Strategic fisheries closure balances harvest opportunity and stock diversity in a large Alaska river basin

Effective conservation of exploited species requires balancing harvest opportunities with the protection of biodiversity. In Pacific salmon, biodiversity among populations contributes to basin-wide resilience, yet spatiotemporal dynamics of adult migrating Chinook salmon remain poorly understood in many large salmon-producing watersheds, creating uncertainty about management impacts. Declining abundance in western Alaska has led to restrictions in subsistence harvest and challenges for upstream communities. In the Kuskokwim River, a large salmon-producing river, a front-end closure limits early-season fishing to reduce exploitation of fish migrating to the upper watershed. To quantify stock-specific effects of this strategy, we reconstruct spatiotemporal dynamics of Chinook salmon return timing across six years using otolith isotope signatures. We demonstrate a consistent relationship between seasonal run timing and watershed origin, with earlier migrants contributing disproportionately to upper watershed regions. A longer simulated closure provided greater protection for upper watershed stocks but with a tradeoff of lost harvest opportunity. Protection varied substantially among years due to migration timing, highlighting how fixed closure strategies interact with dynamic ecological processes to influence overall efficacy.