Much to his dismay, longtime kelp farmer Shigeki Aiki found that his konbu seedlings had many fewer leaves that were to be processed for food.

Only one to two out of every 10 survived the high ocean temperatures between September and October last year.

Aiki, 62, who has cultured kelp or more than 30 years, is concerned about the effects of the high water temperatures in Rausu, located on the Shiretoko Peninsula in Japan's main island of Hokkaido.

Famed for its pricy “Rausu konbu” kelp, cultivators saw the seaweed’s output down by 50 to 80 percent at more than one farm last year. Konbu are cultivated on ropes set up in the ocean.

Last autumn, the ocean surface temperature reached “an unprecedented level” for local fishermen of nearly 25 degrees.

“Higher water temperatures cause konbu roots to rot,” Aiki said. “If this phenomenon ends in a single year, everything will be fine. If it continues for two to three years, that would render my life difficult, though.”

Global warming is bringing on a succession of negative effects on a range of marine creatures across Japan, such as the relocated habitats of fish and fluctuations in seafood catches.

Concerns are growing that the summer heat wave expected this year as well may further exacerbate the situation.

NEW FISH IN NORTHERN WATERS

“Ise-ebi” spiny lobsters have recently gone on display at Iwate Prefecture’s fishery science museum in Miyako, drawing considerable attention. They have been hauled ashore locally since last fall.

Ise-ebi live primarily in warmer waters. Their northernmost fishing ground was previously thought to be the region off Ibaraki Prefecture near Tokyo.

The museum operator stated that two ise-ebi were spotted for the first time in 2021 in local Miyako Bay and Yamada Bay. While none were confirmed in 2022, 18 were discovered through late December in 2023.

“That is likely due to the influence of global warming,” noted a museum representative, pointing to the fact that the water temperature was 2 to 4 degrees higher than usual last year.

At a market in Ishinomaki, Miyagi Prefecture, fish species from southern waters, including giant trevally and spangled emperor, can likewise be seen this year although they were not available there previously.

CATCH FLUCTUATIONS NATIONWIDE

Data from the Japan Meteorological Agency shows the sea surface temperatures along the Japanese archipelago have risen an average of 1.28 degrees over the past 100 years.

The mercury hit a record high for the period from June last year through February this year for the third season in a row for the first time since record-keeping began in 1982.

Many fish species are believed to have changed their habitats due to the recent rise in seawater temperatures.

The cutlassfish catch has declined to one-sixth that of 10 years previously in the three prefectures of Ehime, Wakayama and Oita. Whereas the seafood is renowned as a specialty of western Japan, the catch was up 25-fold to 551 tons in Iwate, Miyagi and Fukushima prefectures in northeastern Japan. 

The yellowtail heads southward from Hokkaido for the Sea of Japan in the fall and is caught heavily off the coasts of Toyama, Ishikawa and Niigata prefectures. Yellowtail served during the coldest season is a well-known specialty, but the species’ yield has more than halved over the last decade.

In the meantime, the yellowtail production off Hokkaido shot up 20 times from that in the 1990s.

Seeing a spike in the catches of certain seafood varieties, some regions are moving to make those newcomers local delicacies, such as launching new brands. But it remains unclear whether these efforts will successfully pan out.

The Japanese Spanish mackerel heralds the arrival of spring in the Seto Inland Sea, as its kanji name comprised of radicals representing “fish” and “spring” suggests. The species has notably changed its distribution pattern due to the rise in ocean surface temperatures.

Until the first half of the 1990s, the fish could be found in the Seto Inland Sea and elsewhere in the East China Sea. The mackerel’s fishing grounds have shifted northward from the northern Kyushu region to the Sanriku region.

None of the Japanese Spanish mackerel were traditionally caught off Niigata Prefecture. However, catches started increasing around 2000 and reached a peak of 556 tons in 2016.

The output of the mackerel variant plummeted by upward of 200 tons year on year to 74 tons in 2022. With the circumstances worsening, the catch for 2023 came to 1.7 tons, or 21 percent of the level the previous year, by September.

“Hundreds of the mackerel were caught daily in seasons with good harvests, but the fish may have headed farther northward owing to the unusually hot weather,” said Daisuke Akai, 46, captain of a stationary net fishing boat in Niigata Prefecture.

Akai continued, “A species called grunt, which is typically found en masse off Nagasaki Prefecture and other places in Kyushu, can be caught these days at times. The only option for us might be catching whatever fish we encounter.”

TOTAL CATCH DROPS

The total seafood catch in Japan has been on a continuous decline.

Changes in fisheries conditions stemming from global warming, alongside the shrinking population of fishermen and their advanced age as well as overfishing and various other factors, have emerged as problematic in recent years.

According to statistics from the Ministry of Agriculture, Forestry and Fisheries, the nationwide fishery production, including that from aquaculture, reached a peak of 12.82 million tons in 1984. The figure sank on a continual basis to 3.91 million tons in 2022, the lowest level since 1956, when comparable counts first became available.

Masanori Miyahara, a former deputy director-general of the Fisheries Agency, who has long been involved in the implementation of fishery policies, said fishing should be halted to wait for resources to recover at the time of a poor catch, in principle, under a normal fish control method.

However, this countermeasure does not appear to be enough to bring seafood output back toward recovery, given that keeping pace with rapid environmental changes associated with global warming with this alone looks unrealistic.

Citing an example of saury, Miyahara said juvenile fish from the species used to grow in nutrient-rich waters off Japan. Fry are now driven to offshore areas by the altered Kuroshio current deriving from global warming.

They are more likely to become thin and die in waters with few food sources far from the coasts. On top of that, non-Japanese fishing boats navigate the open ocean to overhunt saury, creating a vicious cycle resulting in poor catches.

The Fisheries Agency is beefing up aquatic resource control through restricting fishing. Among the eight currently regulated variants are saury and bluefin tuna.

The aim is preventing the cycle of declining catches by urging fishermen not to hunt small fish that should not be caught.

The ultimate goal of the Fisheries Agency is raising the fishery production to 4.44 million tons by fiscal 2030. It is gearing up to cover several more variants, including yellowtail and anchovy, under its regulation program.

Consisting of Miyahara and other experts, a privately run group called the fishery forum aiming at resource recovery proposed five approaches to achieve a sustainable form of fishing for the Fisheries Agency last spring.

The group argued efforts should be bolstered to gather data on environmental changes in the seas. It recommended the budgets and personnel for resource control and surveys should be improved as well. 

Another suggestion is promoting the active commitment of fishermen to processes to set resource control targets.

Regulating the hunting of small fish is alike proposed, while the group stated that subsidies have to be offered for fishermen to lease boats with ease and ensure a stable revenue source.

In March this year, the fishery forum compiled a report as well.

“As oceanic environmental changes are transpiring nationwide and worldwide, a new style of resource research and management needs to be stepped up while harboring a sense of crisis,” the document recommends.

The report insists that the government should commission private bodies to conduct conventional fishery-relevant analyses, so that state-affiliated organizations can concentrate on much more advanced surveys themed on global warming.

“Fishermen, the government, academics and other parties must share in a sense of alarm in a bid to take flexible approaches with an eye on the coming 10 years, and not rely on precedents,” Miyahara said. 

(This article was written by Takuya Miyano, Eiji Zakoda and Tomoyuki Yamamoto.)