TOKYO – In May, Japanese fisherman Tadasuke Nakamura noticed he had an abnormally large haul of bluefin tuna in his set net off the Pacific coast of Hakodate, on Japan’s northern island of Hokkaido.

Hundreds of the prized sushi fish crowded the net, but he had to let many of them go.

Japan has an annual catch quota and if Nakamura had kept the haul he would have had no quota left for the colder months when bluefin tuna are fattier and tastier, and fetch a higher price.

“It’s truly upsetting to have to release fish that are right there in the net,” said Nakamura, whose method of fishing involves anchoring large fixed nets close to the shore.

Fishermen in Japan have reported an abnormal surge in the number of the once-endangered bluefin tuna in surrounding waters in 2026 in what experts say may be partly due to changing migratory patterns linked to climate change.

The phenomenon is another example of how climate change may be altering marine life, with serious consequences for those whose livelihoods have long depended on the sea.

In Nakamura’s hometown of Hakodate, the fishing industry is already grappling with a severe decline in the population of the once ubiquitous squid.

Quota limits catch size

Like Nakamura, many fishermen have been unable to capitalise on the abundance of the species early in the season.

An international quota system in place since 2015 means Japan is allowed to catch no more than 8,421 tonnes of bluefin tuna weighing 30kg or more in 2026 in the waters of the western and central Pacific, extending south of New Zealand and covering about a fifth of the world’s surface.

While Japan’s quota was increased by 50 per cent from 2024 for 2026 and 2025, the sheer scale of the surge in the bluefin tuna population means many Japanese fishermen are close to reaching their 2026 quota.

Set-net fishermen are also finding that when they re...