Shifting stage-specific constraints on productivity shape recovery potential for Yukon River Chinook salmon

Identifying key life history periods in which population productivity is constrained represents a persistent challenge in conservation and natural resource management. For species with complex life cycles, such as Pacific salmon (Oncorhynchus spp.), population dynamics may be shaped by interactions between natural and anthropogenic impacts occurring across multiple habitats and life history stages. In such cases, a stage-structured modeling approach is useful for identifying key life history periods and processes therein acting to drive realized abundance trends. Here, we develop an integrated life-cycle model to explore stage-specific constraints on population productivity and recovery potential for Yukon River Chinook salmon. The Yukon River has historically supported one of the largest stock complexes of Chinook salmon in the world, forming the basis of important fisheries that are vital to the well-being of communities in this region. However, returns of Chinook salmon to the Yukon River have declined substantially, prompting conservation concerns and limitations on harvest opportunities. Our results point to periods of low juvenile recruitment as likely contributors to declining abundance levels over the past two decades, supporting previous studies implicating factors operating in the early (i.e., spawner-to-juvenile) life history stages. However, we find that elevated natural mortality in later, post-juvenile life history stages has increasingly limited population productivity and recovery potential in recent years following a protracted marine heatwave period. Collectively, our results emphasize how shifting conditions can induce novel stage-specific survival bottlenecks in species with complex life cycles, with important implications for conservation and management outcomes.