Algae That Killed Marine Life In Hokkaido From Russia

A red tide that has devastated marine life off the northernmost main island of Hokkaido was apparently caused by algae drifting from Russia on an ocean current, Japanese researchers have said.

The plague caused massive salmon and sea urchin deaths, causing damages totaling 7.6 billion yen ($67 million) to the local fishing industry. This figure is expected to increase further in the days and weeks to come.

Researchers from Hokkaido University suggested that the phytoplankton, which has been blooming since mid-September, reached Hokkaido via the Kuril Current.

The study by Takahiro Iida, a researcher specializing in dynamic environmental analysis, Takeshi Yoshimura, an associate professor of marine chemistry, and their colleagues took water samples from Akkeshi Bay in the east of ‘Hokkaido, using a university training ship between October 5 and October 13.

They watched the red tide drift in bands and measured things like salt concentration, water temperature and tidal direction at around 30 locations between 2 and 20 km offshore.

Readings of salt concentration and water temperature indicated the characteristics of the cold Kuril Current, according to the group.

The Kuril Current descends to the coast of Hokkaido and the northeast Tohoku region after flowing south along the Kuril Islands from Russia.

Its salt density and water temperature are lower than those of the Black Current, which flows north from the East China Sea to the southern coast of Japan.

The researchers also estimated the volume of phytoplankton in the waters off Hokkaido from images taken by the Shikisai global change observation satellite operated by the Japan Aerospace Exploration Agency (JAXA).

They found that a high density of phytoplankton existed northeast of Etorofu, one of the Northern Territory islands whose ownership is disputed between Japan and Russia, on September 4.

Water with high concentrations of phytoplankton that arrived near the eastern tip of Hokkaido on September 16 bloomed there even more before spreading along the coast from the Nemuro and Hidaka areas on October 9.

Studies by the Fisheries Research Department of the Hokkaido Research Organization, the University of Tokyo Graduate School and other research institutes have shown that the devastation of seafood resources in ‘Hokkaido caused by the red tide was triggered by Karenia Selliformis, a variety of phytoplankton that can multiply abundantly even in relatively low conditions. temperatures.

“It has not yet been determined exactly where Karenia Selliformis first occurred, but it is highly likely that it flowed south from the Russian coast through the Kuril Current,” Iida said. “With further analysis, we hope to uncover the mechanism of the red tide that formed in cold waters so that we can predict when the next red tide will occur.”

Dead sea urchins that have turned white and no longer have spines lie on the seabed in a fishing area in an image taken by the Akkeshi Fishing Cooperative in Hokkaido. (Provided by Akkeshi Fishing Cooperative)

The Hokkaido prefectural government announced on Oct. 21 that its estimate of damage to the local seafood industry as of Oct. 18 was 7.6 billion yen, up sharply from 4.6 billion. yen as of October 8.

Prefectural officials said 21,300 salmon died, resulting in a loss of around 55 million yen in fishing revenue.

Losses due to the death of about 2,300 tons of sea urchins, a coveted delicacy, were estimated at 6.84 billion yen. The figure is expected to rise further as fisheries officials are still trying to assess the damage in the Hidaka area.

(This story was compiled from reports by Shigehito Nakazawa and Yuta Kayaba.)

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