Research on Species Distribution and Population Dynamics of the Reintroduced Chinese Alligators in Chongming Dongtan, Shanghai

The Chinese alligator is a critically endangered species that is endemic to China, with fewer than 200 individuals in the wild and over 13,000 in captivity. Reintroduction is crucial to restore its wild population, and Dongtan Wetland Park (DWP) in Shanghai is one of the reintroduction sites. However, the population size and viability were unclear due to inconsistent post-monitoring and lack of program evaluation. No further introduction or management plans were devised. Current literature also had little quantitative research on Chinese alligator habitat selection. To understand DWP population status, this study first conducted population surveys using spotlight count. N-mixture models were employed to estimate the population size, and an average size of 54 individuals was calculated. Then, we examined the impact of environmental factors on Chinese alligator habitat selection in DWP by conducting habitat surveys and applied species distribution models. Finally, this paper used the software Vortex to identify factors influencing population growth and simulate population development. Vortex is commonly used for population viability analysis and has been used on crocodilian species. We discovered that high vegetation coverage and a moderate presence of trees had a positive impact on alligator presence, while high mortality rates, low percentage of females breeding, and the percentage of males at birth exceeding 50% could severely hinder population growth. The viability analysis showed that the population is viable, and reintroduction may not be needed in the short term. Finally, we recommended that the park should construct more proper habitat with riparian cover and elevated ground for nesting females. Systematic and consistent monitoring should be established in DWP to provide long-term data. If monitoring shows low recruitment rates, reintroducing alligators from diverse genetic lineages should be considered.