Possible range decline of Ganges River Dolphin Platanista gangetica (Mammalia: Cetartiodactyla: Platanistidae) in Indian Sundarban

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Sangita Mitra
Mahua Roy Chowdhury


Recent survey reports and observations from rivers in southern West Bengal (India) indicate the extirpation of Ganges River Dolphin (GRD) from the Indian Sundarbans. The present study undertaken during 2011–16 reviews the possible factors accountable for the disappearance of this obligatory freshwater cetacean from the major waterways of the Sundarbans, India and conclude that it is due to reasons of anthropogenic and geo-climatic origin.  Sundarbans, the largest contiguous mangrove forest on earth encompassing almost 10,000km2 of India and Bangladesh is located at the head of the Bay of Bengal within 21.533–22.666 0N and 88.083–89.850 0E, of which 62% lies within Bangladesh and 38% in India (Spalding et al. 2010).  The landscape is a network of mudflats and islands at the deltaic mouth of the rivers Ganga, Brahmaputra and Meghna created by accumulated sediments carried by the snow-fed Himalayan rivers and their tributaries along with anastomosing tidal water channels.  Historic reports reveal the occurrence of GRD in the Sundarbans waters of both India and Bangladesh (Anderson 1879).   Current  data, however, confirms the disappearance of Platanista gangetica but there is continued occurrence of Orcaella brevirostris in the Indian part of the estuary.  Analysis of causative factors in light of existing evidence validates the potential extirpation of Platanista from the majority of the Sundarbans in India, except for its persistence in only the westernmost segment in the lower reaches of river Hooghly as confirmed by this study.  The present study also records the habitat preferences and limiting factors affecting GRD distribution, and maps the decline of its range.

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