Tough Places and Safe Spaces: Can Refuges Save Salmon from a Warming #Climate? — USGS

Study reach shown within the context of the mainstem Columbia River and major tributaries (a). Pink and green polygons highlight available spawning area for Grande Ronde River summer steelhead and Snake River fall Chinook Salmon evolutionarily significant units (ESUs). Colored points in (b) correspond to significant cold-water refuges (CWRs) between Bonneville Dam and the Snake River confluence. (c) The mean daily temperature for modeled portion of mainstem Columbia River reservoirs (gray-scale lines) and CWRs (colored lines corresponding to points in [b]).

Click the link to read the release on the USGS website (Jason Dunham):

The importance of thermal refuges in a rapidly warming world is particularly evident for migratory species, where individuals encounter a wide range of conditions throughout their lives. In this study, we used a spatially explicit, individual-based simulation model to evaluate the buffering potential of cold-water thermal refuges for anadromous salmon and trout (Oncorhynchus spp.) migrating upstream through a warm river corridor that can expose individuals to physiologically stressful temperatures. We considered upstream migration in relation to migratory phenotypes that were defined in terms of migration timing, spawn timing, swim speed, and use of cold-water thermal refuges. Individuals with different migratory phenotypes migrated upstream through riverine corridors with variable availability of cold-water thermal refuges and mainstem temperatures. Use of cold-water refuges (CWRs) decreased accumulated sublethal exposures to physiologically stressful temperatures when measured in degree-days above 20, 21, and 22°C. The availability of CWRs was an order of magnitude more effective in lowering accumulated sublethal exposures under current and future mainstem temperatures for summer steelhead than fall Chinook Salmon. We considered two emergent model outcomes, survival and percent of available energy used, in relation to thermal heterogeneity and migratory phenotype. Mean percent energy loss attributed to future warmer mainstem temperatures was at least two times larger than the difference in energy used in simulations without CWRs for steelhead and salmon. We also found that loss of CWRs reduced the diversity of energy-conserving migratory phenotypes when we examined the variability in entry timing and travel time outside of CWRs in relation to energy loss. Energy-conserving phenotypic space contracted by 7%–23% when CWRs were unavailable under the current thermal regime. Our simulations suggest that, while CWRs do not entirely mitigate for stressful thermal exposures in mainstem rivers, these features are important for maintaining a diversity of migration phenotypes. Our study suggests that the maintenance of diverse portfolios of migratory phenotypes and cool- and cold-water refuges might be added to the suite of policies and management actions presently being deployed to improve the likelihood of Pacific salmonid persistence into a future characterized by climate change.

Map of the Columbia River watershed with the Columbia River highlighted. By Kmusser – self-made, based on USGS and Digital Chart of the World data., CC BY-SA 3.0,

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