Blind nets and insufficient rainfall have prevented mature hilsa from moving up the Hooghly from the bay this monsoon, said scientists studying the movement of the fish whose delight depends as much on the salinity of the sea as on the softness of the water. from the river.

On Sunday, fishermen from Kakdwip in southern 24-Parganas had ventured onto eight trawlers and returned with around 300kg of hilsa, less than half the yield they said they expected at this time of the year. year. Each fish they caught weighed between 500 and 550 grams, far from ripe fish weighing a kilogram or more.

Several fishermen said they expected a larger catch in the next few weeks, but were not sure it matched that of recent years, when the monsoon yield of the Silvery Delicacy was well above expectations.

Scientists expect this monsoon’s trend to continue as rainfall has remained erratic.

Typically, the hilsa moves from the sea to the river to lay eggs. Migration begins in June.

In order for fish to move up a river, the salinity of the river water in the estuary must drop. This only happens when there is heavy rainfall for a considerable period and the concentration of salt in the river water is diluted.

“When fish come into fresh water, they suck water into the body, which causes the gonads to hydrate. When this hydration occurs, the ovary swells and the membrane around it bursts, releasing the eggs, ”said Asim Kumar Nath, who studied hilsa migration at Sidho-Kanho-Birsha University.

“Hilsa is a very delicate fish and environmental changes affect its physiology. Unless the fish reaches a particular size, its egg yolk remains underdeveloped.

A mature hilsa lays 10 to 12 lakh eggs, of which only a very small fraction hatches. Scientists said that years with heavy rainfall, such as 2011 and 2012, saw a more robust flow of hilsa into rivers.

“Those were years of bumper making. Over the past two years, the volume of hilsa harvest has declined, leaving fishermen struggling to support themselves, ”said Bijan Maity, from the Kakdwip Fishermen Welfare Association.

Besides insufficient rainfall, scientists blame the trend of illegal fishing for hilsa pawns and the state government policy of allowing fishermen to venture into the waters early, before the onset of the monsoon.

In Bangladesh, there is a general ban on hilsa fishing between May 20 and July 23. The ban by the government of Bengal is from April 15 to June 14. Scientists have blamed the length of the Bengal ban on baby hilsa netting in parts of Frasergunge, Namkhana, Diamond Harbor and Kakdwip in South 24-Parganas.

In Bengal, the capture, sale and purchase of hilsas weighing less than 500 g is prohibited and is a recognizable offense. So it is in Bangladesh.

“We have to have tough laws like in Bangladesh where a fisherman is jailed for six months if he is caught catching a small hilsa,” said Jayanta Pradhan, deputy director of fisheries (marine).

For hilsa lovers, the pleasure of savoring an adult ilish is hard to match.

“Those who weigh around 2 kg or more have their own taste. We don’t see them these days. But such hilsas – with a wide abdomen – are always a chef’s dream, ”said Anjan Chatterjee, owner of Oh! Calcutta restaurant chain. “We have not yet started the Hilsa festival this year due to the low supply of good quality fish. “