Putting watershed restoration in context: alternative future scenarios influence management outcomes

Predicting effects of habitat restoration is an important step for recovery of imperiled anadromous salmonid populations. Habitat above three major hydropower dams in the Lewis River watershed, southwestern Washington, USA, will soon become accessible to anadromous fish. We used multiple models to estimate habitat conditions above dams and fish population responses. Additionally, we used scenario planning to predict how habitat and fish will respond to potential future trends in land use due to human population growth and riparian conservation policies. Finally, we developed a hypothetical management strategy (i.e., a set of prioritized restoration projects in specific locations within the watershed) as an example of how a fixed amount of restoration funds might be spent to enhance the success of reintroducing fish above dams. We then compared predicted outcomes from this new strategy to those of six previously modeled strategies. We estimated how the choice of the best management strategy might differ among alternative future scenarios. Results suggest that dam passage will provide access to large amounts of high-quality habitat that will benefit fish populations. Moreover, conservation of existing riparian areas, if implemented, has the potential to improve conditions to a much greater extent than restoration strategies examined, despite expected urban growth. We found that the relative performance of management strategies shifted when fish were allowed to migrate above dams, but less so among alternative futures examined. We discuss how predicted outcomes from these seven hypothetical management strategies could be used for developing an on-the-ground strategy to address a real management situation.