Anthropogenic restocking of gharial individuals prevents genetic isolation of gharial population in Girwa River, India by geographic barriers imposed by a barrage
Abstract Gharial (Gavialis gangeticus) is a critically endangered fresh water crocodile endemic to the Indian subcontinent. The species has suffered > 95% decline in population and habitat size. A small population of gharials comprising of 50 breeding adults is resident in a 20 Km stretch of the River Girwa in Katerniaghat wildlife sanctuary, India. Gharials in this 20 Km stretch have been genetically isolated since 1976 by a barrage that functions as a barrier to gene flow. A captive rear and release program has been initiated since 1979 under Project Crocodile for restocking declining wild gharial populations. Thousands of gharial eggs were collected from gharial populations at Girwa and Chambal Rivers. Hatchlings from the collected eggs were captive reared at a common location in Kukrail Gharial Centre, India and released back to multiple gharial populations including the isolated population at Girwa. This restocking programme was not preceded by a genetic screening of captive animals or wild populations to identify genetic diversity and genetic structure of both captive and wild animals. In this study we investigate whether release of captive reared gharials into the resident population at Girwa River has prevented genetic isolation caused due to barriers imposed by the barrage. Using a combination of empirical analysis using microsatellite markers and a systematic review of data from previous workers on molecular characterization of gharial populations, we analysed genetic differentiation in gharial populations at Girwa and Chambal. We found similar genetic variability in gharial populations of Girwa and Chambal. There was low inter population genetic differentiation and evidences of genetic migration between the two populations. Our findings indicate that anthropogenic intervention via release of captive animals has compensated for the genetic isolation in Girwa population caused by the barrage.