How to estimate population size in crocodylians? Population ecology of American crocodiles in Coiba Island as study case

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AbstractReliable estimates of crocodylian population size are desirable for both understanding the ecology and natural history of species and developing sound conservation and management plans. However, choosing appropriate methods to estimate population numbers can be difficult due to the paucity of comprehensive analyses regarding their effectiveness, robustness, and applicability. We estimated the American crocodile population size in the southern tip of Coiba Island, Panama, using both spotlight surveys (Messel's and King's visible fraction estimations) and mark–recapture (POPAN formulation–superpopulation) methods. We assessed and compared the outcomes of these methods with the overall capture record for the study area from 2009 to 2013, evaluating their applicability, accuracy, strengths, and limitations. Using historical and current capture data, we defined a minimum population size of ~112 non‐hatchling animals in our study area, which was larger than both Messel's (19.00 ± 7.50 individuals) and King's (25.71 ± 7.25 individuals) population size estimates, revealing that these latter approaches clearly underestimate population numbers. We estimated a total population size that range between 147 and 257 individuals based on POPAN formulation grouping the data by sex and age groups as the most plausible population size of the American crocodile population in this area at the time. We analyzed and discussed sources of bias in population size estimations for all methods used in the present study, providing recommendations to minimize errors and improve estimations. Finally, we analyzed and compared population ecology attributes obtained in our study with what have been reported in other insular and coastal areas across the American crocodile range, increasing knowledge about the ecology of the species.