Mahananda river survey records 190 dolphins, warns of fishing threats to Red List species

Soumen Bakshi, WCT

  • A November 2021 survey 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 hook lines continues to remain a challenge in the river.
  • Unregulated sand mining, pollution, solid waste dumping and construction of embankments for flood control have negatively impacted Mahananda 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 Bengal, a total of 190 individuals were counted by two teams of scientists from the Wildlife Conservation Trust (WCT). This survey, claimed to be the first such assessment, adds to the state-wide tally of dolphins in Bihar primarily, which was around 1700, the highest for any state in India. Over 70% of the 190 dolphins recorded were in the stretch of the river that lies in Bihar’s districts.

The Mahananda is a 360 km river, one of the tributaries of the Ganges, that originates in Darjeeling and traverses through the Indian states of Bihar and West Bengal. Around 14 dolphins were sighted 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 Botany professor at Bhagalpur University in Bihar.

“The Mahananda, until now, remained the only major Indian river where Ganges dolphins were known to be present. But their status had never been assessed for the entire stretch. It’s always a great feeling to be the first to do something so significant,” Dey said.

The recent November 2021 survey covered a 250 km stretch over 10 days, states the report published recently. 

Image shows two men in a small rowboat in a river looking at a construction project in the background
The people of the Mahananda plains eke out their living largely through fisheries, besides agriculture and some local construction work. Photo by Nachiket Kelkar.

Nachiket Kelkar, head of Riverine Ecosystems and Livelihoods Program at WCT, who led one of the two survey 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 referred to 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 as it was navigable. Upstream of this stretch, the Mahananda flows along the Indo-Bangladesh border near Darjeeling.

According to the report, this new survey will contribute significantly to closing the existing information gap in the  International Union for Conservation of Nature (IUCN) Red List Assessment for Ganges river dolphins (Platanista gangetica gangetica). The survey also marks the first baseline documentation of biodiversity, fisheries, and human use/misuse of the river which will help in future surveys, biodiversity assessments, and conservation planning.

Read more: Gangetic dolphins struggle to communicate as their underwater homes get noisy

The main rivers and states where major populations occur are the Ganga (in Uttar Pradesh, Bihar, Jharkhand, West Bengal), Brahmaputra, Kulsi and Subansiri tributaries (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, states the report.

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. 

Image shows a Gangetic dolphin in a water body with distant trees in the background
190 Ganges river dolphin individuals were counted in a recent survey in the Mahananda river in Bihar. Photo by Subhasis Dey.

Qamar Qureshi, a scientist at Wildlife Institute of India told Mongabay-India, “Ganges river dolphins have evolved and adapted themselves to the detrimental factors like pollution. The copious water level in the Bihar rivers also manages to dilute pollutants. Had there been less water, there won’t have been a dolphin.” He said human activity such as sand mining needs to be properly allocated and designated. Qureshi is also heading the ongoing nation-wide Project Dolphin, which takes into account the estimation of the Ganges river dolphin population and related river ecosystem. 

Mahananda as a dolphin habitat

The teams observed that some of the bridge sites with embankments led to the formation of deep pool habitats, which may be serving as refuges for Ganges river dolphins in the peak dry season.

The teams also noticed a decline in the number of dolphins in the Kishanganj district as the number of individuals counted came down from 14 to 3 in the stretch from Sonapur Hat to Dauk confluence from the assessment of April 2019 to November 2021.  Low water levels followed by net mortality were considered the threat factors. 

Dey of WCT said, “We too recommended in the report that future monitoring needs to be undertaken to estimate population trends in specific river sections under district-level forest divisions and in transboundary areas of West Bengal and Bihar, in relation to hydrological change and fisheries management systems.” 

Impact of human activities on dolphins

The people of the Mahananda plains eke out their living largely through fisheries, besides agriculture and some local construction work. In Malda district, fishing is directly controlled by cooperative leases granted to members of villages residing on river banks.

“There are cases of frequent river dolphin mortality due to entanglement in the diversity of nets used by local fishers,” said Kishan Yadav, a local resident.

WCT teams have also observed four boats using the method of fishing with oil-baited hook lines. This method of fishing with oil-baited hook lines is fatal for dolphins because dolphin oil is illegally obtained after killing live dolphins or using dead dolphins (their carcasses) to extract oil. 

“It must be further investigated if fishers on the Mahananda are also a part of clandestine supply chains in Eastern India that deal with sale or procurement of dolphin oil,” the report said.

Other than this, factors such as unregulated sand mining in the upper reaches of Mahananda, pollution, solid waste dumping at village and bridge sites, and construction of embankments for flood control embankments have badly impacted river ecology.

Chief wildlife warden of Bihar, Prabhat Kumar Gupta told Mongabay-India, “We are promoting dolphin conservation. The state government has also has issued a notification by which anyone who rescues a Ganges river dolphin or releases it from his net into the river can claim a reward of Rs. 20,000.”

Despite anthropogenic pressure and intensive fisheries, the researchers are still hopeful about dolphin conservation through active community participation.

WCT’s Kelkar said, “The community living in the stretch between Rupauli and Dakra English villages (Katihar district) have displayed interest in learning about dolphins. This can be conducive for outreach towards community-based conservation planning.”

Sighting of other species

A total of 123 species of birds, including early wintering migratory birds and raptors, was recorded during the survey along the river floodplain and adjacent tracts. The surveyors did not observe any other aquatic species. 

A flock of Ruddy Shelducks
A flock of ruddy shelducks on the Mahananda. Photo by Soumen Bakshi.

“We expected turtles but were shocked to find a complete absence of turtle sightings. From villagers, we came to know of the excessive hunting of the species by locals.” Kelkar said adding that no other aquatic species such as gharials or otters were spotted either.

According to Chaudhary, there is no mention of gharial/crocodile or otters in the Mahananda in the old records dating back to the last 50 years. A gharial sighting was recorded in the Kosi river in 2018 after a long gap. This sighting in the Kosi river was of two individuals, that were of near-adult or sub-adult in size.


Banner image: Ganges river dolphin. Photo by Soumen Bakshi, WCT.

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