American Crocodile Population Dynamics

Moler, Paul

A total of 391 crocodiles were tagged on Key Largo, and 200 of these were recaptured a total of 530 times. All but 2 recaptures were of known-age animals. The sex ratio of animals > 1m in length was 2:1 in favor of males. Sixty-five crocodile nests were located on Key Largo during the period 1978-1990, of which 34 (52.3%) produced some young. A total of 373 hatchlings were tagged, annual production ranging from 0 to 74 hatchlings. Hatchling survival varied from year to year, probably as a function of rainfall, survival being lower in years of low rainfall. Estimated first year survival for the period 1979-1988 was 20.4%. Age specific survival increased markedly in the second year to 64.9%. Annual survival of crocodiles older than 5 years probably exceeds 80% and may approach 100%. Hatchlings grow rapidly for the first 4 months, but then growth essentially stops with the advent of cooler winter temperatures. This period of little or no growth lasts for about 3 months, and rapid growth resumes in late March or early April. Minimum size of sexual maturity may be reached in 8-10 years, but it is not known whether crocodiles are reproductively competent at this age. At sheltered nest sites, hatchling crocodiles tend to remain together for a period of 4-5 weeks and then disperse. Many disperse only short distances, but movements.of 8-10 km have been recorded within the first 3 months. From the nesting area on North Key Largo, crocodiles disperse throughout the adjacent mangrove swamps, and 10 individuals have been recaptured or salvaged along U.S.Highway 1 and on the mainland at distances of 12.8-112 km. Of these, 6 for which sex is known were all males. Although a few crocodiles are known to have died of exposure to freezing weather, the greatest identifiable source of loss is highway mortality.