The benefits of climate change mitigation to retaining rainbow trout habitat in British Columbia, Canada

Climate change is increasing stream temperatures and thereby changing habitat suitability for a variety of freshwater fishes. We investigate how suitable stream habitat for rainbow trout ( Oncorhynchus mykiss ), a valuable cold-water species, may change in British Columbia, Canada, currently near the north end of their range. We examine a no-mitigation climate change scenario (RCP 8.5), and one with moderate mitigation (RCP 4.5). We used a watershed-scale regression model incorporating topographic, hydrological and climatic variables to estimate current and projected maximum weekly average stream temperatures throughout the province. We then calculated the potential change in suitable habitat within rainbow trout’s native range, in low- and high-relief watersheds and watersheds with lakes traditionally stocked for recreational fishing. We considered deviations from the species optimal growth and biotic community temperature ranges, as well as exceedances of its survival threshold . We found that future warming will shift suitable rainbow trout habitat in British Columbia to higher relief areas, with the no-mitigation scenario leading to a loss of 39 to 61% of total kilometres of suitable stream habitat. The moderate mitigation would dramatically reduce climate change effects, resulting in minor changes to the amount of suitable stream habitat (+ 2 to − 8% from current conditions). About half (41% to 53%) of the current range is retained under the moderate mitigation scenario, and much of this is close to population centres reliant on the ecosystem services provided by rainbow trout. Our analysis offers guidance for watersheds that might be prioritized for adaptation measures, e.g., stocked watersheds are projected to suffer large losses in suitable habitat under both scenarios. Our work shows the regional value of climate mitigation and how at-risk watersheds can be identified and targeted for management interventions. Our work provides a template for such assessments for other geographies and species.