Context: 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.

Background

• 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.
• Once the construction of Farakka's new 'navigational lock' is completed, a lot of hilsa will be available in the river Ganges. 
• Such is the claim of L&T Geostructure under Larsen & Toubro Limited, which is responsible for making the lock. The company has said that this initiative is mainly for the smooth travel of the ship.

Key Points

• Before the formation of the Farakka barrage in the 1970's, there was a hitherto hilsha from Bangladesh to Allahabad. But after the construction of the dam it closed due to the navigation lock. So Hilsa can not go to India.
• After nearly 40 years, the country has created a new navigation lock design. The implementation of this design will end if the hilsa drought in India.
• India's internal river authorities hope, at this time, the eggs-breeding hilsa will be reached by the Farakka dam, in Elahabad or in Prayagraj of India.
• In the breeding season of Hilsa, eight meters of the gate will keep opened from 1am to 5am in the morning so that the hilsa can enter India.
• According to fish scientists, this time, the hilsa went against the torrent. However, no vessels will be able to navigate during this time; because it requires 25 meters wide space.
• According to an official of the company, once this navigational lock is made, the supply of hilsa will increase from Farakka to Prayagraj in Uttar Pradesh. Hilsa fish from Bangladesh will flow upstream of the Ganges towards India.
• Fish passes to be built at Farakka also known as fish ladders or fish ways aim to assist fish in crossing obstacles presented by dams and barrages.

Hilsa fish migration

• 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.

What affected the fish movement?

• 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.

What are fish ladders?

• 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.