After disastrous 2015, more Idaho sockeye return to spawning grounds this year

More sockeye salmon returned to Idaho’s Snake River basin this year, thanks to cooler weather in July and strategic water releases to help the endangered fish.

About 44 percent of the adult sockeye counted at Bonneville Dam on the Columbia River made it back to spawning grounds in Idaho’s Sawtooth Valley, said Paul Kline, the Idaho Department of Fish and Game’s assistant fisheries chief.

Last year, hot water in the Columbia and Snake rivers killed nearly the entire run. Less than 1 percent of the run survived the 2015 migration, compared to about 40 percent during a typical year, Kline said Wednesday during a Northwest Power and Conservation Council meeting in Spokane.

“Two poor returns in a row would be a travesty,” said Guy Norman, a Washington representative on the four-state council, which plans for the Northwest’s power needs while mitigating the effects of the federal hydropower system to fish and wildlife.

Idaho’s sockeye have the toughest migrating conditions of Northwest salmon. They spawn at elevations of more than 6,500 feet and swim more than 900 miles to the ocean, passing through a gauntlet of eight major dams. After one to three years in the ocean, they return as adults to their Idaho spawning grounds.

Just a handful of sockeye made it back to the Sawtooth Valley each year until a captive breeding program began in 1991.

This year, about 470 of the 1,032 adult Snake River sockeye counted at Bonneville Dam returned to Idaho.

Kline credited this year’s higher success rate to cooler-than-expected July weather and cold water releases from the reservoir behind Dworshak Dam. The U.S. Army Corps of Engineers was able to keep the tail races below 68 degrees at Lower Granite and Little Goose dams by releasing cold water from the reservoir.

Hot water is lethal to salmon. They’ll stop migrating when they encounter high temperatures and they’re more susceptible to disease.

“They fungus up and die,” Kline said.

Last year’s combination of low river flows and hot air temperatures was deadly to fish in both the Columbia and Snake. In addition to sockeye mortality, sturgeon also died.

Keeping the water cool enough for fish has become a challenge in parts of the basin, Kline said.

The water released from Dworshak Reservoir is cooler than 50 degrees. But that water eventually mixes with warmer water in downstream reservoirs on the Snake River. So, the cold water releases don’t benefit lower stretches of the Snake, Kline said.

In August, several environmental groups said they would sue the federal government over the lack of a long-term plan to address hot water in the Columbia and Snake rivers.