Multiple environmental drivers across life stages influence Yukon River Chinook salmon productivity

Recent declines of Yukon River Chinook salmon (Oncorhynchus tshawytscha) populations have severely impacted people residing in the Yukon and Alaska. Evidence-based conservation strategies focused on stock recovery and adaptation are urgently needed but are limited by our understanding of what is driving declines, particularly in Canadian portions of the Yukon River basin. We examined how multiple environmental drivers may be influencing Canadian-origin Yukon River Chinook salmon productivity for eight populations over a 28-year period. We found that productivity was related to various environmental and ecosystem processes acting cumulatively over multiple life stages and across broad geographic scales. Productivity decreased in association with warmer upriver migration temperatures, wetter freshwater juvenile rearing habitats, and increasing abundances of potential marine competitors. In contrast, productivity increased in years with warmer and snowier winters and earlier spring onset. We found that different populations had similar relationships with environmental drivers, with potentially negative implications for regional fisheries stability. Our findings provide insight into how Chinook salmon are responding to rapid environmental change and can help inform salmon conservation initiatives and sustainable harvest strategies.