Amberjack are swimming up to Hokkaido. Salmon are heading to Sakhalin. And brightly colored crimson sea bream are migrating from the tropics to the waters of the Izu Peninsula. As the planet warms, fish native to Japanese waters are swimming from south to north in pursuit of their desired temperatures, wreaking change on the nation’s regional diets and culture in the process.
The drastic rate of change is particularly evident in Japan, since its oceans are heating up at rates more than double the global average. That equates to an average temperature gain of 1.33 degrees Celsius for waters around Japan in the past 100 years. But this drastic shift is far from evenly distributed.
From Hokkaido to the Izu Peninsula to western Japan, the climate crisis is having chaotic and varied effects on Japan’s bays, channels, inlets and oceans — changing menus, customs, and even livelihoods.
Warming in the north
Japan’s most rapidly warming seas can be found in the north: the Sea of Japan and Pacific Ocean off of Tohoku, in particular. Researchers say that global warming is behind these changes.
“It’s not a one-to-one effect, but higher temperatures result in changes to wind patterns, which cause changes in currents, which cause changes to sea temperatures,” says Shusaku Sugimoto, a disaster mitigation researcher at Tohoku University.
Another major force is the Kuroshio Current, which brings water from the tropics up to Shikoku and alongside the south coast of Japan. The current was in an altered state called a “meander” for an abnormally long seven years and nine months up until last spring, carrying uncharacteristically warm temperatures to parts of Honshu and Tohoku, a phenomenon researchers say may be linked to human-caused climate change.
Per Sugimoto and Norihisa Usui of the Meteorological Research Institute, waters off the coast of eastern Tohoku have been about 6 degrees over preindustrial averages for the last two years — with even higher changes of up to 10 degrees observed below the ocean surface. For comparison, 6 degrees is the difference between taking a dip in the waters of Sagami Bay off Enoshima in August versus late November; 10 degrees is the difference between August and February.
The Sanriku Coast of Miyagi, Iwate and Aomori prefectures is a unique marine environment and biodiversity hotspot due to its position as a meeting point between cold and warm water currents. But in recent years, unusual warm currents have been dominating, transforming the aquatic biosphere. “Phenomena that scientists used to think were impossible have happened, such as when a warm current flowed in 2023 all the way to Aomori,” Sugimoto says.
Sugimoto explains that these warm waters have resulted in massive changes for local fishers. As they end up catching completely different fish from standard fare, they become unable to sell their catch on the market, as restaurants are unwilling to adapt their menus to feature unfamiliar fish.
Some of these changes in Tohoku include the decline of salmon, kelp, amberjack and mackerel, replaced by species like hairtail and blowfish. Takao Ohama, managing procurer at the national conveyor-belt sushi chain Kura Sushi, says the types of fish, amount of catch, and the seasons fish appear are all changing.
“We used to mainly acquire wild-caught buri (amberjack) from around Honshu, but for the last two to three years, they tend to be more available in increasingly northern regions such as Hokkaido,” Ohama says. “Buri are definitely moving further north.”
To make matters worse, scorching-hot summer temperatures have caused aquaculture amberjack to die off in regions like Shikoku and southern Kyushu. “The amount available on the market is decreasing drastically,” he says.
Changing dinner plates
Salmon harvests in Hokkaido and Tohoku are in the midst of a tumble. Per the Hokkaido Prefectural Government, Hokkaido’s 2025’s salmon catch through mid-December hauled in about five times fewer salmon than the 2022 total.
While ocean temperatures have changed more rapidly in the north, seafood culture all across Japan is being affected.
“Tachiuo (hairtail) used to be a distinctive fish characteristic of Osaka Bay, but their numbers have been decimated almost to nothing in the past three to four years as they move toward Chiba and Ibaraki,” Ohama says. Hairtail is a uniquely Osaka regional fish, both in terms of fishing culture and regional cuisine — one nearly lost in the span of a few short years.
These changes are just as present on the mild Izu Peninsula, under the jurisdiction of the warm Kuroshio Current. A local diver and guide for Izu Geopark, Kazuya Asakura, says that of late, rainbow-colored tropical fish have been spotted in abundance. The presence of these fish, unthinkable 10 or 20 years ago, is causing an excited frenzy for divers, but to scientists and fishers, they are a more foreboding sign.
“Waters have gotten warm enough such that tropical organisms can survive the winter and actually reproduce,” Asakura says. “Not only are waters getting too warm for the previously local fish, but now they have to compete for territory with the newcomers.”
While Izu tends to have warm waters in general, Asakura says that the baseline winter temperatures have gone up from 13 C in the past to around 16 C in recent years.
The Kuroshio Current may be the key to understanding warming waters both in Izu and across Japan. Usui says that, while the seven-year-long “meander” of the Kuroshio Current in itself was unprecedented, the current as a whole is growing warmer and moving northward. Furthermore, an extension from the Kuroshio Current called the Tsushima Warm Current is playing a part in heating up the Sea of Japan. The warming, northward movement, and meander of the Kuroshio Current all cause diverse changes in weather and land climate across Japan, bringing more humidity, rain, and storms to Kanto and other regions.
Changing culture
One of the biggest ecological problems in Izu, however, does not have to do with fish but with seaweed. Tengusa is the kelp used to make tokoroten, a gelatinous dish famous in Izu. But according to data from the Izu Peninsula Geopark, ever since the Kuroshio Meander began, tengusa harvests plummeted. “Damage has been done to family businesses and successors,” Asakura says. “Izu is in the process of losing one of its cultural traditions.”
A lack of successors doesn’t apply just to tengusa, but also to fisheries and aquaculture in Izu more broadly. Plummeting revenue margins due to changes in available fish make jobs in Yokohama and Tokyo much more appealing for the younger generation, accelerating depopulation. In the city of Ito, for example, the population declined from 71,473 in 2015 to 63,494 in 2025, a drop of over 11%. “Sea temperature changes are intricately intertwined with population decline,” Asakura says.
Across Japan, businesses and enterprising individuals are trying to make the best of the changes. Kura Sushi, for one, has been hyperaware of changes to fish acquisition across Japan. As a result, the company implemented a lengthy list of policies to adapt and preserve their supply of fresh fish: contracts that promise fishers a certain amount of purchases, introducing new products to their lineup like mahi-mahi sushi and investing in aquaculture techniques and technology. Because Japanese customers are reluctant to try new foods, Ohama says they introduce new fish for cheap, around ¥150 yen for a plate, and circulate them on the conveyor belt to start to build up trust.
“It’s crucial that we keep good prices on the market for fishers across Japan,” Ohama says. “Unfortunately, the traditional thought process that we need to eat specific kinds of fish at specific times of year is becoming difficult and unrealistic.”
Ohama says he hopes to see broad changes made across governments, industry and consumers, in order to circulate and consume the fish actually being caught by fishers today.
In Izu, new initiatives make use of traditional fishing areas for tourism, such as experiences with pro fishers and scuba diving. But as of now, people aren’t taking advantage of warmer waters to go swimming outside of the traditional season, says Asakura.
“Sea and land leisure go hand-in-hand, if it’s too hot outside, you still can’t safely do water activities,” Asakura adds, an increasingly common occurrence on the Izu Peninsula.
Warming seawaters across Japan are devastating konbu harvests in Hokkaido, killing off aquaculture mackerel, and seeing a wide variety of creatures from spiny lobster to octopi moving their territory north year over year. But the most drastic changes in areas like Tohoku and Izu have the potential to wipe out traditional livelihoods and regional specialties in a single warm current’s unlikely deviation.
Under a climate crisis reality where unpredictable deviations to ocean temperatures are the norm, even experts can be left at a loss.
“It’s hard to predict the future, because our previous models couldn’t have predicted current events,” Sugimoto says. “There will be changes to currents, rainfall, storms, and water temperatures that we cannot anticipate now.”
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