Evaluating the Consequences of Physical Barriers on Fish During Long-distance Upstream Migrations Through Rivers

Migration allows animals to exploit conditions across distinct habitats to maximize their potential fitness. These movements are dependent on connectivity between habitats that make it possible for animals to move unencumbered. In freshwater ecosystems, dams and other barriers can compromise connectivity and restrict the movement of migrating fish (among other organisms). The central objective of this thesis was to evaluate the consequences of physical barriers on fish during long-distance upstream migrations through rivers. This thesis generates multiple lines of evidence to evaluate that objective, including a literature synthesis, as well as ecological, social science, and physiological data, with much of this research focusing on Chinook salmon of the upper Yukon River that undertake one of the world's longest inland salmon migrations. First, I conducted a synthesis to identify the broad scale impacts of hydropower barriers on inland fish. Next, I evaluated the potential for a fishway to restore connectivity for upper Yukon River Chinook salmon beyond a hydropower barrier situated in a terminal reach of their migration. I then considered how the knowledge developed in the preceding chapters can inform the practice of fish passage by surveying fish passage engineers and scientists on the state of collaboration and knowledge dissemination in the field. Finally, I assessed the efficacy of an ex-situ approach to off-setting the impacts of barriers - hatchery production. This research revealed that the impacts of barriers on long-distance fish migrations (and the broader ecosystem) can be severe, but that approaches can be taken to minimize these impacts (Chapter 2). Fishways are one such approach, but they are not always effective for long-distance migrants like the upper Yukon River Chinook salmon (Chapters 3-5). Part of the solution may be more frequent collaboration and knowledge dissemination amongst fish passage professionals to enhance the effectiveness of fish passage facilities (Chapter 6). Hatcheries may complement fish passage efforts, though the physiological differences between hatchery and wild fish should be considered (Chapter 7). Findings from this thesis highlight the importance of maintaining connectivity for migratory fish to the benefit of the ecosystems and people that depend on them.