Status, Distribution and Conservation Threats of Endangered Cetacean Platanista gangetica gangetica Roxb. in Subansiri River, Northeastern India

Critically endangered Ganges River Dolphin (Platanista gangetica gangetica Roxb.) is found in substantial numbers in the downstream of Subansiri river, a major tributary of the River Brahmaputra. Best estimates of 21, 23 and 26 dolphins were recorded in 2005-06, 2006-07 and 2007-08 respectively. Until recently, the Subansiri river was considered one of the safe havens for residential dolphin due to relatively healthy downstream environment coupled with awareness of river bank inhabitants. Water environment of the un-damming Subansiri river strongly influence the existence of dolphin population. However, compositional changes of their distribution may have occurred after regulation of the river by the 2000 MW Lower Subansiri Hydroelectric Projects, whose construction has begun. Only 25 cumec/sec water will be released to the downstream after operation of the project against the present minimum flow discharge of 188 cumec/sec. This huge irreversible reduction (87.60%) in water discharge will make the downstream extremely vulnerable for this IUCN's red listed mammal, the dolphin. Flushing of reservoir sediment will accelerate the degradation by increasing, decreasing the riverbed and water table respectively. To protect the ecological and social security of the downstream, in general, and Ganges dolphin in particular, the minimal environmental flows for long term sustaining of the recently declared India's national aquatic animal is to be calculated and executed accordingly.