Reinforcement of gharial in the Gandak River, India for population restoration

Summary

The gharial (Gavialis gangeticus), Critically Endangered and the most aquatic of all crocodilians, has declined by an estimated 96-98% since the mid-20th century due to hunting, egg collection and habitat loss, and survives in only a few Indian and Nepali rivers. In the transboundary Gandak River, where a 2010 survey found just 15 remaining gharials, the Wildlife Trust of India and the Bihar Forest Department began a reinforcement program in 2014 using captive-born, captive-reared gharials from Patna Zoo, where breeding had been underway since 2002-2003. Release-stock sub-adults were fed live fish for six weeks to sharpen hunting skills, individually sexed and marked by tail-scute mutilation, and fitted with two satellite transmitters and four VHF tags for tracking; 30 sub-adults (3 males, 27 females) were transported roughly 300 km by road in moistened jute bags inside custom wooden crates and released in three batches between April 2014 and February 2015. Post-release monitoring combined bank-based point observation, boat surveys and radio telemetry, and found 60% of released gharials still alive six months on, a notably higher survival rate than the 7% reported in a comparable Nepali river reinforcement, with some released animals dispersing 75-100 km downstream and one apparently traveling over 1,000 km. Long-distance movement made consistent tracking difficult, especially after seasonal floods and across the India-Nepal border. The project rates itself successful, citing an 18-of-30 re-sighting rate after six months, evidence that captive-reared gharials share habitat with wild individuals, and successful colonization of new stretches of river through dispersal.