The case of the disappearing Hilsa

In West Bengal, the aggregate Hilsa yield between 2001 and 2011 declined from 80,000 tonnes to 20,000 tonnes. In Allahabad, the yield is close to a startling zero in 2006. These statistics alone prove that the Hilsa, a quintessential delicacy for Bengalis in both India and Bangladesh, is caught in a struggle for existence.

Parineeta Dandekar, associate director at the New Delhi-based South Asia Network on Dams Rivers and People, referred to a case study in the  essay ‘Damaged Rivers, Collapsing Fisheries: Impacts of Dams on Riverine Fisheries’ which revealed that the massive migration of the Hilsa is a consequence of the construction of the Farakka Barrage dam on the Bhagirathi river. “Post Farakka, the largest tributary of the River Ganga, Hilsa yield dropped from 91kg/km in the 1960s to near zero in 2006 in Allahabad,” she said.     

In Patna, she found that the catch rate dropped from 97.17 kg/km to 1.20 kg/km during the same period. The fish is caught from coastal and estuarine waters before they migrate upstream for spawning. A change in the Hooghly estuary’s water regime in West Bengal has led to a decline in fish production, making the the Hilsa inaccessible to the lower rungs of the middle class Bengali. Environmental scientists have suggested a strategic change in the management and preservation of the Hilsa domain to save the fish from extinction.

Apparently, the situation is not so gloomy in Bangladesh, which produces more than half the global Hilsa yield. Hilsas generate revenues that account for 1.3 per cent of Bangladesh’s GDP (Gross Domestic Product). Yet, the country’s bio-scientists are far from complacent. M Gulam Hussain and Islam Hoq from the technological staff of the department of fisheries, Bangladesh Fisheries Research Institute, noted in a study that the main regime for growth has shifted from inland water bodies to marine waters. The point was further endorsed by a study that was jointly undertaken by the Central Inland Fisheries Research Institute (CIFRI), Centre of Oceanography, Jadavpur University in India and the  Dhaka University of Bangladesh.

Explaining the contrast between the 20 pc fall and three-fold rise in Hilsa yield from inland waters and marine waters respectively, the two bio-scientists wrote, “Hilsa fish ascend for spawning migration from sea into estuaries and most of the river systems of Bangladesh. The essential exogenous semi-saline or freshwater ecological parameters trigger the reproduction of Hilsa parental stocks. The river water nurses millions of larvae which become juvenile and adult Hilsa. At this stage they, again, migrate towards the sea.”

The Hilsa’s migration to marine waters was, however, never coveted.The traditional habitat of the fish is the Bengal delta in the Bay of Bengal, the world’s largest flooded wetland, comprising the combined basin of three main river systems: Bhagirathi, Padma (two tributaries of Ganga) and Meghna, a tributary of Brahmaputra. Hilsa also has a presence in the Persian Gulf, Red Sea, Arabian Sea, Bay of Bengal, Vietnam Sea and China Sea. The riverine habitat of the fish is spread over the Satil Arab, the Tigris and Euphrates of Iran and Iraq, the Indus of Pakistan and the Irrawaddy of Myanmar.

The CIFRI identified the preponderance of dams as the  cause for significant alterations in the state of hydrology and that as a consequence, riverine fisheries collapse and exotic species grow. Water quality, Parineeta Dandekar points out, “is a crucial component in fisheries and the release of untreated effluents and domestic sewage kills fishes several times a year.”