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Dozens of Japanese huchen, an endangered fish in the salmon family, have been found dead in rivers this summer in the northern Hokkaido region of Soya.

Experts say the fish, dubbed the “phantom fish” for its scarcity, probably died because of a deficiency of oxygen in the water, as the hot summer caused high water temperatures and not enough rain.

Dead Japanese huchen found in the Sarufutsu River system in Hokkaido | COURTESY OF MITSUKI KURODA / VIA KYODO
Dead Japanese huchen found in the Sarufutsu River system in Hokkaido | COURTESY OF MITSUKI KURODA / VIA KYODO

A local conservation group has called on fishermen to avoid fishing for them until water levels return to normal.

Mitsuru Kawahara, 51, a member of the conservation group for Japanese huchen, has found about 40 of them dead along the Sarufutsu River system since the beginning of August.

The place smelled of dead fish, some of which had been eaten by animals, and those that were still alive were hanging by a thread, he said.

“(The fish that were alive) were barely floating. Some of them were so weak they were bumping into rocks in the water,” said Kawahara, adding it was the first time he has seen something like this in the 15 years he has worked to protect the species.

“It was shocking, as if I had witnessed the effects of climate change with my own eyes,” he said.

In July, the Meteorological Agency’s Sarufutsu observatory posted an average temperature of 18.9 degrees Celsius, the highest since it started taking records in 1979. The amount of rainfall for the month was 8.5 millimeters, the second-lowest amount ever.

Dead Japanese huchen were also found in the Teshio River system in the town of Toyotomi in northern Hokkaido.

According to Mitsuki Kuroda, 25, a researcher at Hokkaido University who was doing research into the fish in August, many of the fish had their mouths open and whitened fins, a typical sign of oxygen deficiency.

The fish probably died after the rising water temperature caused their metabolism to increase, which meant they needed more oxygen, Kuroda pointed out. A shortage of rain meant that the oxygen level in the water was low, causing them to die, he said.

But because Kuroda has not been able to work out how many fish have died so far, he is not sure how it will affect the ecological system.

“It’s important to continue monitoring the species, including checking the number of spawned eggs, to see if they have declined during the breeding season,” said Kuroda.

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