Gharial (Gavialis gangeticus) populations and human influences on habitat on the River Chambal, India

Abstract

The gharial, Gavialis gangeticus (Gmelin 1789), a piscivorous reptile of Asian river systems, is increasingly threatened by diverse human pressures. Three survey expeditions were launched to monitor gharial populations, notable wildlife, and the activities and attitudes of local people in a 110 km stretch of the Chambal River in the National Chambal Reserve (NCS), India. Only 15% of gharial observed in December 2009 were in the upstream 54% of the surveyed river length. This coincides with the highest density of disturbance including water pumps, fishermen, and the highest growth in fishing activity since December 2008. Although fishing is recognized as a significant threat to gharial, no strong relationship was found between numbers of gharial and fishermen. However, numbers of water pumps, indicative of the intensity of agricultural activity, had a negative relationship with gharial numbers. This relationship was strengthened by omitting the upstream (Pali to Rameshwaram) survey reach, the tourist area of the NCS, which is also potentially affected by upstream reaches. The downstream 46% of surveyed river length in December 2009 supported 85% of gharial (consistent with trends in other surveys), including 91.6% of males and 81.8% of juveniles. This reach is classified as a High Population Recorded Area of high potential conservation importance, also containing better habitat quality and lower human disturbance. A positive relationship was found between gharial numbers and sand habitat features. However, the Davar to Ghoonsai survey reach had low gharial numbers despite abundant sand features, perhaps due to a substantial length of the Ghoonsai sand bank having been converted or agriculture. This may have significant implications for gharial conservation. Copyright © 2011 John Wiley & Sons, Ltd.

Vertebrate fauna of the Chambal River Basin, with emphasis on the National Chambal Sanctuary, India

“…Threats: The Chambal faces severe extractive and intrusive pressures in the form of water impoundment and abstraction, sand-and stone-mining, fishing, poaching, riparian agriculture, livestock grazing, firewood collection, miscellaneous domestic activities, and infrastructural development (Hussain 2009;Nair 2010;Katdare et al 2011;MoEF 2011;Tarun Nair 2006, 2008-2013.…”

“…Up-and downstream effects of dams are well-known, stemming from inundation, flow manipulation, and fragmentation. Dams obstruct the dispersal and migration of organisms, and these and other effects have been directly linked to loss of populations and entire species of freshwater fish (Nilsson et al 2005 river, due to which species become more vulnerable to netting and dynamiting (Dubey & Mehra 1959;Katdare et al 2011). Additionally, reduction in the number of inaccessible islands results in increased destruction of nests of Gharials, turtles and ground-nesting birds like skimmers and Black-bellied Terns (Sundar 2004;Nair 2010).…”

“…Sand-mining destroys crucial breeding areas and is one of the most serious threats to the survival of species that lay their eggs on sand deposits. Stonemining, common in the upper sections of the river, causes considerable disturbances to wildlife, destroys key breeding habitats like otter-holts and provides easy access to ammunition for dynamite fishing (Katdare et al 2011).…”

“…due to inadequate allocation of field personnel to patrol the sanctuary. Illegal fishing and turtle poaching are rampant, using a variety of methods (gill net, baited hook-line, dynamite) and these also claim other species like Gharials, Mugger, river dolphins, otters and several birds (Dubey & Mehra 1959;Vyas 2004;Nair 2010;Taigor & Rao 2010;Katdare et al 2011). Gill nets are particularly responsible for entangling and drowning juvenile Gharials, thereby impacting survival and recruitment of smaller size-classes.…”

“…Riparian agriculture and associated activities like constant human disturbance from irrigational pump operation and crop protection, and risks of water pollution from agro-chemical use and oil leaks also contribute substantially to habitat loss, degradation and pollution (Katdare et al 2011).…”