Receding glaciers are contributing to warming stream temperatures, and that’s dangerous for salmon.
Glaciers on Mount Baker have receded more than 1,000 feet in the last 20 years, reducing the amount of melt that helps cool streams during warm summer months.
Salmon returning to the Sauk and Suiattle rivers are delaying their spawning by waiting for fall temperatures and cooler water, said Scott Morris, Sauk-Suiattle Tribe’s water quality coordinator.
A University of Washington (UW) study commissioned by the Skagit Climate Science Consortium predicts all glaciers in the Skagit River watershed will have melted by 2100 unless global carbon emissions can be reduced. This is especially alarming considering that the Skagit River watershed is the most glaciated watershed in the lower 48 states, Morris said.
Multiple studies show maintaining stream temperatures below 13 degrees Celsius (55.4 degrees Fahrenheit) is essential to spawning salmon, while temperatures below 16 degrees Celsius (60.8 degrees Fahrenheit) are needed for juvenile salmon to thrive.
The more water temperatures exceed these levels, the more problems salmon face, Morris said. They can suffer increased susceptibility to disease, impaired incubation and feeding, and delayed migration.
Natural resources departments at several tribes are studying or implementing measures to mitigate stream warming. One possibility is to identify areas where deep, cold groundwater upwells into streams and protect these cold water refuges. Native plants could further shade the streams that serve as salmon nurseries, and mitigate warmer stream temperatures caused by climate change.
The Sauk-Suiattle Tribe installed its first logjam on the Sauk River in the early 2000s and is monitoring stream temperatures in other rivers and tributaries.
“In addition to providing refuges for young salmon, the logjams also slow stream flows into side channels and prevent erosion,” natural resources director Jason Joseph said.
If global carbon emissions stop increasing by 2040, climate models cited in the UW study show that the highest-elevation glaciers (above 6,560 feet) will continue to store pockets of ice and provide some glacial melt in summer, which could help mitigate some impacts to salmon.
Meanwhile, protecting and restoring cold water refuges will benefit migrating salmon, according to a Cold Water Refuges Project plan developed by the EPA for the Columbia River in partnership with tribes, states of Washington and Oregon, NOAA Fisheries and others. The report found that at the end of August in an average year, about 65,000 steelhead and 5,000 fall chinook used eight refuges between the Bonneville Dam and the Dalles Dam to escape warm summer river temperatures as they migrated to spawning grounds.
Sauk-Suiattle tribal natural resources staff collect adult chum salmon in a side channel of the Sauk River for a hatchery program in 2014. In recent years, salmon in the Sauk and Suiattle rivers are delaying spawning because of increasing water temperatures in the region. Photo: Kari Neumeyer. Story: Richard Walker
