Bengal has third-highest riverine dolphin count in India: Report released by PM
Telegraph | 6 March 2025
A national enumeration has found that Bengal is home to 815 river dolphins.
The Population of River Dolphins in India 2024 estimated India's dolphin population at 6,327, spread across eight states and three riverine ecosystems — the Ganga, the Brahmaputra, and the Beas. The study was conducted from 2021 to 2024.
Prime Minister Narendra Modi released the report at the Gir National Park on Monday.
Bengal has the third largest population of dolphins and is behind Uttar Pradesh (2,397) and Bihar (2,220).
But Bengal stands out, having recorded two species — the Gangetic dolphin (Platanista gangetica), the national aquatic animal of India, and the Irrawaddy dolphin (Orcaella brevirostris), which can adjust both in freshwater and saltwater.
The enumeration exercise estimated Bengal's Ganetic dolphin population at 815. The exercise also estimated 108 Irrawaddy dolphins in the Sunderbans.
However, the second estimate was not included in the total Indian population because it was meant to estimate the river dolphin population.
In Bengal, the survey covered 2,366km of the Ganga and the Sunderbans.
The mainstream Bhagirathi-Hooghly riverine ecosystem was studied. It included stretches from Farakka to Ganga Sagar; from the Farakka Barrage to the Bangladesh border; and rivers like the Rupnarayan, the Dwarakeshwar, the Haldi and the Churni.
In total, 12 rivers were surveyed, which translated to a distance of 2,366km. The lowest dolphin count was pegged at 665; the estimated population was 815, and the population range was 763 to 870.
The 483km Farakka Barrage to Diamond Harbour stretch of the Hooghly was the longest surveyed in Bengal. The survey pointed to 429 dolphins in the stretch, the maximum for one stretch in the state. A 79km stretch of the Rupnarayan from Bandar (West Midnapore) to Gadiara (Howrah) had an estimated population of 167 dolphins.
The highest encounter rate — 3.6 per kilometre — was witnessed on Bakshi Canal (in Bagnan in Howrah), a part of the Rupnarayan river system.
The average encounter rate for Bengal was 0.3 per kilometre.
"The study has shown that Bengal has a healthy dolphin population. It also reflects the forest department's efforts to raise awareness about dolphins. A bulk of the dolphin deaths can be attributed to fishing nets. We are conducting regular awareness campaigns among the fishing community," said Nilanjan Mallick, additional principal chief conservator of forests of Bengal and director of the Sundarban Biosphere Reserve.
Dolphins often get trapped in fishing nets when they rise to the surface to get enough air to breathe. But once trapped in nets, they cannot rise to breathe. Fishermen know instantly when a dolphin is trapped, but there have been instances when they were killed to extract oil from the blubber, to be used as bait for fish.
A total of 58 rivers were covered, of which 28 were surveyed on boats and 30 accessed through road surveys. The enumeration was challenging because dolphins surface for only around 1.26 seconds and dive for around 107 seconds.
Not all dolphins surface at the time of the count.
To account for that "availability error, a hydrophone was dragged underwater along with the survey boat, to record dolphin presence underwater by recording dolphin clicks, which is used to calibrate the visual observation for unavailability," the report said.
The data was collected for "dolphin abundance, river habitat type, extent of anthropogenic pressure and presence of other aquatic fauna". The raw data was then analysed.
The Hooghly waterway is set for a major infrastructure upgrade, that includes construction of new jetties and the remodelling of old ones. It will be done by the state transport department.
"The population estimation is a boost for us. Now, we know which stretches of the river have a stable dolphin population. The construction must be done in a way that it does not harm the dolphins," said Mallick.
The World Bank is co-funding the project. Representatives of the different agencies, along with those from the forest department and WWF-India and the Central Pollution Control Board have held meetings to find a balance between infrastructure upgrade and protection of the aquatic ecosystem.
A group of researchers is already studying the noise levels in the Hooghly to determine how habitable the river is for dolphins, one of its most intelligent residents.
The national dolphin population exercise was done under Project Dolphin, launched by the Prime Minister on August 15, 2020. The survey covered over 8,000km, covering eight states, across the Ganga and the Brahmaputra rivers along with their tributaries and the Beas river.