1976 - 1979 
Thue, E. B., E. S. Rutherford, and D. G. Buker (1983) Age, growth, and mortality of the 
common snook, Centropomus undecimalis, in Everglades National Park, Florida. Rep. T-683. 
South Florida Research Center, Everglades National Park, Homestead, FL. 33 pp. 
A study was made of age, growth and mortality of 325 snook, Centropomus undecimalis 
(Bloch), collected from sport fishermen in Everglades National Park from May 1976 
through December 1979. Fish sampled ranged in length from 284 - 940 mm FL (x = 
643 ± 11 mm) and in weight from 0.7 - 11.6 kg (x = 3.03 ± 0.17 kg). Females ranged 
in length from 464 - 940 mm (x = 680 ± 25 mm) and in weight from 1.0 - 11.6 kg (x" 
= 3.64 ± 0.49 kg). Males ranged in length from 284 - 889 mm (x = 632 ± 14 mm) and 
in weight from 0.7 - 7.2 kg (x = 2.84 ± 0.18 kg). Mean lengths of fish were largest in 
spring and smallest in winter. There were no differences in mean length among areas of 
capture. Snook were aged by scale annuli. Annulus formation occurred in spring (March 
- May). Ages of fish were mainly four- and five-yr olds. Recruitment to the fishery 
began at age two and was completed by age six. The oldest fish sampled was eight 
years old. The overall sex ratio favored males 3/1, but the ratio decreased steadily 
with age. The mean age of females was significantly greater than the mean age of 
males. There were no differences in mean age of fish among areas of capture. Mean 
calculated growth of all snook was 375 mm FL in the first year and 57 - 90 mm FL 
thereafter. Females were significantly larger than males in calculated mean lengths at 
ages one through four. Calculated fish lengths at age differed among areas of capture. 
Fish taken from the Whitewater Bay - Coot Bay area were larger at ages one through 
four than fish of the same age taken from the north Florida Bay - Cape Sable area. 
Sexual differences in length-weight relationship were noted. Females weighed more at a 
given length then males. Annual mortality rate of all fully recruited fish for the period 
1976 - 1979 was 78%. Female mortality was lower than male mortality. Conditional 
fishing mortality was twice as high as conditional natural mortality for males but was 
the same for females. Conditional natural mortality and exploitation ratio was higher 
for males than for females. 
1976 - 1981 
Dunson, W. A., and F. J. Mazzotti (1989) Salinity as a limiting factor in the distribution of 
reptiles in Florida Bay: a theory for the estuarine origin of marine snakes and turtles. 
Symp. on Florida Bay: A Subtropical Lagoon. Miami, FL. June, 1987. Bull. Mar. Sci. . 
44(1 ):229-44. 
Salinity is hypothesized to be the major abiotic factor limiting the colonization of 
Florida Bay by estuarine reptiles. This premise is supported by the small number of 
species of reptiles found in the bay in comparison with freshwater, the distinct 
osmoregulatory specializations of the few estuarine specialists that occur there, and a 
remarkable cline in the ability to tolerate seawater found among modern-day estuarine 
and coastal reptiles. This latter cline in osmoregulatory abilities is believed to 
represent a model of the evolutionary stages through which pelagic snakes and turtles 
have passed in developing adaptations for life in the open sea. Florida Bay is an 
especially useful site for the study of such adaptations since it is the only known 
location in this hemisphere where three specialized estuarine reptiles are sympatric: 
the American crocodile (Crocodylus acutus), the diamondback terrapin (Malaclemys 
terrapin), and the mangrove snake (Nerodia clarkii compressicauda). Small populations 
of freshwater turtles and the alligator also occur in tidal creeks along the northern 
shore. Recent advances in the study of turtles suggest that the single most important 
factor in determining tolerance to high salinity is the amount of seawater swallowed 
incidentally with food ingestion. This finding needs to be extended to other reptiles to 
test the hypothesis that fish eaters, such as snakes, that do not crush or bite chunks 
225 
