West Bengal’s most delectable fish, Hilsa, has rushed to Assam in the wake of the recent cyclone Phailin. The super cyclone compelled shoals of the fish to escape from the Bay of Bengal shelf to Brahmaputra, instead of taking the Hooghly route.
According to marine ecologists, this temporary change in its migratory route is due to the sudden increase in salinity and abrupt changes in temperature and pressure along the Bay of Bengal coast.
The latest refuge of this mouthwatering fish is along the 50-km stretch of the Brahmaputra from Jaleswar in Goalpara district to adjacent Dhubri in Assam. “The cyclone Phailin and the accompanying changes it caused along the coastal waters of Bay of Bengal, has forced the fish to flee to the upstream of Brahmaputra and its tributaries from the Bay of Bengal,” said Dr Abhijit Mitra, Faculty Member, Department of Marine Science, University of Calcutta.
He said there are three routes by which Hilsa migrates from the Bay of Bengal to upstream rivers for spawning. One is Hooghly River in the Western sector of Indian Sunderbans, second is Matla River in the Central part of Indian Sunderbans and the third is Brahmaputra in Bangladesh Sunderbans, whose upstream region is through Assam.
While, Matla had been lying silted and blocked, Hooghly has been rendered more saline due to the recent impact of Phailin. Hence, Hilsa is directly escaping to the upstream region of Brahmaputra in Assam.
Monsoon is the breeding season for the fish. In West-Bengal, the spawning grounds of Hilsa are located in Hooghly. Much like the Salmon of North America, the Hilsa, enters the river from the sea to swim upstream for hundreds of kilometres and spawn, following which it returns to its salty abode.
However, due to prolonged monsoon this year, breeding season of Hilsa is still in process.
However, the sudden cyclone and depression disturbed its spawning grounds, Dr Mitra pointed out. On an average, there has been an increase of between 45 per cent to 52 per cent salinity along the coastal waters of Bay of Bengal. Salinity continues to be up by 21 per cent to 25 per cent, said Kunal Mandal, researcher, marine ecology, from University of Calcutta. The situation has compelled the fish turn from Hooghly to Brahmaputra for protection of its juveniles and refuge, he added.
Dr Mitra added that the fish has a sensitive lateral line, which is a system of sense organs on its back. This also enables it to detect sudden fluctuations in temperature, pressure, chemical characteristics of water, prior to cyclone/disturbance.
However, this unexpected Hilsa boom in this part of Assam has brought down its price from Rs 800 to Rs 1,000 to Rs 200 to Rs 250/kilo in Dhubri market. At source of the river on the south bank it is still less, between Rs 80 and Rs 100 per kg.
Mandal who had been observing the phenomenon said the local market is unable to absorb the rise, forcing fish traders to send the surplus to Cooch Behar and Siliguri in Bengal at a wholesale price of Rs 250 per kg. There is so much fish in the river that they are able to catch it without much effort, he said.