Incorporating local information to predict thermal stress for diverse species

Pacific salmonids are incredibly diverse and critical for both ecosystems and human consumers. Although salmon conservation recognizes the importance of diversity for viability, most previous studies have oversimplified phenology and life history diversity that dictate local environmental exposure and influence responses to climate change. I combined subpopulation-level spatial distributions and phenologies with monthly stream temperature to explore modern and future patterns in freshwater thermal stress for 449 subpopulations across 21 coho salmon (Oncorhynchus kisutch) and steelhead trout (O. mykiss) management units, 14 of which are listed as either Threatened or Endangered under the United States Endangered Species Act. Under modern conditions, 37% of coho and 90% of steelhead subpopulations were exposed to thermally stressful conditions. Under a simple 2°C climate warming scenario, 91% of subpopulations and the majority of subpopulations in 20 of 21 management units would be thermally stressed during at least one life stage. For diverse species like salmon, incorporating local-scale phenology, spatial, and climatic information is imperative to identify subpopulations that will be negatively impacted by future climate warming without mitigating actions.