It is late afternoon at Mohana, the fish market on the outskirts of Digha, a sea resort in West Bengal. After a brief pause in the rains, suddenly a rain cloud glides in from the outer rim of the horizon. And what was a gentle breeze a moment earlier gathers force. There is commotion at the office of Digha Fishermen and Fish Traders' Association as traders run for the wireless set. Barun Kumar Maity, whose boat Ma Tara is out 80 km in the sea, frantically calls his mates on board. "Stay there. Wind again. Look for new shoals. They must be coming. Don't worry about the costs. The prices are good. Over."

DYING YOUNG: The catch along the Digha coast consists increasingly of young hilsa

Tenualosa ilisha. Or hilsa, the Indian shad. The silvery harvest of the waters of the two Bengals (West Bengal and Bangladesh) is the choicest fish delicacy among Bengalis. However, as Maity's command crackling on the radio telephone suggests, there is something amiss in the movement of the migratory fish that lives in the sea but swims to freshwater rivers to spawn. But, for some years now, the hilsa is struggling to change its breeding behaviour. It would rather lay eggs 300 m under water, in the sandy beds of the Bay of Bengal. The result is an ecological disaster, with the hilsa juveniles accounting for 90 per cent of the fishermen's catch in terms of volume.

The coast along Digha, 12 km up to the harbour at Sankarpore, is home to over 1,200 motorised boats-either seabed-hugging trawlers or mechanised boats carrying noose-like gill nets. Trawlers, chasing prawns, catch anything that falls in their way, while "gill-netters" use mesh sizes that can catch very young fish. Consequently, the traditional hilsa weighing 1.5 kg or more has become a rarity in the markets of Kolkata and the 500-gm fish rules the roost, selling at Rs 100 a kilo. "At this rate," says B.C. Jha, principal scientist at the Central Inland Fisheries Research Institute (CIFRI), Barrackpore, Kolkata, "the hilsa of the traditional variety will perish in a decade or two."

Why has the hilsa become shy of swimming upriver? Fish experts point their accusing fingers at the Farakka Barrage, 450 km upstream on the Bengal-Bihar border. The barrage was built on the Ganga in 1975 with a fish ladder to allow the hilsa its right of way. "It is not working," says Jha, "with the migratory fish unable to negotiate the height unless there is a flood."

However, the threat to the hilsa's existence does not come from the barrage alone. Its biggest bogey is the gill net, a monofilament trap measuring 70 cm from corner to corner, that catches young hilsa by its gill, asphyxiating it to death. But it is difficult to put a size limit on the mesh of the fishing net as the net that traps hilsa also catches pomfret, sole, sardine, cuttlefish, mullet and snapper, all of which are prized foreign-exchange earners, with West Bengal alone accounting for 40 per cent of India's exports of marine products. "How can we widen the mesh for a single species?" wonders Prabhat Hazra, chairman of the Digha association.

At CIFRI, scientists are probing a larger issue: do the shoals that traditionally swam up the Hooghly represent a subspecies of the Tenualosa family, or are they the same as the other varieties found in the waters of Bangladesh, Myanmar and Thailand? "If the stock of hilsa we find in Bengal is specific to the Hooghly river then the total stock will be eliminated," says biotechnologist M.P. Brahmane. "If it has the ability to adapt to a different climate, there is hope for its survival."

The market does not bet on its survival, though. Hazra says the changed spawning habit of the fish and the overfishing near the coast are compelling the boats to graze the seabeds farther away. He gives the hilsa not more than 10 years in Digha, which accounts for 65 per cent of the total catch in India. The slaughter of the juvenile fish has even changed the economics of the trade, with the rare big ones being kept in coldstores only to be released when the demand peaks at Rs 350 a kg.

Fishermen say the only way to save the species is to impose a three-month ban on its netting and selling between May and July. "I feel guilty," says Maity, "when I bring the infants to the market." The message should reach the policy makers at the Writers' Buildings in Kolkata.