Meta-Analysis of Beaver Dam Impacts on Pacific Salmon Reveals Variable Outcomes Across Species–Life Stage Combinations

Abstract

Beaver-based habitats (BBH) in streams are rapidly growing in number as beaver populations expand and are an increasingly common tool used in riverine restoration projects aiming to improve degraded freshwater Pacific salmonid habitat. Though the prevalence of BBH has increased through time, there has yet to be an investigation of how BBH affect Pacific salmonids specifically. This study used both quantitative and qualitative data from 225 published reports to analyze unique species-life stage combinations of Pacific salmonid responses to BBH versus reference sites without BBH via meta-analysis techniques. Our results reveal novel patterns of Pacific salmonid species-life stage specific responses to BBH, but in some cases these patterns were different between the quantitative and qualitative results. The egg and juvenile life stages of most Pacific salmonid species exhibit a positive response to BBH, while resident adult trout and spawner life stages have a much more complex, mixed response to BBH across species. We discuss the implications of these results has for future BBH projects, and identify opportunities to further untangle the complex relationship between beaver dams and Pacific salmonids.