An investigation of Ichthyophonus infection related in-river mortality in Yukon River Chinook salmon from multiple knowledge systems: Indigenous, local, and western science

Abstract

The recent historic low salmon returns in the Yukon River contribute to an ongoing humanitarian crisis for subsistence users and Indigenous Peoples with cultural and well-being ties to salmon. After over a decade of relative calm, the marine parasite Ichthyophonus has undergone a resurgence and is once again infecting Yukon River Chinook salmon (Oncorhynchus tshawytscha; king; Taryaqvak; Ggaal; Gath; Łuk choo, hereafter referred to as king salmon) at high rates, with currently unknown consequences for survival of migrating adults. This thesis pairs multiple knowledge systems to assess the prevalence, severity, and impact of Ichthyophonus on adult Yukon River king salmon during their upriver spawning migration. Organized as two chapters, I conducted work that suggests highly infected king salmon may experience mortality before reaching spawning grounds due to Ichthyophonus and its interactions with other stressors. Infection severity significantly declined as fish migrated upriver, consistent with selective mortality of severely diseased fish. However, infection prevalence remained largely unchanged during migration, which we attribute to detection limits of testing coupled with infection progression. Through dialogues at community gatherings facilitated in two fishing-dependent Yukon River communities, I sought to co-interpret research findings alongside the Tribal Council and community members. Participants highlighted Ichthyophonus as only one of a myriad of co-occurring challenges faced by Yukon River king salmon and consistently voiced concerns that a focus on disease would be used to assign blame for salmon declines that they felt were more attributable to factors such as marine bycatch, and overfishing. Overall, the approach and findings contribute to an elevation of, and stronger inclusion of, Indigenous Knowledge, Tribal governance, local knowledge, and ecological stewardship within western fisheries science and management. While this thesis provides evidence that Ichthyophonus may indeed contribute to king salmon mortality in-river, it should not be used to diminish the voices of community dialogue participants who emphasized the importance of considering the impacts of industrial fisheries, broader environmental factors, as well as historical and cross- jurisdictional management practices when explaining the low salmon abundance and population declines. I dream this thesis will contribute to mending a proverbial collective fishing net to steward fisheries by uplifting Tribal sovereignty and governance, intentionally weaving together many ways of knowing to guide us toward more equitable, respectful, and restorative salmon management for future generations.