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:
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.
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.
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.
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.
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
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. 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.