvae from hatchery
spawns were more stenohaline than older life stages,
particularly during the first two weeks after hatching
with best survival at about 30%o (Crocker et al. 1 981 ,
Holt et al. 1 981 a, Overstreet 1 983). One article reports
tolerance from <1 to 50%o and a preference of 20 to
40%o salinity (Ward and Armstrong 1 980). Larvae and
post-larvae collected in the wild were found over a
salinity range of 8 to 36.4%o (Yokel 1966, Peters and
McMichael 1 987, Van Hoose 1 987). One study reports
spawning occurring during a salinity range of 14.7 to
18.5%o (Hein and Shepard 1986a).

Salinity - Juveniles and Adults: Both juveniles and
adults are euryhaline (Gunter 1942, Gunter 1956,
Simmons and Breuer 1962, Yokel 1966, Perret et al.
1980, Crocker et al. 1981, Holt et al. 1981a, Benson
1982, Daniels and Robinson 1986). They are very
efficient osmoregulators with the ability to tolerate
abrupt changes in salinity which is especially important
to juveniles in the estuarine environment. Juveniles
appear more tolerant to low salinity, whereas adults
which are less dependent on estuarine areas and
spend more time at sea are more tolerant of high

294

Red drum, continued

salinity (Yokel 1 966, Crocker et al. 1 983). Both groups
have been collected trom salinities ranging from 0 to
45%0, but only rarely at 50%o or above (Gunter 1945,
Simmons 1957, Simmons and Breuer 1962, Yokel
1 966, Franks 1 970, Perret et al. 1 971 , Christmas and
Waller 1973, Juneau 1975, Tarver and Savoie 1976,
Bonin 1 977, Swift et al. 1 977, Barret et al. 1 978, Ward
and Armstrong 1 980, Perret et al. 1 980, Crocker et al.
1981, Holt et al. 1981a, Daniels and Robinson 1986,
Loftus and Kushlan 1 987, Peters and McMichael 1 987).
Juveniles and adults appear to prefer salinities from 20
to 40%o with maximum growth for juveniles occurring at
35%o (Bonin 1977, Perret et al. 1980, Ward and
Armstrong 1 980, Crocker et al. 1 981 , Holt et al. 1 981 a,
Benson 1982, Peterson 1986). One report found the
greatest abundance of small juveniles (1 7-58 mm total
length (TL)) in salinities below 15%o (Gunter 1945).
Captive juveniles survived best at salinities of 1 .3%o or
greater (Miranda and Sonski 1985).

Dissolved Oxygen: Fry can not survive low dissolved
oxygen (DO) concentrations of 0.6 to 1.8 parts per
million (ppm) (Overstreet 1983). Large juveniles have
been reported in waters with oxygen concentrations of
5.2 and 8.4 ppm (Barret et al. 1978).

Other: The maximum ammonia (NH3) concentration
allowing normal growth of larvae is 0.1 1 mg/l, but older
fish are able to tolerate higher concentrations (Holt and
Arnold 1983).

Movements and Migrations: The red drum is relatively
non-migratory with no major coastwise movements,
but does have broad random movements, loosely
coordinated temperature induced migrations, and
strong offshore or deep water spawning migrations
(Simmons and Breuer 1962, Moe 1972, Adkins et al.
1979, Perret et al. 1980, Ward and Armstrong 1980,
Osburn et al. 1 982). Larger fish (>750 mm) appear to
move greater distances than smaller fish (Bryant et al.
1989). Tagging studies have shown little intra-bay
movement or bay-Gulf travel except, perhaps, for short
periods, and a few infrequent individuals with some
extensive movement (Simmons and Breuer 1962,
Beaumariage 1 969, Pafford 1 981 , Osburn et al. 1 982,
Bryant et al. 1989). These studies also indicated that
fish tagged in the Gulf of Mexico tended to stay there
(Simmons and Hoese 1959, Simmons and Breuer
1 962). Eggs, larvae, and early juveniles are carried by
tides and currents in late fall into the shallow estuaries
and bays with peaks occurring in October. Larvae tend
to move through barrier island passes in mid-channel
surface waters with the tidal current (King 1 971 , Bass
and Avault 1 975, Holt et al. 1 981 a, Benson 1 982). Fish
move from bay shores farther into the estuary to quiet
back water areas as they grow, eventually occupying
secondary bays considerable distances from their origi-

nal point of entry (Yokel 1 966, Perret et al. 1 980, Peters
and McMichael 1987). Young drum will leave these
shallow areas when about 40 to 1 20 mm TL and move
into primary bays and somewhat deeper waters (>1 .8
m). This movement may be accelerated by cold
temperatures (Pearson 1928, Yokel 1966, Osburn et
al. 1982, Peters and McMichael 1987). Movement of
sub-adults (<3 years) in bays appears limited with
schools remaining in a single locale for several months
(Osburn et al. 1 982). Most of their movements appar-
ently consist of responses to temperature and salinity,
and foraging which can be considerable even if these
fish remain within a small general area (Pafford 1981,
Overstreet 1983). As juveniles approach 200 mm TL
during their first spring, they may remain in deep water
areas of bays or congregate near passes usually in
large aggregations (Simmons and Hoese 1 959, Peters
and McMichael 1987). Sub-adults may remain in the
bays throughout the year, but older fish (>2) move into
the open Gulf in fall and winter, and possibly during late
summer (Perry 1970, Perret et al. 1980, Hein and
Shepard 1 986a, Matlock 1 987, Beckman et al. 1 988).
This seasonal movement is a general, gradual one with
fish disappearing offshore presumably to spawn
(Pearson 1928, Benson 1982). Class I juveniles leav-
ing bay systems in the fall probably reenter with older
juveniles the following spring in a more contracted
migration (Pearson 1928, Ward and Armstrong 1980,
Benson 1982). Migrating fish may use salinity gradi-
ents as predictive cues for directed movements from
estuarine to oceanic habitats and back (Owens et al.
1 982). Results from recent studies suggest large fish
in offshore waters may have a more extensive migra-
tion over time than was previously thought. These
movements may be due to the abundance of specific
food items, causing the red drum to continually migrate
in a relatively consistent pattern in order to optimize
feeding in specific rich and different areas on a sea-
sonal basis (Overstreet and Heard 1 978, Pafford 1 981 ,
Overstreet 1983).

Reproduction

Mode: This species has separate male and female
sexes (gonochoristic). Fertilization is external, by
broadcast of milt and roe into the water column, and
egg development is oviparous. Mature adults probably
form spawning aggregations (Johnson and Funicelli
1991). Red drum are multiple batch spawnwers, with
group-synchronous oocyte maturation (Wilson and
Nieland 1994).

Spawning: The spawning season typically lasts from
summer through early winter, but its onset and duration
vary with photoperiod, water temperature, and possi-
bly other factors (Holt et al. 1981a, Overstreet 1983).
Spawning can start as early as August in some parts of
the study area, but it usually begins in September and

295

Red drum, continued

ends in early January with peaks occurring in mid-
Septemberthrough October, and then declining (Welsh
and Breder 1924, Gunter 1945, Yokel 1966, Boothby
and Avault 1 971 , Christmas and Waller 1 973, Heffernan
1973, Sabins and Truesdale 1974, Perret et al. 1980,
Holt et al. 1 981 a, Benson 1 982, Overstreet 1 983, Lee
et al. 1 984, Hein and Shepard 1 986a, Peterson 1 986,
Matlock 1987, Van Hoose 1987, Murphy and Taylor
1990). Gonadosomatic index (GSI) studies in the
northern Gulf of Mexico suggest an 8 to 9 week
spawning season, mid-August to early October (Wil-
son and Nieland 1994). Based on the presence of
larval red drum in the northern Gulf of Mexico, it can be
inferred that spawning occurs August through Novem-
ber, with a peak from September through October
(Ditty 1986, Ditty et al. 1988). Spawning principally
occurs in nearshore coastal waters on the Gulf side of
barrier islands, usually in or near the passes and
channels between islands where currents can carry
the eggs to shallow inside waters (Higgins and Lord
1 926, Pearson 1 928, Gunter 1 945, Breuer 1 957, Yokel
1 966, Sabins and Truesdale 1 974, Perret et al. 1 980,
Holtetal. 1981a, Benson 1982, Lee et al. 1984, Hein
and Shepard 1986a, Matlock 1987, Peters and
McMichael 1987, Murphy and Taylor 1990). Freshly
spawned eggs were recovered during one investiga-
tion in water depths ranging from 1 .5 to 2.1 m (Johnson
and Funicelli 1991). One study estimated spawning
occurring 7.3 to 21.9 m offshore of a natural pass in
Texas (Heffernan 1973). In Florida, ripe adults have
been collected 4.8 km offshore in the Gulf of Mexico
suggesting that some offshore spawning may also
occur (Murphy and Taylor 1 990). Some spawning can
also occur inside large estuaries. Spawning activities
are initiated in early evening or night (Guest 1 978, Holt
et al. 1981b, Overstreet 1983, Johnson and Funicelli
1991), in an average salinity of 28%o and in tempera-
tures of 21 ° to 24°C (Hopkins et al. 1 986, Johnson and
Funicelli 1991).

Fecundity: Captive fish spawn repeatedly and produce
large numbers (about 1 million per spawn) of small
buoyant eggs (Vetter et al. 1983). The estimated
number of oocytes from a female with a standard
length (SL) of 758 mm was 61,998,776 when calcu-
lated by volumetric means or 94,513,172 using the
gravimetric method (Overstreet 1983). In one experi-
ment, 10 to 12 spawns per fish over 90 to 100 days
were typical with one captive fish spawning 31 times
over 90 days, while another reported 3 females spawn-
ing 52 times in 76 days producing an estimated total of
60 million eggs. Captive fish spawned about 1 million
eggs per spawn during the first 45 days, dropping to 1 0
to 100 thousand thereafter. The maximum recorded
spawn was 2,058,000 perfish during one night (Arnold
et al. 1979, Overstreet 1983), and a maximum indi-
vidual annual fecundity is estimated as 30,000,000 for

9 to 14 kg fish (Overstreet 1983). In the northern Gulf
of Mexico, Wilson and Nieland (1994) reported a
typical batch spawning frequency of 3 days, and a
batch fecundity range of 160,000 to 3.27 million eggs
for females 3 to 33 years old.

Growth and Development

Egg Size and Embryonic Development: Eggs develop
oviparously. They are buoyant, and their shape is
spherical with a mean diameter of 0.95 mm and a range
of 0.86 to 0.98 mm diameter (Ditty and Shaw 1994).
Usually one and up to six clear oil globules averaging
0.27 mm (0.24-0.31 mm) are present. Theperivitelline
space varies in size, but is generally less than 2% of the
egg diameter (Holt et al. 1981b, Vetter et al. 1983).
Eggs spawned at 24°C and 28%> hatch in 19 to 20
hours (Arnold et al. 1979), 22 hours when spawned at
23°C and 36%o (Vetter et al. 1 983), and 28 to 29 hours
at 22 to 23°C (Holt et al. 1981b). Live eggs float with
the oil globule on top, and animal pole downward. Holt
et al. (1 981 b) has thoroughly described the embryonic
development of this species. Hatching usually occurs
in late summer to early winter, peaking in September
and October (Matlock 1987).

Age and Size of Larvae: Larvae are less than 8.0 mm
SL, and those 8 to 15 mm SL are considered transi-
tional juveniles (Peters and McMichael 1 987). Larvae
are either transparent with no pigment patterns at
hatching, or have a compressed band of dendritic
melanophores on the ventral surface of the body in the
yolk sac region (Holt et al. 1981b). Newly hatched
larvae are negatively buoyant with a SL range of 1.71
to 1 .79 mm (mean 1 .74). Three days after hatching, at
25°C, the mouth forms, eyes are pigmented, and more
time is spent swimming to stay near the surface. The
swim bladder is well developed by day 4 and larvae
remain in a horizontal position in the water column with
little effort (Holt et al. 1 981 b). The yolk sac is present
in larvae 3 to 5 mm TL, but has disappeared at 7 mm
TL. Temperature has a pronounced effect on larval
growth (Holt et al. 1 981 b, Lee et al 1 984, Comyns et al.
1 984). In laboratory raised fish, the yolk sac stage can
range from 40 hours at 30°C to 85 hours at 20°C (Holt
et al. 1981a, Holt et al. 1981b), and larval weight
increase can average 17.74 |ig/day at 24° and 30.25
(ig/day at 28°C. Larvae in the field grow at faster rates
than similar aged laboratory spawned larvae (Comyns
et al. 1989). Wild larvae have an average weight gain
of 141 |ig/day at 27.8° to 29.0°C. The growth rate for
wild larvae smaller than 4 mm is about 0.3 mm/day, but
growth increases rapidly in sizes greater than 4 mm
(0.42 mm/day for 4 to 6 mm larvae). Two distinct
growth periods are evident in early larval development.
One extends from hatching through depletion of the
yolk sac, while the other begins with the onset of active
feeding. Growth rate in terms of SL was low in the first

296

Red drum, continued

stage, averaging less than 0.06 mm/day or more (Lee
etal. 1984).

Juvenile Size Range: Transformation to the juvenile
stage occurs at a total length (TL) of approximately 12
mm (Ditty and Shaw 1994). The size range for the
juvenile stage is from 8.0 mm SL until about 40 mm TL
(Gunter 1 945, Peters and McMichael 1 987). Above 10
mm TL, pigment rapidly appears with distinctive color
patterns at about 25 mm TL. Twenty to 50 dark distinct
blotches are present at this point from the lateral line to
the dorsal fin on each side of the trunk. At 36 mm TL,
a pronounced chromatophore enlargement at the base
of the upper part of the caudal fin appears that results
in the characteristic black ocelli. Juveniles are morpho-
logically identical to adults by 42 mm TL except for a
slightly more pointed caudal fin and lack of distinct
ocelli. Ocelli are faintly visible at 50 mm TL and are very
apparent at 75 mm TL. Brown lateral blotches enlarge
with the fish until it reaches 1 50 mm TL, and then tend
to fade and finally disappear (Pearson 1 928, Simmons
and Breuer 1962). Growth tends to be sporadic in
juveniles, averaging 18.8 mm TL/month or 20.4 mm
SL/month for the first 7.5 months of life (Bass and
Avault 1975). Other estimates based on Texas red
drum report sizes of 320 to 360 mm SL for the first year,
500 mm SL for the second year, 550 to 600 for the third
year, 875 mm SL for the sixth year, 925 mm SL for the
seventh year, and 975 to 1000 mm SL for the eighth
(Miles 1950). Growth has been expressed modally in
year class lengths of: 340 mm SL first year, 540 mm SL
second year, 640 mm third year, 750 mm SL fourth
year, 840 mm SL fifth year; 330 to 356 mm first year,
484 to 559 second year, 660 to 762 mm third year, 890
to 965 fourth or fifth year (Johnson 1978). Growth is
rapid until age 4 or 5 years and then slows markedly
(Murphy and Taylor 1990). Sexual maturity occurs at
the end of the third, fourth, or fifth year with 5 year old
fish constituting the bulk of the spawning population.
Males mature at smaller sizes than females with most
mature at age 1 or 2, and all mature by age 3 years.
Some females are mature by age 3, and all are mature
by age 6 years (Pearson 1928, Simmons and Breuer
1962, Johnson 1978, Benson 1982, Murphy and Tay-
lor 1 990). Red drum generally mature at approximately
700 to 800 mm TL (Miles 1950, Simmons and Breuer
1962), with 50% of the males maturing when they
reach a fork length (FL) of 529 mm and 50% of the
females mature by 825 mm FL (Murphy and Taylor
1990). Smaller ripe fish are occasionally found. Ma-
ture fish have been collected in Texas as small as 425
mm TL. Males are presumed to mature at a smaller
size than females and have been reported to reach
maturity at 320 to 395 mm in Mississippi. Another study
reported ripe males 500 mm SL and ripe females 550
mm SL from Texas samples (Gunter 1 945, Miles 1 950,
Perretetal. 1980). In Florida, some males and females

are mature by 400 and 600 mm FL, respectively (Yokel
1966, Murphy and Taylor 1990). A Louisiana study
reported spawnable males ranging 779 to 1 1 30 mm TL
and spawnable females ranging 850 to 1 135 mm TL
(Hein and Shepard 1 986a). Wilson and Nieland (1 994)
reported that both males and females reach maturity in
the northern Gulf of Mexico at four years of age, when
females are 690-700 mm fork length (FL) and 4.0-4.1
kg total weight (TW), and males are 660-670 mm FL
and 3.4-3.5 kg TW.

Age and Size of Adults: Average adult size is 800 to 850
mm SL (Pearson 1 928, Miles 1 949). This is a long lived
species with fish surviving over 37 years (Johnson
1 978, Mercer 1 984, Beckman et al. 1 988, Murphy and
Taylor 1 990). A 36 year old female was 995 mm FL and
weighed 1 1 .96 kg, and a 37 year old male was 940 mm
FL and weighed 10.49 kg (Beckman et al. 1988).
Pearson (1928) recorded a 1520 mm TL fish. The
largest red drum caught by hook and line was caught
in North Carolina waters and weighed 42.69 kg (WRGF
1991). The red drum fishery is largely comprised of
newly recruited fish. The mean size and age of this
population depends heavily on recent recruitment
(Tilmant et al. 1989). Beckman et al. (1988) have
derived Von Bertalanffy growth equations for both
sexes of red drum by length and by weight.

Food and Feeding

Trophic Mode: All free swimming life stages are car-
nivorous. Juveniles appear to hunt for food using a
sweep style method to search for suitable prey (Fuiman
and Ottey 1993).

Food Items: The red drum diet consists of food items
from five major groups: copepods, mysid shrimp, am-
phipods, decapods, and fish (Bass and Avault 1975,
Levine 1 980). Utilization of these groups is determined
by prey size and availability (Boothby and Avault 1 971 ,
Bass and Avault 1975, Overstreet and Heard 1978,
Morales and Dardeau 1 987), and so their dominance
in the diet of red drum may vary among locations.

Larvae: The major prey of larval red drum are copep-
ods, including cyclopoids, calanoids, and harpacticoids,
as well as various other zooplankton (Bass and Avault
1975, Benson 1982, Peters and McMichael 1987).
Larvae up to 9 mm TL subsist on copepods and their
nauplii that range from 0.06 to 1 .5 mm TL (Bass and
Avault 1975, Comyns et al. 1989). The calanoid
Acartia sp. is eaten most frequently, but species of
cyclopoids, harpacticoids, and other calanoids are
also consumed.

Juveniles: Although they appear in the diet of juveniles
10 to 39 mm TL, copepods cease to be important in
volume by 1 0 to 1 9 mm TL. Mysid shrimp, particularly

297

Red drum, continued

Mysidopsis almyra, are eaten by fish 1 0 to 1 69 mm TL,
but are most important in small juveniles 10 to 49 mm
TL, constituting 70 to 100% of their diet (Bass and
Avault 1 975, Peters and McMichael 1 987). Fish 30 mm
TL and over eat small crustaceans like schizopods and
amphipods (Darnell 1 958). Gammarid amphipods are
consistently found in 10-109 mm TL fish and are a
dominant food item in fish 30 to 60 mm TL (Bass and
Avault 1975, Peters and McMichael 1987). Generally,
at least five species of amphipods, including Ampelisca
sp. and Carinogammarius sp., are a minor part of the
diet, but are moderately important in fish 30 to 49 mm
TL. A large variety of decapods are eaten by fish 8 to
1 20 mm TL. The first to appear in the diet are caridean
shrimp, usually grass shrimp (Palaemonetes sp.), as
well as zostera shrimp (Hippolyte zostericola), bay
shrimp (Crangon sp.), and snapping shrimp (Alpheus
sp.). These are eaten until fish reach 150 to 159 mm
TL. Penaeid shrimp, including white shrimp, pink
shrimp, and brown shrimp, enter the diet offish 70 to 79
mm, and become important for fish 90 to 99 mm TL and
larger (Miles 1949, Bass and Avault 1975, Overstreet
and Heard 1 978, Peters and McMichael 1 987). Crabs,
though insignificant in the size classes from 30-69 mm
SL, begin to gain importance in juveniles >70 mm long
but remain secondary to shrimp (Morales and Dardeau
1987). At 100 to 175 mm TL, the chief food items are
small penaeid shrimp, palaemonetid shrimp, small
mullet, silversides, gobies, and small crabs (Simmons
and Breuer 1962, Morales and Dardeau 1987). Blue
crab and other portunid crabs are eaten by fish 40 to 49
mm TL, and are a common food item for fish 70 to 79
mm TL. Other crabs are found predominantly in larger
juveniles (>105 mmTL)and include fiddler crabs (Uca
sp.), heavy marsh crab (Sesarma reticulatum), mud
crabs, Eupagurus spp., and spidercrab (Libinia dubia),
but these are generally unimportant (Miles 1 949, Bass
and Avault 1 975, Peters and McMichael 1 987, Morales
and Dardeau 1987). Crabs predominate in the diet of
fish 1 84 to 625 mm TL, particularly blue crab and Harris
mud crab (Rhithropanopeus harrisii), and some fish as
well (Darnell 1958). Fish play a substantial role in the
diet of juveniles >1 5 mm TL, but were most abundant
in juveniles > 90 mm TL (Bass and Avault 1 975, Peters
and McMichael 1987). Juveniles 20 to 29 mm TL
began eating other sciaenids, usually spot, but also
some Atlantic croaker. Other fish consumed include:
speckled worm eel (Myrophis punctatus), gulf menha-
den, anchovies (Anchoa sp.), inshore lizardfish
(Synodus foetens), mullet, inland silverside (Menidia
beryllina), darter goby(Gobionellus boleosoma), and
bay whiff (Citharichthys spilopterus).

Food habits vary little in fish 250 to 924 mm SL
(Boothby and Avault 1 971 ). Smaller fish generally eat
smaller sized items, but the three main groups, shrimp,
crabs, and fish, are eaten by all size classes. No

noticeable difference has been observed between the
diets of males and females (Boothby and Avault 1 971 ).
Red drum 245 to 745 mm TL have been found to
consume algae, grass, eggs, cysts, detritus, mud and
sand, annelids, ostracods, amphipods, fish, penaeid
shrimp, and squid. Specific prey items include grass
shrimp, blue crab, mud crabs, bay shrimp (Crangon
sp.), estuarine ghost shrimp (Callianassajamaicense),
mullet, speckled worm eel {Myrophis punctatus), na-
ked goby (Gobiosoma bosci), sheepshead minnow,
gulf pipefish (Sygnathus scovelli), anchovies, menha-
den, hardhead catfish, rainwater killifish (Lucaniaparva),
spot, and blackcheektonguefish (Symphurus plagiusa)
(Pearson 1 928, Gunter 1 945, Knapp 1 949, Reid 1 955,
Reid et al. 1956, Simmons 1957, Breuer 1957, Bryan
1 971 , Diener et al. 1 974). Although crustaceans as a
group exceed fish in frequency of occurrence and per
cent volume of stomach contents, fish are consumed
more frequently, in greater numbers, and in greater
volume than shrimp or crabs alone. Plant and sub-
strate material that occurs in stomach contents are
probably taken incidentally during feeding activities.
Fish are generally more prevalent in the diet of red
drum during winter and spring months, menhaden
being a favorite. Crustaceans become increasingly
more important during late spring and by summer are
the main staple and continue as such until late fall.
Shrimp appear more frequently in stomach contents in
the spring, summer, and fall. Crabs are more frequent
than shrimp only in the winter (Boothby and Avault
1971). Other organisms eaten by juveniles contributed
little to stomach contents volume with the possible
exception of polychaetes, especially Glycera americana
(Bass and Avault 1975, Peters and McMichael 1987,
Morales and Dardeau 1 987). These were eaten by 30-
1 39 mm TL fish, but were most important to 60-79 mm
TL fish (Bass and Avault 1 975, Overstreet and Heard
1 978). Echinoderms are eaten regularly by large fish,
but are not an important diet item (Overstreet and
Heard 1978). Other species consumed in addition to
the main food species are: molluscs- Atlantic mud-
piddock (Barnea truncata), false angelwing (Petricola
pholodiformes), white baby-ear (Sinum perspectivum);
crustaceans- lesser blue crab (Callinectes simulis),
calico box crab (Hepatus epheliticus), lady crab
(Ovalipes ocellatus), longwrist hermit crab (Pagurus
longicarpus), iridescent swimming crab (Portunus
gibbesi), sea lice (Squilla sp.); echinoderms- Mellita
quinquiespen'orata, Sclerodactyla briareus; fishes-
striped killifish (Fundulus majalis), southern kingfish
(Menticirrhus americanus), pinfish, oyster toadfish
(Opsanus tau), Florida pompano, and hogchoker
{Thnectes maculatus) (Pearson 1928, Miles 1949,
Boothby and Avault 1 971 , Overstreet and Heard 1 978).
Bivalve molluscs, bivalve mollusc siphons, isopod crus-
taceans, and a marsh rat have also been reported from
stomach contents, but these items are not typical

298

Red drum, continued

(Pearson 1928, Peters and McMichael 1987).

Biological Interactions

Predation: Predation on red drum has not been well
studied (Killam et al. 1 992). Larvae and juveniles are
potential prey items of larger piscivorous fish including
larger red drum. Juvenile red drum feeding along the
shorelines of mariculture ponds are subject to preda-
tion by piscivorous wading birds (Castiglione pers.
comm).

Factors Influencing Populations: Red tides, caused by
the blooms of certain dinoflagellates, that occur during
the spawning season can affect larval survival rates
and possibly impact recruitment of the affected year-
class in following years (Riley et al. 1989, Killam et al.
1 992). Several organisms are known to parasitize red
drum possibly as a consequence of the diverse foods
consumed, and these can affect health and mortality
(Yokel 1966, Perret et al. 1980, Overstreet 1983,
Landsberg 1993). Known parasites include: Sporozo-
ans- Hennequya ocellata; Parvicapsula renalis, Trema-
todes- unidentified; Cestodes- Poecilan cistrium
robustum (known as spaghetti worm) infecting muscles
and often resulting in fish being discarded by fisher-
men; Copepods, which parasitize red drum the most
heavily, include- Brachiella qulosa, B. intermedia,
Echetus typicus, Lernaennicus radiatus, Caliqus
latifrons, C. repax, C. bonito, C. elongatus, C.
haemulonis, and Lernanthropus paenulatus,
Lernaennicus affixus; Isopods- Nerocila sp. (Simmons
1 957, Yokel 1 966, Perret et al. 1 980, Hein and Shepard
1986b, Landsberg etal. 1991, Landsberg 1993); Bar-
nacles- Balanus improvisus, are known to attach to the
flanks of red drums (Overstreet 1 983). The destruction
of estuarine nursery habitat utilized by late larval and
juvenile stages, as well as growth overfishing and
recruitment overfishing, are thought to have a serious
impact on red drum (NMFS 1986).

Personal communications

Castiglione, Marie C. NOAA NMFS SEFSC Galveston
Lab., Galveston, TX.

Swingle, Wayne. Gulf of Mexico Fishery Management
Council, Tampa, FL.

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304

Striped mullet

Mugil cephalus
Adult

10 cm

(from Goode 1884)

Common Name: striped mullet
Scientific Name: Mugil cephalus
Other Common Names: common mullet, black mul-
let, Biloxi bacon, liza, gray mullet, muletcabot (French),
lisa pardete (Spanish) (Broadhead 1 953, Breuer 1 957,
Christmas and Waller 1 973, Kuo et al. 1 973, Finucane
et al. 1978, Fischer 1978, NOAA 1985).

Classification (Robins et al. 1991)
Phylum: Chordata
Class: Osteichthyes
Order: Perciformes
Family: Mugilidae

Value

Commercial: Mullet comprise one of the most impor-
tant fisheries of the southern United States with com-
bined 1993 Gulf of Mexico landings for black and
striped mullet totaling over 14,319 mt and selling for an
average of $0.41 per pound (Anderson 1 958, Lee et al.
1980, Newlin 1993, O'Bannon 1994). Commercial
fishing for mullet takes place mainly from September to
December (NOAA 1985), and Gulf coast landings
contributed 84% of the total U.S. catch in 1 992 (Newlin
1 993). Florida contributes the greatest amount to Gulf
of Mexico mullet production (5, 1 04 mt), and this comes
primarily from the west central coast of the state (Killam
et al. 1992, Newlin 1993). This production amount is
followed by Louisiana (2,733 mt), Alabama (580 mt),
Mississippi (215 mt), and Texas (1 6 mt). Striped mullet
is considered an important food fish, and is usually
marketed locally. It is also taken for its roe, which is
prized as a delicacy and exported to Asian markets
(Render et al. 1995). Mullet are most frequently
marketed as fresh or salted (Fischer 1978, Shipp
1986). This is also considered a prime species for

mariculture (Broadhead 1953, Christmas and Waller
1 973, Bishop and Miglarese 1 978). Despite this good
reputation as a food fish, striped mullet is commonly
considered oily and poor tasting west of the Mississippi
(although one researcher reports it as being quite
palatable) and is primarily used only as bait (Kilby
1 949, Reid 1 955, Arnold et al. 1 960). Recent efforts to
enhance the image of both mullet and mullet roe as an
export product have met with considerable success,
thus its commercial importance may increase further in
the future (Shipp 1986, Killam et al. 1992). Mullet are
caught by gill nets, trammel nets, stop nets, haul
seines, yard seines, hook and line, and cast nets
(Broadhead 1 953, Broadhead and Mefford 1 956, Ander-
son 1958, Fischer 1978). The gill nets and trammel
nets are the most effective means of capture, with haul
and yard seine second in choice. Hook and line, and
cast net catches are incidental. The rising popularity of
mullet flesh and roe as food items, and the use of more
efficient fishing gear and methods have led to increas-
ing harvest regulation by the Gulf coast states. In order
to manage the Gulf of Mexico fishery, the Gulf States
Marine Fisheries Commission has developed a fishery
management plan (FMP) for this species (Leard et al.
1995).

Recreational: Striped mullet is valued as a bait fish by
sport fishermen, and is also indirectly important as a
forage species for game fishes (Kilby 1949, Arnold et
al.1960). Fishery information forthe recreational catch
in the Gulf of Mexico showed a total of over 1 .6 million
mullet caught in 1992 (O'Bannon 1993). Sport fisher-
men take striped mullet with the same gear that com-
mercial fishermen use (Manooch 1984, Collins 1985).
The importance of mullet as a recreational species may
be underestimated. When recently compared to a

305

Striped mullet, continued

Table 5.40. Relative abundance of striped mullel
31 Gulf of Mexico estuaries (from Volume 1).

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

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 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

group of other popular recreational species from the
inshore Gulf (spotted seatrout, sand seatrout, sheep-
shead, red drum, and black drum), mullet ranked
second in Florida, third in Mississippi, and fourth in
Alabama (Leard pers. comm.).

Indicator of Environmental Stress This species has
been used by the U.S. Environmental Protection Agency
(EPA) to study the toxicology of crude oil (Minchew and
Yarbrough 1977). Another study indicates that the
results of striped mullet responses to DDT at different
temperatures have application for the development of
water quality criteria in Australia (Powell and Fielder
1982).

Ecological: Striped mullet is an important forage fish
and forms a major component in the flow of energy
through the estuarine system by feeding at the lowest
trophic levels and providing food to birds and many
important commercial and game fish (Kilby 1949,
Fontenot and Rogillio 1 970, Moore 1 974, Sogard et al.
1989).

Range

Overall: Striped mullet occur world-wide in warm tropi-
cal, sub-tropical, and temperate waters 42° N to 42° S
(46° N in Mediterranean and Black Sea), but are less
common in equatorial areas (Anderson 1958, Moore
1974, Hoese and Moore 1977, Martin and Drewry
1978, Lee et al. 1980, Ward and Armstrong 1980,
NOAA 1985, Shipp 1986). Juveniles are often col-
lected outside the above latitudes, usually in the fall.
On the U.S. east coast, they are most abundant from
Cape Hatteras southward, but also occur in the Chesa-
peake and Mid-Atlantic region, and occasionally as far
north as Nova Scotia (Lee et al. 1 980). They are found
on the U.S. west coast from San Francisco Bay south-
ward, and in coastal waters of the Hawaiian Islands
where they are known as 'ama'ama (Squire and Smith
1977).

Within Study Area: Striped mullet occurs throughout
the Gulf of Mexico in shallow marine and estuarine
habitats (Gunter 1945, Moore 1974, Ward and
Armstrong 1 980). This fish is very common along the
west coast of Florida, and is most abundant along the
south Florida coasts. It is also one of the most
numerous species in the bay flats along the Texas
coast (Gunter 1945, Broadhead 1953, Collins 1985,
Killam et al. 1992) (Table 5.40).

Life Mode

All stages are pelagic, occurring primarily in the shal-
low part of the water column, although some deep
recoveries have been reported (Arnold and Thompson
1958, Thomson 1966, Hoese and Moore 1977,
Finucane et al. 1978, Martin and Drewry 1978, Ward

306

Striped mullet, continued

and Armstrong 1980). Fertilized eggs are spherical,
positively buoyant, and non-adhesive. Eggs and lar-
vae are generally neustonic. Larvae are planktonic
until 1 0 to 1 2 days from hatching and are then capable
of sustained swimming (Kuo et al. 1973, Martin and
Drewry 1 978). Pre-juveniles, juveniles, and adults are
nektonic and form schools ranging from a few individu-
als up to several hundred (Breder 1940, Kilby 1949,
Arnold and Thompson 1958, Arnold et al. 1960,
Thomson 1966, Hoese and Moore 1977). Activity
related to feeding has been recorded during both day
and night (Hiatt 1 944, Darnell 1 958, Tabb and Manning
1 961 ), although light is believed necessary for school-
ing (Thomson 1 966). A Florida study observed diurnal
activity (Sogard et al. 1989).

Habitat

Type: Striped mullet live in a wide range of habitats and
depths depending on life stage, season, and location.
It is one of the most abundant fishes in shallow Gulf
waters, and often has the highest biomass (Hellier
1962). It is most abundant in waters near shore,
occupying virtually all shallow marine and estuarine
habitats including open beaches, flats, lagoons, bays,
rivers, salt marshes, and grass beds (Gunter 1945,
Kilby 1949, Breuer 1957, Renfro 1960, Hellier 1962,
Franks 1 970, Perret et al 1 971 , Swingle 1 971 , Christ-
mas and Waller 1973, Moore 1974, Henley and
Rauschuber 1 981 , Cech and Wohlschlag 1 982, Sogard
et al. 1989). Spawning occurs near the surface of
offshore waters, but larvae sink during post-hatch
growth periods (Ditty and Shaw 1996). Eggs and
larvae occupy offshore marine habitat where they
undergo early development, then as prejuveniles enter
the bays and estuaries to mature. This occurs from
November to June after they have reached 15 to 32 mm
in total length (TL), with the greatest occurrence from
December to February (Gunter 1945, Renfro 1960,
Hellier 1962, Hoese 1965, Franks 1970, Perret et al.
1971, Swingle 1971, Christmas and Waller 1973,
Swingle and Bland 1974, Hildebrand and King 1975,
Tarver and Savoie 1976, Ward and Armstrong 1980,
Nordlie et al. 1982). This species has been reported
from fresh to hypersaline waters and from waters with
depths of a few centimeters to 1,385 m, but most are
collected within 40 m of the surface (Gunter 1945,
Breuer 1957, Simmons 1957, Arnold and Thompson
1 958, Perret et al. 1 971 , Swingle 1 971 , Christmas and
Waller 1973, Moore 1974, Pineda 1975, Finucane et
al. 1 978, Martin and Drewry 1 978, Ward and Armstrong
1980, Henley and Rauschuber 1981, Cech and
Wohlschlag 1982, Cornelius 1984, NOAA 1985). This
species appears to prefer depths of <3 m in inshore
waters.

Substrate: The striped mullet prefers softer sediments
such as mud and sand which contain decaying organic

detritus, but it also occurs overfinely ground shell, clay,
mud and sand mixtures, silt, and silt-clay mixtures
(Kilby 1949, Breuer 1957, Tabb and Manning 1961,
Franks 1970, Swingle 1971, Ward and Armstrong
1980, Cornelius 1984). In inshore areas, it also fre-
quents grass beds of Thalassia and other macro-
phytes, especially at night (Thomson 1 966, Zimmerman

1969, Bishop and Miglarese 1978, Henley and
Rauschuber 1 981 ), and has also been observed around
patches of Ruppia (Franks 1970).

Physical/Chemical Characteristics:
Temperature - Eggs: Egg development has been
recorded over a range of 10° to 31 .9°C in both labora-
tory and field observations with the optimum range
occurring at 21° to 24°C (Kuo et al. 1973, Nash et al.
1 974, Sylvester et al. 1 975, Sylvester and Nash 1 975,
Finucane et al. 1978, Ward and Armstrong 1980).

Temperature - Larvae: Ditty and Shaw (1996) col-
lected 1 ,983 larval mullet in the northern Gulf of Mexico,
at temperatures ranging from 16.7 to 27.0°C (mean
34.4°C). Larval development occurs from 15.9° to
29.1 °C, with optimum growth and survival occurring at
20° to 22°C (Kuo et al 1 973, Nash et al. 1 974, Sylvester
and Nash 1975, Ward and Armstrong 1980). The
ability to survive and grow over a broad thermal range,
despite the probability of temperatures at spawning
sites varying very little, may be a preadaptation to
accommodate temperature changes as the larvae sink
vertically through the water (Sylvester and Nash 1 975).
Pre-juveniles occur at minimum temperatures of 5.0°
to 9.0°C up to a maximum exceeding 30°C (Christmas
and Waller 1973, Martin and Drewry 1978, Ward and
Armstrong 1980).

Temperature - Juveniles and Adults: Juveniles and
adults appear able to adjust to a wide range of tem-
peratures (Breuer 1957, Ward and Armstrong 1980).
Recorded collections are from 5.9° to 37.0°C, but the
ability to withstand short periods of 40°C has been
observed (Gunter 1 945, Kilby 1 949, Hellier 1 962, Franks

1 970, Perret et al. 1 971 , Swingle 1 971 , Dunham 1 972,
Moore 1974, Pineda 1975, Tarver and Savoie 1976,
Ward and Armstrong 1980). Reported temperature
preferences are 20° to 30°C for juveniles, and >16° to
30°C for adults (Ward and Armstrong 1980).

Salinity - Eggs: Striped mullet eggs are stenohaline.
Spawning and development are reported to occur at 28
to 36.5%o, with optimum egg survival occurring at 30 to
33%o (Kuo et al. 1 973, Sylvester et al. 1 975, Finucane
et al. 1978, Ward and Armstrong 1980). Eggs have
much less tolerance to salinity variation than larvae,
but have a greater tolerance to sea water (Sylvester et
al. 1975).

307

Striped mullet, continued

Salinity - Larvae: Larvae are stenohaline at hatching
and become increasingly euryhaline with size (Nordlie
et al. 1982). Early larvae are poly- to euhaline in
salinities from 26 to 35%> and are unable to tolerate
fresh water. Older larvae are able to tolerate salinities
from 16 to 36.5%o with reported optimal ranges being
32 to 33%o and 26 to 28%o (Kuo et al. 1 973, Sylvester
et al. 1 975, Finucane et al. 1 978, Ward and Armstrong
1980, Nordlie et al. 1982). Ditty and Shaw (1996)
collected 1,983 larval mullet in the northern Gulf of
Mexico, at salinities ranging from 23.5 to 36.8%o, with
a mean of 23.4%o. By the pre-juvenile stage, osmotic
regulatory abilities and salinity tolerances reach a
definitive state, and the mullet becomes euryhaline
(Nordlie et al. 1982). Pre-juveniles have been re-
corded from a range of 0 to 54%o with a preference for
<1 to 40%o (Gunter 1 945, Swingle 1 971 , Christmas and
Waller 1973, Ward and Armstrong 1980).

Salinity - Juveniles and Adults: Both juveniles and
adults are euryhaline with similar tolerances. They
have been observed in salinities ranging from 0.0 to
75%o, but adults appear to prefer median salinities of
approximately 26%o, and juveniles range from 20 to
28%o (Gunter 1 945, Kilby 1 949, Simmons 1 957, Hoese
1960, Renfro 1960, Hellier 1962, Perret et al. 1971,
Dunham 1972, Christmas and Waller 1973, Swingle
and Bland 1974, Pineda 1975, Tarver and Savoie
1976, Finucane et al. 1978, Martin and Drewry 1978,
Ward and Armstrong 1980, Cornelius 1984). The
capability to tolerate salinities ranging from 0 to 35%o
appears when individuals have reached a standard
length (SL) of 40-69 mm and are 7.5-8.5 months old
(Nordlie et al. 1982).

Dissolved Oxygen (DO): Eggs and larvae prefer higher
concentrations of oxygen (about 4 mg/l) and are not
able to tolerate ranges as low as juveniles and adults
can (Ward and Armstrong 1 980, Cech and Wohlschlag
1 982). Two possible mechanisms for tolerance to low
oxygen levels have been examined. Enhanced hemo-
globin concentrations found in striped mullet would
enable it to meet seasonally heavy oxygen demands
during the warmest months and the autumn spawning
period (Cech and Wohlschlag 1982). Aerial respiration
in the upper posterior portion of the pharynx using air
obtained by jumping, rolling, or holding the head aboye
water and moving air into the upper pharyngeal cham-
ber may also provide supplementary oxygen for respi-
ration (Hoese 1985).

Movements and Migrations: The striped mullet gener-
ally does not make long migrations. Movements are
predominantly inshore-offshore and occur during fall
and winter when large schools leave bays and estuar-
ies in order to spawn in offshore Gulf waters. After
spawning, adults return to inshore habitats. Most

striped mullet move less than 33 km from their spawn-
ing site (Kilby 1949, Broadhead 1953, Broadhead and
Mefford 1956, Moe 1972, Hoese and Moore 1977,
Ward and Armstrong 1980). However, a tagging study
conducted in Florida Bay and along the west coast of
Florida showed a northwesterly coastwise movement,
especially during the spawning season, with one indi-
vidual recaptured 500 km from where it was released
(Funicelli et al. 1989). One study found that a prefer-
ence existed for bay waters and suggested an organic
compound present in these waters may guide mullet
back to their native area (Kristensen 1 964). At lengths
of 16 to 20 mm SL (40 to 45 days old), pre-juveniles
migrate to inshore and estuarine waters in the spring
months. Entry of juveniles into estuarine areas begins
in November, and continues through February (Ditty
and Shaw 1996). After entering bay systems from
offshore waters, they migrate to nursery areas which
are thought to be secondary and tertiary bays. Most
juveniles spend the end of their first year in these
coastal waters, salt marshes, and estuaries, and over-
winter in deeper parts of these areas. However, some
migrate offshore during the fall as sub-adults to mature
and spawn when colder temperatures set in (Henley
and Rauschuber 1981, Collins 1985). Movement of
mullet is otherwise random and usually restricted to a
broad coastal area (Broadhead 1953, Broadhead and
Mefford 1956, Broadhead 1958, Moe 1972).

Reproduction

Mode: This species has separate male and female
sexes (gonochoristic). Fertilization is external, by
broadcast of milt and roe into the water column. Devel-
opment is oviparous. There are occasional occur-
rences of hermaphrodites, but they are considered
atypical (Thomson 1966).

Spawning: Spawning may begin in October to mid-
November and last until March. Peak spawning gen-
erally occurs from December through February in the
Gulf of Mexico, but there is regional variation. Peak
spawning in the northern Gulf of Mexico in November-
December, over or beyond the Continental Shelf at sea
surface temperatures >25°C (Ditty 1986, Ditty and
Shaw 1996). In Florida, the general spawning period
is from December to February, while off the Texas
coast, the spawning season usually extends from
October to December (Breder 1940, Gunter 1945,
Broadhead 1953, Reid 1955, Anderson 1958, Arnold
and Thompson 1958, Broadhead 1958, Arnold et al.
1 960, Christmas and Waller 1 973, Wagner 1 973, Moore
1974, Sabins and Truesdale 1974, Fahay 1975,
Finucane et al. 1 978, Ward and Armstrong 1 980). Ripe
adults collect in passes in large schools and migrate
offshore. The return of spent adults begins 10 days
later and continues until May (Gunter 1 945, Arnold and
Thompson 1958, Moore 1974, Sabins and Truesdale

308

Striped mullet, continued

1 974, Hoese and Moore 1 977). Spawning takes place
in offshore marine waters of the Gulf of Mexico over a
broad area of the continental shelf (Anderson 1958,
Arnold and Thompson 1958, Finucane et al. 1978,
Henley and Rauschuber 1981, Nordlie et al. 1982).
Adults have been observed spawning during the night
40 to 50 miles southeast of the Mississippi River delta
at the surface of waters 91 5-1 647 m deep (Arnold and
Thompson 1958). Newly spawned eggs have been
recovered in plankton trawls 89 to 98 km off the Texas
coast in the northwest Gulf of Mexico in waters 131 to
1 83 m deep. These eggs were probably spawned over
the edge of the continental shelf (Finucane et al. 1 978).
Spawners occur in small groups of 3 to 6 fish swimming
close to the surface in an erratic manner (Arnold and
Thompson 1958). Males stay slightly behind a single
female pressing against her and from time to time
visibly quiver (Breder 1940, Arnold and Thompson
1958). No direct evidence on spawning salinities and
temperatures is available, but spawning is apparently
unsuccessful at low salinities (Christmas and Waller
1973, Martin and Drewry 1978). Hormonal spawning
in a laboratory study was best induced at 23.8° to
23.5°C, and natural spawning at 21 °C (Kuo et al. 1 973,
Sylvester et al. 1975) in salinities ranging from 30 to
32%o (Kuo et al. 1 973, Nash et al. 1 974, Sylvester et al.
1975).

Fecundity: Fecundity has been estimated in laboratory
studies as being 648 ± 62 to 849 ± 62 eggs/g body
weight (Shehadeh et al. 1973, Nash et al. 1974) with
recorded releases ranging from 0.76 to 7.2 million
eggs/female (Martin and Drewry 1978, Ward and
Armstrong 1980). Field studies of Louisiana mullet
report individual fecundities of 270,000 to 1,600,000
eggs, and relative fecundities of 798 to 2,61 6 eggs per
gram body weight, for females in a size range of 290 to
445 mm FL (Render et al. 1995). Total individual
fecundity correlates with female size, but relative fe-
cundity does not. Females generally produce only one
set of ova per year (i.e. isochronal) (Render et al.
1995). However, it has been suggested that Florida
striped mullet may spawn more than once in a season
(i.e. heterochronal or batch) (Thomson 1966). Fertili-
zation rates in the laboratory have ranged from 53 to
95% (Kuo et al. 1973, Shehadeh et al. 1973, Nash et
al. 1974).

Growth and Development

Egg Size and Embryonic Development: Render et al.
(1 995) report that oocyte diameter prior to spawning is
0.6 to 0.7 mm, swelling to 0.9 to .95 mm during
hydration. Eggsarenonadhesive, spherical, and trans-
parent to straw-colored (Martin and Drewry 1978,
Ward and Armstrong 1980). Sizes average 0.93 to
0.95 mm (Kuo et al. 1 973, Shehadeh et al. 1 973, Nash
et al. 1 974, Sylvester et al. 1 975, Finucane et al. 1 978).

They are characterized by a single large oil globule with
a uniform diameter ranging 0.30 to 0.36 mm and
averaging 0.33 mm (Kuo et al. 1 973, Nash et al. 1 974,
Finucane et al. 1 978). Kuo et al. (1 973) and Nash et al.
(1 974) have made thorough descriptions of the striped
mullet's embryonic development. Hatching time is
temperature dependent. Incubation period is 36 to 38
hours after fertilization (AF) at 24°C and 48 to 50 hours
AF at 22°C (Kuo et al. 1973, Nash et al. 1974).

Age and Size of Larvae: The TL at hatching is 2.1 mm
to 2.88 mm TL with a reported average of 2.65 ± 0.23
mm TL (Kuo et al. 1 973, Nash et al. 1 974, Sylvester et
al. 1975, Finucane et al. 1978). At hatching, the yolk
sac is ovoid or oblong-ellipsoidal with the oil globule
near the center or rear of the yolk sac (Martin and
Drewry 1978). The mouth opens on day 2 to 3. Larvae
are independently active at this point, and their eyes
are sufficiently pigmented for finding food. The yolk
sac is absorbed by day 5 (24°C) (Kuo et al. 1 973, Nash
et al. 1974, Ward and Armstrong 1980). Most growth
during the yolk sac stage occurs during day 1 with larval
TL's increasing from 2.65±0.23 mm to 3.36+0.03 mm.
The oil globule is still present after the yolk sac is
absorbed. Feeding commences at day 5 (24°C) and
becomes intensive on day 9 (24°C) or day 14 (22°C)
(Kuo et al. 1973). Silvering begins in the abdominal
area, spreading dorsally, and is complete on day 25
(24°C) when larvae are approximately 10.9 mm TL.
This marks the end of the larval stage (Kuo et al. 1 973,
Martin and Drewry 1 978). Pre-juveniles are referred to
as being in the "querimana" stage (Thomson 1966).
The duration of this stage is temperature dependent,
and lasts from 30 to 90 days and has a size range of
about 11 to 52 mm TL (Anderson 1958, Martin and
Drewry 1 978). Growth rates in the wild include: 25 mm
SL fish in January of class 0 year increasing to 1 1 6 mm
SL in January of class 1 year; 1 8 mm SL fish in October
increasing to 65 mm SL by mid-April; and 26 mm TL fish
increasing to 88 mm TL from February to July (Gunter
1945, Kilby 1949, Hellier 1962). However, reported
growth rates for this and other classes vary widely with
climate and other factors (Martin and Drewry 1978).
Scales begin forming when individuals are about 8 to
1 0 mm SL and 1 1 mm TL, and are complete by 1 2 to 1 4
mm SL and 1 8 mm TL (Anderson 1 958, Kuo et al. 1 973,
Martin and Drewry 1978). Nostrils double and the full
number of fin rays form at 11.9 mm TL (Martin and
Drewry 1978). Fish 20 mm SL weigh 2.3 g (Franks
1 970). The adipose eyelid is evident at 28 mm TL, and
is well developed by 50 mm TL. The third anal ray
changes to a hard spine at 41 to 50 mm TL and this
marks the end of the prejuvenile stage (Anderson
1958, Martin and Drewry 1978).

Juvenile Size Range: Juveniles have a size range of
about 44 to 200 mm SL (Gunter 1 945, Anderson 1 958,

309

Striped mullet, continued

Martin and Drewry 1 978). Fin morphology is the same
as that of adults (Martin and Drewry 1 978). The caudal
fin achieves its final form when the fish has a fork length
(FL) of 1 1 0 mm, and the scales change suddenly from
that of a prejuvenile to an adult when above 30 mm TL.
The circuli of the posterior (exposed) region become
complete and less densely packed than those of ante-
rior region. Lateral stripes are generally like those of
adults, becoming increasingly distinct from 44 to 60
mm SL (Martin and Drewry 1978).

Age and Size of Adults: The life span for the striped
mullet is up to 7 years for males, and 8 years for
females (Martin and Drewry 1 978, Ward and Armstrong
1980) with a probable average life span of about 5
years (Hellier 1962), although a 13 year old fish has
been reported (Collins 1985). Adults grow at a rate of
38-64 mm per year (Broadhead 1953). The recorded
size range for adults in the study area is 200 to 760 mm
TL (Kilby 1949, Breuer 1957, Hellier 1962, Franks
1970, Perret et al. 1971, Moore 1974, Pineda 1975,
Tarver and Savoie 1976, Hoese and Moore 1977,
Collins 1985). Average sizes for size classes 1 through
5 have been recorded in SL as 1 1 6 mm, 1 81 mm, 230
mm, 277 mm, and 324 mm with mean weight increases
of 31 g, 84 g, 1 1 6 g, and 1 67 g for the first through the
fourth year (Hellier 1 962). One weight recorded for a
238 mm SL fish was 345.0 g (Franks 1970). Adults
become reproductively mature at 3 years of age or
greater when they reach lengths of 200 to 255 mm TL
for males and 250 to 350 mm TL for females, or 230 mm
to 285 mm FL for males and 243 to 290 mm FL for
females (Gunter 1945, Broadhead 1953, Arnold and
Thompson 1 958, Moore 1 974). The weight of spawn-
ing females ranges from 600 to 1 400 g (Sylvester et al.
1975). Thomson (1966) has developed a Von
Bertalanffy equation to describe the growth of striped
mullet.

Food and Feeding

Trophic Mode: Larvae are carnivorous, with a diet
consisting of planktonic material that probably includes
microcrustaceans (Harrington and Harrington 1961,
Bishop and Miglarese 1978, De Silva 1980, Ward and
Armstrong 1980). Pre-juveniles change from carni-
vores to omnivores to herbivores as size increases.
The trophic transition begins at 15 mm SL and is
completed before metamorphosis, usually by 35 mm
SL. Feeding by juveniles and adults occurs littorally in
shallows by sucking up bottom surface material, strain-
ing it through an elaborate pharyngeal sieving mecha-
nism (Hiatt 1 944, Broadhead 1 958, Darnell 1 958, Tabb
and Manning 1961), and spitting filtered debris from
the mouth (Thomson 1966). Feeding occurs day and
night, and digestion is aided by a gizzard which grinds
up the tough food items ingested (Hiatt 1944, Broadhead
1958, Darnell 1958, Thomson 1966). Although chiefly

herbivorous, striped mullet may opportunistically feed
on animal matter, especially in the fall when an above-
normal protein intake may be required for gonad matu-
ration (Bishop and Miglarese 1978).

Food Items: The prejuvenile diet consists of plant
debris, algae (diatoms), copepods (eggs, nauplii,
adults), mosquito larvae, and fish residue (Harrington
and Harrington 1961). Juveniles and adults generally
prefer organic detritus, diatoms, filamentous algae,
organic matter, benthic organisms, plant tissue, fora-
minifera, and plankton of correct particle size, but they
have also been observed with fish scales, sponge
spicules, and minute gastropods in their stomach con-
tents (Hiatt 1 944, Broadhead 1 958, Darnell 1 958, Tabb
and Manning 1961, Moore 1974). Juvenile striped
mullet may feed on "marine snow", macroscopic sus-
pended aggregates of mixed mineral, detrital, algal,
and bacterial composition (Larson and Shanks 1996).
Mullet that graze on submerged sediments may filter
out and reject the coarser particles, and ingest the
smaller ones, which contain a higher proportion of
absorbed organic matter and adsorbed microorgan-
isms (Odum 1968b). In coastal Georgia, mullet have
been observed feeding on dinoflagellates during "red
tide" events (Odum 1968a). Adult striped mullet have
been observed actively feeding on a swarm of swim-
ming polychaetes, Nereis succinea (Bishop and
Miglarese 1978).

Biological Interactions

Predation: Piscine predators include: red drum, spot-
ted seatrout, hardhead catfish, southern flounder, bull
shark, alligatorgar(Lep/sosfeL/ssparu/a), and longnose
gar (L osseus) (Gunter 1945, Breuer 1957, Simmons
1957, Darnell 1958). Wading birds also prey upon this
species (Sogard et al. 1989).

Factors Influencing Populations: An EPA study has
shown that crude oil may serve as a non-specific stress
agent that lowers resistance of mullet to disease
(Minchew and Yarbrough 1 977). It is also considered
possible that crude oil can act as a medium for patho-
genic bacteria growth, and adversely affect the zoop-
lankton serving as food for mullet. A number of
parasites have been isolated from mullet including:
nematodes, leeches, blood trypanosomes, ciliates,
spiny-headed worms, bacteria, protozoa, copepods,
and tapeworms (Reid 1 955, Overstreet 1 974, Paperna
1 975). There is concern that the expanding roe fishery
may result in overharvest of mullet populations in some
areas (Clement and McDonough 1997).

310

Striped mullet, continued

Personal communications

Lazauski, Skip. Alabama Department of Conservation
and Natural Resources, Gulf Shores, AL.

Leard, Rick. Gulf States Marine Fisheries Commis-
sion, Ocean Springs, MS.

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314

Code goby

Gobiosoma robustum
Adult

1 cm

(from Fritzsche 1978)

Common Name: Code goby
Scientific Name: Gobiosoma robustum
Other Common Names: robust goby
Classification (Robins et al. 1991)
Phylum: Chordata
Class: Osteichthyes
Order: Perciformes
Family: Gobiidae

Value

Commercial: The code goby has no commercial value,
other than as a minor forage fish for commercially
important species.

Recreational: The code goby has little recreational
value, although it is somtimes kept in marine aquaria,
and may be observed by recreational divers and
snorkelers.

Indicator of Environmental Stress: This species is
generally not used in studies of environmental stress.

Ecological: The code goby is a small predator, and is
one of the dominant species of shallow grass flats
(Hildebrand 1 954, Springer and Woodbum 1 960, Hoese
and Jones 1964, Zimmerman 1 969, Odum 1971). It is
also considered the most abundant goby in the saline
waters of northern Florida Bay (Tabb and Manning
1961).

Range

Overall: This species is found from the Chesapeake
Bay to Florida and throughout the Gulf of Mexico to the
Yucatan (Ginsburg 1933, Dawson 1969, Schwartz
1971, Hoese and Moore 1977). It is abundant in
shallow sea grass meadows especially in Florida and

northern Gulf of Mexico (Ginsburg 1933, Hildebrand
1954, Springer and Woodburn 1960).

Within Study Area: The code goby is common along
the Gulf coast from the Laguna Madre, Texas to Florida
Bay, Florida in shallow grass flats (Ginsburg 1933,
Hildebrand 1 954, Bohlke and Robins 1 968, Zimmerman
1969). It is considered absent from many of the low-
salinity estuaries of Louisiana (Czapla et al. 1991)
(Table 5.41).

Life Mode

This is a demersal species (Zimmerman 1969, Odum
1 971 ). Observations from different activity studies are
inconclusive, possibly due to the difficulty in collecting
this "secretive" resident of sea grass beds (Springer
and Woodburn 1960, Hoese and Jones 1964,
Zimmerman 1969, Krull 1976, Shipp 1986).

Habitat

Type: The habitat preferences of early life stages are
well known. Eggs have been found attached to shells
or sponges (Fritzsche 1978). Adults are primarily
collected from oligohaline to euhaline estuaries in
shallow water seagrasses, particularly Thalassia, but
also in Diplanthera, Ruppia, Halodule, and Cymodocea
grass beds. Adults are also found in bays, beach
ponds, oyster reefs, river sloughs, rocky channels, and
among mangrove roots (Breder 1942, Bailey et al.
1954, Hildebrand 1954, Kilby 1955, Springer and
Woodburn 1960, Springer and McErlean 1961, Tabb
and Manning 1 961 , Tabb et al. 1 962, Hoese and Jones
1964, Hoese 1965, Zimmerman 1969, Bonin 1977,
Hoese and Moore 1 977, Huh 1 984, Thayer et al. 1 987).
They are uncommon in deeper waters, with most
collections occurring at depths of a few centimeters to

315

Code goby, continued

Table 5.41 . Relative abundance of code goby in
Gulf of Mexico estuaries (from Volume /).

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

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 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

6.1 m (Breder 1942, Springer and Woodburn 1960,
Springer and McErlean 1961, Huh 1984). They are
found in association with pigfish {Orthopristis
chrysopteris), gulf pipefish (Syngnathus scovelli), and
dusky pipefish (Syngnathus floridae) (Hildebrand 1 954).

Substrate: Adults are primarily collected over muddy
bottoms of grass beds, but they also occur over sand
bottoms with covering vegetation such as mangrove
roots or seagrasses (Thalassia). They can also occur
over bottoms of sand, and mud with shell (Bailey et al.
1 954, Kilby 1 955, Tabb and Manning 1 961 , Tabb et al.
1962, Dawson 1969, Wang and Raney 1971,
Zimmerman 1969, Lee et al. 1980, Huh 1984).

Physical/Chemical Characteristics:
Temperature: Egg development has been observed
from 15.5° to 18.5°C (Fritzsche 1978). Temperature
tolerances are unknown for both larvae and juveniles.
Adults have been collected over a range of 10.0° to
34.8°C (Bailey et al. 1954, Reid 1954, Springer and
Woodburn 1960, Dawson 1966, Wang and Raney
1971, Bonin 1977, Fritzsche 1978). Peak abundance
has been reported to occur at an average temperature
of 23°C (Krull 1976, Bonin 1977).

Salinity: Salinity tolerances of eggs, larvae, and juve-
niles are not well known. Adults have been found over
a wide salinity range, occurring from 2.1 to 37.6%o.
They are reported to prefer intermediate to moderately
high salinities ranging from 22 to 32%o (Bailey et al.
1954, Reid 1954, Kilby 1955, Gunter 1956, Springer
and Woodburn 1 960, Tabb et al. 1 962, Dawson 1 966,
Wang and Raney 1971, Bonin 1977, Lee et al. 1980,
Loftus and Kushlan 1987).

Movements and Migrations: The code goby is thought
to reside throughout the year in seagrass beds
(Zimmerman 1 969), with no reported migratory behav-
ior. Some movements associated with temperature
fluctuations have been observed (Huh 1984, Krull
1 976). Studies in Florida bays report movement of this
fish to shore during the coldest months, and then back
out into bays as temperatures increase (Kilby 1955,
Reid 1954).

Reproduction

Mode: This species has separate male and female
sexes (gonochoristic). Fertilization is external, and
development is oviparous.

Spawning: Spawning has been observed throughout
the year in the Gulf of Mexico particularly during late
spring and early summer with a peak reported in May
(Dawson 1966, Dokken et al. 1984, Huh 1984). This
extended spawning season may be due to the short
mild winters found in the study area coupled with

316

Code goby, continued

frequent warming periods. Variations in spawning
behavior are possibly due to the different temperature
patterns found throughout the range of this species
(Dawson 1966, Dokken et al. 1984). Temperatures
greater than 19°C may be necessary for spawning to
occur, but repression has been noted at temperatures
greater than 30°C in Florida populations (Springer and
McErlean 1 961 , Dokken et al. 1 984). Spawning occurs
during falling salinities (<45%o) in Texas (Dokken et al.
1984) and from 19.2 to 23.0%o in Florida populations
(Springer and McErlean 1961). Eggs are usually
attached to the underside of shells or sponges and are
guarded by males (Breder 1942).

Fecundity: Both left and right ovaries ripen equally with
approximately equal numbers of eggs. In Tampa Bay,
a 27 mm standard length (SL) female was reported with
349 eggs in the right ovary, and 346 eggs in its left. The
number of eggs produced appears to be related to the
size of the female with 56 per ovary observed in a 15
mm SL fish and 397 per ovary observed in a 28 mm SL
fish. Eggs are apparently spawned in toto, but two
spawnings per season are considered possible
(Springer and McErlean 1961).

Growth and Development

Egg Size and Embryonic Development: Ovarian eggs
are transparent until a diameter of 0.102-0.136 mm is
attained, and then they become more opaque. Eggs
are ripe at 0.476-0.782 mm (Springer and McErlean
1961). Fertilized eggs are elliptical, opaque, slightly
yellowish with a clear envelope. Their length varies
from 1 .30-1 .40 mm in June to 1 .55-1 .70 mm in March,
while width varies from 0.50 mm in June to 0.60-0.70
mm in March (Breder 1 942, Fritzsche 1 978). Eggs are
fastened by filaments attached to the chorion at the
germinal end, and have an opaque, slightly yellowish
yolk with a widely variable number of oil droplets
scattered over its surface (Springer and McErlean
1961, Fritzsche 1978). In fertilized eggs of unknown
age collected on March 14, near Charlotte Harbor,
Florida, the head was large and prominent 22.25 hours
after collection. After another 26.25 hours, the embryo
formed, somites were visible after another 41. 25 hours,
and the heart was visible and beating after another
27.5 hours. Total observation period covered 117.25
hours with the embryos dying before hatching (Breder
1942, Fritzsche 1978).

Age and Size of Larvae: Little information is available
on the larval stage of this species.

Juvenile Size Range: Described specimens of juvenile
code goby are 5.6 to 8.78 mm SL (Shropshire 1932,
Springer and McErlean 1961). All fin elements are
present by 5.6-8.5 mm SL (Springer and McErlean).
Increase in pigmentation, appearance of tubular nos-

trils and a series of rows of papillae on lower jaw,
forehead, and cheeks occur by 8.78 mm SL (Shrop-
shire 1932). Growth rate is moderate with 0-class fish
reaching 26.9 to 28.4 mm total length (TL) by the end
oftheirfirstyear(SpringerandWoodburn 1960, Dawson
1966).

Age and Size of Adults: Young of the year can achieve
sexual maturity when only a few months old. Minimum
sizes noted for sexually mature adults are 13.1 mmTL
and 14.6 mm SL for females (Springer and McErlean
1961, Dawson 1966), and 16.5 mm TL for males
(Fritzsche 1978). Maximum reported sizes are 31.5
mm TL for females (Dawson 1 966), and 44 mm SL for
males with males being larger on the average than
females (Springer and McErlean 1961). Maximum
reported size for this species is 55.5 mm TL or 45.0 mm
SL for an unsexed fish (Ginsburg 1933). The code
goby is considered an annual fish with very few indi-
viduals living over one year, although some males are
reported to live up to 2 years (Springer and McErlean
1961).

Food and Feeding

Trophic mode: The code goby is a small benthic
predator.

Food Items: Code gobies feed principally on amphi-
pods, mysids, chironomid larvae, decapod shrimp,
copepods, isopods, gamarids, cladocerans, ostracods,
small molluscs, and some algal filaments and detritus
when 15 to 35 mm SL (Reid 1954, Springer and
Woodburn 1 960, Odum 1 971 ). Smaller individuals, 7-
15 mm SL, have been found to eat harpacticoid
copepods, juvenile mysids, cumaceans, and many
penate diatoms (Odum 1971).

Biological Interactions

Predation: Reported predators include inshore lizardfish
(Synodus foetens), spotted seatrout, and gray snapper
(Springer and Woodburn 1960, Tabb and Manning
1961, Thayer et al. 1987).

Factors Influencing Populations: The size and abun-
dance of seagrass beds and drift algae biomass may
affect the abundance of the code goby by providing
both habitat and refuge for this species (Kulczycki et al.
1981).

317

Code goby, continued

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macro-fauna occurring in Turtle grass {Thalassia
testudinumKorug) surrounding Ransom Island in Red-
fish Bay, Texas. M.S. thesis, Texas A&l Univ., Kingsville,
TX, 129 p.

319

Spanish mackerel

Scomberomorus maculatus
Adult

10 cm

(fromGoode 1884)

Common Name: Spanish mackerel

Scientific Name: Scomberomorus maculatus

Other Common Names: mackerel, horse mackerel,

bay mackerel, spotted mackerel, Spaniard, spotted

cybium (Earll 1883, Pew 1966); thazard tachete

(French); carite pintado, sierra (Spanish) (Fischer 1 978,

NOAA1985).

Classification (Robins et al. 1991)

Phylum: Chordata

Class: Osteichthyes

Order: Perciformes

Family: Scombridae

Value

Commercial: This is a prized commercial species.
Most fishing occurs along the south Atlantic coast from
Cape Hatteras, North Carolina to the Florida Keys, and
in the eastern Gulf of Mexico from the Florida Keys to
the Mississippi River delta (Moe 1972, Dwinell and
Futch 1973, Powell 1975, Trent and Anthony 1978,
Sutherland and Fable 1 980, Johnson 1 981 , Fable et al.
1987, Palko et al. 1987). The fishery is seasonal, and
peak harvest periods vary in different areas of the Gulf
(Collette and Nauen 1983, Klima pers. comm.). Com-
mercial landings for the Gulf of Mexico in 1992 were
804.2 mt with 1 52.4 mt landed 0 to 4.8 km offshore.and
651 .8 mt landed 4.8 to 322 km offshore (Newlin 1 993).
Florida produced nearly 90% of the commercial catch
with landings totaling about 709 mt in 1 992. The peak
harvest in Florida has historically been from December
through February (Klima pers. comm.). However, the
commercial fishery in Florida has been practically
eliminated by a recent net ban (DeVries pers. comm.).
Landings in Alabama, Mississippi, and Louisiana for
1 992 were 66.7, 2.3, and 26.3 mt respectively (Newlin
1993), while annual landings in Texas have been less

than 907 kg (Dwinell and Futch 1973, Hoese and
Moore 1977, Trent and Anthony 1978). The principal
commercial gear used has been run-around gill nets
with some hook and line catches, but in Mississippi
most of the commercial harvest comes as bycatch from
shrimping trawls in offshore waters (Klima 1 959, Trent
and Anthony 1 978, Sutherland and Fable 1 980, Benson
1982). In U.S. federal waters of the Gulf of Mexico,
regulations have been enacted pertaining to minimum
size, gear type, harvest quotas, and closed season
(GMFMC 1 996a). Most of the catch is marketed fresh,
frozen, or smoked (Collette and Nauen 1983, Shipp
1986). The flesh becomes rancid very quickly, and is
often treated with antioxidants and EDTA to prolong
shelf life.

Recreational: Spanish mackerel is an important game
fish along the U.S. Atlantic and Gulf of Mexico coasts.
It is prized for both its fighting ability and high food
quality (Klima 1959, Moe 1972, Dwinell and Futch
1 973, Powell 1 975, Hoese and Moore 1 977, Trent and
Anthony 1978, Sutherland and Fable 1980, Johnson
1981, Benson 1982, Fable et al. 1987). The most
productive recreational fishing area is along the Atlan-
tic coast from Cape Hatteras, North Carolina to the
Florida Keys, followed by the eastern Gulf of Mexico
from the Florida Keys to the Mississippi River, and then
from the Mississippi River to the Mexican border in
waters <4.8 km from shore. The principal fishing
method is hook and line while trolling or drifting, with
some catches in Florida made from boats, piers, jetties,
and beaches by casting, live bait fishing, jigging, and
drift fishing (Trent and Anthony 1978, Palko et al.
1987). Regulations for recreational fishing of this
species vary among the Gulf states (GSMFC 1993).
Minimum length and bag limits have also been enacted

320

Spanish mackerel, continued

Table 5.42. Relative abundance of Spanish mack-
erel 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

Apalachicola Bay

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 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

in U.S. federal waters of the Gulf of Mexico (GMFMC
1996b).

Indicator of Environmental Stress This species, along
with others, has been used to study heavy metal
contamination in marine fish. No levels of contamina-
tion were found that might constitute a threat to public
health (Meaburn 1978).

Ecological: This is a high trophic level, pelagic carni-
vore that feeds predominantly on fish in the marine
environment and in higher salinity, seaward portions of
estuaries (Benson 1982, Shipp 1986, NOAA 1993).

Range

Overall: This species is distributed along the western
Atlantic coast from Nova Scotia to Florida, along the
north coast of Cuba, and in the Gulf of Mexico from the
Florida Keys to the Yucatan Peninsula, Mexico (Erdman
1949, Powell 1975, Collette and Russo 1978, Collette
et al. 1978, Sutherland and Fable 1980, Collette and
Nauen 1 983, Shipp 1 986, Fable et al. 1 987, Gilhen and
McAllister 1 989). This is a summer visitor all along the
U.S. Atlantic coast as far north as New York, and
occurs less regularly along the southern coasts of New
England. It occasionally strays into colder waters
northward with captures of single fish reported from
Maine (Bigelow and Schroeder 1 953) and Nova Scotia
(Gilhen and McAllister 1989), but is most common in
subtropical and tropical coastal waters (Shipp 1986).
The center of abundance appears to be the Atlantic
coast of Florida (Dwinell and Futch 1973, Trent and
Anthony 1978, Fable et al. 1987). Populations of the
Gulf of Mexico and Atlantic may comprise two distinct
stocks (Johnson 1981, Skow and Chittenden 1981).

Within Study Area: The Spanish mackerel occurs from
the Florida Keys to the Rio Grande River (Table 5.42),
but is generally less common west of the Mississippi
River delta (Dwinell and Futch 1973, Collette and
Russo 1978, Fable et al. 1987).

Life Mode

The Spanish mackerel is an epipelagic and neritic
species and is often found in large schools (Higgins
and Lord 1926, Franks et al. 1972, Moe 1972, Christ-
mas and Waller 1 973, Powell 1 975, Rice 1 979, Benson
1982, Collette and Nauen 1983). Schools occur near
the water surface and, in the past, have covered
several square kilometers of area (Berrien and Finan
1 977). Activity and feeding appear to be evenly distrib-
uted between day and night (Tabb and Manning 1 961 ,
Zimmerman 1969, Moe 1972).

321

Spanish mackerel, continued

Habitat

Type:

Larvae occur most frequently offshore over the inner
continental shelf (1 2 to 34 m) in polyhaline to euhaline
waters (Wollam 1 970, McEachran and Finucane 1 978).
Abundance appears to be greatest in the northeastern
Gulf of Mexico (Lukens 1989). The most frequent
collections of larvae are made in water depths ranging
5.0 to 1 2.8 m, but larvae have been found in waters as
deep as 91 .5 m (Dwinell and Futch 1 973, Lyczkowski-
Shultz 1987).

Juveniles are found offshore and in beach surf. They
are sometimes reported from lower river outflows,
estuaries, sounds, bays, lagoons, and marshes, but
are generally not considered estuarine dependent
(Gunter 1945, Baughman 1947, Reid 1956a, Reid
1 956b, Zimmerman 1 969, Swingle 1 971 , Franks et al.

1972, Christmas and Waller 1973, Dwinell and Futch

1973, McEachran and Finucane 1978, Benson 1982,
Lukens 1989). They occur in oligohaline to euhaline
salinities, but appear to prefer euhaline water (Gunter
1945, Reid 1956, Franks et al. 1972, Christmas and
Waller 1 973, Dwinell and Futch 1 973, McEachran and
Finucane 1978). Most juveniles are collected from
waters 9.1 to 18.3 m deep, but collection depths can
range from the surface down to 91 .5 m (Franks et al.
1972, Dwinell and Futch 1973).

Adults are typically found offshore in neritic waters and
along coastal areas, usually very near barrier islands
and particularly their passes. They frequent shallower
depths and are seldom found deeper than 73.2 m (Earll
1883, Higgins and Lord 1926, Gunter 1945, Klima
1 959, Springerand Woodburn 1 960, Pew 1 966, Franks
et al. 1 972, Christmas and Waller 1 973, Rice 1 979). In
Florida, most inhabit coral reefs, off-shore currents,
and tide rips of clear tropical waters (Klima 1 959, Moe
1 972). Adults are seldom taken near river mouths or in
low salinity waters (Earll 1883), but one study from
Florida reports that they enter tidal rivers on flood tides
to feed on shrimp migrating seaward (Tabb and Man-
ning 1961). One fish has also been captured in the tidal
portion of a south Texas river (Bryan 1 971 ). They will
enter estuaries and bays, especially high salinity ar-
eas, during seasonal migrations, but are considered
rare and infrequent in many Gulf estuaries (Reid 195.6a,
Simmons 1957, Klima 1959, Parker 1965, Pew 1966,
Zimmerman 1969, Powell 1975, Benson 1982). They
are collected from salinities ranging from oligohaline to
euhaline with an apparent preference for euhaline
waters (Gunter 1 945, Reid 1 956a, Franks et al. 1 972,
Christmas and Waller 1973, Dwinell and Futch 1973,
McEachran and Finucane 1978).

Substrate: Juvenile mackerel seem to prefer clean
sand (Benson 1982), but substrate preferences for
other life stages of this pelagic fish have not been
reported.

Physical/Chemical Characteristics:
Temperature: This species prefers warmer waters,
and generally favors water temperatures 20° C or
greater (Shipp 1986). Larvae are found in the north-
western Gulf of Mexico from 19.6° to 29.8°C, and are
reported to prefer ranges of 21 ° to 27°C and 20.2° to
29.8°C (McEachran and Finucane 1 978, Benson 1 982).
They have been found in Florida from 28.4° to 30.5°C
(Dwinell and Futch 1973). Juveniles occur over a
range from 10° to 34.9°C (Gunter 1945, Perret et al.
1971, Wang and Raney 1971, Franks et al. 1972,
Christmas and Waller 1973, Dwinell and Futch 1973,
Perret and Caillouet 1974). The occasional appear-
ances of juveniles in Texas bays seem to be limited to
waters above 24°C (Zimmerman 1969), and they are
most abundant in samples at 25°C or higher (Perret et
al. 1971). Adults have been reported occurring over a
range of 21 ° to 32°C and to seldom enter waters below
1 8°C (Earll 1 883, Gunter 1 945, Springerand Woodburn
1960, Fritzsche1978).

Salinity: Salinities at larvae collection sites range from
28.3 to 37.4%o (Dwinell and Futch 1973, McEachran
and Finucane 1978, Benson 1982), and larvae are
most abundant at 28.3 to 34.4%o (McEachran and
Finucane 1 978). Juveniles can be found over a salinity
range of 0.21 to 37.4%o (Kelley 1965, Dugas 1970,
Bryan 1971, Perret et al. 1971, Swingle 1971, Wang
and Raney 1971, Franks et al. 1972, Christmas and
Waller 1973, Dwinell and Futch 1973, Perret and
Caillouet 1974), but occur most often in salinities
exceeding 10%o (Perret et al. 1971, Swingle 1971,
Benson 1982). Adults are generally associated with
marine salinities (Fritzsche 1 978), and reported salini-
ties range from 31.1 to 36.7%0 in Texas and Florida
(Gunter 1 945, Springer and Woodburn 1 960).

Movements and Migrations: This species migrates
seasonally. Its movements are along coastlines and
can be extensive, depending on water temperature
(Powell 1975, Moe 1972, Benson 1982, Collette and
Nauen 1983). Three major migration routes are hy-
pothesized: along the Mexican-Texan coast; along the
northern Gulf of Mexico coast and west coast of Florida;
and along the Atlantic (Johnson 1 981 ). In the eastern
Gulf, these fish move northward in the Gulf during late
winter and spring appearing off the central west coast
of Florida about the first of April (Moe 1 972, Sutherland
and Fable 1 980). Movements continue westward and
terminate along the northern Gulf coast. During fall,
migration is back southward to the wintering grounds in
south Florida waters (Moe 1 972, Sutherland and Fable

322

Spanish mackerel, continued

1 980). In the western Gulf, spring migration apparently
occurs as schools move to the north and east along the
coast (Wollam 1970, Benson 1982). This movement
also terminates in the northern Gulf of Mexico, with
abundant numbers off Alabama and Mississippi from
April through late fall, and in Texas from March to
October with an August peak (Gunter 1945, Springer
and Pirson 1 958, Pew 1 966, Franks et al. 1 972, Helser
and Malvestuto 1987). Movement in the fall is back
southward beginning about September (Gunter 1945,
Wollam 1 970, Benson 1 982). The wintering ground for
both eastern and western fish is believed to be in the
Campeche-Yucatan area (Sutherland and Fable 1 980,
Johnson 1 981 ). Fish are caught throughout the year,
indicating that some fish move offshore during cold
weather and do not migrate (Perret et al. 1971, Moe
1972, Christmas and Waller 1973).

Reproduction

Mode: This species has separate male and female
sexes (gonochoristic). Fertilization is external, by
broadcast of milt and roe into the water column (Berrien
and Finan 1977). Development is oviparous.

Spawning: The onset of spawning probably varies with
latitude, with fish in the northern part of the range
ripening later than those in the southern part (Berrien
and Finan 1977). Active and ripening oocytes are
present throughout the spring and summer (April
through mid-September) in Florida, with spawning
probably occurring May through September (Klima
1959, Moe 1972, Powell 1975, Berrien and Finan
1977, Schmidt et al. 1993). In the western Gulf of
Mexico, developing gonads are seen May through
September when water temperatures reach 22°C, and
spent individuals become increasingly abundant from
July to September (Earll 1883, Hoese 1965, Wollam
1970, Rice 1979, Finucane and Collins 1986,
Lyczkowski-Shultz 1 987). Some spawning may occur
in April or October and spawning throughout the year
is considered possible in Florida (Finucane and Collins
1986). Based on the presence of larval Spanish
mackerel in the northern Gulf of Mexico, it can be
inferred that spawning occurs April through October,
with a peak from August to September (Ditty 1986,
Ditty etal. 1988). Spawningcanoccurdayornightwith
multiple spawnings possible over a prolonged season
(Ryder 1 882, Klima 1 959, Powell 1 975, Benson 1 982,
Collette and Nauen 1983, Lyczkowski-Shultz 1987).
Spawning takes place in inner shelf waters probably in
the vicinity of barrier islands and passes at depths of 1 2
to 1 8 m. Spawning also occurs occasionally over the
middle and outer shelf, possibly as deep as 200 m
(McEachran and Finucane 1978, Benson 1982).
Spawning temperatures range from 21 to 31 °C, but are
usually in excess of 22°C and seldom below 18°C
(Hoese 1965, Benson 1982). Salinities for spawning

range from 30 to 36.5%, (Hoese 1965, Benson 1982).
Peak spawning seems to be during June through
August with the eastern and northeastern Gulf of
Mexico probably being the most important spawning
area (Klima 1 959, Moe 1 972, McEachran and Finucane
1978). There is some evidence of spawning near
Mississippi Sound (Lukens 1989).

Fecundity: This species is a fractional spawner (Berrien
and Finan 1977). Fish in south Florida are sexually
mature in their second or third year of life according to
otolith annulations counted in one study (Klima 1 959).
Another investigator considers these observations to
have been overestimated by one year; therefore, fish
less than 1 year old may have been mature (Powell
1 975). Many class I fish observed had ripe oocytes, but
examinations made of these fish during the spawning
season suggested eggs were not advanced enough to
be spawned that season. Spanish mackerel are prob-
ably not fully mature until age class II with the bulk of the
spawning population composed of class III and older
fish (Powell 1975, Lukens 1989). Fecundity increases
with length and weight (Earll 1883, Godcharles and
Murphy 1986). Estimates of fecundity are 1.5 million
for a 2.7 kg female while a 0.45 kg fish had an estimated
300,000 eggs (Earll 1883). Fecundity ranges from
100,000 to 2,000,000 eggs for fish ranging 295 to
>2,415 g and with fork lengths (FL) of 312 mm to 626
mm (Berrien and Finan 1977, Finucane and Collins
1986).

Growth and Development

Egg Size and Embryonic Development: Development
is oviparous. Eggs are buoyant, transparent and
smooth with a single oil droplet 0.25 mm in diameter.
They are round in shape and 0.91 -1 .1 5 mm in diameter
(Earll 1883, Ryder 1882, Benson 1982). The perivi-
telline space is approximately 0.1 mm across. Hatch-
ing is primarily during summer months and occurs
about 25 hours after fertilization at 26°C (McEachran
and Finucane 1978, Fritzsche 1978, Godcharles and
Murphy 1986).

Age and Size of Larvae: The larval stage lasts from
2.56 to 1 3 mm TL. Larvae are 2.56 mm TL or 2.0 mm
standard length (SL) at hatching and attain 2.8 SL
within 3 days (Fritzsche 1 978, McEachran and Finucane
1978). Other investigators have reported preserved
specimens ranging in size from 1.6 to 11.8 mm SL
(Richardson and McEachran 1 981 , Lyczkowski-Shultz
1 987). The yolk sac is absorbed by 3. 1 8 mm TL on the
fourth day (Wollam 1970, Fritzsche 1978). Larval
growth rate has been estimated as 1.15 mm/day
(DeVries et al. 1990).

323

Spanish mackerel, continued

Juvenile Size Range: Juveniles range from 1 3.5 to 225
mm TL in size. Eight preopercular spines are present
at 1 4 mm TL, and two at 22-25 mm TL (Fritzsche 1 978,
Lukens 1989). Females mature at lengths ranging
from 250 mm to 450 mm FL, while males can reach
maturity anywhere from 209 mm to 336 mm FL. The
longest immature fish were a 320 mm FL female and a
340 mm FL male. Some age class 0 fish reach sexual
maturity, but 100% maturity of a cohort is not reached
until at least age class II for males and age class III for
females. The majority of spawning fish is probably
made up of age class III fish >350 mm FL (Powell 1 975,
Helser and Malvestuto 1 987, Lukens 1 989, Schmidt et
al. 1993).

Age and Size of Adults: The average weight range of
fish taken by recreational and commercial anglers is
0.7-1.8 kg, with most larger fish averaging about 4-5
kg. The maximum reported weight is 1 1 kg (Pew 1 966,
Meaburn 1978, Benson 1982). Growth rates among
adults are rapid until year 5 in females and year 6 in
males, and then slow appreciably (Fable et al. 1987).
Females reach up to 802 mm FL and grow faster than
males which have been recorded up to 723 mm FL
(Collette and Ftusso 1978, Fable et al. 1987). Maxi-
mum life spans reported for Spanish mackerel have
been 1 1 years for females and 7 years for males
(Collette and Russo 1978, Fable et al. 1987, Schmidt
etal. 1993). However, males have been reported up to
10 years in Florida (DeVries pers. comm.). It is be-
lieved that females generally live longer than males
(Fable et al. 1 987). Von Bertalanffy growth equations
have been developed from otolith samples for male
and female Spanish mackerel (Helser and Malvestuto
1987, Schmidt etal. 1993).

Food and Feeding

Trophic mode: The Spanish mackerel is a fast moving
surface feeder in pelagic waters, and is primarily pis-
civorous (Finucane et al. 1990).

such as nudibranch larvae, amphipods, penaeid shrimp,
and euphausiids. Older juveniles and adults prefer
various small fish which can form up to 100% of their
diet. Juveniles and small adults (70-420 mm FL) prey
chiefly on various anchovies, and also herrings and
wrasses. Larger adults (525-675 mm FL) consume
other fishes mainly herrings and jacks (Saloman and
Naughton 1983, Lukens 1989, Finucane et al. 1990).
Spanish mackerel probably become more opportunis-
tic as they increase in size with food items varying
according to availability. Other animals such as squid,
crabs, and shrimp can become important diet compo-
nents at this point (Saloman and Naughton 1 983, Pew
1966, Rice 1979, Benson 1982). Fish that are preyed
on include: sciaenids, alewife, flatfish, menhaden,
cutlassfish (Trichiurus lepturus), scaled sardine
(Harengula jaguna), Atlantic thread herring
(Opisthonema oglinum), Spanish sardine (Sardinela
aurita), striped muilet and other mullet, needlefish
(Strongylura spp.), jacks (Caranx spp.), lookdown
(Selene vomer), inland silverside (Menidia beryllina)
and other silversides, striped anchovy (Anchoa
hepsetus) and other anchovies, butterfish (Peprilus
triacanthus), northern harvestfish (Peprilus paru), spa-
defish (Chaetodipterus faber), silver perch, and round
scad (Decapturas punctatus) (Earll 1883, Kemp 1949,
Breuer 1949, Knapp 1949, Miles 1949, Simmons and
Breuer 1964, Pew 1966, Rice 1979, Naughton and
Saloman 1981, Lukens 1989, Finucane et al. 1990).
Anchovies may be more important in juvenile diets
because of their smaller size being more easily swal-
lowed by the smaller juvenile mackerel mouth parts
(Naughton and Saloman 1981). Important inverte-
brate components include various penaeid shrimp
(white, pink, and brown shrimp), sealice (Squilla sp.),
grass shrimp (Palaemonetes sp.), sand shrimp
(Crangon sp.), squid (Loligo sp.), swimming crabs
(Portunidae), and mud crabs (Xanthidae) (Kemp 1 949,
Miles 1949, Naughton and Saloman 1981, Saloman
and Naughton 1983).

Food Items: The Spanish mackerel is a fast moving
voracious predator. They usually feed in loose schools,
and feed on schooling prey that occupy the same
pelagic habitat, including herrings and sardines
(Clupeidae), jacks (Carangidae), anchovies
(Engraulidae), and squids (Saloman and Naughton
1 983, Shipp 1 986 Lukens 1 989, Finucane et al. 1 990).
Shallow continental shelf waters are the favored feed-
ing areas, but the mackerel will occasionally forage in
the lower, saltier portions of estuaries. Larvae and post
larvae are principally piscivorous (Finucane etal. 1990).
Larval jacks, herrings, and anchovies occur frequently
in larval mackerel stomach contents. Other fish spe-
cies consumed by mackerel larvae include:
lanternfishes, flatfishes, and puffers. Fish eggs were
also found to be a food item as well as invertebrates

Biological Interactions

Predation: This species is a major prey item of sharks,
including bull shark, dusky shark (C.obscurus), smooth
hammerhead (Sphyrna zygaem), porbeagle (Lamna
nasas), tiger shark (Galeocerdo cuvierf); and also of
dolphins (Tursiops truncatus) (Kemp 1949, Lukens
1989).

Factors Influencing Populations: A potential exists for
damage of eggs and larvae present near the water
surface by oil pollution (Lukens 1 989). The popularity
of this species as a food and game fish may have
contributed to a decline in its abundance.

324

Spanish mackerel, continued

Personal communications

Klima, Edward F. NOAA National Marine Fisheries
Service, Galveston, TX.

Collette, B.B., J.L. Russo, and L.A. Zavala-Camin
1977. Scomberomorus brasiliensis, a new species of
Spanish mackerel in the western Atlantic. Fish. Bull.,
U.S. 76:273-280.

DeVries, Douglas A. NOAA National Marine Fisheries
Service, Panama City, FL.

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325

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328

Gulf flounder

Paralichthys albigutta
Adult

5 cm

(from Fischer 1978)

Common Name: gulf flounder

Scientific Name: Paralichthys albigutta

Other Common Names: sand flounder, flounder, fluke,

cardeau trois yeux (French), and lenguado tresojos

(Spanish) (Ginsburg 1 952, Fischer 1 978, NOAA 1 985,

Gilbert 1986).

Classification (Robins et al. 1991)

Phylum: Chordata

Class: Osteichthyes

Order: Pleuronectiformes

Family: Bothidae

Value

Commercial: In 1992, U.S. commercial fishery land-
ings for flounders were fifth in quantity and eighth in
value (O'Bannon 1994). Flounder landings in the
Atlantic and Gulf for the group that includes this spe-
cies totaled 7,098 mt and was valued at nearly 23
million dollars. The Gulf flounder contributes a varying
amount to this commercial catch recorded as "fluke",
depending on location. This is an important commer-
cial species in Florida, but much less so in the other
Gulf coastal states (Swingle 1 971 , Fischer 1 978, Benson
1 982, NOAA 1 985, Van Voorhees et al. 1 992). In 1 992,
approximately 77.6 mt of flounders were landed in
Florida with a value of over $175,000 (Newlin 1993).
Most fish are taken by otter trawls, fyke nets, weirs, fish
traps, pound nets, gill nets, trammel nets, beach seines,
and gigging (Ginsburg 1952, Fischer 1978, Manooch
1984). Gill and trammel nets were outlawed in Texas
waters in 1988. Many are taken incidentally by com-
mercial shrimpers (Fischer 1978, Benson 1982).
Catches are marketed as eitherfresh orfrozen product
(Fischer 1978, NOAA 1985).

Recreational: Gulf flounder are more important as a
game fish than as a commercial species, although
most anglers do not preferentially seek them. Fish are
taken by bottom fishing with hook and line, and by
gigging in shallow waters at night (Warlen 1975,
Manooch 1984). In 1991, reported recreational land-
ings of gulf flounder for the Gulf coast states (except
Texas) totaled 284,000 fish, most of which were landed
in Florida (241,000 fish) (Van Voorhees et al. 1992).
Actual sport catches were probably greater as a large
number of unidentified "flounders" were also reported
during the same period. Minimum size and daily bag
limits may vary among the Gulf states (GSMFC 1 993).

Indicator of Environmental Stress: Gulf flounder are
not typically used in studies of environmental stress.

Ecological: Although this species is not especially
abundant in most areas, it is important as a demersal
carnivore.

Range

Overall: The gulf flounder is found from Oregon Inlet,
North Carolina (Powell pers. comm.), to the waters off
Padre Island, Texas, including the upper Laguna Madre.
It is also reported from the western Bahamas (Hoese
and Moore 1 977, Shipp 1 986). It is not known to occur
in the coastal waters of Mexico (NOAA 1985).

Within Study Area: In U.S. Gulf of Mexico estuaries,
gulf flounder occur from Florida Bay to Mississippi
Sound, but not in the low salinity estuaries of Louisiana
(Table 5.43). They occur in small numbers in Texas
westward to the Rio Grande (Topp and Hoff 1972,
Shipp 1986).

329

Gulf flounder, continued

Table 5.43. Relative abundance of gulf flounder
31 Gulf of Mexico estuaries (from Volume 1).

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

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 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 and larvae are planktonic. Postlarvae become
demersal after metamorphosis. Juveniles and adults
are demersal (Bond 1979).

Habitat

Type: Eggs are marine and neritic. Larvae are marine
and neritic, becoming estuarine. Juveniles and adults
are estuarine and marine. Adults are neritic, and are
found offshore as far as the mid-continental shelf in
depths up to 50 m. They prefer shallow waters (<30 m)
of bays and the nearshore Gulf of Mexico (Ginsburg
1952, Miller 1964, Powell 1974, Stokes 1977, Benson
1982). It rarely enters areas with reduced salinities,
and never enters freshwater (Gilbert 1986). It is
considered probable that gulf flounder in excess of 2 or
3 years of age reside exclusively in the Gulf (Stokes
1977).

Substrate: Gulf flounder typically occur over hard sand
bottoms. Juveniles have been reported in association
with seagrass beds (Ginsburg 1952, Reid 1954,
Springer and Woodburn 1960, Stokes 1977, Fischer
1978, Hoese and Moore 1977).

Physical/Chemical Characteristics
Temperature: The reported range of temperatures
where the Gulf flounder occurs is 8.3° to 32.5° C (Reid
1 954, Springer and Woodburn 1 960, Wang and Raney
1971, Stokes 1977).

Salinity: This fish ranges from the seawater zone to the
seaward end of the mixing zone of estuaries. It
reportedly prefers higher salinities (>20%o) (Gunter
1945, Powell and Schwartz 1977). Collections have
been reported from salinities ranging from 6 to 60%o
(Reid 1954, Simmons 1957, Springer and Woodburn
1960, Williams and Deubler 1968, Wang and Raney
1 971 , Topp and Hoff 1 972, Powell 1 974, Stokes 1 977,
Powell and Schwartz 1977). Williams and Deubler
(1 968) reported that postlarvae are found in estuarine
habitats at salinities >22%0. In North Carolina, juveniles
were collected in salinities ranging from 6 to 35%o, but
the majority occurred above 20%o (Powell and Schwartz
1977).

Turbidity: Stokes (1 977) stated that Gulf flounder were
not present in waters with turbidity greater than 65
Jackson Turbidity Units (JTU).

Migrations and Movements: Adults migrate out of the
estuaries to neritic offshore waters during fall and
winterto spawn. Timing of the movement is associated
with the advent of falling water temperatures. Stokes
(1 977) reported that the Gulf flounder begins to move
offshore when water temperatures fall from 23° to
14.1 °C, and that peak immigration of juveniles coin-

330

Gulf flounder, continued

cided with temperatures around 16°C. Beginning in
late spring to early summer, the adults and juveniles
return to the estuarine habitats (Reid 1954, Springer
and Woodburn 1960, Stokes 1977).

Reproduction

Mode: This species has separate male and female
sexes (gonochoristic). Fertilization is external, by
broadcast of milt and roe into the water column. The
eggs float at or near the surface of the water, and
development is oviparous (Gilbert 1986).

Spawning: Spawning occurs during late fall and early
winter (November to February) in marine neritic waters
(Ginsburg 1952, Reid 1954, Springer and Woodburn
1960, Topp and Hoff 1972, Stokes 1977). Larvae of
Paralichthys species are known to occur in the north-
ern Gulf of Mexico from September through April, with
a peak from December to February (Ditty et al. 1 988).

Fecundity: Little information on gulf flounder fecundity
is available (Gilbert 1986).

Growth and Development

Egg Size and Embryonic Development: Eggs are
spawned oviparously. Eggs are spherical, with an
approximate mean diameter of 0.87 mm, and one oil
globule with an approximate diameter of 0.18 mm
(Powell and Henley 1995).

Age and Size of Larvae: Recently-hatched larvae are
approximately 2.0 mm notochord length (NL) (Powell
and Henley 1 995). Larvae appear in the eastern Gulf
of Mexico from December through early March (Reid
1 954, Topp and Hoff 1 972). The standard length (SL)
of postlarvae ranges 7-10 mm SL, and averages 8.4
mm (Deubler 1958). A full complement of fin rays is
present by approximately 8.5 mm SL (Powell and
Henley 1 995). In general, at any given size, larval gulf
flounder (P. albigutta) are further developed than south-
ern flounder (P. lethostigma) (Powell and Henley 1 995).
There are differences in pigmentation patterns be-
tween the two species, but these may be difficult to
discern with field-collected specimens.

Juvenile Size Range: The growth rate of juveniles up to
a size of 50 mm appears to be rapid (Reid 1 954), and
size-at-age is highly variable for this species (Fitzhugh
pers. comm.). Stokes (1977) calculated total length
(TL) growth rates of males and females. Males during
their first year (age 0) ranged in size from 10 to >300
mm TL, and had an upper weight of 1 50 g, while those
in their second year (age I) ranged 221-350 mm in size
with an upper weight of 270 g. In first year females
sizes ranged from 10 to 400 mm TL, with an upper
weight of 270 g. Maturation occurs around 1 45 mm SL
for females (Topp and Hoff 1 972), and 50% of females

are mature by age I (Fitzhugh pers. comm.).

Age and Size of Adults: Stokes (1977) noted ripe
females were two years old and stated that females
grow more rapidly and attain greater sizes than males.
Females during their second year range in size from
291 to>400mm, and have an upper weight of 0.57 kg.
Third year females have a size range of 361-420 mm
TL and an upper weight of 1.01 kg. The maximum
reported size is 71 0 mm TL with a weight of 5 kg (Topp
and Hoff 1972). Actual life spans probably exceed
three years (Manooch 1 984). Females may live up to
seven years, and males up to four years (Fitzhugh
pers. comm.). Length-weight relationships for North
Carolina gulf flounder have been determined by Safrit
and Schwartz (1988).

Food and Feeding

Trophic mode: The gulf flounder is a benthic carnivore.

Food Items: Small juveniles, 10-50 mm TL, feed pre-
dominantly on invertebrates; mostly crustaceans, es-
pecially mysids and amphipods. Juveniles above 45
mm consume both small fish and crustaceans, includ-
ing penaeid shrimp and portunid crabs. At 100-150
mm TL they are primarily piscivorous. Noted prey
include menhaden, bay anchovy and other anchovy
species, inshore lizardfish (Synodusfoetens), longnose
killifish (Fundulus similis), pipefishes, grunts, pigfish
{Orthopristis chrysoptera), pinfish, Atlantic croaker,
mullets, and code goby (Gobiosoma robustum) as well
as a number of unidentified forms (Reid 1 954, Springer
and Woodburn 1960, Topp and Hoff 1972, Stokes
1977, Benson 1982).

Biological Interactions

Predation: Information on predation of flounder is scarce.
Juveniles are probably the most susceptible to preda-
tion due to their smaller size. Known and suspected
species that prey on flounder species in the Gulf of
Mexico are: tigershark (Ga/eocerdo cuwer),gafftopsail
catfish (Bagre marinus), inshore lizard fish (Synodus
foetens), various searobins (family Triglidae), various
sculpins (family Cottidae),jewfish (Ep/nep/ie/us/fa/ara),
and larger-sized southern flounder (Kemp 1 949, Miles
1949, Dieneretal. 1974, Tanaka et al. 1989).

Factors Influencing Populations: Paralichthys
lethostigma and P. albigutta are very difficult to distin-
guish from each other during the larval stage (Woolcott
et al. 1968). Early stages are often summarized as
"Paralichthys species" (King 1 971 , Ditty et al. 1 988) or
just "southern flounder" (Stokes 1 977). Adult southern
flounder generally outnumber gulf flounder in the north-
ern Gulf of Mexico, and catches containing the two
species are not usually separated. This makes catch
data forthe two species difficult to analyze. The shrimp

331

Gulf flounder, continued

fishery unintentionally catches large numbers of juve-
nile flounder, almost all of which are discarded (Gunter
1945, Matlock 1991). This reduces the number of
sexually immature fish available for recruitment into
the population and fishery. The gulf flounder appearto
be restricted to the higher salinity portions of estuaries
(>20%o), unlike the southern flounder (Gilbert 1986,
Nelson etal. 1992).

Personal communications

Fitzhugh, Gary R. NOAA National Marine Fisheries
Service, Panama City, FL.

Powell, Allyn B. NOAA National Marine Fisheries
Service, Beaufort, NC.

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Diener, R. A., A. Inglis, and G.B.Adams. 1974. Stom-
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waters, a Texas estuarine area. Contrib. Mar. Sci.
18:7-17.

Ditty, J.G.,G.G.Zieske, and R.F.Shaw. 1988. Season-
ality and depth distribution of larval fishes in the north-
ern Gulf of Mexico above latitude 26°00'N. Fish. Bull.,
U.S. 86(4):81 1-823.

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.

Gilbert, C.R. 1986. Species Profiles: Life histories and
environmental requirements of coastal fishes and in-
vertebrates (South Florida) southern, gulf and summer
flounders. U.S. Fish Wildl. Serv. Biol. Rep., 82(1 1 .54),
27 p.

Ginsburg.l. 1952. Flounders of the genus Paralichthys
and related genera in American waters. Fish. Bull.,
U.S. 52:267-351.

Miles, D.W. 1949. A study of the food habits of the
fishes of the Aransas Bay area. M.S. thesis, Univ.
Houston, Houston, TX, 70 p.

Miller, J. M. 1964. A trawl survey of the shallow gulf
fishes near Port Aransas, Texas. M.S. thesis, Univ.
Texas, Austin, TX, 102 p.

Newlin.K. (ed.). 1993. Fishing Trends and Conditions
in The Southeast Region, 1992. NOAA Tech. Memo.
NMFS-SEFSC-332, 88 p.

O'Bannon, B.K. (ed.). 1994. Fisheries of the United
States, 1993. Current Fisheries Statistics No. 9300.
NOAA/NMFS Fisheries Statistics Div., Silver Spring,
MD, 121 p.

332

Gulf flounder, continued

Powell, A. B. 1974. Biology of the summer flounder,
Paralichthys dentatus, in Pamlico Sound and adjacent
waters, with comments on P. lethostigma and P.
albigutta. M.S. thesis. Univ. North Carolina, Chapel
Hill, NC.

Powell, A.B., and T. Henley. 1995. Egg and larval
development of laboratory-reared gulf flounder,
Paralichthys albigutta, and southern flounder, P.
lethostigma. Fish. Bull., U.S. 93:504-515.

Powell, A.B., and F.J. Schwartz 1977. Distribution of
Paralichthid flounders (Bothidae: Paralichthys) in North
Carolina estuaries. Chesapeake Sci. 18:334-339.

Reid, G.K. 1954. An ecological study of the Gulf of
Mexico fishes in the vicinity of Cedar Key, Florida. Bull.
Mar. Sci. 4:1-94.

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. No. 20. American Fisheries Society, Bethesda,
MD, 183 p.

Safrit, G.W., and F.J. Schwartz. 1988. Length weight
relationships for gulf founder, Paralichthys albigutta,
from North Carolina. Fish. Bull., U.S. 86(4):832-833.

Topp, R.W., and F.H. Hoff, Jr. 1972. Flatfishes
(Pleuronectiformes). Mem. Hourglass Cruises Vol. 4;
Part 2, 135 p.

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.

Warlen, S.M. 1975. Night stalking flounder in the
ocean surf. Mar. Fish. Rev. 37(9):27-30.

Williams, A.B., and E.E. Deubler. 1968. Ten year
study of mero-plankton in North Carolina estuaries:
Assessment of environmental factors and sampling
success among bothid flounders and penaeid shrimps.
Chesapeake Sci. 9:27-41.

Woolcott, W.S., C. Beirne, and W.M. Hall, Jr. 1968.
Description and comparative osteology of the young of
three species of flounders, genus Paralichthys. Chesa-
peake Sci. 9:109-120.

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

Simmons, E.G. 1957. An ecological survey of the
upper Laguna Madre of Texas Publ. Inst. Mar. Sci,
Univ. Texas 4:157-202

Springer, V.G., and D.K.Woodburn. 1960. An ecologi-
cal study of the fishes of the Tampa Bay area. Fla.
Board Cons. Mar. Res. Lab. Prof. Pap. Ser. 1:1-104.

Swingle, H.A. 1971. Biology of Alabama estuarine
areas-cooperative Gulf of Mexico estuarine inventory.
Ala. Mar. Res. Bull. 5:1-123.

Tanaka, M., T. Goto, M. Tomiyama, and H. Sudo.
1989. Immigration, settlement and mortality of floun-
der (Paralichthys olivaceus) larvae and juveniles in a
nursery ground, Shijiki Bay, Japan. Netherlands J. Sea
Res. 24:57-67.

333

Southern flounder

Paralichthys lethostigma
Adult

10 cm

(from Fischer 1978)

Common Name: southern flounder
Scientific Name: Paralichthys lethostigma
Other Common Names: mud flounder, doormat, hali-
but (Reagan and Wingo 1985); southern large floun-
der, fluke (Gilbert 1 986), cardeau de Floride (French),
lenguado de Florida (Spanish) (Fischer 1978, NOAA
1985),saddleblanket.
Classification (Robins et al. 1991)
Phylum: Chordata
Class: Osteichthyes
Order: Pleuronectiformes
Family: Bothidae

Value

Commercial: In 1992, U.S. commercial fishery land-
ings for flounders were fifth in quantity and eighth in
value (O'Bannon 1994). Flounder landings in the
Atlantic and Gulf for the group that includes this spe-
cies totaled 7,098 mt and were valued at nearly 23
million dollars. The southern flounder is fished com-
mercially throughout its range. Landing data are often
grouped with two other species (Paralichthys albigutta
and P. dentatus), making the relative importance of
each species difficult to ascertain. In Texas, southern
flounder account for most of the flounder caught. In the
northwestern Gulf of Mexico, most of the southern
flounder catch is landed incidentally in commercial
shrimp trawls. In 1992, approximately 451.8 mt of
flounders were landed in Texas and Louisiana with a
value of over $1 .2 million. Most fish are taken by otter
trawls, fyke nets, weirs, fish traps, pound nets, gill nets,
trammel nets, beach seines, trotlines, and gigging
(Ginsburg 1 952, Fischer 1 978, Manooch 1 984, Gilbert
1986, Matlock 1991, Newlin 1993, Hightower pers.
comm.). Gill and trammel nets were outlawed in Texas
waters in 1988. This fish is marketed mostly as fresh

product and is used primarily as table fare (Fischer
1978, Matlock 1991).

Recreational: The southern flounder is a popular rec-
reational species throughout its range (Shipp 1978).
Fish are taken by hook and line and by gigging in
shallow waters at night (Warlen 1975, Manooch 1984).
In 1991, recreational landings of southern flounder
along the G ulf coast states (except Texas) was 1 02,000
fish in Florida, 126,00 fish in Mississippi, and 471,000
fish in Louisiana (Van Voorhees et al. 1992). Esti-
mated recreational landings along the Texas coast,
calculated from data provided by Osborn and Fergusson
(1 987), averaged 94,258 kg from 1 983 to 1 986. Actual
sport catches were probably greater as a large number
of unidentified "flounders" were also reported during
the same period. Minimum size limits and daily bag
limits vary among the Gulf states (GSMFC 1993).

Indicator of Environmental Stress: This species is not
typically used in studies of environmental stress.

Ecological: Southern flounder are important predators
in estuarine ecosystems, feeding on small crustaceans
as juveniles, and becoming piscivorous as they grow
(Diener et al. 1974, Fitzhugh et al. 1996). Southern
flounder have been introduced into freshwater reser-
voirs of Texas in an experimental effort to control
problem fish populations and improve recreational
fishing (Lasswell et al. 1981).

Range

Overall: On the U.S. east coast, this species ranges
from Albermarle Sound, North Carolina, southward to
the Loxahatchee River, Florida. In the Gulf of Mexico,
it is present from Florida to Texas and northern Mexico

334

Southern flounder, continued

Table 5.44. Relative abundance of southern floun-
der in 31 Gulf of Mexico estuaries (from Volume /).

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

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 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

(Hoese and Moore 1977, Lee et al. 1980, Manooch
1984). It is not common in the southwest Florida
estuaries, and its range is apparently not continuous
around the southern tip of Florida.

Within Study Area: The southern flounder is distributed
throughout the coastal and estuarine habitats of the
U.S. Gulf of Mexico from Florida to Texas, and is
particularly abundant along the Texas coast (Ginsburg
1 952, Hoese and Moore 1 977, Manooch 1 984, Reagan
and Wingo 1985, Gilbert 1986) (Table 5.44).

Life Mode

Eggs are planktonic, buoyant, and float at or near the
surface (Arnold et al. 1 977). Larvae are planktonic and
can be found throughout the water column (King 1 971 ).
King (1971) has shown no difference between night
and day larval distributions. Juveniles and adults are
demersal, and they are more active at night (Powell
and Schwartz 1977).

Habitat

Type: Eggs are marine, occurring in neritic waters.
Early larval stages are marine, while postlarvae be-
come estuarine. Juveniles and adults are estuarine,
riverine and marine in coastal areas usually depending
on size of the flounder and hydrography (Fischer 1 978,
Lee et al. 1 980, Shipp 1 986). Southern flounder can be
found at depths up to about 40 m (Fischer 1978).

Substrate: Southern flounder frequent fine unconsoli-
dated substrates of clayey silts and organic-rich muddy
sands (Fischer 1978, Lee et al. 1980, Gilbert 1986,
Powell and Schwartz 1977). Juvenile fish have been
reported in association with seagrass beds (Stokes
1 977). In marshes they appear to be equally abundant
in vegetated and non-vegetated habitats (Minello et al.
1989). Juveniles and adults are associated with fine
sediments in flooded Spartina marshes, seagrasses
and muddy substrates while in estuaries (Stokes 1 977,
Wardetal. 1980).

Physical/Chemical Characteristics
Temperature: This is a eurythermal species. The
reported temperature range for eggs is 9.1 to 22.9°C
with 14°C preferred; and for larvae 2 to 30°C with a
preferred range of 20 to 25°C (Ward et al. 1980).
Juveniles are apparently widespread over water tem-
peratures ranging from 2 to 31 .2° C. Adults are found
in temperatures ranging from 7 to 32°C and show a
preference for temperature between 14 and 22° C
(Pineda 1 975, Ward et al. 1 980, Prentice 1 989). Young
southern flounder appear to be more tolerant of cold
than adults, and both groups show increasing toler-
ance to cold as salinity is increased (Prentice 1989).
Temperature appears to have a greater effect on
growth than salinity (Peters 1 971 ). Adults in salt water

335

Southern flounder, continued

will cease feeding below 7.3°C (Prentice 1989).

Salinity: The southern flounder is euryhaline. Larvae
have been found in salinities of 10 to 30%o (Ward et al.
1980). Salinities in which juveniles have been col-
lected range from 2 to 60%o, but they apparently prefer
waters that are 2 to 37%> (Ward et al. 1980). Adult
southern flounder have been collected in waters with
salinities that range from 0 to 60%o, with a preference
for 20 to 30%o (Ward et al. 1980). Adults, while in
estuaries, prefer the mixing and tidal fresh zones
(Gunter1945).

Dissolved Oxygen (DO): Deubler and Posner (1963)
demonstrated avoidance behavior in juvenile southern
flounder when dissolved oxygen levels fell below 3.7
mg/l, for temperatures 6.1°, 14.4°, and 25.3° C.

Migrations and Movements: Adults emigrate from the
estuaries to spawn in deeper offshore waters during fall
and winter. The migrations coincide with falling water
temperatures (Gunter 1945, Kelley 1965, Shepard
1986). Males usually leave estuaries for the Gulf
earlier than females (Stokes 1 977). Hoese and Moore
(1977) report severe "northers" will result in mass
emigrations, while moderate to warm winters cause
flounders to leave dispersed over longer periods of
time. Stokes (1 977) indicates that only those emigrat-
ing are gravid. Some juveniles and adults overwinter
in the deeper holes and channels of bays and estuaries
(Ogren and Brusher 1977, Stokes 1977, Ward et al.
1980). Postlarvae and juveniles immigrate into the
bays and estuaries from late winter to spring. Williams
and Deubler (1968) indicated postlarval immigration
correlates with lunar phase. In addition, adults migrate
back into estuarine habitats throughout spring and into
summer. Juveniles tend to migrate to low salinity
water, often going up into river channels (Williams and
Deubler 1968, Pineda 1975). Stokes (1977) reported
that local movements within and between estuaries
rarely exceeded 18 km.

Reproduction

Mode: The southern flounder has separate male and
female sexes (gonochoristic). Fertilization is external,
by broadcast of milt and roe into the water column. The
eggs are buoyant, and float at or near the water surface
(Arnold et al. 1977, Gilbert 1986). Development is
oviparous.

Spawning: Spawning occurs during late fall and early
winter in marine neritic waters (Sabins and Truesdale
1974, Reagan and Wingo 1985, Gilbert 1986) with a
December peak reported in Louisiana (Shepard 1 986).
In laboratory studies, Arnold etal. (1977) reported that
males attended females for a period of 3 weeks prior to
spawning. At spawning, the females would swim to the

surface and release eggs which were immediately
fertilized by the attending male. Larvae of Paralichthys
species are known to occur in the northern Gulf of
Mexico from Septemberthrough April, with a peakfrom
December to February (Ditty et al. 1988).

Fecundity: Arnold et al. (1 977) reported that 1 3 spawns
from 3 pairs of southern flounder produced a total of
120,000 eggs.

Growth and Development

Egg Size and Embryonic Development: Eggs are
spawned oviparously. Eggs are spherical, with an
approximate mean diameter of 0.91 to 0.92 mm, and
one oil globule with an approximate diameter of 0.18
mm (Henderson-Arzapalo et al. 1988, Powell and
Henley 1995). In a laboratory study, spawned eggs
hatched in 61 -76 hours at 1 7°C and 28%o (Arnold et al.
1977).

Age and Size of Larvae: Recently-hatched larvae are
approximately 2.1 mm notochord length (NL) (Powell
and Henley 1 995). Larvae, 40 to 46 days old and 8 to
1 1 mm long, begin metamorphosis into the postlarval
stage. Transformation is complete by about 50 days
(Arnold et al. 1 977). Optimal growth in early postlarvae
occurs at high salinities (Deubler 1960); while ad-
vanced postlarvae grow better at salinities of 5 to 1 5%o
(Stickney and White 1973). In general, at any given
size, larval gulf flounder (P. albigutta) are further devel-
oped than southern flounder (P. lethostigma) (Powell
and Henley 1995). There are differences in pigmenta-
tion patterns between the two species, but these may
be difficult to discern with field-collected specimens.

Juvenile Size Range: The minimum size of settled
juveniles overlaps that of the postlarvae in some cases
(10-15 mm TL). Peters (1 971 ) concluded P. lethostigma
grows faster at warm temperatures and low salinities.
Size-at-age is highly variable for this species, and age
0 year classes are known to develop bimodal length-
frequency distributions (Fitzhugh et al. 1996). This
may be the result of faster growth after an ontogenetic
shift to piscivory at a size of 70 to 180 mm TL. Size
estimated after the first and second year of growth is
201 and 250 mm TL for male, 225 and 364 mm TL for
female southern flounder (Stokes 1977). Immature
fish >170 mm TL have distinctive gonads and matura-
tion occurs by the second year in fish ranging from 341
to 560 mm TL. Maturity occurred in one study at 243
mm TL for females and 1 70 mm TL for males (Shepard
1985).

Age and Size of Adults: Stokes (1977) reported a 3 to
5 year life span for this species. Females appear to
grow faster, live longer, and attain greater size than
males (Stokes 1977). The largest individuals reported

336

Southern flounder, continued

range from 595 to 910 mm TL(Ginsburg 1952, Hoese
and Moore 1977, Stokes 1977).

Food and Feeding

Trophic Mode: The southern flounder is carnivorous
during all life stages. Larvae feed on pelagic zooplank-
ton, while juveniles and adults feed on crustaceans,
and benthic and pelagic fishes (Gilbert 1986). Young
southern flounder are dominant predators in Texas
estuaries on small brown shrimp during the spring
(Minelloetal. 1989).

Food Items: Larvae feed on zooplankton (Peters 1 971 ).
Small crustaceans, particularly mysids, but also grass
shrimp, penaeid shrimp, amphipods, and crabs make
up the diet of small juveniles (10-160 mm TL) (Diener
et al. 1974, Stokes 1977, Minello et al. 1989). Larger
juveniles and adults are basically piscivorous, feeding
on small benthic and pelagic fishes; but, shrimp, crabs
and polychaetes are also utilized to a lesser extent
(Darnell 1958, Fox and White 1969, Powell 1974,
Stokes 1977, Powell and Schwartz 1979, Overstreet
and Heard 1982). In a North Carolina study, inverte-
brate prey included the mysids Mysidopsis bigelowi
and Neomysis americana, and fish prey included bay
anchovy, spot, and croaker (Fitzhughetal. 1996). The
ontogenetic shift to piscivory occurred as fish grew
from 70 to 180mmTL.

Biological Interactions

Predation: Information on predation of flounder is scarce.
Larvae and juveniles are probably the most suscep-
tible to predation due to their smaller size. Known and
suspected species that prey on flounder species in the
Gulf of Mexico are: tiger shark (Galeocerdo cuvier),
gafttopsail catfish (Bagre marinus), inshore lizard fish
(Synodus foetens), various searobins (family Triglidae),
various sculpins (family Cottidae), jewf ish (Epinephelus
itaiara), and larger-sized southern flounder (Kemp
1949, Miles 1949, Diener et al. 1974, Tanaka et al.
1989).

Factors Influencing Populations: Southern flounder
and gulf flounder are very difficult to distinguish from
each other during early life stages (Woolcott et al.
1968). Early stages are often summarized as
"Paralichthys species" (King 1971) or just "southern
flounder" (Stokes 1 977). Adult southern flounder gen-
erally outnumber gulf flounder in the northern Gulf of
Mexico, and catches containing the two species are
not usually separated. This makes catch data for the
two species very hard to analyze. The shrimp fishery
unintentionally catches large numbers of juvenile floun-
der, almost all of which are discarded (Gunter 1945,
Matlock 1991). This reduces the number of sexually
immature fish available for recruitment into the fishery.

Personal Communications

Fitzhugh, Gary R. NOAA National Marine Fisheries
Service, Panama City, FL.

Hightower, Margot. NOAA National Marine Fisheries
Service, Galveston, TX.

Powell, Allyn B. NOAA National Marine Fisheries
Service, Beaufort, NC.

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339

Glossary

ABYSSAL ZONE— Ocean bottom at depths between
4,000 and 6,000 m.

AQUACULTURE— The rearing of aquatic (marine or
freshwater) vertebrates, invertebrates, or algae, to be
harvested for commercial or subsistence purposes.
See MARICULTURE.

ABYSSOPELAGIC— Living in the water column at
depths between 4,000 and 6,000 m; the abyssopelagic
zone.

ADDUCTOR MUSCLE— A muscle that pulls a part of
the body toward the median axis of the body. In bivalve
molluscs, this muscle is used to close the shell halves
and hold them together.

ADHESIVE — Sticky and tending to adhere; e.g., adhe-
sive eggs.

AGE-GROUP — A term used to designate year-classes
in fishes; a division date of January 1 is used in the
northern hemisphere. See YOUNG-OF-YEAR, YEAR-
LING, and TWO-YEAR-OLD.

AGGREGATION — A group of individuals of the same
species gathered in the same place but not socially
organized or engaged in cooperative behavior. Com-
pare to SCHOOL.

ALGAE — A collective, or general name, applied to a
number of primarily aquatic, photosynthetic groups
(taxa) of plants and plant-like protists. They range in
size from single cells to large, multicellular forms like
the giant kelps. They are the food base for almost all
marine animals. Important taxa are the dinoflagellates
(division Pyrrophyta), diatoms (div. Chrysophyta), green
algae (div. Chlorophyta), brown algae (div.
Phaeophyta), and red algae (div. Rhodophyta).
Cyanobacteria are often called blue-green algae, al-
though blue-green bacteria is a preferable term.

AMBICOASTAL — Used in reference to enclosed bay
systems to denote both estuarine and marine coasts.

AMPHIPODA— An order of laterally compressed crus-
taceans with thoracic gills, no carapace, and similar
body segments. Although most are <1 cm long, they
are an important component of zooplankton and benthic
invertebrate communities. A few species are parasitic.

ANADROMOUS — Life cycle where an organism spends
most of its life in the sea, and migrates to fresh water to
spawn. Compare to CATADROMOUS.

ANNULUS — Annual growth mark on a scale, bone
(e.g., otolith), or other hard structure.

ANTHROPOGENIC— Refers to the effects of human
activities.

AREAL — Refers to a measure of area.

ASCIDIAN — A tunicate (class Ascidiacea) that has a
generalized sac-like, cellulose body and is usually
attached to the substratum.

AUTOTROPH — An organism using sunlight or inor-
ganic chemical reactions as a source of energy to
synthesize organic matter. Compare with
PHOTOTROPH and HETEROTROPH.

BATCH SPAWN — Discontinuous episodes of spawn-
ing, either of gametes or offspring. Individuals or
populations that release gametes or offspring with
greater continuity are serial or sequential spawners.

BATHYAL— The zone of ocean bottom at depths of
200 to 4,000 m, primarily on the continental slope and
rise.

BATHYMETRIC— Pertaining to depth measurement.
Also refers to a migration from waters of one depth to
another.

BATHYPELAGIC— Ocean depths from 1,000 to 4,000
m.

BENTHIC— Pertaining to the bottom of an ocean, lake,
or river. Also refers to sessile and crawling animals
which reside in or on the bottom.

BIGHT— An inward bend or bow in the coastline.

BIOMASS— The total mass of living tissues (wet or
dried) of an organism or collection of organisms of a
species ortrophic level, from a defined area or volume.

BIVALVIA— Bilaterally symmetrical molluscs (also re-
ferred to as Pelecypoda) that have two lateral calcare-
ous shells (valves) connected by a hinge ligament.
They are mostly sedentary filter feeders. This class
includes clams, oysters, scallops, and mussels.

BRANCHIAL — A structure or location on an organism
associated with the gills.

BROADCAST SPAWNER— Planktonicreleaseof float-
ing or sinking (demersal) gametes (eggs, sperm) or of
offspring. May be continuous or periodic in duration.
See BATCH SPAWN.

341

Glossary, continued.

BRYOZOA — Small moss-like colonial animals of the
phylum Bryozoa.

BUOYANT — Able to remain afloat in a liquid, or rise in
air or gas.

BYCATCH— See INCIDENTAL CATCH.

BYSSAL THREAD— A tuft of filament, chemically simi-
lar to silk, that attaches certain molluscs to substrates.

CALANOIDA — An order of free-living, largely plank-
tonic copepods with very long first antennae.

CALCAREOUS — Composed of calcium or calcium
carbonate.

CARAPACE — The hard exoskeletal covering of the
dorsal part of a crustacean.

CAR APACE Wl DTH— The total width of a crustacean's
carapace, often used as a standardized measurement
for crabs.

CARIBBEAN PROVINCE— A tropical marine zoogeo-
graphic province of the Atlantic continental shelf that
includes southern Floridaf rom Cape Canaveral around
to the Tampa Bay region, and the Central and South
American coast from near Tampico, Mexico to Ven-
ezuela.

CARNIVORE— An animal that feeds on the flesh of
other animals. See PARASITISM and PREDATION.

CAROLINIAN PROVINCE— A warm-temperate ma-
rine zoogeographic province of the Atlantic continental
shelf extending approximately from Cape Hatteras,
North Carolina southward to Cape Canaveral, Florida
on the U.S. east coast, and from Florida's Tampa Bay
region westward to Cape Rojo near Tampico, Mexico
on the Gulf coast.

CATADROMOUS — A life cycle in which an organism
lives most of its life in fresh water, but migrates to
saltwater to spawn. Compare to ANADROMOUS.

CERCARIA— A heart-shaped, tailed, larval stage of a
trematode (fluke) produced in a mollusc host, which is
released from the mollusc, sometimes then encysting,
and subsequently infecting a vertebrate host.

CESTODE — A parasitic, ribbon-like worm having no
intestinal canal; class Cestoda (e.g., tapeworms).

CHELAE — The forceps-like pincers in crustaceans.

CHELIPED — The large grasping claw of many crusta-
ceans.

CHEMOTAXIS — A response movement by an animal
either toward or away from a specific chemical stimu-
lus.

CHORDATA— A phylum of animals which includes the
subphyla Vertebrata, Cephalochordata, and
Urochordata. At some stage of their life cycles, these
organisms have pharyngeal gill slits, a notochord, and
a dorsal hollow nerve cord.

CHROMATOPHORE— A pigment cell or group of cells
which under the control of the nervous system can be
altered in shape or color.

CILIA — Hair-like processes of certain cells, often ca-
pable of rhythmic beating that can produce locomotion
or facilitate the movement of fluids.

CIRCULUS — A ringlike arrangement.

CIRRI — Flexible, thread-like tentacles or appendages
of certain organisms.

CLEITHRUM — clavicular elements of some fishes.

CLINE — A series of differing physical characteristics
within a species or population, reflecting gradients or
changes in the environment (e.g., body size or color).

COLONY — A group of organisms living in close prox-
imity. An invertebrate colony is a close association of
individuals of a species which are often mutually de-
pendent and in physical contact with each other. A
vertebrate colony is usually a group of individuals
brought together for breeding and rearing young.

COMMENSALISM — A relationship between two spe-
cies, where one species benefits without adversely
affecting the other.

COMMERCIAL VALUE— Economic attribute of mar-
ketablefishes, invertebrates, orothermarine resources,
the harvest, culture, processing, ordistribution of which
occur with sufficient financial return to support a spe-
cialized, expert and usually regulated trade.

COMMUNITY — A group of plants and animals living in
a specific region under relatively similar conditions.
Further definitions are often applied, such as the algal
community, the invertebrate community, the benthic
gastropod community, etc.

342

Glossary, continued.

COMPETITION — Two types exist - interspecific and
intraspecif ic. Interspecific competition exists when two
or more species use one or more limited resources
such as food, attachment sites, protective cover, or
dissolved ions. Intraspecific competition exists when
individuals of a single species compete for limited
resources needed for survival and reproduction. This
form of competition includes the same resources in-
volved in interspecific competition as well as mates and
territories. It is generally more intense than interspe-
cific competition because resource needs are essen-
tially identical among conspecifics. See NICHE.

CONGENER — Referring to other members of the same
genus.

CONSPECIFIC— Referring to other members of the
same species.

CONTINENTAL SHELF— The submerged continental
land mass, not usually deeper than 200 m. The shelf
may extend from a few miles off the coastline to several
hundred miles.

CTENOPHORA — A phylum of mostly marine animals
that have oval, jellylike bodies bearing eight rows of
comb-like plates that aid swimming (e.g., ctenophores
and comb jellies).

CYCLOPOIDA — An order of marine and freshwater,
planktonic and benthic copepods.

DECOMPOSERS— Bacteria and fungi that breakdown
dead organisms of all types to simple molecules and
ions.

DEMERSAL — Refers to swimming animals that live
near the bottom of an ocean, river, or lake. Often refers
to eggs that are denser than water and sink to the
bottom after being laid.

DEPOSIT FEEDER— An animal that ingests small
organisms, organic particles, and detritus from soft
sediments, or filters organisms and detritus from such
substrates.

DESICCATE— To dry completely.

CONTINENTAL SLOPE— The steeply sloping seabed
that connects the continental shelf and continental rise.

COPEPODA — A subclass of crustaceans with about
4,500 species, including several specialized parasitic
orders. The free-living species are small (one to
several mm) and have cylindrical bodies, one median
eye, and two long antennae. One order is planktonic
(Calanoida), one is benthic (Harpacticoida), and one
has both planktonic and benthic species (Cyclopoida).
In most species, the head appendages form a complex
apparatus used to sweep in and possibly filter prey
(especially algae). Thoracic appendages are used for
swimming or crawling on the bottom. One of the most
abundant groups of animals on earth, they are a major
component of aquatic food webs.

CREPUSCULAR— Relates to animals whose peak
activity is during the twilight hours of dawn and dusk.

CRUSTACEA— A large class of over 26,000 species of
mostly aquatic arthropods having five pairs of head
appendages, including laterally opposed jaw-like man-
dibles and two pairs of antennae. Most have well-
developed compound eyes and variously modified
two-branched body appendages. The body segments
are often differentiated into a thorax and an abdomen.
Some common members are crabs, shrimp, lobsters,
copepods, amphipods, isopods, and barnacles.

CTENIDIA — The comblike respiratory apparatus of
molluscs.

DETRITIVORE — An organism that eats small frag-
ments of partially decomposed organic material (detri-
tus) and its associated microflora. See DECOM-
POSER.

DETRITUS— Small pieces of dead and decomposing
plants and animals; detached and broken-down frag-
ments of an organic structure.

DIATOMS — Single-celled protistan algae of the class
Bacillariophyceae that have intricate siliceous shells
composed of two halves. They range in size from about
10 to 200 microns. Diatoms sometimes remain at-
tached after cellular divisions, forming chains or colo-
nies. These are the most numerous and important
groups of phytoplankters in the oceans, and form the
primary food base for marine ecosystems.

DIEL — Refers to a 24-hour activity cycle based on daily
periods of light and dark.

DIMORPHISM— A condition where a population has
two distinct physical forms (morphs). In sexual dimor-
phism, secondary sexual characteristics are markedly
different (e.g., size, color, and behavior).

DINOFLAGELLATE— A planktonic, photosynthetic,
unicellular algae that typically has two flagella, one
being in a groove around the cell and the other extend-
ing from the center of the cell.

343

Glossary, continued.

DIRECT DEVELOPMENT— See EMBRYONIC DE-
VELOPMENT.

EPIBENTHIC — Located on the bottom, as opposed to
in the bottom.

DISPERSAL — The spreading of individuals through-
out suitable habitat within or outside the population
range. In a more restricted sense, the movement of
young animals away from their point of origin to loca-
tions where they will live at maturity.

DISSOCHONCH— The adult shell secreted by newly-
settled clam larvae or plantigrades.

DISTRIBUTION— (1 ) A species distribution is the spa-
tial pattern of its population or populations over its
geographic range. See RANGE. (2) A population
depth distribution is the proportion or number of all
individuals, or those of various sizes or ages, at differ-
ent depth strata. (3) A population age distribution is the
proportions of individuals in various age classes. (4)
Within a population, individuals may be distributed
evenly, randomly, or in groups throughout suitable
habitat.

DIURNAL — Refers to daylight activities, or organisms
most active during daylight. See DIEL.

ECHINODERMATA— A phylum of radially-symmetri-
cal marine animals, possessing a water vascular sys-
tem, and a hard, spiny skeleton (e.g., sea stars, sea
urchins, and sand dollars).

ECTOPARASITE— A parasite that attacks (and usu-
ally attaches to) a host animal or plant on the outside.
Feeding periods and/or attachment time may be brief
compared to internal (endo-) parasites.

EELGRASS — Vascular flowering plants of the genus
Zostera that are adapted to living under water while
rooted in shallow sediments of bays and estuaries.

EMBRYONIC DEVELOPMENT— The increase in cell
number, body size, and complexity of organ systems
as an individual develops from a fertilized egg until
hatching or birth. In direct development, individuals at
birth or hatching are essentially miniatures of the
adults. In indirect development, newly hatched indi-
viduals differ greatly from the adult, and go through
periodic, major morphological changes (larval stages
and metamorphosis) before becoming a juvenile.

EMIGRATION— A movement out of an area by mem-
bers of a population. See IMMIGRATION.

ENDEMIC — Refers to a species or taxonomic group
that is native to a particular geographical region.

EPIDERMAL — Refers to an animal's surface or outer
layer of skin.

EPIFAUNA — Animals living on the surface of a sub-
strate.

EPIPELAGIC — The upper sunlit zone of oceanic water
where phytoplankton live and organic production takes
place (approximately the top 200 m). SeeEUPHOTIC.

EPIPHYTIC — Refers to organisms which live on the
surface of a plant (e.g., mosses growing on trees).

EPIPODAL — A structure or location associated with
the leg or foot; typically refers to arthropod anatomy.

ESCARPMENT— A steep slope in topography, as in a
cliff or along the continental slope.

ESTUARY — A semi-enclosed body of water with an
open connection to the sea. Typically there is a mixing
of sea and fresh water, and the influx of nutrients from
both sources results in high productivity.

EUHALINE— A category in the Venice system of es-
tuarine salinity classification; water with salinity of 30 to
40 parts per thousand (%o).

EUPHOTIC— Refers to the upper surface zone of a
water body where light penetrates and phytoplankton
(algae) carry out photosynthesis. See EPIPELAGIC.

EURYHALINE— Refers to an organism that is tolerant
of a wide range of salinities.

EURYTHERMAL— Refers to an organism that is toler-
ant of a wide range of temperatures.

EXTANT — Existing or living at the present time; not
extinct.

FAUNA — All of the animal species in a specified re-
gion.

FECUNDITY— The potential of an organism to pro-
duce offspring (measured as the number of gametes).
See REPRODUCTIVE POTENTIAL.

FILTER FEEDER— Any organism that filters small
animals, plants, and detritus from water or fine sedi-
ments forfood. Organs usedforfiltering include gills in
clams and oysters, baleen in whales, and specialized
appendages in crustaceans and marine worms.

344

Glossary, continued.

FINGERLING— Refers to a small juvenile fish that is
about 100 mm long.

FLAGELLATE — Refers to cells that have motility or-
ganelles or microorganisms that possess one or more
flagella used for locomotion.

FLORA — All of the plant species in a specified region,
including algae.

FOOD WEB (CHAIN)— The feeding relationships of
several to many species within a community in a given
area during a particular time period. Two broad types
are recognized: 1) grazing webs involving producers
(e.g., algae), herbivores (e.g., copepods), and various
combinations of carnivores and omnivores, and 2)
detritus webs involving scavengers, detritivores, and
decomposers that feed on the dead remains or organ-
isms from the grazing webs, as well as on their own
dead. A food chain refers to organisms on different
trophic levels, while a food web refers to a network of
interconnected food chains. See TROPHIC LEVEL.

FORAGE SPECIES — An organism that occurs in large
numbers and comprises a significant prey base for
predatory animals.

FORAMINIFERIDA — A chiefly marine order of proto-
zoans with mosty multichambered shells.

FORK LENGTH— distance from the tip of the snout to
the notch in the caudal fin.

GASTROPODA— The largest class of the Phylum
Mollusca. This group includes terrestrial snails and
slugs as well as aquatic species such as whelks,
turbans, limpets, conchs, abalones, and nudibranchs.
Most have external shells that are often spiraled (but
this has been lost or is reduced in some), and move on
a flat, undulating foot. They are mostly herbivorous
and scrape food with a radula, an organ analogous to
a tongue.

GASTRULATION — A stage in early embryogenesis
involving extensive cell movements, and in which the
gut cavity is formed and the three primary layers of the
animal body (ectoderm, mesoderm, and ectoderm) are
placed in position for further development.

GONOCHORISTIC— Refers to a species that has sepa-
rate sexes (i.e., male and female individuals).

GREGARIOUS — Living together in groups, as in
schools, flocks, or herds.

GROUNDFISH — Fish species that live on or near the
bottom, often called bottomfish.

GYNOGENESIS — Embryonic development of an egg
without genetic contribution by a sperm, although
activation by sperm during spawning is required for
development to proceed. Gynogenetic development is
known to occurwithin the unisexual Menidia clarkhubbsi,
an all-female clonal complex which produces diploid
eggs without genetic recombination.

FOULING — Occurs when large numbers of marine
plants and animals attach and grow on various sub-
merged structures (fioats, pipes, and pilings), often
interfering with their use. Fouling organisms include
algae, barnacles, mussels, bryozoans, and sponges.

FRESH WATER— Water that has a salt concentration
of 0.0-0.5 parts per thousand (%o).

FRY— Very young fish; may include both larvae and
young juveniles.

GYRE — An ocean current that follows a circular or
spiral path around an ocean basin, clockwise in the
northern hemisphere and counterclockwise in the south-
ern hemisphere.

HABITAT — The particular type of place where an or-
ganism lives within a more extensive area or range.
The habitat is characterized by its biological compo-
nents and/or physical features (e.g., sandy bottom of
the littoral zone, or in seagrass beds within 3 m of the
water surface).

GAMETE — A reproductive cell. When two gametes
unite they form an embryonic cell (zygote).

GAMETOGENESIS— The formation of gametes.

HAPLOSPORIDIAN— A unicellular protozoan occur-
ring in vertebrate and invertebrate hosts, often causing
disease.

HARPACTICOIDA— An order of mostly free-living,
marine and freshwater, bottom-dwelling copepods.
Some are planktonic, and many are interstitial.

345

Glossary, continued.

HATCHERY-REARED— Distinguished from naturally-
occurring recruits in population, these animals are
raised in captivity for the purposes of release or har-
vest.

HERBIVORE— An animal that feeds on plants (phy-
toplankton, large algae, or higher plants).

HERMAPHRODITIC— Refers to an organism having
both male and female sex organs on the same indi-
vidual.

HETEROTROPH-An organism (e.g. animals and fungi)
which obtains nourishment by consuming exogenous
organic matter. Compare to AUTOTROPH and
PHOTOTROPH.

ISOBATH — A contour mapping line that indicates a
specified constant depth.

ISOPODA— An order of about 4,000 species of dor-
soventrally compressed crustaceans that have ab-
dominal gills and similar abdominal and thoracic seg-
ments. Terrestrial pillbugs and thousands of benthic
marine species are included. Most species are scav-
engers and/or omnivores; a few are parasitic.

ISOTHERM — A contourline connecting points of equal
mean temperature for a given sampling period.

ITEROPAROUS— Refers to an organism that repro-
duces several times during its lifespan (i.e., does not
die after spawning); compare with SEMELPAROUS.

HYDROZOA— A class of the phylum Cnidaria. The
primary life stage is nonmotile and has a sac-like body
composed of two layers of cells and a mouth that opens
directly into the body cavity. A second life stage, the
free-living medusa, often resembles the common jelly-
fish.

JACKSON TURBIDITY UNITS— Measurement of tur-
bidity that relates levels of sample liquid in a graduated
cylinder to visible loss or merging of the image of a
standardized candle, viewed from the top of the col-
umn of water, with the lighted candle at a defined
distance from the bottom of the graduated column.

HYPERSALINE — Water with a salt concentration over
40 parts per thousand (%o).

JUVENILE— A young organism essentially similar to
an adult, but not sexually mature.

IMMIGRATION — A movement of individuals into a
new population or region. See EMIGRATION, MIGRA-
TION, and RECRUITMENT.

INCIDENTAL CATCH— Catch of a species that is not
intended to be caught by a fishery, but is taken along
with the species being sought; also known as
BYCATCH.

INDICATOR OF STRESS— Species whose presence
or absence in an environment has been documented
as correlated with polluted or unpolluted conditions, or
ecological stress of other forms.

INDIRECT DEVELOPMENT— See EMBRYONIC DE-
VELOPMENT.

KINESIS — A randomly directed movement by an ani-
mal in response to a sensory stimulus such as light,
heat, or touch. When the response is directed, it is
called a taxis. See CHEMOTAXIS.

LACUSTRINE — Pertaining to, or living in, lakes or
ponds.

LAGOON— A shallow pond or channel linked to the
ocean, but often separated by a reef or sandbar.

LARVA — An early developmental stage of an organ-
ism that is morphologically different from the juvenile or
adult form, intervening between the times of hatching
and of juvenile transformation. See EMBRYONIC
DEVELOPMENT.

INFAUNA — Animals living within a substrate.

INNER SHELF — The continental shelf extending from
the mean low tide line to a depth of 20 m.

INSTAR — The intermolt stage of a young arthropod.

INSULAR — Of or pertaining to an island or its charac-
teristics (i.e., isolated).

LATERAL LINE — A pressure sensory system located
in a line of pores under the skin on both sides of most
fishes. The system is connected indirectly with the
inner ear and senses water pressure changes due to
water movement (including sound waves).

LC50 — The measured concentration of a toxic sub-
stance that kills 50% of a group of test organisms within
a specified time period.

INTERTIDAL — The ocean or estuarine shore zone
exposed between high and low tides.

346

Glossary, continued.

LITTORAL — The shore area between the mean low
and high tide levels. Water zones in this area include
the littoral pelagic zone and the littoral benthic zone.

MACROALGAE — Relatively large, multicellular, non-
vascular marine or estuarine plants that float, drift
along the bottom, or have hold-fasts that anchor them
to sand, rock, or shell. Larger than and different from
planktonic or benthic unicellular (micro-) algae.

MANTLE — The upper fold of skin in molluscs that
encloses the gills and most of the body in a cavity
above the muscular foot. In squids and allies, the
mantle is below the body and behind the tentacles
(derived from the foot) due to the shift in the dorsal-
ventral axis. The mantle produces the shell in species
having them.

MANTLE LENGTH— The total length of the mantle of
squids and allies.

MARICULTURE — The rearing of marine vertebrates,
invertebrates, or algae, to be harvested for commercial
or subsistence purposes. See AQUACULTURE.

MARINE — Of, pertaining to, living in, or related to the
seas or oceans.

MARSH — Plant community developing on wet, but not
peaty, soil in either tidal or non-tidal areas.

MEAN LOWER LOW WATER (MLLW)— The arith-
metic mean of the lower low water heights of a mixed
tide over a specific 1 9-year Metonic cycle (the National
Tidal Datum Epoch). Only the lower low water of each
tidal day is included in the mean.

MEDUSA — A free-swimming sexual form in coelenter-
ates.

MEG ALOPA — The larval stage of a crab characterized
by an adult-like abdomen, thoracic appendages, and a
developed carapace; occurs afterthe zoeal stage. See
ZOEA.

MEIOFAUNA — Very small animals, usually < 0.5 mm
in diameter, and often planktonic.

MELANOPHORE — A pigment cell containing melanin
that is present in many animals and is responsible for
pigmentation and color changes.

MERISTIC — Refers to countable measurements of
segments or features such as vertebrae, fin rays, and
scale rows. Counts of these are used in population
comparisons and classifications.

MEROPLANKTON — Temporary plankton, consisting
of eggs and larvae; seasonal plankton.

MESOHALINE — A category in the Venice system of
estuarine salinity classification; water with salinity of 5
to 18 parts per thousand (%o).

MESOPELAGIC — Ocean zone of intermediate depths
from about 200-1 ,000 m below the surface, where light
penetration drops rapidly and ceases.

METAMORPHOSIS— Process of transforming from
one body form to another form during development
(e.g., tadpole changing to a frog). See EMBRYONIC
DEVELOPMENT.

METRIC TON (t)— A unit of mass or weight equal to
2,204.6 lb.

MIGRATION — Movement by a population orsubpopu-
lation from one location to another (often periodic or
seasonal, and over long distances). Vertical migra-
tions in the water column may be daily or seasonal
within the same area. Migrations between deep and
shallow areas are usually seasonal and related to
breeding. Many marine birds and mammals have
seasonal latitudinal migrations associated with breed-
ing. See EMIGRATION, IMMIGRATION, RANGE, and
RECRUITMENT.

MILT — The seminal fluid and sperm of male fish.

MIXING ZONE — The portion of an estuary with annual
depth-averaged salinities of 0.5 to 25 parts per thou-
sand (%o).

MOLLUSC — Any invertebrate of the phylum Mollusca,
unsegmented animals with a body consisting of a
ventral foot and a dorsal visceral mass. Most possess
a mantle which secretes a calcareous shell. Common
representatives are snails, mussels, clams, oysters,
and squid.

MOLT — The process of shedding and regrowing an
outer skeleton or covering at periodic intervals. Crus-
taceans and other arthropods molt their exoskeletons,
grow rapidly, and produce larger exoskeletons. Most
reptiles, birds, and mammals molt skin, feathers, and
fur, respectively.

MORPHOLOGY — The appearance, form, and struc-
ture of an organism.

MORPHOMETRICS— The study of comparative mor-
phological measurements.

347

Glossary, continued.

MORTALITY — Death rate expressed as a proportion
of a population or community of organisms. Mortality
is caused by a variety of sources, including predation,
disease, environmental conditions, etc.

MOTILE — Capable of or exhibiting movement or loco-
motion.

MUTUALISM — An interaction between two species
where both benefit. Some authorities consider true
mutualism to be obligatory for both species, while
mutually beneficial relationships that are not essential
for either species are classified as protocooperative.

NIDAMENTAL APPARATUS— A pair of glands that in
squids and their allies lies in the mantle cavity, with their
openings situated close to the oviductal outlet(s). This
structure secretes a mucinous material that aids in the
encapsulation of eggs as they leave the oviduct.

NOCTURNAL — Refers to night, or animals that are
active during the night.

NUDIBRANCH — A group of shell-less marine mol-
luscs commonly known as sea slugs.

OCEANIC — Living in or produced by the ocean.

NACREOUS MATERIAL— A calcareous, lustrous se-
cretion in the inner surface of the shell of many mol-
luscs. Foreign particles lodging between the inner
shell surface and mantle are covered by nacre, often
forming pearls.

NANOPLANKTON — Microscopic, planktonic organ-
isms smaller than 20 microns in diameter.

NATAL — Pertaining to birth or hatching.

NAUPLIUS — A free-swimming larva, the first stage in
the development of certain crustaceans such as
shrimps.

NEARSHORE — Consists of those waters extending
from the beach out to 6 fathoms of depth.

OCEANIC ZONE— Pelagic waters of the open ocean
beyond the continental shelf. See BATHYPELAGIC,
EPIPELAGIC, ABYSSOPELAGIC, MESOPELAGIC,
and NERITIC.

OLIGOHALINE — A category in the Venice system of
estuarine salinity classification; water with salinity of
0.5 to 5.0 parts per thousand (%0).

OMNIVORE — An animal that eats both plant and ani-
mal matter.

OOCYTES — The cells in ovaries that will mature into
eggs.

OSMOREGULATION— The maintenance of proper
water and electrolyte balance in an organism's body.

NEKTONIC— Refers to pelagic animals that are strong
swimmers, live above the substrate in the water col-
umn, and can move independently of currents.

OSTRACODS— A class of widely distributed marine
and freshwater crustaceans whose bodies are com-
pletely enclosed in a bivalve carapace.

NEMERTEA — A phylum of unsegmented, elongate
marine worms having a protrusible proboscis and no
body cavity, and live mostly in coastal mud or sand;
nemerteans.

NERITIC — An oceanic zone extending from the mean
low tide level to the edge of the continental shelf. See
INNER SHELF, LITTORAL, and OCEANIC ZONES.

NEUSTON — Organisms that live on or just under the
water surface, often dependent on surface tension for
support.

NICHE — The fundamental niche is the full range of
abiotic and biotic factors under which a species can live
and reproduce. The realized niche is the set of actual
conditions under which a species or a population of a
species exists, and is largely determined by interac-
tions with other species.

OTOLITHS— Small calcareous nodules located in the
inner ear of fishes used for sound reception and
equilibration. They are often used by biologists to
assess daily or seasonal growth increments.

OUT-MIGRATION— Movement of animals out of or
away from an area (e.g., juvenile sciaenids moving
from estuaries to the ocean).

OVIGEROUS— The condition of being ready to re-
lease mature eggs; egg-bearing.

OVIPAROUS— Refers to animals that produce eggs
that are laid and hatch externally. See OVOVIVIPA-
ROUS and VIVIPAROUS.

OVIPOSITION— The process of placing eggs on or in
specific places, as opposed to randomly dropping or
broadcasting them.

348

Glossary, continued.

OVOVIVIPAROUS— Refers to animals whose eggs
are fertilized, developed, and hatched inside the fe-
male, but receive no nourishment from her. See
OVIPAROUS and VIVIPAROUS.

PALP— An organ attached to the head appendages of
various invertebrates; usually associated with feeding
functions.

PARALARVA— A cephalopod mollusc in its first post-
hatching growth stage that is pelagic in near-surface
waters during the day, and that has a different life mode
than older conspecifics.

PARASITISM — An obligatory association where one
species (parasite) feeds on, or uses the metabolic
mechanisms of the second (host). Unlike predators,
parasites usually do not kill their hosts, although hosts
may later die from secondary causes that are related to
a weakened condition produced by the parasite. Para-
sitism may also be fatal when high parasite densities
develop on or in the host.

PARTS PER THOUSAND— A standard unit for mea-
suring salinity, abbreviated as %o or ppt.

PARTURITION— The act of giving birth, e.g., the live
birth of bull shark pups. Compare to SPAWN.

PATHOGEN— A microorganism or virus that produces
disease and can cause death.

PEDIVELIGER— The larval stage of bivalves during
which a functional pedal (footlike) organ develops.

PELAGIC— Pertaining to the water column, or to or-
ganisms that live in the water column and not near the
bottom.

PELAGIVORE— A carnivore that feeds in the water
column.

PELECYPODA— A synonym for the mollusc class
BIVALVIA.

PHOTOPERIODISM— The responses of an organism
to changes in light intensity or in length of days; e.g.,
seasonal and cyclic events such as migrations or
reproductive cycles of animals.

PHOTOTROPH— An organism (e.g. phytoplankton and
other plants) using sunlight as a source of energy to
synthesize organic matter. Compare with AU-
TOTROPH and HETEROTROPH.

PHYLLOSOMA— The larval stage of lobsters, being a
broad, thin, schizopod larva.

PHYLOG EN Y— Refers to evolutionary relationships
and lines of descent.

PHYTOPLANKTON— Microscopic plants and plant-
like protists (algae) of the epipelagic and neritic zones
that are the base of marine food webs. They drift with
currents, but may have some ability to control their
level in the water column. See ALGAE and DIATOMS.

PISCIVOROUS— Refers to a carnivorous animal that
eats fish.

PLANKTIVOROUS— Refers to an animal that eats
phytoplankton and/or zooplankton.

PLANKTON— Microscopic aquatic plants, animals, and
protists have limited means of locomotion and drift with
currents. See PHYTOPLANKTON and ZOOPLANK-
TON.

PLANTIGRADE— A young, newly settled post-larval
clam.

PLEOPODS — Paired swimming appendages on the
abdomen of crustaceans.

PNEUMATOPHORE— A root rising above the level of
water or soil and acting as a respiratory organ in some
trees (e.g., mangroves).

POLYCHAETA— A class of segmented, mostly ma-
rine, annelid worms that bear bristles and fleshy ap-
pendages on most segments.

POLYHALINE— A category in the Venice system of
estuarine salinity classification; water with salinity of 1 8
to 30 parts per thousand (%o).

POPULATION— All individuals of the same species
occupying a defined area during a given time. Environ-
mental barriers may divide the population into local
breeding units (demes) with restricted immigration and
interbreeding between the localized units. See SPE-
CIES, SUBSPECIES, and SUBPOPULATION.

POSTLARVA— larva following the time of absorption
of yolk; applied only when the structure and form
continue to be strikingly unlike that of the juvenile.

349

Glossary, continued.

PREDATION — An interspecific interaction where one
animal species (predator) feeds on another animal or
plant species (prey) while the prey is alive or after killing
it. The relationship tends to be positive (increasing) for
the predator population and negative (decreasing) for
the prey population. See PARASITISM, SYMBIOTIC,
CARNIVORE, and TROPHIC LEVEL.

PRODUCTION — Gross primary production is the
amount of light energy converted to chemical energy in
the form of organic compounds by autotrophs such as
algae. The amount left after respiration is net primary
production and is usually expressed as biomass or
calories/unit area/unit time. Net production for herbi-
vores and carnivores is based on the same concept,
except that chemical energy from food, not light, is
used and partially stored for life processes. Efficiency
of energy transfers between trophic levels may range
from 10 to 65%, depending on the organisms and
trophic levels. Organisms at high trophic levels have
only a fraction of the energy available to them that was
stored in plant biomass. After respiration loss, net
production goes into growth and reproduction, and
some is passed to the next trophic level. See FOOD
WEB and TROPHIC LEVEL.

PROTANDR Y-A type of hermaphroditism in which and
individual initially develops as a male, then reverses to
function as a female. Common among some species
of shrimps.

PROTISTAN-Pertaining to the eukaryotic unicellular
organisms of the kingdom Protista, including such
groups as algae, fungi, and protozoans.

PROTOGYNY — The condition of hermaphrodite plants
and animals in which female gametes mature and are
shed before maturation of male gametes.

PROTOZOA — A varied group of either free-living or
parasitic unicellular flagellate and amoeboid organ-
isms.

PROTOZOEA — A post-naupliar, pre-zoeal larval stage
in penaeid shrimp. See NAUPLIUS and ZOEA.

PTEROPODS — Group of marine gastropod molluscs
with wing-like extensions to the foot, commonly called
sea butterflies.

PYCNOCLINE — A zone of marked water density gra-
dient that is usually associated with depth; the density
gradient may be due to salinity and/or temperature.

QUERIMANA — Prejuvenile stage in striped mullet that
is identical to the adult form except that it has two anal
spines instead of three, that the adipose eyelid is not
yet apparent, and that the axillary scales are quite
short.

RACE — An intraspecific group or subpopulation char-
acterized by a distinctive combination of physiological,
biological, geographical, or ecological traits.

RADULA — A toothed belt or tongue in the buccal cavity
of most molluscs that is used to scrape food particles
from a surface, or modified otherwise to serve a variety
of feeding habits.

RANGE— (1 ) The geographic range is the entire area
where a species is known to occur or to have occurred
(historical range). The range of a species may be
continuous, or it may have unoccupied gaps between
populations (discontinuous distribution). (2) Some
populations, or the entire species, may have different
seasonal ranges. These may be overlapping, or they
may be widely separated with intervening areas that
are at most briefly occupied during passage on rela-
tively narrow migration routes. (3) Home range refers
to the local area that an individual or group uses for a
long period or life. See DISTRIBUTION and TERRI-
TORY.

RECREATIONAL VALUE— Economic and social at-
tributes of fishes and invertebrates sought by individual
persons as leisure activity.

RECRUITMENT — The addition of new members to a
population or stock through successful reproduction
and immigration.

RED TIDE — A reddish coloration of sea waters caused
by a large bloom of red flagellates. The accumulation
of metabolic by-products from these organisms is toxic
to fish and many other marine species. The accumu-
lation of these metabolites in shellfish makes shellfish
toxic to humans.

PUERULUS — A brief (several weeks), nonfeeding,
oceanic postlarval phase in the development of spiny
lobster.

350

Glossary, continued.

REPRODUCTIVE POTENTIAL— The total number of
offspring possible for a female of a given species to
produce if she lives to the maximum reproductive age.
This is found by multiplying the number of possible
reproductive periods by the average numberof eggs or
offspring produced by females of each age class. This
potential is seldom realized, but this and the age of first
reproduction, or generation time, determine the maxi-
mum rate of population increase under ideal condi-
tions.

RHEOTAXIS — A response movement by an animal
toward or away from stimulation by a water current.

RIVERINE— Pertaining to a riverorformed by a riveror
stream.

ROE— The egg-laden ovary of a fish, or the egg mass
of certain crustaceans.

RUN — A group of migrating fish (e.g., a shad run).

SALT WEDGE — A wedge-shaped layer of salt water
that intrudes upstream beneath a low-density fresh-
water lens that has "thinned" while flowing seaward.

SCAVENGER — Any animal that feeds on dead ani-
mals and remains of animals killed by predators. See
DECOMPOSER and DETRITIVORE.

SCHOOL — A group of aquatic organisms, usually of
the same size, mutually attracted to each other, that
swim together in an organized fashion.

SEAWATER ZONE— The portion of an estuary with
annual depth-averaged salinities of greater than 25
parts per thousand.

SEDENTARY— Refers to animals that are attached to
a substrate or confined to a very restricted area (or
those that do not move or move very little). See
SESSILE.

SETTLEMENT — The act of or state of making a per-
manent residency. Often refers to the period when fish
and invertebrate larvae change from a planktonic to a
benthic existence.

SHOAL— (1) A sand bar in a body of water that is
exposed at low tide. (2) An area of shallow water. (3)
A group of fish (school). (4) As a verb, to collect in a
crowd or school.

SILT — Soil with particles intermediate in size between
sand and clay.

SIPHONS — The "necks" or tubes of clams and other
bivalves that carry water containing food and oxygen
into the gills (inhalant siphon), and then expel water
containing waste products (exhalent siphon).

SLOUGH-A shallow inlet or backwater area whose
bottom may be exposed at low tide. Sloughs are often
adjacent to open estuarine waters, and may have a
channel passing through them.

SPAT — Juvenile bivalve molluscs which have settled
from the water column to the substrate to begin a
benthic existence.

SPAWN— The release of eggs and sperm during mat-
ing. Also, the bearing of offspring by species with
internal fertilization. See PARTURITION.

SPECIES— (1) A fundamental taxonomic group rank-
ing after a genus. (2) A group of organisms recognized
as distinct from other groups, whose members can
interbreed and produce fertile offspring. See POPU-
LATION, SUBPOPULATION, and SUBSPECIES.

SPERMATOPHORE— A capsule or gelatinous packet
(extruded by a male) containing sperm and used to
transfer sperm to females. Spermatophores are pro-
duced by certain invertebrates and some primitive
vertebrates.

SEMELPAROUS— Animals that have a single repro-
ductive period during their lifespan; compare with
ITEROPAROUS.

SESSILE — Refers to an organism that is permanently
attached to the substrate. See SEDENTARY.

SESTON— Microplankton; all bodies, living and non-
living, floating or swimming in water.

SPICULE — A sharp, pointed, siliceous or calcareous
body, as in those forming the endoskeleton of sponges,
corals, and certain protozoans.

SPIT— A long, narrow sand bar or peninsula extending
into a body of water which is at least partly connected
to the shore. See SHOAL.

SPOROCYST— A simple larval stage of parasitic trema-
tode worms. Contact with the host causes a metamor-
phosis from an earlier stage to this stage.

351

Glossary, continued.

STANDARD LENGTH— Distance from the tip of a
fishes snout or lips to the end of the last vertebrae at the
base of the caudal fin.

STENOHALINE — Pertaining to organisms that are re-
stricted to a narrow range of salinities, in contrast to
EURYHALINE.

STENOPHAGOUS-
food items.

-Subsisting on a limited variety of

STENOTHERMAL — Pertaining to organisms that are
restricted to a narrow range of temperatures, in con-
trast to EURYTHERMAL.

STOCK — A related group orsubpopulation. See POPU-
LATION and SUBPOPULATION.

STOMATOPODA — An order of highly specialized car-
nivorous crustaceans commonly referred to as mantis
shrimp.

SUBADULTS— Maturing individuals that are not yet
sexually mature.

SUBLITTORAL — The benthic zone along a coast or
lake that extends from mean low tide to depths of about
200 m.

SUBPOPULATION— A breeding unit (deme) of a larger
population. These units may differ little genetically and
taxonomically. See SUBSPECIES. Subpopulations
may intergrade with some interbreeding, or they may
occupy a common seasonal range prior to the mating
season. The units may have different reproduction
times and be separated spatially or temporally. See
RACE, STOCK, and POPULATION.

SUBSPECIES — A taxonomic class assigned to popu-
lations and/orsubpopulations when interbreeding (gene
flow) between populations is limited, and there are
significant differences in some combination of charac-
teristics between subspecies (e.g., appearance,
anatomy, ecology, physiology, and behavior). While
successful interbreeding can occur when the groups
are in contact, under natural conditions reproductive
isolation is complete and the groups are considered
distinct. Classification of such groups is based on the
comparative study and judgement of phylogenists. A
second epithet for each subspecies is added to the
binomial for the species (e.g., Oncorhynchus clarki
clarki). See SPECIES, POPULATION, and SUB-
POPULATION.

SUBTIDAL— See SUBLITTORAL.

SUPRALITTORAL— The splash zone of land (adja-
cent to the sea) that is above the mean high tide level.

SUSPENSION FEEDER— An animal that feeds di-
rectly or by filtration on minute organisms and organic
debris that is suspended in the water column.

SYMBIOSIS— The relationship between two interact-
ing organisms that is positive, negative, or neutral in its
effects on each species. See COMPETITION, MUTU-
ALISM, PARASITISM, and PREDATION.

SYMPATRIC — Species inhabiting the same or over-
lapping geographic areas.

TAXONOMY — A system of describing, naming, and
classifying animals and plants into related groups
based on common features (e.g., structure, embryol-
ogy, and biochemistry).

TEMPORAL— Pertaining to time. Used to describe
organism activities, developmental stages, and distri-
butions as they relate to daily, seasonal, or geologic
time periods.

TERRITORY — An area occupied and used by an indi-
vidual, pair, or larger social group, and from which
other individuals or groups of the species are excluded,
often with the aid of auditory, olfactory, and visual
signals, threat displays, and outright combat.

TEST — A rigid calcareous exoskeleton produced by
some echinoderms in the class Echinoidea (e.g., sea
urchins and sand dollars).

THERMOCLINE — A relatively narrow boundary layer
of water where temperature decreases rapidly with
depth. Little water or solute exchange occurs across
the thermocline, which is maintained by solar heating
of the upper water layers.

TIDAL FRESH ZONE— The portion of an estuary with
annual depth-averaged salinities of less than 0.5 parts
per thousand (%o).

TINTINNIDAE — A family of ciliated protozoans.

TOTAL LENGTH— Length of a fish measured as a
straight line from the anterior end of the snout to the
distal end of the caudal fin.

TREMATODA — A class of parasitic flatworms of the
phylum Platyhelminthes. Trematodes have one or
more muscular, external suckers and are also known
as flukes.

352

Glossary, continued.

TROCHOPHORE— A molluscan larval stage (except
in Cephalopoda) following gastrulation (embryonic
stage characterized by the development of a simple
gut). It is commonly ciliated, biconically shaped, and
free-swimming; it establishes an evolutionary link be-
tween annelids and molluscs, since both groups dis-
play a similar life stage.

TROPHIC LEVEL— The feeding level in an ecosystem
food chain characterized by organisms that occupy a
similar functional position. At the first level are auto-
trophs or producers (e.g., algae and seagrass); at the
second level are herbivores (e.g., copepods and mol-
luscs); at the third level and above are carnivores (e.g.,
fishes). Omnivores feed at the second and third levels.
Decomposers and detritivores may feed at all trophic
levels. See FOOD WEB and PRODUCTION.

TURBELLARIA— A class of mostly aquatic, non-para-
sitic flatworms that are leaf-shaped and covered with
cilia.

TWO-YEAR-OLD— A fish that is a member of age-
group II, in its third calendar year.

UMBO — A dorsal protuberance on each shell (valve)
of a bivalve mollusc, which rises above the line of
articulation and is the oldest part of the shell.

UPWELLING — The process whereby prevailing sea-
sonal winds create surface currents that allow nutrient-
rich cold water from the ocean depths to move into the
euphotic or epipelagic zone. This process breaks
down the thermocline and increases primary produc-
tivity, and ultimately fish abundance.

YEAR-CLASS — Refers to animals of a species popu-
lation hatched or born in the same year at about the
same time; also known as a cohort. Strong year-
classes result when there is high larval and juvenile
survival; the reverse is true for weak year-classes. The
effects of strong and weak year-classes on population
size and structure may persist for years in long-lived
species. Variation in year-class strength often affects
fisheries. See DISTRIBUTION and STOCK.

YEARLING — A fish that is a member of age-group I, in
its second calendar year.

YOLK SAC LARVA— A larval fish still bearing yolk, also
called a prolarva.

YOUNG-OF-YEAR— Young fish of age-group 0, from
transformation into juvenile until January 1 .

ZOEA — An early larval stage of various marine crabs
and shrimp; zoea have many appendages and long
dorsal and anterior spines.

ZOOPLANKTON— Animal members of the plankton.
Most range in size from microscopic to about 2.54 cm
(1 inch) in length. They reside primarily in the epipe-
lagic zone and feed on phytoplankton and each other.
Although they have only a limited ability to swim
against currents, many undertake diel migrations. Taxa
include protozoa, jellyfish, comb jellies, arrowworms,
lower chordates, copepods, water fleas, krill, and the
larvae of many fish and invertebrates that are not
planktonic as adults.

VELICONCHA — A bivalve larval stage. A veliconcha
has two larval shells and moves by using its velum.

VELIGER — A ciliated larval stage common in mol-
luscs. This stage forms after the trochophore larva and
has some adult features, such as a shell and foot.

VELUM — The ciliated swimming organ of a larval mol-
lusc.

VIVIPAROUS— Refers to animals that produce live
offspring; eggs are retained and fertilized in the female
(as compared to OVIPAROUS).

WATER COLUMN — The water mass between the
surface and the bottom.

353

Table 6. Habitat Associations

Terms used in Table 6. Habitat Associations:

Domain - General habitat of life stages.

• Freshwater- Rivers and lakes above head-of-tide; freshwater lentic and lotic habitats.

Lacustrine - Freshwater lentic areas (lakes) with riverine connections to the sea..
Riverine - coastal plain - River portions in the relatively flat land along a coast.
Riverine - inland - River portions away from the coast.

• Estuarine - Embayment with tidal fresh, mixing, and seawater zones.

Inlet mouth - The seaward end of an estuary.

Channel - The drowned river channel or tributary channels of an estuary.

Inter- and subtidal flats - Broad, shallow estuarine areas.

Salinity range, NEI - Three salinity zones used by the ELMR program for compilation of distribution and

abundance data.

Tidal fresh zone - Salinities of 0.0-0.5%o.

Mixing zone - Salinities of 0.5-25.0%o.

Seawater zone - Salinities >25%o.
Salinity range, Venice system - Five salinity zones according to the Venice system of estuarine
classification.

Limnetic- Salinities of 0.0-0.5%o.

Oligohaline - Salinities of 0.5-5.0%o.

Mesohaline - Salinities of 5-1 8%o.

Polyhaline - Salinities of 18-30%o.

Euhaline - Salinities >30%o.
Temperature range - The temperatures at which a life stage is typically found, from 0°C to >30°C

• Marine - Coastal and offshore

Beach/surf- Shore areas receiving ocean waves and wash.
Neritic - Residing from the shore to the edge of the continental shelf.
Oceanic - Residing beyond the edge of the continental shelf.

Substrate preference - Size of substrate that life stages reside on or in.

• Mud/clay/silt - Fine substrates <0.0625 mm in diameter.

• Sand - Substrates 0.0625-4.0 mm in diameter.

• Pebble/cobble/gravel - Substrates 4-256 mm in diameter.

• Boulder/rocky outcrop/reef- Large substrate >256 mm in diameter, exposed solid bedrock, or coral reef.

• Shell- Mollusc shell substrate, such as oyster.

• Submergent vegetation - Rooted aquatic vegetation that does not grow above the water's surface, e.g., turtle
grass (Thalassia testudinum), shoal grass (Halodule wrightii), and widgeon grass (Ruppia maritima).

• Emergent vegetation - Rooted aquatic vegetation that grows above the water's surface, e.g., cordgrass
(Spartina) and mangrove.

• Floating vegetation - Non-rooted aquatic vegetation, e.g., Sargassum, and other vegetation that can form floating
mats.

• None - No known substrate preferences.

Depth preference -

• Littoral -

Intertidal - From the high tide mark to depths of 1 m.
Subtidal - At depths of 1 -1 0 m.

• Sublittoral -

Inner shelf (10-50 m) - On or over the continental shelf at depths of 10-50 m.
Middle shelf (50-1 00) - On or over the continental shelf at depths of 50-1 00 m.
Outer shelf (100-200 m) - On or over the continental shelf at depths of 100-200 m.

355

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Table 7. Biological Attributes

Terms used in Table 7. Biological Attributes:

Life Mode - The usual location within the water column.

• Benthic - In the bottom sediments.

• Epibenthic - On, but not in, the bottom.

• Demersal - In the water column, but near the bottom.

• Nektonic - In the water column away from the bottom, and capable of locomotion.

• Planktonic - In the water column, but not capable of extensive movements.

Spatial strategy - Use of habitats by life stages.

• Freshwater resident - Resides primarily in freshwater habitats.

• Estuarine resident - Resides primarily in estuarine habitats (salinities >0.5 and <25%°).

• Marine resident - Resides primarily in seawater habitats (salinities >25%o).

• Coastal migrant - Migrates within nearshore waters of the continental shelf.

• Ocean migrant - Migrates in ocean waters beyond the continental shelf.

Mobility -

• Non-mobile - Sessile or sedentary.

• Low mobility- Capable of limited directed movements.

• High mobility- Capable of extensive directed movements.

Feeding Type -

• Filter feeder - Obtains food items by filtering water or fine sediments.

• Non-filter feeder- Obtains food items by other means, such as selective predation.

Prey Items - Food items typically consumed by an organism, such as detritus, phytoplankton, zooplankton, fish,
etc.

Longevity - Average lifespan of a particular life stage, from 1 day to >20 years.

Value-

• Recreational - Often sought and harvested by sport anglers.

• Commercial - Harvested by commercial fishermen for market.

• Ecological - Of major importance in aquatic ecosystems as a predator or prey species, etc.

• Indicator of stress - Often used in studies of environmental stress.

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Table 8. Reproduction

Terms used in Table 8. Reproduction:

Fertilization/development - Method of egg fertilization and development.

• External - Egg fertilization occurs after eggs and sperm are shed into the water.

• Internal - Egg fertilization occurs when a male inseminates an egg within a female.

• Oviparous - Eggs are laid and fertilized externally.

• Ovoviviparous - Eggs are fertilized and incubated internally, and usually released as larvae. Little or no maternal
nourishment is provided.

• Viviparous- Eggs are fertilized, incubated, and develop internally until birth. Maternal nourishment is provided.

Mating Type - Mate selection strategy.

• Monogamous - A single male and a single female pair for a prolonged and exclusive relationship.

• Polygamous - A male mates with numerous females or vice-versa.

• Broadcast spawner - Numerous males and females release gametes during mass spawning.

Spawning strategy - Spawning mode.

• Anadromous - Species spends most of its life at sea but migrates to fresh water to spawn.

• Catadromous - Species spends most of its life in fresh water but migrates to salt water to spawn.

• Iteroparous - Species reproduces repeatedly during a lifetime.

• Semelparous - Species reproduces only once during a lifetime.

• Batch - Species spawns (releases gametes) several times during a reproductive period.

Parental Care - Type of egg protection.

• Protected - Eggs are protected by parent(s); eggs are buoyant or attached to substrates, or eggs develop in the
shelter of a nest.

• Non-protected - Eggs are not protected by parent(s).

Domain - Location of spawning.

• Riverine - Spawning occurs primarily in fresh water, above head of tide.

• Estuarine - Spawning occurs primarily in estuarine waters (to head of tide).

• Marine - Spawning occurs primarily in open marine waters.

Temporal Schedule - Months when spawning typically occurs.

Periodicity - Frequency of spawning events.

'Annual spawning - Spawning once each year, usually during a restricted season.

*2 or more per year - Spawning more than once each year (more than one spawning season).

•2 or more years - Spawning events separated by at least two years.

'Undescribed - Spawning frequency not documented.

Fecundity - Number of eggs typically produced by a mature female, from <100 to >10 million.

Maturation age - The typical length of time for an individual to reach sexual maturity, from < 6 months to > 5 years.

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