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A count of the Ganges River Dolphin (Platanista gangetica gangetica) in two Bihar rivers, Gandak and Ghaghara (both originate from Nepal and eventually join the Ganga), has revealed the presence of 280 dolphins.

The number of dolphins recorded in a 324-km stretch of Gandak river was 155, a drop from the last estimation. The last survey carried out in 2009-10 had recorded the presence of 257 dolphins in the same stretch. However, in a 99-km stretch of Ghaghara river in Bihar — where no study was conducted before — researchers were enthused to find the presence of 125 dolphins.

“Gandak is a regulated river due construction of river barrage on the Indo-Nepal border and thus the river depth is low, while the Ghaghara has deeper stretches. Ganges river dolphin usually prefer a depth of more than 2 metres and diversity in the river channels,” Samir Kumar Sinha, Deputy Director and Division Head (Species Recovery) of the Wildlife Trust of India told The Hindu. Mr. Sinha coordinated the estimation exercise.

The estimation was done following the direct count method recommended by the Cetacean Specialist Group of the International Union for Conservation of Nature. A team of seven completed the survey in a period of about 12 days in late 2018. Experts have pointed out that upcoming activities, such as the construction of National Waterway 37, are likely to pose a major threat to the population of Ganges river dolphin and can change the geo-morphology of the Gandak in the coming years.

Other threats affecting Dolphin habitat in the river at this juncture include regulated discharge from Gandak Barrage, electrofishing (discharging electric current to kill fish) and mosquito-net fishing. In the Ghaghara river, threats posed on the national aquatic animal are from sand mining and the use of chemicals in intensive bank cultivation.

Both the rivers are home to large number of aquatic species including the critically-endangered gharial (Gavialis gangeticus). The estimation also revealed the presence of 32 bird species in Gandak and 17 in Ghaghara. The river system of Bihar, which includes Ganga and its other tributaries, are estimated to contain half of the population of Ganges river dolphin in the country.

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