Why new plan to ‘unlock’ Farakka for hilsa recalls old debate on fish passeshttps://indianexpress.com/article/explained/why-new-plan-to-unlock-farakka-for-hilsa-recalls-old-debate-on-fish-passes-5593626/

Why new plan to ‘unlock’ Farakka for hilsa recalls old debate on fish passes

Like many other debates in gastronomy, the one on the hilsa, too, is about the seamlessness of legend and myth, ecology, history, and culture.

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Hilsa lives most of its life in the ocean, but during the rainy season, when it is time to spawn, the hilsa moves towards the estuary, where the rivers of India and Bangladesh meet the Bay of Bengal.

Among the longstanding gastronomy debates in the subcontinent is the one on the relative merits of the hilsa that comes from the Padma river in Bangladesh versus the variety that is found in the Ganga in India. The advocates of both varieties underline the distinctive sweet-salty flavour of the silver-scaled fish. While those in the east vouch for its fleshy texture, aficionados in the west rest their claims on what the fish does to the taste buds — that sweet-salty flavour is apparently more pronounced in the Ganga hilsa.

Like many other debates in gastronomy, the one on the hilsa, too, is about the seamlessness of legend and myth, ecology, history, and culture.

However, records do attest to certain facts. Among them are the ones that pertain to the annual journey of the fish.

The hilsa’s journey

In scientific parlance, the hilsa is an anadromous fish. It lives most of its life in the ocean, but during the rainy season, when it is time to spawn, the hilsa moves towards the estuary, where the rivers of India and Bangladesh meet the Bay of Bengal. A large part of the shoal travels upstream in the Padma and the Ganga — some are known to move towards the Godavari, and there are records of hilsa migration to the Cauvery. Culinary lore has it that the fish that travel the farthest upstream have the best combination of the flavours of the sea and the river.

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Historical records also show that until the 1970s, the hilsa would swim the Ganga upstream to Allahabad — and even to Agra. The Farakka Barrage, which became operational on the Ganga in 1975, disrupted the westward movement of the hilsa. The barrage had a navigation lock that stopped the fish from swimming upstream beyond Farakka. In Buxar on the border of Bihar and UP, the last recorded catch of the hilsa was made 32 years ago.

Fishway experiments

Earlier this month, the government unveiled a project to facilitate the movement of the hilsa to its spawning grounds of yore. The navigation lock at Farakka will be redesigned at a cost of Rs 360 crore to create a fish pass for the hilsa.

Fish passes — also known as fish ladders or fishways — aim to assist fish in crossing obstacles presented by dams and barrages. They usually consist of small steps that allow the fish to climb over the obstacles and enable them to reach the open waters on the other side. It requires controlling the water running over these ladders — they must be adequate to catch the attention of the fish, but not too strong to deter them from swimming against it.

The most rudimentary first fish ladders are said to have been forged out of bundles of tree branches that helped fish cross difficult channels in Western Europe. In 1837, Canadian lumber mill owner Richard McFarlan patented a fish ladder designed to help fish bypass a dam at his water-powered mill. By the late 19th century, fish passes had become common in the US and Canada.

About the same time, Francis Day, the pioneering fish scientist of colonial India, experimented with fish ladders to enable unhindered movement of the hilsa across anicuts in the Cauvery’s northern distributary, the Kollidam. The experiment was tried for about 40 years before being given up. Fish passes also proved ineffective in North India.

By the middle of the 20th century, the utility and effectiveness of fishways was being seriously debated in the US. A paper in the May 1940 issue of The Stanford Ichthyological Bulletin put the question in perspective: “The devising of a fish pass is fraught with uncertainty, because it is almost impossible to prophesy the behaviour of fish and quite impossible to anticipate the vagaries of water. The subject involves a working knowledge of hydraulics, and while hydraulic engineers conversant with the habits and requirements of fish are rarely to be found, the rules and assumptions of hydraulics themselves are apt to be disconcertingly upset when applied to the functioning of a fish pass. The subject is by no means within sight of finality.”

No clear path yet

More than 75 years later, the predicament endures. A 2013 study led by the American ecologist J Jed Brown noted that “state-of-the-art fish passage facilities have been unsuccessful. Some migratory species, such as sturgeons, do not pass through at all. But even the species that do make it through do so in numbers far less than stated targets”. Brown’s research found that about 2% of American shad, a species closely related to the hilsa, passed through the dams on the Merrimack, Connecticut and Susquehanna rivers in the US.

The new fish pass on the Ganga will cover only 8 metres, a tiny fraction of the Ganga’s width at Farakka. A small number of the hilsa might well sneak through, but it is doubtful if the new fishway will allow large shoals of the fish to return to their former spawning grounds further upstream.