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Climate Change and Western Fishes

Implications of climate change on western fishes, some of the most at-risk species in the U.S.


Peter Bisson
USDA Forest Service Pacific Northwest Research Station


Producer - Michael Furniss
Videography - Ben Nieves
Technical production - Jeffrey Guntle


One of the most important long-term threats to western fishes is climate change. Some of the major effects of climate warming in western North America include (1) Higher temperatures will result in more precipitation falling as rain rather than snow. (2) Snowpack will diminish and seasonal streamflow patterns will be altered. (3) Peak river flows will likely increase. (4) Water temperatures will continue to rise. Not all of these anticipated trends are necessarily harmful to aquatic habitat, and many pale in comparison to other anthropogenic factors, but they do have implications for native fishes. Climate change scenarios predict an increase in large flood events, wildfires, and forest pathogen outbreaks, all of which have some potential to actually improve habitat complexity as a result of flood plain reconnection and large wood recruitment. Many effects of climate warming, however, will have negative habitat consequences for aquatic organisms. A higher frequency of severe floods will result in increased egg mortality owing to gravel scour. Retreating winter snowpacks will run off earlier in the spring, potentially impacting species whose migration to the ocean is timed to coincide with plankton blooms. Summer base flows will be lower, and the network of perennially flowing streams in a drainage system will shrink during the summer dry period, forcing fish into smaller wetted channels and less diverse habitats. Warmer water temperatures will increase physiological stresses and lower growth rates, and summer peak temperatures may approach or exceed lethal levels for salmon and trout. Higher temperatures will also favor species that are better adapted to warmer water, including potential predators and competitors.

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Changes in water temperature, altered hydrologic regimes, and indirect effects on Western U.S. fish due to climate change