Trout once thought extinct poised for return

SENBOKU, Japan >> Kunimasu trout, a species of trout once indigenous to Tazawako lake in Senboku, Japan, are now living near the lake — if not quite in it — for the first time in about 70 years.

Officials of the Yamanashi prefectural government artificially hatched kunimasu fish eggs and loaned the fish to a study and learning facility to be opened in July by the Senboku city government. Ten kunimasu trout began life in the facility near their original habitat in Akita prefecture on May 10.

The water in Tazawako is strongly acidified, making it impossible for kunimasu trout to live in the lake. Some local residents dream of releasing kunimasu trout into the lake in the future.

The water quality in Tazawako began changing in 1940 as highly acidified water from the nearby Tamagawa river was diverted into the lake for electric power generation and to develop farmland. More than 20 fish species, including kunimasu, died off.

The Environment Ministry’s red list of endangered species had categorized kunimasu, which was indigenous to Tazawako, as “extinct.”

But in 2010 a team of researchers from Kyoto University confirmed that a school of kunimasu fish was living in Saiko lake in Yamanashi prefecture, one of five big lakes around Mount Fuji.

The discovery caused a sensation in part because Sakana-kun, a TV entertainer who is also a guest associate professor of Tokyo University of Marine Science and Technology, contributed to the finding.

Documents kept in Senboku reveal 100,000 kunimasu trout eggs were transported to Saiko lake in 1935.

Researchers assume that fish hatched from the eggs and then released into Saiko lake are the ancestors of today’s population.

The 10 kunimasu fish that returned to the Tazawako area this month were 3 years old and about 15 centimeters long. They had been kept by a Yamanashi prefecture-run fishery technical center in the village of Oshino in the prefecture.