Anyone familiar with the Columbia River’s massive salmon die-off a few summers ago might also be concerned about how climate change will affect fish habitats. The 2015 die-off killed more than 250,000 fish and was blamed on record low streamflows and high water temperatures. While coldwater fish such as salmon and trout can adjust to slightly warmer-than-normal temperatures for short periods, abnormally high temperatures for prolonged periods lower oxygen levels, increase the likelihood of deadly diseases, and cause life-threatening physiological stress.
To understand whether the 2015 die-off was an anomaly or part of a longer-term trend, scientists at the Rocky Mountain Research Station’s Aquatic Sciences Lab in Boise, Idaho, compiled temperature records from more than a dozen natural resource agencies monitoring nearly 400 sites along large rivers in the northwestern United States.
Key Findings:Monitoring records indicate that river temperatures during the summer and early fall months have risen about 1 °C over the past 40 years in the northwestern United States.If river warming continues at rates similar to recent decades, water temperatures are expected to rise another 1 °C by 2050 and by 2-3 °C by the end of the century.In many locations, trout and salmon will have to shift into cooler areas or migrate at different times of the year to avoid thermally stressful conditions.River managers may be able to offset warming in some areas and preserve coldwater river habitats by employing various habitat and flow restoration techniques including minimizing flow diversions, increasing shade, enhancing habitat diversity and the number of deep pools, releasing cold water from storage dams during heat waves, and improving fish passages at dams that block access to cooler river sections.