Population status, threats, and evolutionary conservation genetics of Bengal tigers in the Sundarbans of Bangladesh

The Sundarbans is a Tiger Conservation Landscape of global priority that supports one of the most important tiger populations across their current range. In Bangladesh, Sundarbans is the last stronghold of the critically endangered tiger, therefore conserving this flagship species will help to ensure the long-term future of the Sundarbans which has been providing significant economic and ecosystem services to human communities for centuries. However, scientific information is lacking on many aspects of the Sundarbans tigers, including population and genetic status, and detailed patterns of tiger and prey poaching. The objectives of this study were therefore to improve the knowledge base to help design better management strategies for long-term persistence of the Sundarbans tigers. As a consequence of challenges faced in applying conventional census methods in the Sundarbans mangrove habitat, a non-invasive genetic approach was applied to collect samples that were then screened using polymorphic microsatellite markers to estimate density and population size of tigers within the spatially explicit capture-recapture model. DNA analyses provided reasonable population estimates, indicating that a non-invasive genetic approach is a viable method for monitoring tigers and can be applied to monitor tiger populations elsewhere. Bayesian and Maximum likelihood inferences using mitochondrial DNA sequences supported a polyphyletic relationship between tiger population in the Sundarbans and the populations in central India. Together, microsatellite and mitochondrial DNA analyses revealed a signal of fine-scale genetic structure and significant genetic differentiation on a spatial scale which is probably the consequence of limited tiger dispersal due to the presence of wide rivers in the Sundarbans landscape. Systematic field survey across sample areas detected a range of snaring methods used to catch tiger prey and evidence of killing tigers by poisoning prey carcasses with the Carbofuran pesticide. Spatial analysis showed that poachers selected sites that tended to be further away from guard posts, and close to river banks. Based on these results, a range of future management interventions were recommended including the reduction of water-based commercial and resource collection activities to allow tiger dispersal, and regulation of Carbofuran and snare materials to better tackle tiger and prey poaching in the Sundarbans.