The Effect of Stream Restoration on Preferred Cutthroat Trout Habitat in the Strawberry River, Utah

Nicolas R. Braithwaite, Utah State University

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Stream restoration has become a popular management tool for attempting to increase and/or restore fish populations by improving habitat. A section of the Strawberry River, Utah recently underwent a stream restoration project, where the main goals of the project included increasing spawning activity, rearing potential, and resident populations of Bear Lake cutthroat trout Oncorhynchus clarkia utah. The impact of the restoration project on cutthroat trout was investigated by first characterizing preferred habitat for different life stages, investigating habitat as a limiting factor in the system, and then assessing the quality of available habitat by comparing restored/unrestored sections of stream and pre-restoration/post-restoration of the same sections of stream.

Results indicated cutthroat trout in the Strawberry River preferred faster water velocities, shallower depths, moderate substrates sizes, and riffle habitat types for spawning. In contrast, juvenile and adult life stages preferred deeper sections of stream, the presence of cover, and pool habitat types. Limiting factor analyses suggested spawner abundance may be limiting in the Strawberry River and maximum daily temperatures during the summer may be the strongest limiting habitat factor for juvenile and resident adult cutthroat trout. Restoration generally appeared to initiate a shift towards more favorable habitat, especially in terms of increasing near-bed velocity and increasing the proportion of preferred substrate sizes for spawning, and increasing the percentage of pools for juvenile and resident adult life stages. The potential benefits of the restoration remained somewhat ambiguous, a result of relatively small differences observed between study reaches, limited pre-restoration data, high spatial and inter-annual variability within and among control study reaches, and the inherently delayed reaction of ecological responses to physical changes from restoration. However, these issues can be resolved through continued monitoring. Long-term monitoring would allow for the accounting of natural variability to further tease out differences resulting from restoration and differences resulting from natural fluctuations. Additional monitoring would also capture long-term responses, which has the potential to be significant considering the relatively slow response of riparian vegetation to restoration. This study also provides a baseline dataset and template for future long-term monitoring efforts.