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Extinction Risk of Chinook Salmon Due to Climate Change

We conduct population viability analyses of cumulative climate impacts across the life cycle of Chinook salmon

To calculate the cumulative climate effects that influence Chinook salmon extinction risk, we use population dynamic models.  These statistical models are known as life‑cycle models because they integrate multiple climate-related impacts that affect salmon throughout all stages of life.  

Flow chart of salmon life cycle formed from a circle of arrows.  Each arrow labeled with a specific life stage.  Drawings near each arrow show climate-driven mortality risks at each stage, such as summer stream and winter ocean temperatures, upwelling, dams, and river flow
Diagram of salmon life cycle, showing life‑stage transitions and the climatic covariates that affect each life stage. Abbreviations: temp = temperature, BON = Bonneville Dam, LGR = Lower Granite Dam. Credit: NOAA Fisheries

Life cycle model simulations rely on detailed studies of individual life stages and projections of future climate.  They help quantify the potential impacts of climate change and of specific proposed mitigation actions such as dam operations or habitat restoration changes. 

Information from lifecycle models also supports decisions on risk imposed by federal actions, informing environmental impact statements required under the National Environmental Policy Act and biological opinions required under the Endangered Species Act.  

Our lifecycle models project that Snake River spring/summer Chinook salmon populations will decline dramatically in the coming decades.  They show that this decline is due primarily to rising sea surface temperatures and changes in freshwater temperature and flow.  Consistent with these projections, we have already seen record-low returns of salmon species across the West Coast in response to the marine heat wave of 2014-2016.

Topographical map of Columbia River Basin with four graphs showing the number of spawners in small and large populations from 2020 to 2089 under different climate scenarios.  For Camas, Valley, and Bear Valley Creek and the Secesh River the average number of spawners stays constant in a stable climate.  When climate change forcing is imposed, all populations rapidly decline below the quasi-extinction threshold.
Credit: NOAA Fisheries

When climate is assumed to be stable, with historical levels of variability, individual simulations showed variability in spawner numbers but, on average, stayed constant over time (blue line and polygon).  However, when we imposed forcing from climate change, either under the RCP 4.5 (light orange) or RCP 8.5 (dark orange) emissions scenarios, all populations rapidly declined below the quasiextinction threshold.

Illustrated whisker plot showing the decline in percentage of spawning Chinook adults in relation to climate change conditions imposed in the marine vs. freshwater stages, with the latter having much less impact.  Adult abundance is show from the 2020s to the 2060s across many simulations and climate scenarios in relation to a population persistence rate of 100%.  Bar segments below the 100% level (red) represent simulations that resulted in population declines, while bars above 100% (blue) show simulations
Illustrated whisker plot showing the decline in percentage of spawning Chinook adults in relation to climate change conditions imposed in the marine vs. freshwater stages, with the latter having much less impact. Adult abundance is show from the 2020s to the 2060s across many simulations and climate scenarios in relation to a population persistence rate of 100%. Bar segments below the 100% level (red) represent simulations that resulted in population declines, while bars above 100% (blue) show simulations that resulted in population increases. Credit: NOAA Fisheries


Projections from model output show the most dire climate effects on salmon  occurring in the marine life stage.  Therefore, we presently focus on the interspecific dynamics that affect marine survival

Marine Ecosystem Response


We are building a set of endtoend conceptual, statistical, ecosystem models of intermediate complexity  to fully capture our understanding of relationships between species.  These models will explore how climate alters the marine environment and will help us to identify management tools to mitigate these effects on salmon.  

References

Crozier, L. G., B. J. Burke, B. E. Chasco, D. L. Widener, and R. W. Zabel. 2021. Climate change threatens Chinook salmon throughout their life cycle. Communications Biology 4:222. https://doi.org/10.1038/s42003-021-01734-w 

Crozier, L. G., and R. W. Zabel. 2020. Middle Fork and South Fork Salmon River MPGs of the Snake River Spring/Summer-Run Chinook Salmon ESU. R. W. Zabel, and C. E. Jordan, editors. Life Cycle Models of Interior Columbia River Basin Spring/Summer-Run Chinook Salmon Populations, U.S. Department of Commerce, NOAA Technical Memorandum NMFS-NWFSC-156. https://doi.org/10.25923/phfm-wq72.  

Last updated by Northwest Fisheries Science Center on October 12, 2021

Climate