Oily ‘katsuo’ fish may foreshadow climate change and threaten Japanese sushi

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Noriaki Ito, 57, a 106-year-old chef at Tsukasa restaurant, puts wasabi on a piece of raw katsuo (skipjack tuna), in Kochi, Kochi prefecture, Japan May 13, 2022. REUTERS

NAKATOSA, Japan — For half a century, Takeo Nakajo has been fishing for katsuo, or bonito tuna, essential in Japanese cuisine, whether eaten raw, dried or used as a base for broth.

But he and other anglers in Kure, in southwestern Japan’s Kochi prefecture, have seen something worrying over the past two years: unprecedented numbers of unusually fat katsuo.

While heavier katsuo means more money, locals and experts say it points to climate change and a risk to already threatened katsuo numbers due to growing demand and overfishing.

“The fat katsuo must have something to do with the temperature of the water,” said 70-year-old Nakajo. “I have a sense of urgency to think about what if Katsuo doesn’t come to the bay one day.”

Noriaki Ito, the head chef of a century-old Tsukasa restaurant in the city of Kochi, also said he had “never seen such a fat katsuo during this season of the year”.

This is worrying because sea and climate changes have already wiped out other fish “including a crustacean called chambara-gai which was Kochi’s specialty”, Ito added.

Oily 'katsuo' fish may foreshadow climate change and threaten Japanese sushi

A worker pours water over boxes filled with katsuo (skipjack tuna), ahead of a wholesale auction at Kure port in Nakatosa city, Kochi prefecture, Japan May 14, 2022. REUTERS

Native to tropical waters, some Pacific katsuo migrate north each spring on a warm ocean current, making the arc-shaped bay of Kochi a fertile fishing ground.

The bay’s average winter surface temperature has risen by 2 degrees Celsius in the four decades to 2015, according to data from local fisheries labs, and the larger katsuo may be due to high prey in the sea. hotter.

But in the longer term, this warming may prevent mineral-rich water from rising to the surface, leading to fewer plankton and smaller fish to feed on, leading to less katsuo, said Hideyuki Ukeda, an agricultural scientist and vice -president of Kochi University.

It comes as Japan’s aging population threatens the sustainability of local fishing and related businesses such as the production of dried and fermented katsuo and wasabi horseradish – an appetizing condiment hidden under fish in a piece of sushi.

In Kure, a district of Nakatosa city, many fishermen have gone out of business over the past three decades, said Takahiro Tanaka, a fourth-generation owner of a fishmonger who calls himself “sommelier katsuo”.

“We can distinguish different tastes of katsuo, just as ordinary French farmers can savor the intricacies of wine…this place could be one of the last communities in Japan where katsuo is part of everyday culture,” he said. -he adds.

“But without fishermen, it won’t last,” Tanaka said.

Fisherman Nakajo also lamented the aging of the community and the reduced number of successors. “I asked my grandson if he would take over, but he is now studying to work in a government office,” Nakajo said.

Oily 'katsuo' fish may foreshadow climate change and threaten Japanese sushi

Katsuo (skipjack tuna) is kept in ice during a wholesale auction at Kure port in Nakatosa city, Kochi prefecture, Japan May 14, 2022. REUTERS

Sushi culture in peril

Overfishing has already reached catch numbers and dealt a blow to Kochi fishermen who have settled for traditional single-rod fishing methods over large-scale purse seine fishing in the Western Pacific.

Government data shows that the number of catches in Kochi is only a quarter of its peak in the 1980s.

“We have seen a catastrophic decline in landings over the past 10 years or so,” Ukeda said.

“A growing number of people are concerned that we won’t be able to eat katsuo in the near future if things continue like this.”

The production of katsuobushi, dried and fermented katsuo, often used as a shaved condiment on traditional Japanese dishes or as a stock base, is already suffering.

The number of katsuobushi makers in Kochi has shrunk from dozens some 40 years ago to just a few, said Taichi Takeuchi, who runs one in the city of Usa.

“I really don’t know if we can continue this,” Takeuchi said.

Wasabi, the pungent horseradish essential to Japanese cuisine, especially sashimi and sushi, faces similar production challenges.

Typhoons and rising temperatures have hurt production in Okutama, a mountainous region west of Tokyo, said Masahiro Hoshina, 72, head of the local wasabi growers’ association.

“I am extremely worried about the future of our agriculture,” Hoshina said.

The number of farmers in the area is down 75% from the 1950s due to depopulation, and unless something changes, some fear the sushi itself is in danger.

“Combining raw fish and spices, like in katsuo and wasabi, is an art, and we need to maintain both,” Ukeda said. “I never want to think of a future” without them, he added.

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