Tags Current Affairs

Issue

An old project to facilitate the movement of hilsa fish upstream along the Ganga to its spawning grounds may come into implementation this year.

 

Background

In February 2019, the government had unveiled a project to redesign the navigation lock at the Farakka Barrage to create a “fish pass” for the hilsa.

 

Details

• The hilsa (Tenualosa ilisha) is an anadromous fish that lives most of its life in the ocean. 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 while some are known to move towards the Godavari. There are also records of hilsa migration to the Cauvery.

• Historical records 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. 

 

Fish passes

• The role of the Farakka Barrage in disrupting the hilsa’s journey is well documented, and has been discussed in Parliament as well.

• The government told Lok Sabha about plans to create “fish ladders” to help the fish navigate the obstacle posed by the barrage.

• Fish passes are also known as fish ladders or fish ways and 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. 

• 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.

• Research has found that 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.

 

Fish pass at Farakka

• 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. It is doubtful if the new fish way would allow large shoals of the fish to return to their former spawning grounds further upstream.

 

Farakka Barrage

• Farakka Barrage is constructed across the Ganga river located in Murshidabad district of West Bengal, roughly 18 kilometres from the border with Bangladesh.

• The Ganges river splits into two rivers - Bhagirathi-Hooghly River and Padma River, a little after Farakka Barrage and both flow into the Bay of Bengal.

• The purpose of the barrage is to divert water from the Ganges to the Hooghly River for flushing out the sediment deposition from the Kolkata harbour without the need of regular mechanical dredging. 

• In Bangladesh, it is perceived that the barrage has raised salinity levels, contaminated fisheries, hindered navigation, and posed a threat to water quality and public health.

• Lower levels of soil moisture along with increased salinity have also led to desertification. Farakka barrage has been criticized for the floods in Bihar as it is causing excessive siltation in the Ganga.