It’s Getting Hot in Here: Temperature Spikes Are Slammin’ Salmon

Salmon are an important part of the Columbia River ecosystem in the Pacific Northwest, but recent heat waves have been killing off these vital fish. The warm waters are so much of a problem that they could end up destroying up to 80 percent of the existing salmon population.

Record low snow levels in the mountains that feed cold, fresh water into the Columbia River and its tributaries are partly to blame for the warmer water, because the melting snow typically helps cool down the rivers as the temperature rises. Record high temperatures in the region make the problem even worse, as the Columbia River basin has seen unprecedented highs above 100 degrees over the summer of 2015. Water temperatures have increased about two to four degrees compared to average, which causes metabolic stress and increases the risk of disease in the fish.

Salmon populations vary in size from year to year, according to the Washington Department of Fish and Wildlife. Historically, salmon runs in the Columbia River system have reached up to three million fish per year, but population numbers dropped significantly after the creation of the Bonneville dam in 1938. In 2014, sockeye salmon numbers reached a post-dam high of 645,100, and the estimate for 2015 was expected to reach about 500,000 fish before the warm-water conditions hit.

Scientists aren’t just sitting by and watching while salmon populations decline, though. Efforts to stymie the salmon death rate include projects such as releasing cold water from reservoirs into the affected rivers and capturing fish for transport up to colder rivers where they can survive.

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