Almost gone: How the Gangetic Dolphin is struggling to cope with the Ganga's increasing salinity
If you took a holy dip in the Ganges during the recent Kumbh and believed your sins to have been washed away, do say a prayer for the Gangetic dolphins that keep taking hundreds of dips in the revered river every single day of their entire lives.
The gentle — and blind — Gangetic Dolphin is facing yet another anthropogenic threat.
According to the findings of a five-year study conducted in the Sundarbans regions, the rising salinity level in the water is threatening the habitat of the dolphins. The survey was conducted in the lower stretch of the river Hooghly, covering a 97 km stretch of the western, central and eastern Sundarbans in India, intermittently between 2013 and 2016 in different seasons.
Simultaneously, researchers also measured the salinity level of the water. Based on interactions with local fishing communities, the study area was demarcated for boat-based and land-based surveys. The findings of the study were published as a report in the Journal of Threatened Taxa.
A survey of a nearly 100-km stretch of the Sundarbans delta in India adjoining Bangladesh has confirmed the presence of the dolphin populations only in the westernmost segment, in the lower reaches of the river Hooghly, where the salinity is lower than that of natural seawater. The mammals stayed away from the central Sundarbans — where siltation in the waterways has disrupted the freshwater flow, leading to high salinity levels.
The study found “no sighting record for Gangetic dolphin in waterways wherever the salinity level crosses 10 parts per trillion (PPT)”.
The study — led by Sangita Mitra, a senior consultant at the National Biodiversity Authority — goes on to establish that "decline in the range of Platanista gangetica in the Indian Sundarbans" attributing the extirpation to a triple whammy — elevated sedimentation, reduced freshwater discharge and swelling salinity.
Biologist, environmentalist and the Vice Chancellor of Nalanda Open University Dr Ravindra Kumar Sinha, also known as the 'Dolphin Man of India', affirms the findings.
"Gangetic dolphins are freshwater animals and they never enter the sea. They are found in brackish water zones such as those in the Sundarbans estuary. But freshwater flow has declined over the decades and seawater has ingressed, increasing the salinity. They are rarely visible now, whereas once they were plenty," Sinha reportedly said.
Historically, the dolphins covered the entire range of the Ganga. Sinha explains that the biggest threat to Gangetic dolphins is the declining flow in the Ganga, owing to the erection of dams and barrages, and water-intensive agriculture in the basin, contributing to the base flow petering out and fragmenting their habitats.
To corroborate this, records dating to 1879 reveal that these freshwater cetaceans swam along the entire length of the Ganga and Brahmaputra rivers, and all their tributaries from the delta at the Bay of Bengal till the Himalayan foothills. Even in the month of May, when the water in the Ganga was very low, dolphins were reportedly seen as far up the Yamuna in Delhi.
Lead author Sangita Mitra agrees. “The Gangetic dolphin is an obligatory freshwater species and its range has declined due to salinity and other ecological factors. Although the study has not concluded, we would like to draw the attention of the concerned authorities as well as the public about threats to this freshwater habitat as it has a direct implication on Gangetic river dolphin,” she reportedly said. Local extinction of Gangetic dolphins has already been predicted by the Vikramshila Biodiversity Research and Education Centre.
Clearly, there is not too much of a difference between the Gangetic Dolphin and those who make the policy decisions for its conservation — both swim blind.
Unless the policymakers are shaken out of their reverie immediately, we are heading towards mourning the loss of a national symbol.