Population status and factors influencing the distribution of Critically Endangered gharial (Gavialis gangeticus) in a regulated unprotected river system in India

Gharial (Gavialis gangeticus), the last surviving crocodilian member of the genus Gavialis, is endemic to the Indian subcontinent and is listed as one of the priorities species under the Evolutionary Distinct and Globally Endangered framework. Historically, the gharial used to occur in all major river systems of the Indian Subcontinent, now found in isolated stretches, mostly within the boundaries of Protected Areas. The gharial population decreased by over 80 % between the 1950s and 1960s due to habitat degradation, poaching, and mortality from passive fishing. The gharial population is, however, rebounding due to concerted conservation efforts launched in the mid-1970s. One of the largest gharial populations outside of the Protected Area is in the Gandak River, a transboundary northern tributary of the Ganga. However, the habitat association of gharial in relation to the rising anthropogenic stressors is not well-documented from an ecological standpoint in the Gandak River. The present study assessed the population status and factors influencing the gharial distribution in the Gandak River. Boat-based visual encounter surveys were conducted for data collection, and generalized linear models (GLMs) were employed to evaluate the factors influencing gharial distribution. The encounter rate fluctuated along the surveyed river stretches, peaking in the upstream. We observed a positive association with channel depth while a negative one with channel width, livestock presence, fishing nets, and fishing boats. The observed pattern of encounter rate and negative association with anthropogenic variables indicate spatial avoidance of these factors. Overall, conservation interventions, such as adaptive management strategies to reduce and remove these factors, are required for long-term gharial persistence in the regulated unprotected riverscape