Influence of stock-specific migration rate variability on mixed-stock harvest rates for at-risk Fraser River Chinook salmon (Oncorhynchus tshawytscha)

Accurately reconstructing mixed-stock catches in the Fraser River is paramount for managing fisheries that can intercept or target at-risk Fraser River Chinook salmon (Oncorhynchus tshawytscha). However, reconstruction models assume constant in-river migration rates despite a growing body of evidence that Chinook salmon display some of the most variable in-river migration rates of all the Pacific salmon species. I used a spatially explicit, individual based model of Chinook salmon migration and fisheries in the Fraser River to simulate how small changes in migration rate variability affected stock-specific catch outcomes and proportional catch outcomes under a fixed in-river harvest scenario involving three separate stocks, including two at-risk stocks. For the Chilko Summer 52 , Quesnel Summer 52 , and South Thompson 41 stocks tested, increasing migration rate variability led to significantly lower catch outcomes (down 5.9%, 8.1%, and 16.6%, respectively). Increasing migration rate variability did not significantly affect each stocks proportional catch. My results provide valuable insights to managers, highlighting the significance of understanding how migration rate variability influences catch outcomes for at-risk Chinook salmon in the Fraser River. Additionally, these results underscore the importance of integrating migration rate variability into stock assessment models.