Salmon Need Trees

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Wednesday, October 20, 2021

Chinook, coho, and steelhead populations in the Salish Sea have declined by up to 90 percent over the past 40 years. Canada declared several populations of steelhead endangered in 2020. Unpicking exactly how and why fish are crashing has proved hard. Whatever happens to the fish out at sea has been seen as something of a black box, so much recent research has focused on marine survival. Those efforts point to multiple culprits for declining salmon numbers, including climate change, overfishing, reductions in the salmons’ food, and rebounding populations of seals and Steller sea lions that gorge on the fish. Wilson’s research, however, highlights the need to keep our eyes on terra firma.

Logging has long been known to have big impacts on the well-being of fish. Watershed logging was improved after the 1990s “War in the Woods” in British Columbia—salmon streams are better protected under regulations now—but remains a concern. Reducing shade over rivers can boost water temperature, which can be good or bad for spawning fish. Removing roots loosens soils and causes turbidity. Fewer logs may fall into streams, reducing the number of pools and turns that salmon like. A recent study by David Reid, completed when he was a postdoctoral researcher at the University of British Columbia, found the full impacts of logging can take a surprisingly long time to kick in. “It might take decades,” he says.

Wilson’s paper aims to weigh up riverine against marine survival. “It’s nice to see these components linked together,” says Reid.

Read the full story here
Photos courtesy of
John Zada

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