Overheated Rivers put Migrating Fish on Back Burnerby Eric Barker
Lewiston Tribune, August 16, 2001
Temperatures in the Snake River this week have climbed to dangerous levels for salmon and steelhead, causing previously brisk steelhead passage at some lower Snake River dams to slow to a crawl.
Hot weather in the region has pushed water temperatures in Snake River reservoirs into the mid-70's. Temperatures higher than 70 degrees are considered sub-lethal to salmon and steelhead, meaning prolonged exposure puts the fish at risk of death from stress and disease.
"It just increases susceptibility to the large number of things that could happen that we term prespawn mortality," said Sharon Kiefer, anadromous fish coordinator for the Idaho Department of Fish and Game at Lewiston.
At Lower Granite Dam, about 35 miles west of Clarkston, water temperature reached 76 degrees Wednesday and just 12 steelhead were counted climbing the fish ladder there. The passage slowdown comes at a time when biologists are expecting an exceptionally large return of steelhead to the Snake River.
Last week fisheries officials said as many as 200,000 steelhead could return this summer and fall but Kiefer cautioned Wednesday that an ongoing heatwave could shrink that number. She also said, with more than 370,000 steelhead already past Bonneville Dam on the Columbia River, the steelhead run to the Snake River is still expected to be quite large.
"Things are still shaping up such that we would still predict at least 100,000 fish," she said. "Two hundred thousand is still possible, but if you asked me today, that is not the forecast I would put on the table."
If temperatures moderate and the large run does materialize, the department could recommend raising the daily bag limit on steelhead this fall, Kiefer said.
Right now biologists and anglers are at the mercy of mother nature.
"There is not a lot we can do at this point in time except hope for moderation in the weather," Kiefer said.
Steelhead have continued to move into the Snake River from the Columbia in large numbers but passage up the Snake has slowed. On Tuesday more than 1,100 steelhead were counted at Ice Harbor Dam, the first on the Snake River, and 1,268 at Lower Monumental. In contrast, only 35 steelhead were counted at Little Goose Dam, about 73 miles west of Clarkston, and 12 at Lower Granite.
Dworshak reservoir has been releasing about 10,000 cubic feet per second of 48-degree water since July 4 to help cool the Snake River. The U.S. Army Corps of Engineers is scheduled to begin ramping down outflows at Dworshak Aug. 26 and reach minimum flows Aug. 31.
When that happens, a thermal block could develop at the mouth of the Snake River if the hot weather pattern continues, according to Steve Pettit, a fish passage specialist at the Idaho Department of Fish and Game in Lewiston.
A thermal block occurs when the Snake River is 7 degrees or more warmer than the Columbia, making the fish reluctant to enter the warmer water.
He is worried that temperatures in the Lower Columbia River also could rise high enough to slow fish passage.
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