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Science

White spot disease kills Arctic grayling in Scout Lake

KENAI -- State officials have identified warmer lake temperatures as a possible contributing factor to the die-off of hundreds of Arctic grayling this summer.

A state Department of Fish and Game laboratory report says the fish died of ichthyophthiriasis, a relatively uncommon condition in Alaska known as the white spot disease, The Peninsula Clarion reported.

The discovery of the dead fish washed up on the shores of Scout Lake in August was the first incident in Kenai. Other documented cases have been found in Meadow Creek, Big Lake, Six Mile Lane and Cheney Lake.

Biologists found that most of the fish affected in Scout Lake were larger fish. Rainbow trout, even though they were equally vulnerable, and smaller grayling appeared to be unaffected.

"We were real shocked after we found out that the rainbows didn't have it," said Robert Begich, the area management biologist for the Division of Sport Fish in Soldotna.

The disease would have had to be introduced sometime after the lake was treated in 2009 with rotenone, a piscicide, and restocked from the state hatchery in 2010. The disease probably did not come from the state hatchery, as the same grayling have been stocked in various lakes around the state without a problem, Begich said.

The report says that the warmer temperatures of Alaska lakes this summer may have had a negative impact on the fish.

"Grayling are a cold water species, so it's possible that they were more strongly affected by the water temperatures," Begich said.

A long period of higher water temperatures combined with a high number of susceptible hosts could create "the perfect storm for severe disease and mortality to ensue," according to the report.

Some of the grayling in Scout Lake could still have the disease, Begich said. The laboratory report recommends that all equipment used to catch fish in the lake be thoroughly cleaned to avoid spreading the disease.

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