Northwest Fisheries Science Center

Ecosystem Analysis Projects


Dr. Beth Sanderson
Program Manager
Staff Directory

Climate impacts to Pacific salmon

Assessing climate impacts to Pacific salmon

Pie chart showing various effects of climite change to salmon. Summary of the percentage of papers that described each category of salmon responses to variation in climate, based on a review of 1,100 scientific papers on climate change & impacts to salmon 2010–2013.  

A warming climate will alter both freshwater and marine communities, affecting resources for both fishers and endangered fish species. 

For Pacific salmon, climate has diverse affects.  Changes in stream temperature and flow alter fish survival, swimming performance, and metabolic rates, which in turn determine energetic costs and growth.

Climate also affects habitat abundance, diversity, and access.

Finally, the physical environment affects all species, most notably for salmon, both prey and predators.  In response to higher temperatures, predators will likely consume more prey.  Furthermore, warm–water invasive predators such as bass will grow more prevalent.

A review of the scientific literature of climate impacts on salmon reveals the many pathways these influences can take.

In the Ecosystems Analysis Program, our goal is to quantify climate influences on salmon in freshwater and marine environments over all life stages.  Frequently this requires developing novel statistical tools.  We then incorporate these relationships into models that can be used to assess extinction risk.  Our comprehensive, multi–lateral approach has the following specific objectives: 

  • Identify relationships between the environment and population responses such as migration timing and rates of survival.  Using these relationships, develop life–cycle models that can help predict the response of endangered salmon populations to climate change (Crozier et al. 2014).
  • Monitor the state of the science in annual syntheses of the global literature on climate effects on salmon (Crozier 2014).
  • Provide scientific support for resource management actions to protect endangered species (McClure et al 2014).
  • Collaborate with other groups on the Pacific coast, the nation, and the world to enhance our resilience to climate variability and climate change.

Sockeye Salmon Migration

Adult Survival

Bubble chart showing the number of fish passing within the indicated temperature range. Larger circles represents greater numbers of fish passing within a given temperature range (e.g., sample sizes of 23 and 166 are shown).

Rising summer temperature is a particular concern for endangered salmon in the Pacific Northwest and California.  Salmon survive at lower rates when they migrate through warmer water.  In the Columbia and Snake Rivers, we see longer temperature "block–out" periods, when the river is too hot for salmon to migrate. 

We used data from adult Redfish Lake sockeye salmon tagged with passive integrated transponders (PIT tags) to identify predictors of successful migration and survival through specific reaches of the Snake River.  Analysis of covariates including temperature, date, flow, spill, and dissolved gas levels allowed us to identify key factors that predict survival. 

Two bar charts with upper showing adult survival and lower showing temperature for each year from 2008 to 2014. Upper chart shows survival of sockeye salmon during the upstream migration compared with lower chart showing temperature during the same years from 2008 to 2014.

In the chart above, bubbles represent proportions of Redfish Lake sockeye salmon that reach spawning grounds as a function of temperature.  Temperature was measured as these fish passed Ice Harbor Dam on the Snake River. 

We found that after entering the Snake River, exposure to high temperature was the largest determinant of survival for endangered sockeye salmon.  Furthermore, variation in temperature explains most of the variation among years in total migration survival. 

Annual survival from Bonneville Dam to the spawning grounds is highly variable among years, but is much lower during especially warm years, such as 2013.  Cumulative thermal exposure reflects the amount of time salmon spend at specific temperatures during the migration. 

Migration Timing

Scatterplot of sockeye migration timing change to earlier weeks of the year.Mean July temperature (top) and median migration date of sockeye salmon (bottom) at Bonneville Dam.   Regression statistics and lines are shown.  From Crozier et al. (2008a).   

In response to selection against late migrants that are more likely to die from high temperature exposure, Columbia River sockeye have adapted by migrating earlier in the season over the past 60 years.

Much of the annual variation in migration timing reflects a response to Columbia River flow.  This relationship is called a "reaction norm."  But sockeye salmon are migrating earlier now than they did in the 1950s across a wide range of flows.

Plots of shift in reaction norm. Shift in reaction norm for sockeye migration time vs. Columbia River flow levels. 

Population Risk Analyses

Life–cycle models provide a valuable tool for incorporating specific influences of climate and other factors at particular life stages into projections of population growth or decline. But different populations may have different sensitivity or exposure to climate change.

These models help to identify populations that are especially vulnerable to extinction from changes in stream temperature or flow, or from even a slight deterioration of ocean conditions.

Our analyses showed a full range of responses to freshwater climate change among wild Chinook salmon populations from the Salmon River Basin, Idaho, at least over the short term.

Plots of extinction-risk analyses.  

This chart shows how much modeled extinction risk changes from the baseline historical level under two climate change scenarios for the 2040s.  The range of responses for each population reflects the uncertainty in future ocean conditions and freshwater.

Our analyses of climate impacts support proactive measures.  These include

  • Controlling temperatures and increasing flow in the hydrosystem
  • Preserving and restricting harvest in cold–water refugia
  • Intensifying the search for new alternatives to mitigate lower survival in salmon populations as global temperatures rise


Crozier, L.   2014.  Impacts of Climate Change on Columbia River Salmon:  A review of the scientific literature published in 2013.  Pages D1-D50 in Endangered Species Act Section 7(a)(2) supplemental biological opinion:  consultation on remand for operation of the Federal Columbia River Power System.  U.S. National Marine Fisheries Service, Northwest Region.

Crozier, L. G., B. J. Burke, B. Sandford, G. Axel, and B. L. Sanderson   2014.  Adult Snake River sockeye salmon passage and survival within and upstream of the Federal Columbia River Power System. Research report to the U.S. Army Corps of Engineers, Walla Walla, Washington.

Crozier, L. G., M. D. Scheuerell, and R. W. Zabel.  2011.  The next link/button will exit from NWFSC web site Using time series analysis to characterize evolutionary and plastic responses to environmental change: A case study of a shift toward earlier migration date in sockeye salmon.  American Naturalist 178(6):755–773.

Crozier, L. G., R. W. Zabel, and A. F. Hamlett.  2008.  Predicting differential effects of climate change at the population level with life-cycle models of spring Chinook salmon.  Global Change Biology 14(2):236–249.

McClure, M. M., M. Alexander, D. Borggaard, D. Boughton, L. Crozier, R. Griffis, J. C. Jorgensen, S. T. Lindley, J. Nye, M. J. Rowland, E. E. Seney, A. Snover, C. Toole, and K. Van Houtan.   2013.  Incorporating climate science in applications of the U.S. Endangered Species Act for aquatic species.  Conservation Biology 27(6):1222–1233.