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Friday, February 26, 2021

Explained: The Farakka ‘lock’ and hilsa, why there is both hope and apprehension

Fish passes — also known as fish ladders or fish ways — aim to assist fish in crossing obstacles presented by dams and barrages.

By: Explained Desk | New Delhi |
Updated: February 18, 2021 2:37:33 pm
People flock to buy Hilsa in Maniktala market as the first consignment of Hilsa arrived from Bangladesh in September last year. File/Express photo by Partha Paul 

It has been reported that an old project to facilitate the movement of hilsa upstream along the Ganga to its spawning grounds of yore may come to fruition this year.

Back in February 2019, the government had unveiled a project to redesign the navigation lock at the Farakka Barrage at a cost of Rs 360 crore to create a “fish pass” for the hilsa.

The journey of shimmering scales

In scientific parlance, the hilsa (Tenualosa ilisha) is an anadromous fish. That is, 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.

Historical records also show that until the 1970s, the hilsa would swim the Ganga upstream to Allahabad — and even to Agra. But 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 Uttar Pradesh, the last recorded catch of the hilsa was made 32 years ago.

The role of the Farakka Barrage in disrupting the hilsa’s journey is well documented, and has been discussed in Parliament as well. On August 4, 2016, then Union Water Resources Minister Uma Bharti told Lok Sabha about plans to create “fish ladders” to help the fish navigate the obstacle posed by the barrage.

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Fish ladders/fish ways/fish passes

Fish passes — also known as fish ladders or fish ways — 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. For the intervention to work, the water running over these ladders must be controlled — it 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 United States 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 fish ways 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, for fish or the plan

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.

As of the 2019 plan, the new fish pass on the Ganga was to cover only 8 metres, a fraction of the Ganga’s width at Farakka. It seemed likely that only a small number of hilsa might sneak through, but it was doubtful if the new fish way would allow large shoals of the fish to return to their former spawning grounds further upstream.

It is not immediately clear if the plan has been modified. Lovers of the hilsa may have to wait a while longer.

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