Fatty ‘katsu’ fish may portend climate change, posing a threat to Japanese sushi

This trend is worrying because changes in the sea and climate have already wiped out other species of fish

  • By Kantaro Komiya/Reuters, Nakatosa

For half a century, takyo nakaju has been catching katsu, or skipjack tuna – indispensable in Japanese cuisine whether eaten raw, dried, or used as a base for broth.

But he and other fishermen in Kore, in Kochi Prefecture in southwestern Japan, have seen something troubling in the past two years – an unprecedented number of unusually fatty katsu.

While the heavier katsu means more money, locals and experts say it indicates climate change and a threat to the katsu numbers already threatened by increased demand and poaching.

Photo: Reuters

“The fatty katsu must have something to do with the temperature of the water,” said the 70-year-old Nakajo. “I have a sense of urgency thinking what if Katsuo never comes to the bay.”

He’s also “never seen such a greasy katsu during this season of the year,” said Noriaki Ito, chef at the century-old Tsukasa restaurant in Kochi.

This is worrying, Ito added, because changes in the sea and climate have already wiped out some other fish, “including oysters called chambara gai, which were Kochi’s specialty.”

Photo: Reuters

Originally from tropical waters, some Pacific Katsu migrate north on a warm ocean current each spring, making the arc-shaped Bay of Kochi a fertile fishing ground.

The average surface temperature of the bay in winter increased by 2 degrees Celsius in the four decades to 2015, local fisheries lab data show, and the fatter katsu may be caused by the presence of abundant prey in the warmer sea.

Long-term warming may prevent mineral-rich waters from rising to the surface, reducing plankton and the small fish that feed on them, reducing the number of katsuo, said Hiroyuki Okeda, an agricultural scientist and vice president of the University of Kochi.

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 radish – an eye-watering condiment tucked under fish in a piece of sushi.

Many fishermen have gone out of business in the past three decades, said Takahiro Tanaka, a fourth-generation owner of a fishmonger who calls himself “Katsu’s Legs,” in Kuri, a district of Nakatosa Township.

He added, “We can distinguish the different tastes of katsu, just as ordinary French farmers taste a delicate wine…This place may be one of the last Japanese communities where katsu is part of everyday culture.”

But without Hunters, this won’t last,” Tanaka said.

The hunter Nakajo also angered the elderly community and a few of his successors. “I asked my grandson if he would take the position, but now he is studying to work in a government office,” Nakajo said.

Sushi culture is in danger

Overfishing has already hit catch numbers and dealt a blow to fishermen in Kochi who stick to traditional monopole fishing methods versus large-scale trawling across the western Pacific.

Government data shows that fishing numbers in Kochi were only a quarter of their peak in the 1980s.

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

“An increasing number of people fear that we may not be able to eat katsu in the near future if things continue like this.”

Already suffering is the production of katsuobushi, the dried and fermented katsu, which is often used as a condiment shaved over traditional Japanese dishes or as a broth base.

Taichi Takeuchi, who runs one in the USA town, said the number of katsuobushi manufacturers in Kochi has dropped from dozens about 40 years ago to just a few.

“I’m not really sure if we can continue with that,” Takeuchi said.

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