Potential changes in life-history diversity within Snake River spring/summer Chinook salmon in response to climate change

Background/Question/Methods

Salmon life histories are finely tuned to local environmental conditions, which are intimately linked to climate. Highly population-specific migration and spawn timing allow salmon to occupy a relatively broad range of habitats and encourage reproductive isolation within river basins, leading to high local diversity. Climate change will likely shift the optimal phenology in certain populations, as thermal tolerances are exceeded or temperature-dependent growth and development proceed at different rates. I here explore how selection and plastic responses to climate change might affect biocomplexity within Snake River spring/summer Chinook salmon. I first use an empirical model to test whether selection or plasticity, or both, can explain the historical trend in migration timing in Upper Columbia River sockeye and Snake River summer Chinook salmon. I then develop a bioenergetic model of optimal migration timing as a function of spawn timing, temperature and flow along the migration route for representative populations with different life histories within the Salmon River Basin. Finally, I explore potential future evolution in migration and spawn timing of each life history type using an individual based, quantitative genetic model.

Results/Conclusions

Thermal selection for earlier migration timing and a plastic response to river flow and ocean conditions best explain the 11 day shift in migration timing in sockeye since the 1940s. The bioenergetic model of optimal migration timing successfully recreates existing patterns in basin. However, although some characteristics of lower elevation populations might be able viable at higher elevations in the basin, overall climate change is likely to reduce the diversity of viable life histories in this threatened Evolutionarily Significant Unit.