The American crocodile (Crocodilus acutus) is the most widely distributed species of New World crocodiles occurring from south Florida and coastal Mexico down into South America and along the Caribbean. Despite its widespread distribution, C. acutus has experienced severe declines due to overexploitation and loss of habitat for nesting throughout its historical range. In south Florida, the species is at the margin of their northernmost distribution. Successful species conservation is dependent on adequate population dynamics data but age-specific demographics are lacking for long-lived iteroparous species, including the American crocodile. We used a long-term capture-recapture study to assess crocodilian demography, define species’ population growth rate, and outline its conservation status. Surveys were conducted in cooling canals of Turkey Point power plant from 1978 to 2014 where crocodiles were caught, measured, permanently marked, and released. Our objectives were to 1) to describe age-specific survivorship, and 2) to determine population growth rate and its sensitivity to demographic parameters. We performed capture-recapture analyses to estimate annual survival rates and modeled recapture rates. We constructed an age-structured Leslie-Lefkovich matrix to identify parameters most critical to population dynamics and used population projection models to estimate survival probabilities and population growth rate.
Results/Conclusions
A total of 7,427 hatchlings were captured and marked, of which 380 were recaptured during subsequent years for as many as 25 years. Recapture rates were negligible in early years but increased to 0.373 with consistent monitoring after 2008. Survival was strongly age-dependent with hatchlings having lowest survival rates at 16%, juveniles ranged from 58-82% and increased to near 100% at adulthood. Here, hatchling survival was much higher than expected for crocodilians and other reptile species. Age at first reproduction was found to be 7 years old with an age-specific fecundity of 0.45 that increased to 22.2 by age 18 when all females were shown to be reproductive. We estimated asymptotic population growth rate of λ = 1.040 suggesting a 4% annual increase. Sensitivity analysis showed that population growth rate was most dependent on survival of younger crocodiles that were not yet reproductive, contrary to the expected survival of older, reproductive adults. Current management practices are focused on nests and hatchling survival however protection efforts that extend to juvenile crocodiles would be most effective for species survival. Crocodiles, as a large, long-lived, highly fecund species do not conform to the slow-fast continuum, and calls for a redefinition that addresses large, long-lived reptiles.