The endangered Ganges river dolphin heads towards local extinction in the Barak river system of Assam, India: A plea for conservation

Abstract

The Ganges river dolphin (GRD) is an obligate freshwater cetacean that inhabits the Ganges-Brahmaputra-Meghna (GBM), and Karnaphuli-Sangu river basins of India, Bangladesh and Nepal. The other sub-species, Indus river dolphin, is distributed in the disjunct lower Indus basin of India and Pakistan. The global population and distribution range of the GRD has declined in the recent past, and thus the sub-species has been listed ‘Endangered’ by IUCN since 1996. In Assam (India), the Ganges sub-species occurs in the Barak and the Brahmaputra river systems. The Barak river is a tributary of the Meghna river, and is the upstream distribution range of the sub-species in this branch of the GBM river basin. The dolphin inhabits meanderings and confluences of rivers, with prevalence of eddy counter-current and the resultant high aquatic diversity, including prey fish abundance. In the 1970 s–1980 s, the cetacean used to be fairly common in the Barak river system. Of late, it has been extirpated from the tributaries of the Barak river, and currently no longer occurs in any part of the main channel as well. However, it continues to occur in the downstream Kushiyara river (a distributary of the Barak river) which suggests a decline in the upstream distribution range by approximately 135 km. The major factors which affected the decline and the extirpation of the cetacean from the Barak river system include poaching, by-catches and interactions with fisheries including prey-fish depletion, and habitat destruction and fragmentation due to construction of sluice gates, embankments, siltation of rivers, dredging, extraction of water for irrigation and domestic uses, aquatic pollution, and lack of awareness. Thus, for effective conservation of the dolphin, these threats need to be eliminated or managed. This article provides an exhaustive review of the distribution (past and present), population, ecology, threats and conservation recommendations of the GRD in the Barak river system of Assam, India. Further, the article includes data obtained from the recent surveys conducted by the authors in the Barak river system.