Impact of increase in salinity on Gangetic Dolphins

A five-year study by researchers Sangita Mitra (National Biodiversity Authority, Chennai) and Mahua Roy Chowdhury, (a marine biologist from the University of Calcutta, West Bengal) has been published in the Journal of Threatened Taxa.

The research has found that raising water salinity level is threatening the habitat of Gangetic river dolphins.

Findings of the Study

The study was conducted in the lower stretch of river Hooghly, covering 97 km stretch of the western, central and eastern Sundarbans in India between 2013 and 2016 in different seasons. The study area was demarcated for boat-based and land-based surveys based on interaction with local fishing communities. Researchers also measured the salinity level of the water during the different points in the survey. The findings of the Survey are:

  • No sighting record for Gangetic dolphin in waterways wherever the salinity level crosses 10 parts per trillion (ppt).
  • The increase in salinity in the eastern and central region of Sundarbans has affected the habitat of the Gangetic Dolphin.
  • The increase in the salinity was due to hydrological changes such as reduction in freshwater flow, reduced discharge from barrages, runoff from adjacent agricultural lands and river water abstraction for irrigation.
  • The increasing salinity was conducive for marine cetaceans like Indo-Pacific hump-backed and Irrawaddy dolphins as these species can thrive in saline waters.
  • The other major threats to the dolphin habitats are excessive fishing, use of vulnerable fishing gears, noise from motorized boats and lack of awareness among local communities.

Gangetic Dolphin

Gangetic Dolphins are the only surviving freshwater dolphin in India. Gangetic Dolphins are found in the river systems of Ganga, Brahmaputra, Meghna and Karnaphuli- Sangu in Nepal, India and Bangladesh. The IUCN status of the Gangetic Dolphin is Endangered. Gangetic Dolphin is the National Aquatic Animal of India.

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