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The fishery scene on the Hokkaido coast is seeing changes, possibly due to climate change.

Catches of Pacific saury and Pacific flying squid, long caught in the waters around Hokkaido, have dwindled. Fishermen are finding more species usually captured in warmer waters, such as dolphinfish, in their fishing nets.

Fishermen and seafood processors are being forced to adopt to the change that experts believe the rise in sea temperature in recent years may be behind.

Early one morning in October, fresh yellowtails were unloaded at the Osatsube fishing port in Hakodate. Using fixed nets to catch various kinds of fish, local fishermen caught 32 tons of fish on that day, of which 30 tons were adult yellowtails. A decade ago, they used to unload about 100 tons of Pacific flying squid a day, but now they are catching just 50 kilograms.

“Adult yellowtails are compensating for the loss of revenue from squid,” said fisherman Tomoatsu Sato, 35.

In the Oshima area, the catch of yellowtail exceeded that of squid last year for the first time since comparable statistics became available in 1958. Some seafood processors are trying to shift to products other than squid.

“We can’t expect the squid catch to recover anytime soon. We can procure yellowtails at low prices, since their catch is stable,” so the company has been putting more efforts in making products out of yellowtail since two years ago, said Kohei Mizuyama, 79, who heads Sone Foods Co.

According to the meteorological observatory in the Sapporo area, the ocean temperature of the Hokkaido coast has been rising for years. The temperature in the July-September period this year was 2 to 3 degrees Celsius higher than the average of 30 years through 2010. Off the coast of Kushiro, the ocean temperature has been 0.4 to 2.9 degrees higher than normal years since 2010.

Fishermen unload and sort out yellowtails by size at the Osatsube fishing port in Hakodate, Hokkaido, in October. | HOKKAIDO SHIMBUN
Fishermen unload and sort out yellowtails by size at the Osatsube fishing port in Hakodate, Hokkaido, in October. | HOKKAIDO SHIMBUN

It is still unclear what exactly is causing the poor catches of saury, but the warmer water around the Hokkaido east coast and more fishing by foreign vessels are often pointed out as possible factors.

In eastern Hokkaido, where poor hauls of Pacific saury and autumn salmon have continued, fish species from the southern regions have been observed more frequently.

Since five years ago, fishermen in the town of Hamanaka, which is located in the Kushiro region, started seeing dolphinfish that measured 50 to 70 centimeters captured in nets set up for autumn salmon. The Hamanaka fishermen’s cooperative said about 500 kg of dolphinfish were caught in a month from early September, but all of them were shipped for feed and fertilizer because they are not typically eaten by humans.

Also, several sunfish, not sold for consumption, feed or fertilizer, have been caught in nets every year for the past several years. Because they are large and swim slowly in the water, “they bump into ship sonars and damage them, so they are a headache,” said an official at the Hamanaka fisheries cooperative association.

In the Sea of Okhotsk, people have seen bluefin tuna as well — something unusual in Hokkaido waters.

Sho Sakamoto of the Saruru fisheries cooperative shot a scene of several bluefin tuna jumping out of water about 10 km from the coast with his smartphone while he was fishing for octopus in August.

“At first, I thought they were dolphins. It was the first time to see a school of (bluefin tuna) near the shore,” he said.

Others saw signs of dozens of bluefin tuna in August from their ship.

Usually, fishermen will catch only two or three bluefin tuna in fixed nets meant for autumn salmon a year. But this year, more than 20 small bluefin tuna weighing 10 to 20 kg and two marlin tuna more than 1 meter long were captured. But since the total allowable catch for small-scale bluefin tuna is only 200 kg for the area, all of them were released.

“We are seeing small mackerels these days, so (bluefin tuna) may have followed them to the Sea of Okhotsk,” said Kazuyuki Tomita, an executive of the Saruru fisheries cooperative.

Given that the catch of horsehair crabs has also been slumping in recent years, “the sea environment has definitely changed,” Tomita added.

“A rise in sea temperature by 1 degree is similar to a rise in air temperature by 5 to 10 degrees for humans. It’s a matter of life or death for them,” said Takanori Kuribayashi, a researcher at Hokkaido Research Organization.

“It affects the habitats of fish and fish stocks,” he said.

Because of the rise of the sea temperature, researchers have said that harvesting scallops at the Mutsu Bay in Aomori Prefecture, the second largest scallop farming prefecture following Hokkaido, will likely be difficult by the end of this century. Also, some have pointed out that four kinds of kelp in the Pacific Ocean off the Hokkaido east coast will possibly disappear by the end of the 2090s.

“It is hard to predict changes in the sea temperature, since it is affected by factors such as global warming and ‘regime shift,’ which repeats a couple of decades of lower- and higher-temperature periods along with changing weather conditions. But we will continue researching to help forecast the fishing environment,” said Kuribayashi.

This section features topics and issues from Hokkaido covered by the Hokkaido Shimbun, the largest newspaper in the prefecture. The original article was published Nov. 4.

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