Dead in the water: How heatwaves are killing fish

The rise in marine and freshwater fish mortality is an alarming development. (Tarun Kumar Sahu/Mint)
The rise in marine and freshwater fish mortality is an alarming development. (Tarun Kumar Sahu/Mint)


  • For fish eaters, it has become challenging to get hold of seer, Indian mackerel, lobster and crabs without breaking the bank. In places like Goa, India’s favourite party destination, the price of marine fish has almost doubled in the past three months. Here’s the inside story of this inflation.

New Delhi: These days, Mahendra Vinayak Desai, a resident of Chimbel, on the outskirts of Goa’s capital Panaji, has to wake up earlier than usual to purchase seafood, a staple in much of coastal India. At 5 am, the retired lecturer gets a call from a fishmonger, his long-time supplier, giving him details of the day’s catch and the prices. The fishmonger, however, isn’t from his neighbourhood—he’s a good distance away. “I’d rather travel 9km to get fresh fish than purchase the frozen ones from the lady in my locality," says the 68-year-old harmonium accompanist and motivational speaker.

More than 2,000km away, Juthika Biswas, a 60-year-old resident of Kolkata, is also finding it harder to buy fresh seafood. Although Bengalis are partial to freshwater fish, marine fish, such as pomfret and mackerel, have become an important part of their diet. But while they have become popular, these fish are also becoming scarce. “We love to eat Pomfret. As we cannot completely stop having it, we have reduced the quantity of Pomfret as well as prawns," says Biswas.

In much of West Bengal and parts of the east and west coast, placing such limits on fish would have been unthinkable only a few months ago. But a series of heatwaves—unprecedented in their severity, length and frequency—have been coursing through the country, killing the vulnerable, setting off forest fires, and taking maximum temperatures up to nearly 50 degrees Celsius.

While the official human toll as of 1 June stood at 87, the tragedy did not end there.

Life underwater, too, perished before fishermen had a chance to extinguish it. Inland water bodies have been hit hard by the rising temperatures. An alarming 2-5% of fish in lakes and ponds may have been wiped out, according to Trivesh Mahekar, a fisheries scientist at the Indian Council of Agricultural Research-Central Coastal Agricultural Research Institute (ICAR-CCAR), Goa.


“Warmer water temperatures can decrease dissolved oxygen levels and increase the incidence of harmful algal blooms, both of which can affect fish health and survival rates in natural as well as farmed environments," says Mahekar.

Since October 2023, marine heatwaves—unusually high ocean temperatures—have led to extensive bleaching of corals in the Lakshadweep Sea.

In general, for farmed, freshwater or brackish water fish to thrive, the ideal water level should be 1-1.5 metres, says Mahekar. But this year water levels in the ponds that he is studying have shrunk below 1 metre. “I have observed that the water level shrank 67-75 centimetres due to intolerable temperatures, resulting in mortality. This year, fish mortality in my ponds could be around 2-5%. If the temperature keeps rising like this every year, the mortality burden is bound to go up."

It isn’t just ponds and lakes. Since October 2023, marine heatwaves—unusually high ocean temperatures—have led to extensive bleaching of corals in the Lakshadweep Sea, depriving them of essential nutrients and compromising their survival. This, in turn, is threatening marine ecosystems, livelihoods and biodiversity, according to a statement issued by the ICAR-Central Marine Fisheries Research Institute, a leading tropical marine fisheries research body, in May.

Experts say prolonged heat waves lower oxygen levels in water bodies and also cause diseases. These two effects together not only increase mortality among fish but also impact reproduction.

However, a top official of the fisheries ministry, speaking to Mint on condition of anonymity, said that there has been no decline in output so far. “As of now, we haven’t received any reports of fish production getting hurt, especially due to heatwaves," the official asserted. Queries seeking an official response from the fisheries department remained unanswered at the time of going to press. To be sure, government data show production has been rising steadily since the 1980s. More recently, it went up from 12.7 million tonnes (mt) in 2017-18 to 17.5mt in 2022-23.

While production data for 2023-24 is expected this year and 2024-25 will only be available next year, experts believe the scarcity of certain varieties of fish has led to a spike in their prices in the domestic market. Ordering 1kg of seer (king mackerel/kingfish/surmai) on a seafood e-tailer, for instance, can set you back by nearly 3,500.

India’s fish exports, meanwhile, have also declined in value terms. In 2023-24, they dropped to $7.5 billion from around $8 billion in 2022-23, according to the Seafood Exporters Association of India.

Business Impact

 A file photo of fishermen carrying nets.
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A file photo of fishermen carrying nets. (PTI)

The rise in marine and freshwater fish mortality is an alarming development for India, which accounts for as much as 8% of global production and is the third largest fish and aquaculture producer after China and Indonesia.

The fisheries sector plays a crucial role in the national economy and is one of the key contributors to the country’s foreign exchange earnings. In 2022-23, India produced 17.5mt of marine and inland fish, of which rivers accounted for about 75%.

In 2021-22, the country exported 1.36mt of fish—mainly seafood—worth $7.76 billion, an all-time high in value terms, as per the government’s latest data. India primarily exports frozen shrimp, fish, cuttlefish, squid, and dried, live and chilled items.

Marine and inland fish account for over 10% of total exports and 20% of agricultural exports and contribute around 1% of the GDP (gross domestic product) and 5.23% of the agricultural GVA (gross value added) of the country.

In terms of production, Andhra Pradesh is India’s leader, followed by West Bengal, Karnataka, Odisha and Gujarat. In the financial year 2022, Andhra Pradesh produced 4.22mt of fish.

“Domestic production is at least 15% down in April-June of the current financial year compared to last year. We expect better production from the September quarter. However, I don’t think we will reach last year’s production as far as aquaculture or sea-caught shrimp and fish in Andhra Pradesh are concerned," says G. Pavan Kumar, national president of the Seafood Exporters Association of India.

“When you look at West Bengal and Odisha, the stocks of cultured shrimp and fish are also down on year," he adds. Among other factors, Kumar blames an increase in feed, seed and other input costs. That, too, may be down to the torrid summer. According to Mahekar, increased temperatures can affect the metabolism of fish, potentially accelerating growth rates but also increasing their food requirements. This, in turn, can result in higher feed costs.

Belly Up

Fish in lakes, ponds and reservoirs are more vulnerable to heatwaves.
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Fish in lakes, ponds and reservoirs are more vulnerable to heatwaves. (Reuters)

Experts knew they had a problem when fish began floating up dead in the rivers and reservoirs of southern India in significant numbers. Thousands washed up on the shores of the Periyar River in Kerala. Similarly, a large number of fish, each weighing less than half a kilogram, were found dead on the banks of the Mettur Dam in Tamil Nadu on 15 May. Many more floated up in the Krishnagiri Reservoir Project dam, also in Tamil Nadu, due to oxygen depletion on 19 May, according to various media reports.

Fisheries experts and scientists attribute the phenomenon to prolonged dry spells and severe heat waves in southern India, which they say can worsen water pollution. The prognosis is bleak, they add, noting that fish in lakes, ponds and reservoirs are more vulnerable to heatwaves and their mortality rate may worsen if temperatures keep rising in the coming years.

“For Mettur dam, built across the Kaveri River, the state fisheries department came and took samples. People were suspecting it was due to some poison or the effluent mixed with the water and they were investigating in that direction," says Jeyaraj Antony Johnson, senior scientist at the Wildlife Institute of India (WII), an institution into wildlife research and management. “But that was not the case. As an ecologist, I can tell you that it was because of heatwaves followed by the enrichment of microbial biomass (which consumes more dissolved oxygen, critical for fish)," says Johnson.

This year, I expect the mortality rate to go up to 10% overall if the heat is beyond tolerance. —Jeyaraj Antony Johnson

A 2022 study by the US-based Association for the Sciences of Limnology and Oceanography predicted a six-fold increase in the frequency of “mass fish die-offs" across the world by 2,100 due to summerkills (mortalities associated with warm temperature), winterkills (associated with cold temperatures) and infectious pathogens. In the lakes of the northern hemisphere, scientists have observed that the warming of water increases the frequency of fish mass mortality events.

Closer home, on World Fisheries Day 2023, the South Asia Network on Dams, Rivers and People (SANDRP), a network of organizations working on issues related to rivers, communities and large-scale water infrastructure like dams, put together known mass fish death incidents that had taken place in rivers and wetlands across India last year. Most of the fish deaths happened in February, April, May, July and November.

“The salinity and temperature mostly affect fisheries in terms of movement of fish and species variation when they come for migration or breeding," says Asha Giriyan, a fellow at The Energy and Resources Institute (TERI).

Rising temperatures can also cause a shift in the distribution of fish species, as they migrate in search of cooler water. This, in turn, affects the timing of spawning and reproduction. With warmer temperatures, breeding behaviour and spawning locations change.

“Breeding takes place after the arrival of monsoon," explains Johnson. “Once the monsoon is set and the weather becomes cool, breeding happens. Due to a lack of cool water, if the monsoon fails, fish try to move towards the sea. If there are hurdles, they don’t survive, causing substantial mortality. This year, I expect the mortality rate to go up to 10% overall if the heat is beyond tolerance."

Inflationary Effect

Lower production has pushed the price of marine fish up.
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Lower production has pushed the price of marine fish up.

For fish eaters, the heatwaves have made it a challenge to get hold of fresh fish without breaking the bank. People in Goa say that the price of marine fish has almost doubled in the past three months. “We cannot imagine a meal without fish," says retired lecturer Desai. He used to spend around 700-800 daily on buying fish. “But these days I hardly buy any."

The price of seer in Panaji has shot up to 1,000 per kg from 600 in March. Bangda (Indian mackerel), sardine and queenfish, which are rarely available in the market these days, sell for 400-450 a kg, against 100-300 three months ago, says Desai. And lobster prices have doubled to 2,000 per kg from 1,000 over the same period.

In Bengaluru, the price of a large cleaned seer on meat and seafood site Licious is 1,710 for half a kg. White pomfret (small) sells at 899 for 400gm, while mackerel (medium) retails at 249 for 400gm and sardine (medium) at 419 per 650gm.

In Delhi, the price of a 400gm pack of seer on Freshtohome, another meat and seafood site, is 984. A 300gm of black pomfret, which is inferior to its white counterpart in taste, is priced at 886. And a half kg curry cut of barracuda retails at 622.

Among Indian states, consumption is highest in Karnataka, Maharashtra, Assam, Uttar Pradesh, West Bengal, Odisha, Bihar, Kerala and Tamil Nadu. Annual per capita consumption stood at 6.31kg in 2020-21. It has doubled to 13kg in 2022-23, according to the latest data from the National Council of Applied Economic Research. The per capita figure may seem small but there’s wide variation between regions and within states, too.

Lower production has pushed the price of marine fish up while crabs have vanished from the market across the west coast in the past few weeks, says Partha Mukherjee, a wholesaler who sources fish from Kolkata, Surat and Andhra Pradesh and sells at Hiranandani Estate market in Thane, Maharashtra. “Even if some crabs are available, we can offer them for not less than 300-400 per kg," says Mukherjee. He attributed the price rise to the season’s scant rains. “The availability of sea fish will improve from mid-August once the seasonal ban is over," Mukherjee adds. The annual seasonal fishing ban, during the spawning period, is aimed at sustaining marine life. On the West Coast, the ban starts in June, with the monsoon, and runs until the end of July.

The good news is that after the severe heat waves over nearly two months, temperatures in Andhra Pradesh, Tamil Nadu, Telangana and Karnataka have started cooling down with some rain due to the onset of the monsoon over Kerala on 31 May. Whether this will bring fish fries and curries back on the dinner table remains to be seen.

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