Drought ‘refuges’ protect young coho salmon from summer heat

A seven-year project tracking young coho salmon in the Russian River watershed found that some habitats support the young fish even in the midst of extended drought. (California Sea Grant photo)

For young coho salmon, summer is not all fun in the sun: Extended heat and drought can sometimes dry up the small freshwater streams where the endangered fish spend the first year of their lives, leaving them trapped in small pools with limited food and oxygen.

As climate change threatens to bring hotter and drier summers to California, a new study by researchers at UC Berkeley and the California Sea Grant provides conservationists and resource managers with valuable insights on how to continue to protect and restore California’s dwindling coho salmonpopulation.

The research team tracked nearly 20,000 tagged fish in the Russian River watershed over a seven-year period from 2011 to 2017, spanning a time of major drought in California. This watershed is home to a highly endangered population of coho salmon, which nearly collapsed in the early 2000’s, but has been recovering since then through a conservation hatchery program and other efforts.

“We were able to measure survival during this historic drought, which will help us understand how future droughts will impact this population of salmon,” says University of Wisconsin-La Crosse Assistant Professor Ross Vander Vorste, who conducted the analysis for the study as a UC Berkeley postdoctoral researcher in collaboration with California Sea Grant’s Russian River Salmon and Steelhead Monitoring Program.

The researchers discovered that the salmon survival depends