REFEWNCECOPY 

Do Not Remove from the Librarv 

U. - S. Fish and Wildlife Strvice 

Notional Wetlands Research Cenkr 

FWSIOBS-82111.16 700 Cajun Dome Uouievara 

October 1983 TR EL-82.4 Lafuyette, Louisiana 70506 

Species Profiles: Life ~istories and 

Environmental Requirements of Coastal Fishes 

and Invertebrates (South Florida) 

Coastal Ecology Group 

Fish and Wildlife Service Waterways ~xperiment station 

U.S. Department of the Interior U.S. Army Corps of Engineers 
FWS/OBS-82/11.16 

TR EL-82-4 

October 1983 

Species Profiles: Life Histories and Environmental Requirements 

of Coastal Fishes and Invertebrates (South Florida) 

SNOOK 

Will iam Seaman, Jr. 

Sea Grant and School of Forest Resources and Conservation 

and 

Mark Coll ins 

Department of Zoo1 ogy 

University of Florida 

Gainesville, FL 32611 

Project Manager 

Larry Shanks 

Project Officer 

Norman Benson 

National Coastal Ecosystems Team 

U.S. Fish and Wildlife Service 

1010 Gause Boulevard 

S1 idel 1 , LA 70458 

Performed for 

Coastal Ecology Group 

Waterways Experiment Station 

U.S. Army Corps of Engineers 

Vicksburg, MS 39180 

and 

National Coastal Ecosystems Team 

Division of Biological Services 

Research and Development 

Fish and Wildlife Service 

U.S. Department of the Interior 

Washington, DC 20240 
This series should be referenced as follows: 

U.S. Fish andWild1ifeService. 1983. Species profiles: life historiesand 

environmental requirements of coastal fishes and invertebrates. U.S. Fish 

Wildl. Serv. FWS/OBS-82/11. U.S. Army Corps of Engineers, TR EL-82-4. 

This profile should be cited as follows: 

Seaman, W., Jr., and M. Collins. 1983. Species profiles: life histories and 

environmental requirements of coastal fishes and invertebrates (South 

Florida) -- snook. U.S. Fish Wild1 . Serv. FWS/OBS-82/11.16. U.S. Army 

Corps of Engineers, TR EL-82-4. 16 pp. 
PREFACE 

This species profile is one of a series on coastal aquatic organisms, 

principally fish, of sport, commercial, or ecological importance. The profiles 

are designed to provide coastal managers, engineers, and biologists with a brief 

comprehensive sketch of the bi 01 ogical characteris tics and envi ronmental requi rements of the species and to describe hold populations of the species may be 

expected to react to environmental changes caused by coastal development. Each 

profile has sections on taxonomy, 1 ife history, ecological role, environmental 

requi rements, and economic importance, if appl icabl e. A three-ring binder is 

used for this series so that new profiles can be added as they are prepared. 

This project is jointly planned and financed by the U.S. Army Corps of Engineers 

and the U.S. Fish and Wildlife jervice. 

Suggestions or questions regarding this report should be directed to: 

Information Transfer Special ist 

National Coastal Ecosystems Team 

U.S. Fish and Wildlife Service 

NASA-Sl idel 1 Computer Compl ex 

1010 Gause Boul evard 

Slide1 1, LA 70458 

U.S. Army Engineer Waterways Experiment Station 

Attention: WESER 

Post Office Box 631 

Vicksburg, MS 39180 
CONTENTS 

PREFACE .................................. i ii 

CONVERSION FACTORS ............................ v 

ACKNOWLEDGMENTS .............................. vi 

NOMENCLATURE/TAXONOMY/RANGE ........................ 1 

MORPHOLOGY/IDENTIFICATION AIDS ...................... 1 

Comparison with Related Species ..................... 4 

REASON FOR INCLUSION IN SERIES ...................... 4 

LIFE HISTORY ............................... 4 

Spawning ................................ 4 

FecundityandEggs ........................... 5 

Larvae ................................. 5 

Juveniles ................................ 6 

Adults ................................. 6 

GROWTH CHARACTERISTICS .......................... 7 

FISHERY .................................. 10 

Commercial Harvest ........................... 10 

Sport Fishihg .............................. 11 

Fishery Management and Restoration ................... 11 

ECOLOGICALROLE ............................. 12 

ENVIRONMENTAL REQUIREMENTS ........................ 13 

Temperature ............................... 13 

Salinity ................................ 13 

Habitat ................................. 13 

Other Environmental Factors ....................... 14 

LITERATURE CITED ............................. 15 
CONVERSION FACTORS 

--- Metric to U.S. Customary 

Mu1 ti ply -- To Obtain 

mi 11 imeters (mm) 

centimeters (cm) 

meters (m) 

ki lometers (km) 

inches 

inches 

feet 

miles 

square meters (mL) 

square ki lometers (km') 

hectares (ha) 

square feet 

square miles 

acres 

liters (1) 

cubic meters (m3) 

cubic meters 

gallons 

cubic feet 

acre-feet 

mi 11 i grams (mg) 

grams (g) kilograms (kg) 

metric tons (mt) 

metric tons 

kilocalories (kcal ) 

ounces 

ounces 

pounds 

pounds 

short tons 

BTU 

Cel si us degrees Fahrenheit degrees 

U.S. Customary to Metric 

inches 

inches 

feet (ft) 

fathoms 

miles (mi) 

nautical miles (nmi ) 

mi 11 imeters 

centimeters 

meters 

meters 

kilometers 

kilometers 

square feet (ft2) 

acres 

square miles (mi') 

square meters 

hectares 

square k i 1 ome ters 

gal 1 ons (gal ) 

cubic feet (ft3) 

acre-feet 

1 i ters 

cubic meters 

cubic meters 

ounces (02) 

pounds (Ib) 

short tons (ton) 

BTU 

grams 

ki 1 ograms 

metric tons 

kilocalories 

Fahrenheit degrees Celsius degrees 
ACKNOWLEDGMENTS 

We are grateful for the reviews by Gerard Burger, Florida Department of 

Natural Resources, Grant Gi lmore, Harbor Branch Foundation, Fort Pierce, Florida, 

and by Paul Shafland, Florida Game and Fresh Water Fish Commission, Boca Raton, 

Florida. 
Figure 1. Snook. 

SNOOK 

NOMENCLATURE/TAXONOW/RANGE FIORPHOLOGY/IDENTIFICATION AIDS 

Scientific name .... undecimal is (Bloch) 

Preferred common name . (Figure 1) 

Other common names . . thin snook 

Class ......... Order ......... Family. ........ 

. Cen tropovus The snook is an elongate fish of 

up to 140 cm fork length (FL) and may 

.... .Snook weigh as much as 22 kg. It is easily 

distinguished by its dark lateral 

. .Robalo, band and prominent protruding lower 

jaw. Larval and juvenile stages are 

. Osteichthyes illustrated in Figure 3 (Lau and 

. . Perciformes Shafland 1982). 

.Centropomidae 

Geographic range: Coastal waters of 

the tropical and subtropical 

western Atlantic Ocean, from the 

U.S. mid-Atlantic to southeastern 

Brazil, including the insular and 

mainland margins of the Gulf of 

Mexico and Caribbean Sea. In the 

U.S. its center of abundance is 

the brackish coasts of south 

Florida (Figure 2), with a range 

extending from coastal Texas 

possibly as far as Delaware 

(Burgess 1980). Outside Florida, 

the only other permanent 

population in the United States 

is in Texas. 

First dorsal fin with eight 

spines, separated from second dorsal 

fin of one spine and 10 soft rays. 

Anal fin with three spines, six soft 

rays. Pectoral rays 15 or 16. 

Lateral scales 70-77. Gill rakers on 

lower limb of first gill arch 7-9. 

Body robust, sides 1itt1Q 

compressed. Silvery body color is 

shaded olive green. Maxillary 

reaches to or beyond center of eye. 

Pelvic fin does not extend to the 

anus in fish larger than 100 mm 

standard length (SL) . 
CEDAR KEY 

ATLANTIC OCEAN 

ST. PETE RSBURG 

CAPE ROMAN 

GULF OF MEXICO 

THOUSAND ISLA 

Coastal distribution Area of high abundance 

Figure 2. Distribution of s n o o k ( C e n t r o p o m u s u n d e c i m a l i s ) in southern Florida. 
Figure 3. Representative 1 arvae and early juvenile stages of Centropomus 

undecimal is (selected from tau and Shafland 1982). All lengths in mm, St: 

A, 1.5; B, 2.1; C, 3.8; D, 4.6; E, 6.3; F, 12.5; G, 21.9. 

Table 1. Comparison of the Florida species of Centropomus. 

Meristic countsa 

Lateral Gill Fl orida 

Species scales rakers range 

- C. ensiferus 53-60 13-16 Coastal, Miami area 

- C. parallelus 80-90 10- 13 L. Okeechobee, and south on both sea 

coasts 

C. pectinatus - Coastal , Indian River 

to Cal oosahatchee 

River; (specimens from 

Panama City) 

- C. undecimalis 70-77 7-9 Coastal, Statewide 

a~efined by Rivas (1962): Lateral scales are counted along the longitudinal 

row immediately above the 1 ateral 1 ine, from the post-temporal (supracl avicl e) 

to the caudal base. Gill rakers are counted along the lower 1 imb of the first 

arch, including gill raker at angle but not the rudiments. 
Com~arison with Re1 ated Soecies 

Rivas (1949, 1962) recognized 

four species of Centropomus in Florida 

waters, whereas prior to 1949 all 

snook were referred to as C. 

undecimalis. This species is the most 

common and ubiquitous of the four; the 

other three are less abundant and are 

normally restricted to south Florida 

(Table 1). Comparisons by Rivas 

(1962) include drawings and an 

identification key. U.S. range maps 

for each species are plotted in 

Burgess (1980). 

A fifth Atlantic species is 

discussed by Greenfield (1975), who 

provided a key. The comparative 

osteology of all Atlantic species is 

described by Fraser (1968). 

REASON FOR INCLUSION IN SERIES 

Snook is a renowned gamefish in 

Florida, particularly along the lower 

gulf coast. A commercial fishery 

existed until 1957. Snook inhabit 

both fresh- and saltwater but are most 

abundant in brackish estuaries, 

particularly mangrove-f ri nged bays 

and tidal streams. It is a 

carnivorous species at the top of the 

food web. Populations of the species 

have been decl ining as a result of 

fishing pressure and deterioration of 

habitat. 

LIFE HISTORY 

The snook's life cycle is depicted in Figure 4. 

Spawning 

The first recorded account of the 

capture of male and female snook 

extruding milt and eggs was in 1956 

by Volpe (1959). These snook were 

taken from groups that "could be seen 

lying in shallow water just off the 

sandy beaches in the mouths of 

various saline open water passes" of 

southern Florida's gulf coast during 

June and July (Volpe 1959). Marshall 

(1958) examined snook gonads over 

several months and concluded that 

spawning probably began in May and 

may have continued to mid-November, 

although the bulk of spawning most 

likely occurred in May and June. 

Marshall also suggested that the fish 

may not eject all spawn at once. By 

assuming that the collection sites of 

gravid snook were spawning locations, 

Marshal 1 (1958) proposed that snook 

congregate for spawning around the 

mouths of rivers, canals, and passes, 

and along adjacent shore1 ines. This 

agrees with concl us ions of Vol pe 

(1959) and Bruger (in prep). 

Gilmore et al. (1983), using 

juvenile recruitment patterns to 

indicate spawning activity of snook 

on Florida's central east coast, 

found some differences from west 

coast spawning observations. 

Spawning activity is more prolonged 

on the east coast, beginning in April 

and continuing into December. In 

addition, there are two spawning 

peaks, one in June-July and another 

from August to October. Subsequent 

field work has established the peak 

of spawning to be in August, 

according to R. G. Gilmore (Harbor 

Branch Foundation, Ft. Pierce, 

Florida; pers. comm. ) who has 

observed 1 arge school s of gravid 

adults. These differences may be 

associated with differing 

hydrological regimes between the east 

and west coasts. 
RECREATIONAL 

FISHERMEN 

Figure 4. Snook life cycle. (Used with permission of R. Lewis, Mangrove 

Systems Inc., Tampa, Florida.) 

Fecundity and Eggs 

Volpe (1959) estimated a 58.4-cm 

FL female snook to contain 1,440,000 

eggs. This corresponds well to an 

estimate of 1,648,000 eggs for a 

79.5-cm specimen from Haiti (Reebe and 

Tee-Van 1928). 

Lau and Shafland (1982) described 

advanced embryos of 1 aboratory-reared 

snook. The embryos averaged 0.70 mm 

in diameter (range 0.68 to 0.73 mm). 

The yolk averaged 91% of the egg 

diameter, and a single oil globule 

averaging 0.12 mm was located in the 

ventral part of the yolk. The 

embryos had a lateral row and three 

vertical bands of small melanophores 

on the trunk. 

Larvae 

Using 1 a b o r a t o r y - r e a r e d and 

wild-caught material, Lau and 

Shafl and (1982) described snook 
larval development. Newly hatched 

larvae were 1.4-1.5 mm SL and increased to 2.1 mm within 36 h of 

hatching. A large oil globule was 

located beneath the head. By 48 h 

after hatching the eyes became pigmented, the mouth functioned, the 

yolk sac was absorbed, and the gut 

increased in diameter and became 

partitioned. At about 4 days of age 

the swim bladder was visible and the 

oi 1 globule was completely absorbed. 

By the time young snook reached 

26 mm SL they resembled miniature 

adults (Figure 3). In a comparison of 

1 aboratory-reared s nook to 

field-caught specimens, Lau and 

Shafland (1982) found no difference in 

body shape or pigmentation. 

Laboratory-reared specimens, however, 

exhibited meristic variation in 

vertebrae and fin ray numbers not 

observed in those from the wild. 

Juveni 1 es 

On Florida's west coast, Fore and 

Schmidt (1973) searched numerous 

aquatic habitats (e.g., outer beaches, 

open bays, freshwater) in the Ten 

Thousand Is1 ands area before locating 

juvenile snook. These nursery areas 

were brackish, shallow, warm tidal 

streams and dredged canals 

characterized by slow currents and 

soft mud bottoms with little 

submergent vegetation, but often with 

shore1 ine stands of red or white 

mangrove trees. 

On the east coast of Florida, 

Gilmore et al. (1983) found that 

juvenile snook use at least three 

distinct habitats during their first 

year of 1 ife: freshwater tributaries, 

salt marsh, and seagrass beds. Snook 

averaging 27.5 mm SL are found in 

freshwater tributaries, arriving when 

at a length of about 11 mm and most 

leaving when 40-60 mm SL. Snook in 

the salt marsh average 67 mm SL, stay 

for 60 to 90 days, and leave at 

lengths of about 100 mm. Juvenile 

snook then enter seagrass beds and 

reside in the habitat for about 4 

months. Upon reaching a length of 

approximately 300 mm, maturation 

begins and snook migrate from the 

seagrass beds. On Florida's west 

coast Fore and Schmidt (1973) 

collected juvenile snook of 14 to 196 

mm SL from waters with salinities of 

0.3 to 29.7 parts per thousand (ppt), 

and found no correlation between 

salinity and fish length. They 

concluded only that juveniles are 

usually found in brackish waters in 

that area. 

Linton and Rickards (1965) 

encountered juvenile snook in the 

headward regions of several tidal 

creeks in the salt marsh at Sapelo 

Island, Georgia, during summer and 

early autumn. These juveniles are 

believed to have been carried north 

to the area by some combination of 

larval drift and hurricane-induced 

currents, and to have then made their 

way as far up the tidal creeks as 

possible to the same "nursery" 

grounds used by many other fishes. 

Juveniles do not move to the 

high salinity spawning area with 

adults during the summer or fall. 

Rather, they remain in peripheral 

fresh and estuarine waters for at 

1 east the first year. Whether 

juveni 1 e snook are strong school ers 

has not been reported. 

Adults 

Adult snook are found dispersed 

through various freshwater and 

brackish habitats from winter to 
spring. At this time, densities are 

low in many areas and fishermen may 

not specifically seek them. On the 

gulf coast, fishing pressure is 

traditionally high in summer, due to 

the congregation of fishes at and near 

spawning sites. In fact, 45% of the 

snook captured during the year in the 

Naples/Marco Island area are caught 

during the months of June and July 

only (Florida Saltwater Fisheries 

Study and Advisory Council 1982; 

Bruger in prep). On the east coast, 

however, R. G. Gilmore (pers. comm.) 

has observed large concentrations of 

snook in early autumn, with greatest 

landings from August to December. 

Marshall (1958) and Bruger (in 

prep.) found that snook may mature at 

less than 35 cm FL. Approximately 50% 

are mature at 40 cm FL, and virtually 

all are mature at 50 cm FL; according 

to Volpe (1959) and Bruger (in prep.), 

they are in their second and third 

years of 1 ife, respectively (Table 2). 

Table 2. Calculated mean fork length 

of snook by age group (from Vol pe 

1959). 

- -- - -- -- 

Age Size (mm) 

I 163 

I I 342 

I I I 456 

I V56 3 

V 660 

V I 723 

VII 782 

Except for the usually short 

movement to spawning areas, snook are 

nonmigratory. In the Naples/Marco 

Island region, G. E. Bruger (Florida 

Department of Natural Resources, St. 

Petersburg, Florida; pers. comm..) 

tagged 5,493 snook from 1976 to 1981. 

Of the 1,257 returns received by May 

1982, 68.8% had moved 5 mi or less 

from the tagging site, 18.5% moved 

5-10 mi, 5.3% 10-15 mi, and 7.1% 

greater than 15 mi. 

GROWTH CHARACTERISTICS 

The largest snook reported for 

Florida on both the gulf and Atlantic 

coasts were 102 cm FL (Fore and 

Schmidt 1973; Marshal 1 1958). Length 

conversion factors are listed in 

Table 3. 

Table 3. Length conversion formulas 

for juvenile snook in southwest 

Florida, based on 175 specimens 14 to 

196 mm FL (Fore and Schmidt 1973). 

Formula 

SL = -0.369 + 0.870 FL 

FL = -0.424 + 1.150 SL 

FL = -1.531 + 0.909 TL 

TL = 1.684 + 1.100 FL 

SL = -0.577 + 0.789 TL 

TL = 0.732 + 1.268 SL 

According to pub1 ished 

information, snook have a life span 

of at least 7 years, with females 

attaining larger size than males 

(Marshal 1 1958). Length-weight 
relations for populations of juveniles 

(Fore and Schmidt 1973) and adults 

(Marshal 1 1958) in southwest Florida, 

and for adults on the east coast 

(Gilmore et al. 1983) are illustrated 

in Figures 5 and 6. 

The growth rate of snook in 

southwest Florida was illustrated by 

Volpe (1959), and in the Indian River 

by Gilmore et al. (1983) (Figures 7, 

8). The growth rate of larval snook 

was determined in captivity and it may 

present an underestimation due to the 

difficulty associated with laboratory 

maintenance of the fish (Shafland and 

Koehl 1979). Juvenile snook grow 

about 1.0 mm per day, at least during 

warmer periods (Fore and Schmidt 

1973), on both coasts of Florida 

(Gilmore et al. 1983). According to 

Volpe (1959), the rate of growth 1s 

300 400 500 6CO 700 800 900 

FORK LENGTH lmm) 

FORK LENGTH ilnl 

Figure 5. Length-wei ght relationship 

in C. undecimalis of the Ten Thousand 

Isl~nds, Florida ( from Marshal 1 1958). 

4 275 

3 732 - • - 

. 2 658 

LOO W = -4 7720 r 2 R75A log FL 

iFo!+ 4 SChnlrll 19711 

9 - 069 

LOQW = 3c10o + i',ii? UY tL 

r=0'19 1~557 

22424 , , 99) 1162 1112 1 Sni 167, ,843 2o)n i18r i:6, 252: ~b~b 28h"!i1?1 

LOGARITHM OF FOHK LENGTH 

Figure 6. Length-weight relationship 

of juvenile snook, plotted by Gilmore 

et al. (1983) to illustrate their 

data from Indian River and those of 

Fore and Schmidt (1973) from Ten 

Thousand Islands. A1 1 points plotted 

are from Indian River specimens. 

20 

18 

6 

14 

I2 ; 

lo ' 

6 

6 

4 

2 

0 

I0 IS 20 25 30 35 

- 

6 

s 

4 

relatively high to the second year of 

life, slower and fairly uniform to 

the fifth year, and thereafter slowly 

declines (Figure 7). 

2 

0 

AGE GROUP 

- 

- - 

- 

- 

Figure 7. Growth curves showing 

average calculated fork length at end 

of each year of life for southwest 

Florida snook. All fish includes 

those for which sex was not 

determined (from Vol pe 1959). 

;It 
Figure 8. Calculated growth rates of Centro omus undecimalis based on lengthfrequency distribution (from Gi lmore eh. 

450 

400 - 

350 - 

- 300 - E 

- E 

I 

250 - z 

W 

J 

n 

a: 200 - 

Q 

n 

z 

a 

t150- 

100 - 

50 - 

0 

0 

Volpe (1959) determined age of 

snook by using otoliths (Table 2); 

whereas scales were discounted for 

use, the sagitta was validated for 

accuracy. Comparative data (Bruger 

in prep.) on snook of uniform and 

slightly larger size reveal a maximum 

age of eight for snook taken in a 

Florida Department of Natural 

Resources study. 

Coefficient of condition (K) was 

first calculated by Fore and Schmidt 

(1973) for juveniles, and 

subsequently applied hy Gilmore et 

a1 .; both studies (Table 4) used the 

formula: 

AGE IN DAYS 

I I I I I I I I I I I 1 

O JUNE Y= -2.969 + 0.872X r = 0.97 n = 344 

o JULY y = 6.336 + 0.890~ r= 0.96 n = 206 

a AUG ' y= -10.700 + 1.115X r= 0.34 n = 236 

/ 

+ SEPT y = -9.940 + 0.983~ r= 0.96 n = 579 

x OCT y = 2.124 + 0.949~ r= 0.97 n = 344 

0 NOV y = -6.850 + 0.994X r = 0.94 n = 244 

I I I I I I I I 1 1 I I 1 

W: weight (g) 

- 

- 

- 

- 

- 

- 

- 

- 

L: FL (fork length) (mm) 

30 60 90 120 150 180 210 240 270 300 330 360 390 

K values for snook collected at Ten 

Thousand Islands (gulf coast) from 

June through December were higher than 

those for Indian River (Atlantic 

coast) collections made in every 

month of the year. This discrepancy 

is partially a result of minimum K 

values in January and February, which 

reduced the mean for Indian River 
snook (Gilmore et al. 1983). Other 

factors include different fish 

sampl ing techniques and times, and 

environmental and food differences. 

Seasonally adjusted data are more 

comparable between Atlantic and gulf 

coast locations (Table 4). 

Table 4. Coefficient of condition (K) 

for juvenile snook from southern 

Florida. 

Values 

Habitat K K range Season 

~reshwater~ 0.93 0.24-1.36 12 months 

~reshwater~ 0.99 0.24-1.36 June-Dec. 

Tidal 

stream 1.05 0.77-1.52 June-Dec. 

~a rs ha 0.89 0.62-1.37 12 months 

seagrassa 0.96 0.52-1.82 12 months 

a~ilmore et al. 1983. 

b~ore and Schmidt 1973. 

FISHERY 

The south Florida snook fishery 

has been characterized by decl ining 

yields that led to closure of 

commercial harvest in 1957 and 

establishment of a closed summer sport 

season in 1982. It has never been one 

of the State's larger fisheries, yet 

it is and has been of economic 

importance locally. The status of the 

recreational fishery is reflected in 

the 1982 Final Report of the Florida 

Saltwater Fisheries Study and Advisory 

Council, which concluded that "the 

best information available indicates a 

serious problem in the fishery." 

Commercial Harvest 

The snook commercial fishery was 

relatively short-lived. Marshall's 

1958 historical account indicates 

that market demand increased only 

after 1930, and peaked in response to 

World War I1 food shortages. Snook 

were taken both by efforts directed 

toward them and incidental to other 

fisheries. Hook-and-1 ine, snook 

seines (later banned), the snook gill 

net, and other gear such as mu1 let 

trammel nets and gill nets were used. 

Production was concentrated in warmer 

months (Marshal 1 1958) in brackish 

and salt waters. 

In the mid-1950's a decline of 

snook populations was perceived by 

conservation groups and attributed by 

them largely to commerci a1 

exploitation (Vol pe 1959). 

Legislative efforts over a few years 

culminated in passage of a bill 

prohibiting sale of snook in the 

State of Florida and setting a daily 

bag limit of four fish per fisherman. 

Catch of snook from 1941 through 1955 

showed a maximum catch in 1948 of 

800,698 lb (Marshall 1958). In all 

but one of the years reported, west 

coast landings exceeded those on the 

east coast, usually by a factor of 

two. For 1955, the value to the 

fishermen of 451,661 lb was $63,233 

(Marshal 1 1958). 

For this same period there were 

no direct assessments of sport 

fishing harvest. However, incidental 

to a study of movement in 1956, Volpe 

(1958) used tag returns to partition commercial and recreational efforts. 

For the two leading production areas, 

Collier and Lee Counties, he 

estimated that sport exploitation 

accounted for 45% of the total snook 

harvest. 
Limitations of the available 

production data were noted by Marshall 

(1958), who questioned their 

re1 iabil ity as indicators of actual 

fish abundance. Rarshall identified 

possible causes for declines in 

landings, including use of the seine, 

market decl i ne , and reduced 

availability of snook. It was not 

possible, however, to calculate 

catch-effort statistics based on the 

fisheries production records 

available. 

It is important to elaborate on 

the role of habitat as a factor in 

snook availability for fishery 

exploitation. Sensitivity to low 

temperatures (Vol pe 1959) is discussed 

in the habitat section of this paper. 

The fol lowing environmental 

a1 terations were hypothesized by 

Marshall (1958) to be of more 

importance than fishing in the decline 

of C. undecimalis in the 1950's: 

reduced freshwater discharge into 

south Florida estuaries; sewage and 

industrial pollution; dredging and 

filling; mosquito control practices 

including ditching and draining 

marshes, and insecticides. Marshal 1 

concluded that even with no fishing 

pressure, the snook population would 

have decl i ned. 

Sport Fishing 

Since 1957, when legislation made 

it illegal to buy or sell snook, 

harvest has been limited to 

recreational angl ing. Nonetheless, 

pressures on the fishery stock 

continued, and in 1982 emergency 

authority was granted to the Florida 

Department of Natural Resources (FDNR) 

to prohibit taking and possessing 

snook between June 1 and July 31, 1982 

(Sport Fishing Institute [SFI] 1982). 

The SF1 (1982) note also documented 

the FDNR concern that "collapse of 

the snook fishery is likely to 

result" without a prohibition of 

fishing during the spawning season, 

and cited FDNR popu lation estimates 

of mature fish in the gulf coastal 

area of Naples for 1977 (28,000 fish) 

and 1981 (8,600 fish). 

The FDNR study of angl ing in the 

NaplesIMarco Island area found that 

45% of the annual snook catch was 

made in the period June I-July 31 

(Florida Saltwater Fisheries Study 

and Advisory Council 1982; Bruger in 

prep.). This is a time of local 

spawning movement. Furthermore, 

tagging in 1981 revealed recruitment 

failure due to a poor spawning year 

in 1978. This compounded the 

pressure on snook from low 

temperatures and environmental 

pollution (SF1 1982). 

Tagging (Bruger 1981) in this 

area since 1976 indicates a smal I, 

heavily exploited subpopulation of 

snook (Bruger 1980). Data from this 

project are under analysis but not 

yet published, so that further 

discussion of popu lation dynamics is 

not yet possible. 

Fishery Management and Restoration 

Fishery systems are composed of 

three elements that may be managed 

individually or in concert: habitat, 

biota, and fishing. A1 though State 

and 1 ocal governments are sensitive 

to issues concerning habitat 

restoration or protection, the many 

aquatic resource laws and policies in 

Florida are not targeted exclusively 

to snook population conservation. A 

mu1 tiple-use philosophy appl ies to 

management of resources. However, 
conservation of coastal fresh and 

brackish waters will directly benefit 

snook. 

Manipulation of the bioloqy -- of 

~entro~omus undecimal is has been 

addressed bv Florida Game and Fresh 

Water Fish iommission research on fish 

culture. A principal motivation for a 

series of experiments on propagation 

and rearing of snook was the 

suggestion of stocking them in 

freshwater in south Florida. Shafland 

and Koehl (1979) raised the 

possibility that snook fisheries might 

be reestablished as a recreational 

resource while also increasing 

predation on less desirable exotic and 

roughfish species overcrowding many 

areas. In mid-1982, pub1 ic interest 

in saltwater stocking in the Miami 

area was expressed. Results of a 

long-term culture study, including 

review of limitations to finger1 ing 

production, are presented by Chapman 

et al. (1982). 

Management of fishery effort has 

been discussed previously. The 

Florida Saltwater Fisheries Study and 

Advisory Counci 1 (1982) recommended 

that the June-July closed angling 

season be in effect for 5 years, 

during which time monitoring studies 

would be conducted. More recently, 

FDNR establ ished an Emergency Fishing 

Ban that prohibited taking snook of 

any size during January-February 1983. 

ECOLOGICAL ROLE 

Snook a re opportunistic 

carnivores. They tend to be 

piscivorous, with their specific diet 

varying according to the habitat in 

which they reside. In east coast 

freshwaters, juveniles prey upon 

microcrustaceans , palaemonid shrimp, 

and especial ly neonatal mosqui tofish 

(Gambusia affinis). The diet of 

salt-marsh juveniles ic similar, with 

the addition of sheepshead minnow 

(Cyprinodon varie atus). In the 

seagrass haesnook prey 

principal1 y on fish, primarily 

anchovy -(~nchoa mi tchi 11 i ) aid 

and on 

et al. 1983). 

Harrington and Harrington (1961) 

collected juvenile snook in the same 

general areas, but found that at 15 

mm FL the diet was made up of 10% 

fish with the other 90% consisting 

primarily of copepods. By 25 mm FL 

these two percentages were 

essentially reversed, and at 35-45 mm 

FL the proportion of fish in the diet 

remained high, but copepods were 

replaced by palaemonid shrimp. 

On Florida's west coast fishes 

were also the major prey item (80.8% 

by volume) of juvenile snook, with 

sai lfin molly (Poecilia. latipinna) 

the most numerous species. Shrimps 

a re next in importance 

volumetrical ly, followed by portunid 

crabs, insects, and microcrustaceans 

(Fore. and Schmidt 1973). All 

juveniles from 14 to 196 mm FL were 

apparently lumped together for this 

diet study. 

In two studies of larger snook, 

Marshall (1958) and Fore and Schmidt 

(1973) agreed that the adult diet 

consists mainly of fish and 

crustaceans, but they differed on the 

proportions of the various 

components. Marshall (1958) 

identified seven species of fishes, 

two of which (striped mullet [Mugil 

cephal us] and pigfish [Orthopristis 

& chr so teraJ) were not found by Fore (1973), who identified 11 

species. The former study reported 

fish as making up 86.4% by volume of 

the adult diet and the latter 55.1%. 
The two studies were also not in 

agreement on the importance of 

crustaceans, especially crabs, in the 

diet of adult snook. Marshall (1958) 

found that crabs represented only 4.4% 

by volume of the diet, while Fore and 

Schmidt (1973) reported 32.3-y 

volume. 

The wide range of prey of adult 

snook is' attributable to the wide 

range of salinities in which snook are 

found (Marshall 1958). Fore and 

Schmidt (1973) concluded that the 

preponderance of food organisms was 

associated either partial ly or 

entirely with the water column. 

Strictly benthic organisms and bottom 

debris, normally found in the stomachs 

of benthic feeding fishes, occurred 

only rarely in snook, indicating that 

the snook is a pelagic feeder. 

Although the diet of snook overlaps 

that of many fishes, no evidence for 

the existence of competition has been 

reported. No published account of 

important predators on snook was 

found. 

ENVIRONMENTAL REQUIREMENTS 

Temperature 

Nearly all references to snook 

that discuss their distribution 

consider low water temperature as a 

major limiting factor. Storey and 

Gudger (1936) observed that during the 

winter of 1917 when air temperatures 

dipped below freezing at Sanibel Island, Florida, snook were so lethargic that fishermen landed hundreds of 

pounds per boat using dip nets. 

Storey and Gudger (1936) and Marshal 1 

(1958) agreed that a low mean monthly 

water temperature of 15.6"C 1 imi ted 

the range of snook in Florida. More 

recent information on cold water 

i nf 1 uence i s presented by Chamber1 in 

and Armstrong (1977). 

Although young snook have been 

recorded from as far north as New 

York (Schaefer 1972), low water temperatures general ly prevent the 

establishment of permanent populations north of Florida. Linton and 

Rickards (1965) col lected young-ofthe-year snook in Georgia continually 

for 6 months until the water temperature dropped to 18°C in late November, after which no more were caught. 

In an experimental study of temperature effects, Shafland and Foote (in 

review) found that 4-month-old snook 

died at water temperatures of 

12"-14°C. 

Sal i n i t v 

As noted, adult snook occur in a 

wide range of salinities, from 0 ppt 

to full-strength seawater. Snook are 

unable to spawn in freshwater, 

however, since their sperm is 

activated only by saltwater (L. A. 

Ager, Florida Game and Fresh Water 

Fish Commission, pers. comm. as cited 

by Shafland and Koehl 1979). Larvae 

and juveniles are apparently capable 

of surviving the same salinity range 

as adults since Shafland and Koehl 

( 1979) successfully converted 

15-day-old snook from seawater (35 

ppt) to freshwater. 

-- Habitat 

The conspicuous and nearly 

constant feature of the snook's 

habitat in Florida is the presence of 

mangroves (tlarshall 1958). The 

distribution of mangroves throughout 

the State closely parallels that of 

snook, and the larger areas of mangroves typically coincide with maximum snook production. Austin (1971) 

likewise concluded that the presence 

of snook was characteristic of both 

high and low salinity mangrove 

estuaries in Puerto Rico. 
There has been an extensive 

reduction of mangrove swamp, especial - 

ly along Florida's southeast coast. 

Adult snook are still found in a 

variety of other habitats (Figure 4) 

including nearshore reefs, sandy 

beaches, jetties, and other shore1 ines 

in fresh-, brackish, and marine waters 

(Gilmore et al. 1983); however, larval 

and juvenile snook have been found 

only in a restricted range of habitat 

types (see Life History). During 

these life stages, when snook are most 

subject to predation and metabol ic 

requ i remen ts a re high, the 

availability of proper habitats is 

apparently critical (Gilmore et a1 . 1983). The necessity of maintaining 

habitat to sustain populations of 

snook was reiterated at a Snook 

Symposi um he1 d November 20, 1982, 

co-sponsored by FDNR and the 

International Game Fish Association. 

Other Envi ronmental Factors 

Although no studies of the 

oxygen requi rements of adul t snook 

were found, Shafland and Koehl (1979) 

reported that juveniles survived 

overnight minimum dissolved oxygen 

concentrations of 0.4 ppm in small 

grow-out ponds. No thorough study of 

the parasite fauna of snook has been 

reported, despite the fact that 

Marshall (1958) found a prevalence of 

70% for an unidentified nematode in 

the mesenteries and stomach wall and 

an intensity of up to hundreds of 

worms per fish. Other parasites 

reported from snook include 

phi 1 ometra centro omi (Nematoda) in 

the nasal mucosa _le Caballero 1974) and 

Prosthenh stera obesa (~rematoda) in 

Mder (Caballero and Jimenez 1967), both from Mexican waters. 

Howse (1972) reported snook as a new 

host for Lymphocystis virus. 
LITERATURE CITED 

Austin, H. M. 1971. A survey of the 

ichthyofauna of the mangroves of 

western Puerto Rico during 

December, 1967-August, 1968. 

Caribb. J. Sci. 11 (1-2): 27-39. 

Beebe and Tee-Van. 1928. The fishes of 

Port-au-Prince, Haiti. Z oo logica 

10: 1-279. 

Bruger, G. E. 1980. Preliminary 

analyses of snook, Centro omus 

undecimalis, population -+?- ynamics 

in the Naples-Marco Island region 

of southwest Florida. Fla. Sci. 

43 (suppl . ): 25. (Abstr. ) 

Bruger, G. E. 1981. Comparison of 

internal anchor tags and Floy 

FT-63 dart tags for tagging 

snook, Centro omus undecimalis. 

Northeash Sci. 4(2): 

Bruger, G. E. (in prep.) Snook age 

and growth in southwest Florida. 

Burgess, G. H. 1980. Centropomus 

undecimal is (Bloch) , snook. Page 

572 in D. S. Lee et al. Atlas of 

NortFAmerican freshwater fishes. 

N.C. State Mus. Nat. Hist., 

Raleigh. 854 pp. 

Caballero, R. G. 1974. Contribucion 

a1 concimiento de 10s Meatodos de 

peces de 1 os 1 i torales de Mexico: 

111. Dos nuevas formas. Publ. 

Biol. Inst. Invest. Cient. Univ. 

Auton. Nuevo Leon l(4): 33-40. 

Caballero, Y. C. E., and G. F. 

Jimenez. 1967. Presencia de 

Prosthenh stera obesa (Diesing 

-, 1mTrematoda. 

Digenea) en peces comestibles de 

agua dulce de Mexico. Rev. 

Biol . Trop. 15(2): 283-287. 

Chamberlin, J. L., and R. S. 

Armstrong. 1977. Data on cold 

weather conditions along the 

Atlantic and gulf coasts during 

the fall and winter of 

1976-1977. U.S. Natl. Mar. 

Fish. Serv. Mar. Environ. 

Notice. 9 pp. 

Chapman, P., F. Cross, W. Fish, and 

K. Jones. 1982. Final report 

for sportfish introductions 

project. Study I: Artificial 

culture of snook. Florida Game 

and Fresh Water Fish Commission. 

36 PP. 

Florida Saltwater Fisheries Study and 

Advisory Council. 1982. Final 

report. Fla. Dep. Nat. Resour., 

Tall ahassee. 

Fore, P. L., and T. W. Schmidt. 

1973. Biolocly of juvenile and 

adult sn&k, Cen tropomus 

undecimalis, in the Ten Thousand 

Islands. Pages SVI-1-SVI-18 in 

Ecosystems analysis of the Bx 

cypress Swamp and Estuaries. 

U.S. Environ. Prot. Agency Surv. 

Anal. Div., Athens, Ga. 
Fraser, T. H. 1968. Comparative the orinci~al soeci es . osteoloov -" of the Atlantic snooks 

(Pisces, Centro omus). Copeia 

1968(3): 43& 

Gilmore, R. G., C. J. Donohoe, and D. 

W. Cooke. 1983. Observations on 

the distribution and biology of 

east-central Florida populations 

of the common snook, ~entro omus 

undecimalis (Bloch). 

Spec. Suppl . Issue 45(4) 

h 

Part 2. 

Greenfield, D. W. 1975. 

poeyi from Be1 ize, wit 

the Western Atlantic species of 

Centropomus. Copeia 1975(3): 

582-583. 

Harrington, R. W., and E. S. 

Harrington. 1961. Food 

selection among fishes invading a 

high subtropical salt marsh: 

from onset of flooding through 

the progress of a mosquito brood. 

Ecology 42(4): 646-666. 

Howse, H. D. 1972. Snook 

(Centro omus: Centropomidae) : 

new for lymphocysti5, 

including observations on the 

ultrastructure of the virus. Am. 

Midl. Nat. 88(2): 476-478. 

Lau, S. R., and P. L. Shafland. 1982. 

Larva 1 development of snook , Centropomus undecimal is (Pisces: 

Centropomidae) . Copeia 1982(3) : 

618-627. 

Linton, T. L., and W. L. Rickards. 

1965. Young common snook on the 

coast of Georgia. Q. J. Fla. 

Acad. Sci. 28(2): 185-189. 

Marshall, A. R. 1958. A survey of 

the snook fishery of Florida, 

with studies of the biology of 

~entro~ombs undecimal is loch): 

Fla. Board Conserv. Mar. Res. 

Lab. Tech. Ser. No. 11. 37 pp. 

Rivas, L. R. 1949. Checklist of the 

Florida game and commercial 

marine fishes. Fla. Board Conserv. Mar. Lab. Ed. Ser. No. 12. 

46 PP. 

Rivas, L. R. 1962. The Floridafishes 

of the genus Centropomus, commonly known as snook. Q. J. 

Fla. Acad. Sci. 25(1):53-64. 

Schaefer, R. H. 1972. First record 

of a snook from New York waters. 

N.Y. Fish Game J. 19(2): 

182- 183. 

Shafland, P. L., and K. J. Foote. In 

review. A lower lethal 

temperature for fingerling 

snook, Centropomus undecimalis. 

Shafland, P. L., and D. H. Koehl. 

1979. Laboratory rearing of the 

common snook. Proc. Annu. Conf. 

Southeast. Assoc. Fish Wild1 . Agencies. 33: 42'5-431. 

Sport Fishing Institute. 1982. 

Snook given added protection. 

SF1 Bull. No. 335. p. 5. 

Storey, M., and E. W. Gudger. 1936. 

Mortality of fishes due to cold 

at Sanibel Island, Florida, 

1886- 1936. Ecology 17(4) : 

640-648. 

Volpe, A. V. 1959. Aspects of the 

bioloav of the common snook. 

undecimal is l loch j 

Florida. Fla. 

Board Conserv. Mar. Lab. Tech. 

Ser. No. 31. 37 pp. 
50777 -101 -- ~ ~ - .- . - -. . . 

REPORT DOCUMENiATlON : !-LH!~""" : I ~CC,~,,-~: : A .,..,r,n thO 1 

PAGE ! FWS/OBS-82/11.16* I ~- .. - -~ -~ -- -. .-- - . - ----- ~ -- 4. Till? and Sublitlr ! 5. He~on ~r:n 

Species Profiles: Life Histories and Environmental Requirements 1 October 1983 

of Coastal Fishes and Invertebrates (South Florida) -- Snook it - -- 

William Seaman, Jr., and Mark Collins 

Organuar on Name and Address 

Sea Grant and School of Forest Resources and Conservation, and I - .. Department of Zoo1 ogy 11. ~ontracl(~) or Granr(G) NQ 

University of Florida 

Gainesville, FL 32611 

- -- ~ -. - -- - -- -. - - 

12. Swnsoring Or~anizat10n Name and Addicrs 13. Type of Rrwn b Prrtod Cover-c 

National Coastal Ecosystems Team U.S. Army Corps of Engineers 

U.S. 

Fish and 

Department 

Wildlife 

of 

Service Waterways Experiment Station I__: - - ~ ~- the Interior P.O. Box 631 

Washi nqton, DC 20240 Vicksburg, MS 39180 -- pp . 

15. Supp+mentary Notes 

*U.S. Army Corps of Engineers report No. TR EL-82-4 

16. Abstract (Limit: 200 rords) f 

Species profiles are literature summaries on the taxonomy, morphology, range, life 

history, and environmental requirements of coastal finfishes and shellfishes. They are 

designed to assist in environmental impact assessment. The snook (Centropomus undecimal i s) 

is of regional importance in the recreational fishery of south Florida, where its abundance 

centers in mangrove-fringed coastal waters. Commercial fishing is no longer allowed, and 

closed sport seasons have been enacted recently. Serious population declines have been 

caused by degradation of habitat and fishing pressure. Snook exhibit a classic estuarinedependent life cycle, with spawning in nearshore salt waters in warmer months and juvenile 

development in brackish inshore tidal streams, salt marshes, and grass beds. Juveniles 

remain in estuaries for the first year of life, whereas adults range from freshwater to 

oceanic habitats. Snook are carnivorous, non-migratory except for localized spawningassociated movements, and typically achieve sexual maturity in the second and third 

years of life (at 40-50 cm fork length). This species is susceptible to cold, with 15.6"C 

regarded as a lower limiting temperature. 

Estuaries 

Mangroves 

Fishes 

Ecology 

Snook; 

Centropomus decimali is; 

Life history; 

Habitat requirements; Fishing 

1 Unclassified 

I Unl i m i t e d 

I 

. Unclassified .. . 

<,,.. 7 -, - .s;-::; :fl; '> ",,".'I , <'L,U : '. . . 
REGION 1 

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