The maximum number of dolphins were reported in Uttar Pradesh, followed by Bihar, West Bengal, and Assam.
| Photo Credit: The Hindu

The first ever estimate of Gangetic dolphins, the only riverine dolphins in India, has found 6,327 of them in the river Ganga and its tributaries. Previous attempts at mapping the population have relied on vastly different methods, and so the latest number is not useful for insight on whether their numbers have changed over time, experts associated with the study told The Hindu.

According to a press report by the Environment Ministry on Monday (March 3, 2025), commemorated as World Wildlife Day, there are 6,324 Ganges river dolphins, and three Indus river dolphins (a related species). There were an average 3,275 dolphins in the main stem of the Ganga; 2,414 in the Ganga tributaries; 584 in the Brahmaputra mainstream; 412 in the Brahmaputra tributaries; and 101 in the river Beas. The effort began in 2021 and spanned a cumulative distance of 8,507 km.

The maximum number of dolphins were reported in Uttar Pradesh, followed by Bihar, West Bengal, and Assam.

Unlike the counting of tigers, elephants and other land animals in the forest, counting dolphins is uniquely challenging. For one, the animals are underwater and surface only sporadically to breathe. Secondly, unlike the tiger’s stripes and the elephants ears that can be caught on camera and used to distinguish one animal from the other, individual dolphins can’t be uniquely identified this way. For their survey, the researchers travelled by boat at a constant speed using acoustic hydrophones — essentially underwater microphones — that picks up sounds emitted by the dolphins. The animals are blind and rely on echo-location to communicate and move.

“Using hydrophones and two different sets of observers on the boat, we triangulate the presence of a dolphin, and we also have to ensure that the same dolphin isn’t counted twice,” Qamar Qureshi, formerly of the Wildlife Institute of India, and closely connected with the survey, said.

The next survey would likely take place after four years. For the current study, many of the surveyors had to be trained in the new techniques that were required. “The major challenge to dolphins is getting entangled in fishermen’s nets but we are now studying the effect of pollution on the dolphins’ habitat,” Mr. Qureshi added.

The dolphin report was officially made public on Monday by Prime Minister Narendra Modi on a visit to Gujarat, where he chaired a meeting of the National Board for Wildlife. He said that the local populations (in the Gangetic States) were important for conservation measures, and added that school children ought to be encouraged to visit dolphin habitat.