More than a quarter-million sockeye salmon returning from the ocean to spawn are either dead or dying in the Columbia River and its tributaries due to warming water temperatures. Federal and state fishery biologists say water that's 5 to 6 degrees warmer is wiping out at least half of this year's returning population of 500,000 of the cold-water species. The fish become stressed at temperatures above 68 degrees and stop migrating at 74 degrees; much of the Columbia River basin is at or over 70 degrees due to a combination that experts attribute to drought and record heat in June. Thirteen species of salmon and steelhead trout are listed as endangered or threatened in the river's basin, and a spokesman for the National Oceanic and Atmospheric Administration says up to 80% of the population could ultimately perish.
A rep for the US Fish and Wildlife Service says fish congregating in confined areas trying to find cool water makes them a target for pathogens. "When temperatures get warm, it does stress the fish out and they become susceptible to disease," he says. The NOAA spokesman adds that this year's flow in the Columbia River is among the lowest in the last 60 years, though the system has experienced similar low flows without the lethal water temperatures—he says the difference this year has been prolonged hot temperatures, sometimes more than 100 degrees, in the interior part of the basin. Officials are trying to cool flows to below 70 degrees by releasing cold water from selected reservoirs in an attempt to prevent similar fish kills among chinook salmon and steelhead trout, which migrate later in the summer from the Pacific Ocean. (Read more Idaho stories.)