Silver scales and survival ladders: the hilsa recipehttps://indianexpress.com/article/explained/fish-ladders-ganga-help-hilsa-breeding-uma-bharti-2962348/

Silver scales and survival ladders: the hilsa recipe

On August 4, Water Resources Minister Uma Bharti told Lok Sabha that the government was planning to create “fish ladders” in the Ganga near the Farakka Barrage to help hilsa travel upstream to spawn — hopefully improving the catch.

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Is the hilsa (Tenualosa ilisha) a sea or a river fish? Where is it found?

It is what is called an anadromous species — like the salmon, sturgeon and shad, it is born in fresh water, spends most of its life in the sea and returns to fresh water to spawn. The bony fish, with silver scales and a faint streak of pink on its belly, is found in marine, estuarine and riverine environments. The Bay of Bengal, Indian Ocean, and Arabian Sea are its marine homes; the rivers Ganga, Bhagirathi, Hooghly, Brahmaputra, Rupnarayan, Narmada, Cauvery and Godavari are its spawning grounds. The fish also goes to the Indus in Pakistan, Irrawaddy in Myanmar and Bangladesh rivers like Padma, Jamuna, Meghna and Karnaphuli to lay eggs. However, it’s in eastern India and in Bangladesh — to a lesser extent in Sindh, Pakistan — that the fish attains cult status in gastronomy.

So, at what time is the hilsa on the move?

The hilsa’s upstream migration begins in late June and continues until mid October to early November. A second wave of migration occurs from late January to March/early April. The spring spawners return to the sea during the monsoon, where fishers are lying in wait for them. Their cousins who lay eggs in the monsoon return to the sea in late winter and spring — their journey too ending in fishing nets. The hilsa is at its tastiest at this stage: the stay in river waters imparts sweetness to the flesh and reduces its otherwise salty taste to a whiff — and for Bengalis, when combined with mustard, chilly and some other spices, it makes for a lip-smacking mélange.

And how far upstream does it travel?

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It’s a long-distance swimmer that’s been known to travel 1,200-1,400 km from the Bay of Bengal — up the Hooghly and then the Ganga up to Patna and Varanasi, and sometimes even Allahabad, Kanpur and, up the Yamuna to Agra. Back in 1822, Francis Buchanan Hamilton, the Scottish physician who made seminal contributions to Indian zoology and botany, noted, “I have seen [the Ilisha] as high as Agra and Cawnpore. At Patna on the Ganges, and Goyalpara on the Brahmaputra, it is pretty common.” A little over a century later, colonial fishing expert Stanley Howard, while confirming Hamilton’s observations, wrote: “During the monsoon the adult fish ascend the Hooghly… for the purpose of spawning. The spawn is deposited from about the middle of July to the middle of September, and rivers continue to be the home of these fish until the middle of November when the fish return to the sea. Having deposited their spawn the older fish, or what remains of them, meet their fate in nets. The young fish after about two months’ stay in the sea, add considerably to their size and weight, and towards the end of December they return to the estuaries.”

Where does the Farakka Barrage come in?

The commissioning of the Farakka Barrage in 1975 in West Bengal’s Murshidabad district intercepted the hilsa’s journey. The fish could no longer move beyond West Bengal. Central Fisheries Research Institute records show that rarely do hilsa manage to make their way to Patna, and have not been seen in Allahabad for decades now. Two “fish passes” that could have facilitated the hilsa’s movement across the barrage never worked. On the other hand, as the hydrologist Parimal Ray wrote in his 1998 book Ecological Imbalance of the Ganga River System: Its Impact on Aquaculture, “There is a heavy congregation of the fish below the barrage and they are indiscriminately caught before they can breed.”

But what are the fish ladders that Minister Bharti mentioned?

A fish ladder, or fishway, is essentially a structure that allows migrating fish passage over or around an obstacle — dams, culverts, waterfalls — on a river. Fishways give anadromous fish — whose survival depends on migration — a detour, and have been considered critical in keeping up fish stocks. Fish ladders are common in the US, and are of designs that depend on the obstruction, river flow, and species of affected fish. The general principle, however, according to the National Oceanic and Atmospheric Administration (NOAA) of the US Department of Commerce, is the same for all: “the ladder contains a series of ascending pools that are reached by swimming against a stream of water. Fish leap through the cascade of rushing water, rest in a pool, and then repeat the process until they are out of the ladder.”

In 2013, however, the American ecology, anadromous fish and urban waterways expert John Waldman and six colleagues reported that fishways on rivers in the US Northeast were failing. (‘Fish and hydropower on the US Atlantic coast: failed fisheries policies from half-way technologies’, Conservation Letters) They tracked the journey of Atlantic salmon, American shad, river herring, and other species up the Susquehanna, Connecticut, and Merrimack rivers, and found that in some cases, less than 3% of fish made it past the dams. The study results, the Waldman wrote, had significance for proposed or planned dam projects on rivers including the Teesta in India.