- A November 2021 study of the Ganges river dolphin in the Mahananda River may help close the existing information gap in the IUCN Red List Assessment for the dolphin species.
- Dolphin mortality due to entanglement in nets and oil-baited hooklines remains a challenge in the river.
- Unregulated sand extraction, pollution, solid waste dumping and the construction of levees to control floods have negatively impacted Mahananda’s ecology and the survival of dolphins and other riverine species.
In a population estimate of the Ganges river dolphin in the Mahananda River in Bihar and West Bengala total of 190 people were counted by two teams of scientists from the Wildlife Conservation Trust (WCT). This study, which is claimed to be the first of such a review, adds to the total number of dolphins in Bihar in the entire state, which was around 1700, the highest for any state in India. More than 70% of the 190 registered dolphins were in the part of the river that lies within the districts of Bihar.
The Mahananda is a 360 km long river, one of the tributaries of the Ganges, which rises in Darjeeling and flows through the Indian states of Bihar and West Bengal. There were about 14 dolphins to seeed in the upper 45 km of the river in April 2019 by teams led by Subhasis Dey of WCT and Sunil Kumar Chaudhary, a river biologist and former professor of botany at Bhagalpur University in Bihar.
“The Mahananda remained the only major Indian river known to have the Ganges dolphins present, but their status had never been assessed throughout the entire stretch. It’s always a great feeling to be the first to do something so important,” Dey said.
The recent November 2021 study covered a distance of 250 km over 10 days, according to the report recently published.
Nachiket Kelkar, huhhead of Riverine Ecosystems and Livelihoods Program at WCT, who led one of the two research teams, explained the methodology. “We used statistical analysis based on the number of common and unique sightings between our two boats (kayaks). This is a scientifically robust method of survey design and analysis and is also known as the tandem boat double observer method,” Kelkar told Mongabay-India.
The assessment was conducted from Piyajimore in Darjeeling district, West Bengal (near Haptiagachh on the India-Bangladesh border) to the confluence of the Mahananda with the Ganga near Manikchak, Malda district, West Bengal. This stretch was chosen because it was navigable. Upstream from this stretch, the Mahananda flows along the Indo-Bangladesh border at Darjeeling.
According to the report, this new research will significantly contribute to closing the existing information gap in the International Union for Conservation of Nature (IUCN) Rating on the red list for Ganges river dolphins (Platanista gangetica gangetica). The survey too marks the first baseline documentation of biodiversity, fisheries and human use/misuse of the river, which will aid in future surveys, biodiversity assessments and conservation planning.
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The major rivers and states where large populations occur are the tributaries Ganga (in Uttar Pradesh, Bihar, Jharkhand, West Bengal), Brahmaputra, Kulsi and Subansiri (Assam), Kosi (Bihar), Ghaghra (UP and Bihar), Mahananda (Bihar). and West Bengal), Hooghly (West Bengal), Gandak (Bihar), Chambal (UP, MP, Rajasthan) and Rapti (UP). Some other rivers have smaller populations. Bihar, Uttar Pradesh and Assam, in that order, have the highest populations, the report says.
The Ganges river dolphin falls under Schedule I of the Indian Wild Life (Protection) Act and has been declared an endangered species by the IUCN. The dolphin is considered an indicator of freshwater ecosystem degradation.
Qamar Qureshi, a scientist at the Wildlife Institute of India, told Mongabay-India: “Gangean river dolphins have evolved and adapted themselves to the harmful factors such as pollution. The abundant water level in the Bihar rivers also manages to trap pollutants. If there had been less water, there would have been no dolphin.” He said human activities such as sand extraction must be properly allocated and designated Qureshi also leads the ongoing nationwide Project Dolphin, which takes into account the estimation of the Ganges dolphin population and associated river ecosystem.
Mahananda as a habitat for dolphins
The teams noted that some of the embankment bridge sites led to the formation of deep pool habitats, which can serve as refuges for the Ganges river dolphins during the dry peak season.
The teams also noticed a decline in dolphin numbers in Kishanganj district as the number of individuals counted dropped from 14 to 3 in the Sonapur Hat to Dauk confluence stretch of the April 2019 to November 2021 assessment. Low water levels followed. by net mortality were considered the threat factors.
Dey from WCT said: “We also recommended in the report that future monitoring should be carried out to estimate population trends in specific river sections under district level forest divisions and in transboundary areas of West Bengal and Bihar, with regard to hydrological change and fisheries management systems.”
Impact of human activities on dolphins
The people of the Mahananda plains make a living largely from fishing, in addition to farming and some local construction work. In the Malda district, fishing is directly controlled by cooperative leases granted to members of villages living on riverbanks.
“There are cases of frequent deaths of river dolphins due to entanglement in the diversity of nets used by local fishermen,” said Kishan Yadav, a local resident.
WCT teams also observed four boats using the oil-baited hookline fishing method. This method of fishing with oil-baited hooklines is deadly to dolphins because dolphin oil is obtained illegally after killing live dolphins or using dead dolphins (their carcasses) to extract oil.
“It should be further investigated whether fishermen on the Mahananda are also part of clandestine supply chains in eastern India engaged in the sale or purchase of dolphin oil,” the report said.
Apart from that, factors such as unregulated sand extraction in the upper Mahananda, pollution, the dumping of solid waste at village and bridge sites, and the construction of levees for flood-limiting dikes have had a major impact on the river ecology.
Bihar’s chief conservationist Prabhat Kumar Gupta told Mongabay-India: “We are promoting dolphin conservation. The state government has also issued a notice offering a reward to anyone who rescues a river dolphin from the Ganges or releases it from its net into the river.” of Rs. 20,000.”
Despite anthropogenic pressures and intensive fishing, the researchers are still hopeful about dolphin conservation through active community participation.
Kelkar of WCT said: “The community living in the stretch between the English villages of Rupauli and Dakra (Katihar district) has expressed an interest in learning about dolphins. This can be conducive to achieving community-based conservation planning.”
Sighting of other species
A total of 123 species of birds, including early wintering migratory and raptors, were recorded during the survey along the river’s floodplain and adjacent tracts. The surveyors did not observe any other aquatic species.
“We were expecting turtles but were shocked to find that no turtles were sighted. From villagers we learned about the excessive hunting of the species by the locals.” Kelkar said adding that no other aquatic species such as gharials or otters were also seen.
According to Chaudhary, there is no mention of gharial/crocodile or otters in the Mahananda in the ancient records dating back to the last 50 years. After a long hiatus, a gharial was sighted in the Kosi River in 2018. This sighting in the Kosi River was from two individuals, who were near-adult or sub-adult.
Banner Image: The river dolphin of the Ganges. Photo by Soumen Bakshi, WCT.