Sensitivity to climate change
In general, coho salmon likely exhibit sensitivity to warmer water temperatures (freshwater and ocean) and lower summer flows. Freshwater temperature and flow regimes: Central California represents the southern extent of the range for coho salmon, suggesting that they may be less sensitive to increases in water temperature than other species of Pacific salmon (i.e. pink, chum, and sockeye). However, due to their reliance on streams for freshwater rearing, coho are likely sensitive to both altered flow and thermal regimes. Juveniles prefer low-velocity habitat often in off-channel areas; reduced summer flows may increase the likelihood that such off-channel habitats become inaccessible, thermally stressful, or hypoxic. Early run timing individuals might be more sensitive to fall flood events, which are projected to increase in Washington, and may also be more sensitive to warmer water temperatures and lower flows during peak migration timing (i.e., mid-August to September). Later run timing individuals should be less sensitive because they migrate as adults during cooler periods of the year and their embryos are not yet buried in the gravel during late fall flooding. However, late run individuals may be more likely to have embryos or recently emerged fry threatened by spring flooding that is predicted to increase in severity and frequency. In general, coho salmon populations may be less resilient to episodic mortality events caused by climate stressors, because they exhibit only moderate levels of life history diversity and do not have as much variation in age-at maturity as do sockeye salmon and Chinook salmon. Marine: Increases in ocean and estuarine temperature, increased stratification of the water column, and/or changes in the intensity and timing of coastal upwelling may alter primary and secondary productivity, with potential impacts on growth, productivity, survival, and migrations of salmonids. For example, cool Pacific-Decadal Oscillation (PDO) years have historically coincided with high returns of coho salmon, while warm PDO cycles coincided with declines in salmon numbers. Cooler SSTs during the winter prior to and after smolt migration have also been linked to higher coho survival. In general, changes in coastal ocean habitat quality and productivity could negatively impact coho salmon.
Exposure to climate change
- Increased water temperatures (freshwater and sea surface)
- Lower summer flows