This work is associated with the U.S. Geological Survey, Across Trophic Level System Simulation (ATLSS) Program and has the objective of supplying empirical information, particularly involving reproductive physiology, needed to develop a population model for the American alligator (Alligator mississippiensis). Nest monitoring at the Everglades National Park has shown that mean water levels in the park are closely correlated with nest production by the alligators. It is known that reproductive performance of the alligator is related to food quality and availability. However, the detailed effects of water levels on the availability of prey, their quality as a food item, the presence or absence of toxins or parasites, and the resulting effect on fertility are not known. Previous work on the alligator has shown that critical nutrients in the alligator diet affect health status, growth and specific reproductive parameters. Recently it has been shown that fatty acid profiles of fat in the diet affects egg fertility, embryonic survival, and possibly hatchling vigor. A knowledge of prey availability, quality and composition is necessary to predict its effect on health status, fertility, growth, and development in the alligator population of the Everglades. Consequently, knowledge of the effect of water levels and other environmental factors on prey availability and food value is necessary to predict its effects on health status, growth, development and reproductive performance. Thus, with appropriate data, the effects of water levels on nest-rate, clutch size, percent fertile eggs, embryo survival, hatch rate and hatchling vigor could be predicted by changes in types of prey available, quantities, quality and their potential for toxins and/or parasites. Quality or biological value of the dietary protein depends on its digestibility, amino acid profiles and sufficient energy for its utilization. Toxins and/or parasites in the prey can, of course, affect all parameters. Therefore, any predicted effect of nutrient status of the habitat should be confirmed by an evaluation of body condition, health status and breeding condition of the population. Body condition and health status of the alligator population are evaluated by measuring parameters such as death rates (size-gender-puberty profiles) physical condition, morphometrics, clinical values, pathology and microbiology. Breeding condition or reproductive potential of the population is evaluated by a determination of reproductive parameters such as percent adult females, sex ratio, nest rate, clutch size, egg quality, percent fertile (banded) eggs, embryo survival, hatch rate and hatchling vigor. These parameters are measured as quantitative evaluation-variables. This research offers methods to estimate these variables, accurately compare them with control samples, and provide a cost for each determination. The results provide the potential of allowing a more accurate prediction of the effects of water levels and other environmental factors on growth rate, development, and reproductive performance of the alligator.

Our initial studies on Everglades alligators have shown significant differences in size and shape of the eggs produced in the park and the hatchlings produced are significantly smaller than those from control areas. However, growth performance of the hatchlings does not appear to be significantly different from that of control animals. It has also been determined that body condition of the adults seems to be poor and clinical values of the animals indicates a chronic inflammation in at least some of the animals. These findings need to be confirmed; the cause and source of the inflammation needs to be identified and the effect of water levels on the presence and concentration of pathogens and toxins needs to be established. These factors may strongly influence the reproductive rate, growth performance, and energy requirements of the population. The evaluation variables to be determined in our study provide critical data to support the development of an individual based American alligator model. The proposed experimental design should give accurate estimations of the evaluation variables for a single year; however, fluctuations in water levels require that data be collected over several years to provide Everglades Evaluation variables with a margin of error suitable for a reliable model which will allow planners to predict the effects of water levels on the alligator population.

The general objectives of the work are as follows:

1. Monitor the reproductive potential of the alligator population in the Southern Everglades (Everglades National Park) over a 5-year study period.
2. Monitor the prey quality over the study period.
3. Monitor egg quality over the study period.
4. Monitor health status of the alligators over the study period.
5. Determine associations between reproductive potential, prey quality, egg quality, and health status over the study period.

Random samples of 145 eggs from different clutches were collected in the Southern Everglades. Forty-one eggs were determined to be infertile or had very early embryonic death. Hatch rate for the fertile eggs and stage of embryonic deaths were recorded. Samples of 144 eggs from the Rockefeller Refuge in Louisiana were used as controls. Egg statistics and growth performance of the hatchlings were determined for both experimental and control groups. Egg statistics (35 factors or variables) determined for 1997 will be compared with values determined in 1995 and 1996 and with the factors obtained from 15 areas (lakes and farms) over 10 years in 10 X 15 two-way ANOVA. The comparisons involved the 20 factors determined in over 7,000 observations. Health status of the Everglades alligators was determined in 1997. Blood samples were drawn from 16 animals from the Northern Everglades (conservation areas) and transmitters were implanted in the animals in order to track them. Thirty blood samples were taken from animals captured in the Southern Everglades (Everglades National Park) and 20 variables (clinical values) compared with animals raised in captivity but hatched from eggs collected in the Southern Everglades or Louisiana (45 animals). The values obtained for the three groups and normal values obtained from animals captured in other areas were compared.

A significant part of the funding for this research was provided from the U.S. Department of the Interior South Florida Ecosystem Restoration Program "Critical Ecosystems Studies Initiative" (administered through the National Park Service) and from the U.S. Geological Survey, Florida Caribbean Science Center. Additional funding for the "Across Trophic Level System Simulation" was also provided by the Environmental Protection Agency and the U.S. Army Corps of Engineers.

SELECTED REFERENCES

Cardeilhac, P.T., 1991, Diagnosis and treatment of infertility in captive alligators, final reports for the Aquaculture Market Development Aid Program: Florida Department of Agriculture, Tallahassee, Florida, v. I-III, 1987-1991.

Cardeilhac, P.T., Fleming, M.O., and Bass, O.L., 1996, An evaluation of egg quality and hatchling growth potential for American alligators in the Southern Everglades: Proceedings International Association for Aquatic Animal Medicine, v. 27, p 72-76.

(This abstract was taken from the Proceedings of the South Florida Restoration Science Forum Open File Report)