Status and distribution of the endangered Gangetic dolphin (Platanista gangetica gangetica) in the Brahmaputra River within India in 2005.

A population assessment survey of the endangered Ganges river dolphin was made between February and April 2005 in the Brahmaputra River starting from Assam-Arunachal Pradesh border to the India-Bangladesh border. One hundred and ninety seven dolphins were recorded in the entire 856 km river stretch with an encounter rate of 0.23 dolphins per km. Encounter rates of dolphin in different sectors were significantly different. Calves and subadult encounter rates were recorded as highest in the Brahmaputra stretch within the Kaziranga National Park. No significant difference was found between the number of calves and subadults, calves and adults as well as subadults and adults. The variations in depth structure of the river were highly significant along different stretches. The number of dolphins occurring in different depths was found to be significantly different and the highest number was found in a depth of 4.1-6 m. Gill net encounter rate was significantly different in different stretches of the river with maximum encounter rate recorded from Goalpara to Dhubri. Accidental killing through gill net and poaching of dolphin for oil are the most dangerous threats to the survival of these dolphins. Close monitoring of dolphins and their habitats involving local communities are required for long term conservation of the species in the Brahmaputra River.

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