Estimating population status and site occupancy of saltwater crocodiles Crocodylus porosus in the Ayeyarwady delta, Myanmar: Inferences from spatial modeling techniques

Abstract

Saltwater crocodiles Crocodylus porosus are listed as critically endangered in Myanmar because they are limited to Meinmahlakyun Wildlife Sanctuary (MKWS) in the Ayeyarwady delta region. Little contemporary data exists on their distribution and population size which hinders effective conservation and management. We conducted standardized spotlight surveys and camera trap surveys along the rivers inside MKWS, and two nearby reserved forests. We used Hierarchical N-mixture models, Spatial Count models, and the relative abundance index to estimate site use by and population sizes of saltwater crocodiles in the Ayeyarwady delta. To address biases in detectability, we used maximum-likelihood and Bayesian approaches (1) to assess occupancy (site use) and population parameters of saltwater crocodiles, and (2) to assay abiotic and anthropogenic factors affecting it. Saltwater crocodiles were more likely to be abundant and occupy in the waterways inside MKWS than the reserved forests, and in the narrow and low salinity waterways than the wide and high salinity ones. Abundance of saltwater crocodiles was lower in areas with the human settlements than in areas with no settlement. Creeks within MKWS had moderate salinity and no human settlement and therefore it can be regared as the last remaining optimal saltwater crocodile habitat of the Ayeyarwady Delta. We estimated the saltwater crocodile population sizes in MKWS were 75 ± 9.92 individuals as absolute spotlight index, 58 ± 8.02 individuals as the maximum likelihood estimate of the N-mixture models and 68 ± 10.00 individuals as the Bayesian estimate of the spatial count models. Current population estimates of saltwater crocodiles are lower than the previously reported population size in 1999, and the declining population is now restricted to MKWS. We suggest developing buffer zones in the reserved forests around the wildlife sanctuary to increase habitat areas for saltwater crocodiles and to improve the outlook for long-term saltwater crocodile survival in Myanmar.