[NO COPY OF PAPER AVAILABLE. ABSTRACT FROM SCHMIDT (1991).] This study is 
designed to evaluate the need for additional openings through the causeways in the area 
of Cross Key, from the Florida mainland to Key Largo. Information on this area is 
needed to develop plans for four-laning this section of US 1 in relation to current and 
past water management practices involving circulation, hypersalinity, and changes in 
freshwater flow. It was found that salinities on either side of Cross Key may be high 
during the dry season and under drought conditions. It was recommended that no further 
structures were needed to obtain relief from hypersaline conditions in the Cross Key 
area. 
1979 - 1980 
Gruber, S. H. (1982) Role of the lemon shark, Negaprion brevirostris (Poey), as a predator 
in the tropical marine environment: a multidisciplinary study. Florida Sci. . 45:46-75. 
Sharks are numerically important members of many marine communities, yet little is 
known of their role in these ecosystems. Recent technical developments in laboratory 
and field have facilitated investigation of the autecology of the lemon shark Negaprion 
brevirostris (Poey). This littoral shark is abundant, lives well in captivity and is 
ideally suited for investigation. During 1979 and 1980, 984 young sharks were marked 
and released during a study of population dynamics. Each was injected with tetracycline 
for age validation. We tracked individual sharks for hundreds of kilometers via 
ultrasonic telemetry thus determining activity rates, movements, home range and diel 
periods. We evaluated blood gas parameters, food intake, digestion, growth, resting and 
routine metabolism in the laboratory. These data provide estimates of the energy 
budget of the lemon shark and form a basis for understanding the flow of energy from 
environment to shark. Our tentative conclusion is that an adult lemon shark must 
remove nearly 1500 g of fish daily (1.6 x 10 6 calories) to account for its vital 
activities. 
1979 - 1980 
Lutz, P. L., and A. C. Dunbar-Cooper (1982) The nest environment of the American 
crocodile, Crocodylus acutus. Rep. T-671. South Florida Research Center, Everglades 
National Park, Homestead, FL. 38 pp. 
In the nesting seasons of 1979 and 1980 selected crocodile nests from Florida Bay 
were studied to examine the nest environment throughout incubation. Nest 
temperatures ranged from 29.0 - 35.5°C, the higher temperatures more associated 
with the latter part of the season. A small diurnal fluctuation was recorded over 25 
days of monitoring a normal sand nest. Nest soil water values varied considerably 
(4.89 - 36.14%). Marl tended have higher amounts of water throughout the incubation 
period. All eggs lost water over the incubation period. The greatest loss appeared to 
occur towards the end of the season. The amount of water loss is determined by the egg 
shell permeability and the water vapor gradient across the egg shell, the latter being 
dependent on the hydration of the soil. In the most complete set of data the average 
water loss found was very similar to that found for birds (15%). The average birth 
weight of the hatchlings was 0.64 of the initial egg mass, also very similar to that 
found for birds. The oxygen diffusivity of sand was much greater than that of marl. In 
marl the diffusivity was strongly influenced by water content. In all nests there was a 
decline in oxygen and rise in C0 2 over incubation, i.e. developing embryos will naturally 
experience hypoxic, hypercapnic conditions. The changes were very variable between 
nests, though they appeared to be greater in mud nests. It appears that in several cases 
minimum nest oxygen levels were reached before the end of incubation. It is suggested 
that the metabolic rate of the nest clutch of Crocodilus acutus regulated by oxygen and 
carbon dioxide levels in the nest. This allows C. acutus to use soils of quite different 
and varying gas permeabilities for nesting sites. 
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