Progress 10/01/01 to 10/01/02
Outputs
Normal values for reproductive parameters such as nest rate, fertile eggs per nest, and hatchling yield for the alligator population on a particular habitat are determined by a moving-median-of-3 method using the median annual values for each parameter collected over 5 or more years of environmental steady-state. Normal values for lake Griffin in Central Florida was determined over an 11-year steady-state period from 1983 through 1993. Normal nest rate for the lake was 170 nests (SD = 7.4 nests) containing 47 eggs per nest (SD = 1 egg) giving a total egg yield for the lake of 7990 eggs with 93.9% (SD = 1%) of the eggs fertile and an embryonic mortality of 40.5% (SD = 0.65%). Normal potential hatchlings yield in a steady-state year for the lake was 4,500 based on the product of fertile egg production and embryonic mortality levels. Potential hatchlings yield for the lake began a declining trend from the determined normal levels in 1994 as follows (% of normal): 1994
(92.8%), 1995 (74.6%), 1996 (56.3%) and 1997 (3.0%). Nest rate decreased to 73% of normal in 1994 but did not significantly change over the 4-year period 1994 through 1997. Eggs per nest and percent fertile eggs decreased by less than 10% over the period of decline; however, embryonic mortality increased to 2.4 times the normal level and was the principle cause of the decline in potential hatchlings yield. Ninty two percent of the embryonic deaths occurred before day-10 of a normal 70-day developmental period for artificial incubation. Median alligator egg yolk concentrations of 34 organic contaminants and 10 metals were determined for samples of eggs collected from Lake Griffin in 1988, 1993 and 1997 to determine changes in concentrations of the contaminants over the test period. Increases in contaminant concentrations would be compared to increases in embryonic death rates. Yolk contaminant concentrations for 1988 and 1993 yolks were considered steady-state levels since the lake had
normal potential hatchling yields in those years. The contaminants included 18 organochlorine compounds 16 polyaromatic hydrocarbons and 10 metals. Five of the 18 organochlorine compounds tested could be detected in the yolks of 1997 eggs (concentration in ppb): p,p'-DDE (462), Dieldrin (88), cis-Nonachlor (33), trans-Nonachlor (28) and Endrin (14). None of the 1997 yolk concentrations of these 5 organochlorine compounds, nor any combination of the 5, were greater than 1988 or 1993 yolk concentrations. Steady-state yolk concentrations in ppm of the following metals were determined for Lake Griffin (S.D.): Hg 0.031 (0.001), As <0.19, Se <0.2, Cd <1.0, Pb <2.0, Zn 17.2 (0. 4), Ni <1.0, Cr <5.0, Al 44.7 (3.1), Cu <2.50 and Fe 29.9 (4). With the exception of Al, metal concentrations did not significantly change over the study period and were not significantly different from concentrations found in eggs from other alligator populations. There does not appear to be any correlation of egg
yolk contaminant concentrations with the increase in embryonic death rates.
Impacts
A declining trend in potential hatchling yield for lake Griffin in Central Florida was detected by methods using the American alligator as a sentinel to monitor Southern wetlands. The decrease in hatchling yield could not be correlated with alligator egg yolk concentrations of 34 organic and 10 metal contaminants.
Publications
- Cardeilhac, P. T. Winternitz, D. Barnett J. D., Bass O.L., Wolff, W.R. (1999) The American Alligator as a Sentinel for for the Environmental Status of Southern Wetlands. Proceedings International Association for Aquatic Animal Medicine. 30: 69-70.
- Cardeilhac P. T. , Winternitz D. L., Barnett J. D., Bass, O. L. Wolff, W.F. (1999) The Moving Median Method to Estimate Normal Egg Parameters for Alligator Populations in the Southern Everglades, Southwest Louisiana, and Lake Griffin Proceedings International Association for Aquatic Animal Medicine. 30: 155-159.
- Cardeilhac, P.T., Winternitz D.L., Barnett J.D., Froelich E.,Foster K.O., and Ashley, J. D. (1998). Declining Reproductive Potential of the Alligator Population On Lake Griffin in Central Florida. Proceedings International Association for Aquatic Animal Medicine, Vol. 29 pp 30 - 36
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Progress 10/01/00 to 10/01/01
Outputs
The mean contribution by mass of individual prey items to the diets of large (>152 cm) alligators has been determined by examining stomach contents of 253 animals from 1995 through 1997. Prey items that comprise more than 4% of the mean dietary mass are (%): snakes (33), birds (25), mammals (15), turtles (12), fish (10), and amphibians (5). Collecting samples of each prey item and determining individual nutrient and contaminant concentrations were used to estimate total nutrient and contaminant contributions by a prey item to the diet of the alligator. Mean nutrient and contaminant contributions by a prey item were the product of the fractional mass contribution of the prey item to the diet and the concentration of the component in the prey item. The average prey diet for everglades alligators on a dry weight basis contains 63% protein, 17.9% fat, 18.6% ash and approximately 4,500 cal per kg. The average prey diet on a dry weight basis contains 250 ppm Fe, 120 ppm Zn,
4 ppm Cu, < 0.5 ppm Se, 3.3 ppm Hg, <3.5 ppm Cd, < 7 ppm Cr, < 4 ppm Pb, < 4 ppm Ni, and <0.75 ppm As. Protein contributions to the diet by prey items are (%): birds (30); snakes (26); mammals (16); turtles (12); fish (7); and amphibians (4). Fat contributions by prey items to the diet are (%): birds (50), mammals (20), turtles (14), snakes (10), fish (3), and amphibians (1). Ash contributions by prey items to the diet are (%): snakes (43), birds (25), mammals (13), turtles (12), fish (6), and amphibians (3). Energy contributions by prey items to the diet are (%): birds (38), snakes (21), mammals (18), turtles (13), fish (6), and amphibians (3). Mercury was the only metal component of the diet detected at levels considered potentially toxic. The mercury concentration of prey items was (ppm): (%): snakes (2.5), turtles (0.37), fish (0.24), amphibians (0.15), birds (0.064), and mammals (0.036). Mercury contributions by individual prey items to the diet are (%): snakes (89), turtles (4),
fish (3), birds (2), amphibians (0.8), and mammals (0.6). Snakes were the only prey item that contained mercury at a concentration of > 0.5 ppm and they contribute most (89%) of the mercury in the diet of the large everglades alligator.
Impacts
Snakes were identified as the major contributor of mercury to the prey diets of large alligators and mercury was the only contaminant detected at potentially toxic levels.
Publications
- Cardeilhac, P. T., McClellen W. M., Cardeilhac J. P., Dixon, H. M., Barnett, J. M., Barr, B. Wolfe W. R., Bass, O. L. and Fleming M. D. (2001) The Source of Nutrients and Contaminants of Alligators in the Everglades National Park. Proceedings International Association for Aquatic Animal Medicine. 32: p. 3.
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