Ecological baselines and emerging threats: Evaluating the status of the Black softshell turtle (Nilssonia nigricans) in Assam’s protected floodplain habitats

Abstract

This  study  provides  a  comprehensive  assessment  of  the  morphology  and  distribution of the critically endangered black softshell turtle (Nilssonia nigricans), with insights into its ecology across four protected areas in Assam. We used an integrative approach combining visual encounter surveys with community-based engagement methods with local communities and forest personnel. We examined the ecological characteristics of N. nigricans in the wild, including its seasonal activity patterns, basking and habitat preferences, opportunistic feeding behaviour, and documented the primary anthropogenic threats to the species. We provide a refined understanding of the distribution of N. nigricans in the Brahmaputra River floodplains by integrating 244 hours of transect survey effort and 73 georeferenced observations compiled from field surveys and secondary sources. Our systematic review indicates a distribution of the species across northeast India, Nepal, and Bangladesh which extends beyond protected areas and temple ponds to encompass the broader floodplain landscape. Additionally, we analysed habitat use patterns and identified critical habitat features such as sandy nesting banks and undisturbed basking sites that are essential for the survival of the species. The results underscore the importance of prioritising specific habitats within these national parks for targeted conservation action.  We also highlight the role of community stewardship in supporting in-situ conservation through habitat protection and awareness programs. This research forms a foundation for future ecological research, including GIS-based habitat suitability mapping to identify priority corridors, and telemetry-based movement studies, aimed at securing the remaining populations of N. nigricans in Northeast India.