At the intersection of fisheries and climate change: Emergent challenges for Pacific salmon management in a warming world

At the intersection of fisheries and climate change: Emergent challenges for Pacific salmon management in a warming world Michael Douglas Tillotson Chair of the Supervisory Committee: Professor Thomas P. Quinn School of Aquatic and Fishery Sciences A changing environment is not a new challenge for Pacific salmon (Oncorhynchus spp.). This group of fishes has proven resilient, persisting over millions of years while surviving massive changes in climate and physical habitats. There is therefore reason to believe that salmon will be able to adapt to the changes anticipated in association with global climate change. Indeed, the level of warming predicted for the coming century seems a surmountable challenge for salmon at the genus level. However, climate change is impacting and will continue to impact individual populations, driving marked changes in their ecology, abundance and life-histories. The distinction between species and population is important because the majority of ecological, cultural and economic values provided by salmon are manifest at local or regional scales and tied to specific populations, species and life-history types. Furthermore, it is typically at these scales that fisheries and fish habitats are managed. Although the influence of past climate variability on the productivity of salmon populations demonstrates sensitivity of these species to environmental change, unanticipated and unintuitive outcomes are possible given the complexity and diversity of the species and their life-histories. Understanding past variability and predicting future trajectories of salmon populations therefore requires an in-depth understanding of the mechanisms that link environmental change to population productivity. This information can help to ensure that fisheries management serves to increase resilience of salmon populations and avoids actions that amplify potential negative consequences of climate change. This dissertation seeks to contribute to the informed management of Pacific salmon in a warming world through development of theory and in-depth exploration of cases where salmon populations have responded to changing environments. Chapter 1 considers the underappreciated phenomenon of temporal selection in fisheries and its implications for climate adaptation by salmon and other fishes. Chapter 2 tests a series of hypotheses that link observed warming in Lake Iliamna, Alaska to changes in sockeye salmon life-history and productivity. Chapter 3 describes a novel pattern of adult mortality in spawning sockeye salmon and demonstrates that low streamflow can create habitat conditions under which density-dependent spawning failure may occur. Chapter 4 describes changes in reproductive timing of Cedar River, Washington sockeye salmon and examines the relative influence of natural and artificial selection on phenological change and climate change resilience. Collectively, this research demonstrates some of the diverse responses that can be expected in salmon populations responding to climate change, emphasizes the importance of life-history and phenological diversity as adaptive pathways for populations impacted by climate change, and argues for management that maximizes these forms of diversity.