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35% of this Year's Snake River Sockeye Run Presumed Dead by Betsy Z. Russell Spokesman-Review, August 19, 2016

About 35 percent of this year's Snake River sockeye salmon run hasn't shown up at Lower Granite Dam, and the fish are probably dead, the Army Corps of Engineers said Thursday. S-R reporter Becky Kramer writes that about 1,240 adult Snake River sockeye were counted at Bonneville Dam on the Lower Columbia earlier this summer. But only 788 of those fish have been detected at Lower Granite, the farthest upstream dam of the four Lower Snake River dams.

"They're presumed to have perished," said Army Corps spokesman Bruce Henrickson.

This year's results are better than 2015, when 98 percent of the Snake River sockeye run died because of high temperatures in both the Columbia and the Snake, Henrickson said. Last year was the hottest on record.

Adult sockeye are particularly vulnerable to hot water, because their migration to spawning grounds coincides with the hottest part of summer. Water temperatures above 68 degrees are dangerous for salmon.

The Army Corps has been pumping cool water into the fish ladders at Lower Granite and Little Goose dams this summer to reduce the "thermal barrier" that stops salmon from migrating upstream. The pumping appears to be helping, officials said.

But salmon advocates say more must be done to protect fish from lethal temperatures in reservoirs behind the dams on both the Columbia and Snake. On Monday, they filed a notice of intent to sue the U.S. Environmental Protection Agency over the agency's failure to address high temperatures in the river system. Dams contribute to temperature problems by creating slack water reservoirs that heat up in the sun.

Snake River sockeye returned in record numbers in 2014, when more than 2,700 adult fish passed over Lower Granite Dam.