Evaluating Ichthyophonus-Associated Mortality of Yukon River Canadian-Origin Chinook Salmon

Ichthyophonus disease (ichthyophoniasis) resulting in natural en route mortality of Canadian-origin Yukon River Chinook salmon (Oncorhynchus tshawytscha) is a leading hypothesis to explain two successive years (2020 and 2021) of failure to achieve U.S./Canada border passage objectives per the Yukon River Salmon Agreement despite adequate run sizes detected near the mouth of the Yukon River and unprecedented harvest restrictions. This project will 1) determine if ichthyophoniasis is associated with en route mortality; 2) estimate the lethal Ichthyophonus infection “threshold” range for Canadian-origin Chinook salmon to assess the risk that observed infections pose to the annual salmon run; and 3) develop a model to assess the proportion of the annual Canadian-origin Chinook salmon run past Pilot Station sonar with infections above the lethal threshold. A fish health assessment will also be conducted to assess other relevant diseases/factors that can influence the course of ichthyophoniasis.

This project contributes to sustaining salmon populations by researching the leading hypothesis of ichthyophoniasis as a main contributor for the dramatic difference in Chinook abundance estimates between sonar projects on the Yukon River. Clarifying how this disease causes en route mortality and developing a model and methods for ongoing monitoring will facilitate management of the stock and maximize subsistence fishing opportunity on both sides of the border.