Thankachan Polayalil has been a fisherman for 42 of his 65 years, long enough to remember when fish were visible from land, brimming just beyond the palm trees of the Malabar Coast.

Now his boat is equipped with an echolocation machine, but fish still are hard to find and the catch isn’t nearly as diverse. The anchovies are gone, and the mackerel now often swim in deeper water, making them harder to snare.

Joy Valiaparinb, another fisherman at Chellanam Fishing Harbour, said he regularly pushes off at 2 am, knowing it can take hours just to spot fish.

Often, according to fishermen along Southwestern coast, they find nothing. Climate change is making an already difficult search for fish harder, according to scientists at the Central Marine Fisheries Research Institute in Kochi.

Fish populations are always shifting, sometimes drastically, and overfishing has emptied waters once teeming with life, they said.

But as climate change has warmed coastal waters by more than half a degree Celsius over the past three or four decades, scientists say, fish populations have sought cooler waters — often away from where fishermen are used to finding them. That has forced fishermen to spend more on nets, fuel and ice to keep fish fresh as they spend more time at sea. They stay afloat only because fish prices are rising as shortages grow, and they can find a market for almost anything that shows up in their nets, they say.

On a January morning, the Chellanam Fishing Harbour beach is strewn with silvery oil sardines piled into red and yellow baskets. It’s evidence of a good catch, something now relatively ra

Fishermen say sardines are a favourite because the fish is popular and relatively affordable for buyers. Even if there are other fish, (fishermen) always say if oil sardines aren’t there, there is a shortage of fish, said PU Zacharia, a CMFRI principal scientist with expertise in climate change and marine fisheries. Oil sardines used to swim in India almost exclusively around the Malabar Coast — but climate change has pushed them east and north-east, into waters around Mumbai and Kolkata, scientists say. Fish all over are migrating toward the globe’s poles, often seeking the cooler water they are used to as the ocean warms, the scientists say.

With buyers in Mumbai, Gujarat, and West Bengal not as used to eating oil sardines, the fish caught there are often shipped south, losing value and freshness in transit, said Zacharia.

Fishermen are also struggling to catch mackerel, another long-time staple. More mackerel are now found at depths where the water is cooler, forcing fishermen on days-long trawling operations that require expensive nets, more manpower, more fuel, and more ice to keep the fish fresh. One fisherman, from the coastal city of Kanyakumari, said fuel for an average trip has risen from around ₹70,000-₹2,00,000 over the last seven years.

Finding a way forward

Hoping to help fishermen adapt to changing conditions, CMFRI scientists are beginning to model the ways climate change may influence movement of sardines, mackerel, and other species in decades to come.

They hope their models will predict the size and species of future catches.