Ecological consequences of flow regulation by Run-of-River hydropower on salmonids

Streams are dynamic, disturbance-driven ecosystems, where flow plays a dominant role structuring biological communities. Anthropogenic activities on streams change natural patterns of flow and disturbance, which in turn alters the conditions to which resident fishes are adapted, and their survival and fitness. Run-of-river (RoR) hydropower projects are an example of an anthropogenic activity that may alter stream ecosystems by temporarily diverting a proportion of stream flow to produce electricity. RoR hydropower projects have increased considerably in number and importance in the last three decades in both British Columbia and worldwide. Although there is a perception that RoR hydropower has minimal effects on stream ecosystems due to the small physical footprint of projects, we know surprisingly little about the impacts of RoR hydropower on fish populations. In this thesis, I use a combination of published research, empirical data, and models to evaluate a range of hypotheses regarding how RoR hydropower may affect fish populations, concentrating on salmonid species whose freshwater habitats often overlap with RoR projects. In Chapter 2, I synthesize the impact pathways by which RoR hydropower may influence salmonid populations, inferred from studies of reservoir-storage hydropower and salmonid ecology. In Chapter 3, I use empirical data to quantify increases in water temperature due to RoR flow diversion and explore the possible consequences for resident fish growth with bioenergetics models. In Chapter 4, I evaluate how stranding from anthropogenic flow fluctuations affects the long-term population dynamics of coho salmon (Oncorhynchus kisutch) in RoR-regulated rivers using a matrix model integrating both the strength and timing of freshwater density dependence. Finally, in Chapter 5, I quantify the high level of uncertainty in how much compensation habitat is required to offset chronic mortality incurred by multiple life-stages of coho salmon. The global emergence of RoR hydropower projects emphasizes the importance of understanding their effects on aquatic ecosystems. Overall, our capacity to protect and restore threatened salmonid populations rests upon our ability to not only better understand the pathways of impacts, but also the effectiveness of both natural (density dependence) and human (habitat compensation) interventions that can be used to offset anthropogenic mortality.