Research in freshwater climate change adaptation is often focused on high-elevation tributaries rather than mainstem rivers because they are often less degraded. While large/mainstem rivers can be predominantly warm, they also often exhibit patches of cool water, which can nonetheless provide vital refuge habitat for coldwater fish. Studies have shown that fish can regulate their body temperatures by occupying small patches of cool water, emphasizing the potential conservation significance of these coldwater refuges.

The purpose of this project is to understand how coastal cutthroat trout, a coldwater salmonid, use coldwater habitats on the Willamette River floodplain during stressfully warm summer temperatures. This project builds on previous research focused on several coldwater alcoves that are heavily exploited by cutthroat trout during the summer. While the previous research has documented the timing of fish movement onto these alcoves, fish diet and condition while on alcoves, and how fish exploit oxygen-temperature microhabitats within refuge habitats, this project will tackle larger-scale questions of fish movement and habitat use throughout the summer using radio telemetry. This project will help reveal the timing and direction of fish movement, location of coldwater refuges used by fish, percentage of tagged fish that use refuge habitats, and individual survival throughout the season. Because our ability to effectively restore and maintain these coldwater habitats depends on better understanding how fish use them and what makes them functional, information collected through this project will provide managers and policy-makers with accessible, decision-relevant science to guide climate adaptation actions for at-risk cutthroat trout populations.