Sea surface warming has led to a significant change in fish habitat in the Sundarbans over the past two decades.
This has affected fish harvesting in the region. Fishing is the largest employment generator after agriculture in the delta.
Sundarbans, the single largest block of tidal mangrove forest shared between India and Bangladesh, is spread over hundreds of islands and has rich bio-diversity.
The region is also a major source of a range of commercially important fish like Hilsa (
Rise in Sea Temperature
According to the survey carried out jointly by the Centre for Science and Environment (CSE) and Department of Marine Sciences of University of Calcutta, in 2011, the sea surface temperature (SST) in the Bay of Bengal has been increasing at the rate of 0.5 degree Celsius per decade since 1980 compared to a global increase of 0.06 degree Celsius per decade between 1970 and 1999.
Increasing temperature has impacted the marine habitat and evenness of availability of different fish species.
The study carried out in Western and Central Sundarbans area, commercial fishes catch have declined by nearly a third as compared to other species.
Most of the commercial fish varieties go deeper into the water, thereby impacting harvest ratios substantially.
Over a two-decade period beginning 1990 commercially viable fish percentage (in a catch) has reduced to 37 per cent from the previous 75 per cent in Central Sundarban region. Similarly, there was a jump in non commercial fish catch to 40 per cent from the previous 35 per cent in Western Sundarbans during the period.
Change in Habitat
“A fall in commercial fish catch is mainly because of rise in the sea surface temperature and sometimes increased pollution levels in water,” Mr Aditya Ghosh, lead researcher, CSE, told Business Line .
According to him, a rise in water surface temperature impacted the marine eco-system as well.
The survey found that certain species like the Indian mackerel have moved deeper in the water, thereby hinting at increasing unavailability of these fish in the upper levels.
“With fish changing their routes and breeding areas; the ecosystem in the water is getting altered. It equally impacts the food chain with a large number of fish fighting for limited resources,” Mr Ghosh said.