Management Strategy Evaluation for Salmon Fisheries in the Kuskokwim River

The Kuskokwim River is facing a time of transition with large observed changes in its salmon populations and the freshwater and marine ecosystems they inhabit. Historically home to one of the largest Chinook salmon stocks in the world and productive Chum salmon stocks, the Kuskokwim River supported vibrant commercial and subsistence fisheries until the 1990s when abundances declined to the point where only subsistence fisheries have persisted. Abrupt changes in abundance and demographics of salmon within this watershed, including the concurrent collapse of both Chinook and Chum salmon in 2019, has fostered concern over the future sustainability of Kuskokwim salmon fisheries and a desire to explore alternative management practices.



In response, a Management Strategy Evaluation (MSE) process was initiated in 2020 with the objective of bringing together watershed residents and fishery participants, fishery management agency scientists, and university researchers to co-develop a more comprehensive understanding Kuskokwim River salmon-human-environment system and explore future fishery management alternatives. Specifically, the objectives of this MSE process were to identify hypotheses for what processes were responsible for the current Kuskokwim salmon collapse, identify objectives for the management of regional salmon fisheries and ideal outcomes for both salmon populations and salmon-dependent human communities, and co-develop a simulation framework to explore trade-offs among alternative inseason harvest strategies, across a range of future conditions.



Based on the knowledge shared by MSE participants at workshop-style meetings, a multi-species, age-structured, closed-loop simulation model for Kuskokwim River Chinook, Chum, and Sockeye salmon was developed to evaluate alternative harvest strategies under varying productivity conditions. The model integrated three components: 1) annual life-cycle population dynamics, 2) daily in-season harvest processes, and 3) management strategies combining fishing schedules and mesh size regulations. In total, 108 scenarios were evaluated, which consisted of 36 harvest strategies being evaluated across three productivity scenarios. In addition to long-term simulations, we also developed an interactive inseason management application using R Shiny to provide insights into real-time decision-making for both mangers and subsistence harvesters, which was tested and revised based on feedback received at several collaborative MSE workshops.



Results from long-term simulations indicated that under current productivity conditions, most strategies achieved escapement goals for Chinook and Chum salmon (>50% probability), but no strategy was able to consistently achieve Chinook salmon subsistence needs. Moreover, extended fishing with 5-6-inch mesh sizes were generally able to meet subsistence goals for Chum and Sockeye salmon. Higher productivity scenarios expanded the number of viable management strategies, although trade-offs remained persistent among species, while low productivity scenarios severely constrained all fishing strategies. Collectively, results from long-term simulations demonstrate key trade-offs in multi-species fishery management, and the inseason management tool developed here complements these findings by allowing fishery managers and harvesters to explore how daily decisions influence outcomes, providing a practical platform for exploring complex trade-offs in Kuskokwim fishery management practices.

All funds were spent within their appropriate period of performance.

The Kuskokwim River is facing a time of transition with large observed changes in its salmon populations and the freshwater and marine ecosystems they inhabit. Home to one of the largest Chinook salmon stocks in the world, it supported vibrant commercial and subsistence fisheries until the 1990s when abundances declined to the point where only subsistence fisheries have persisted. Abrupt change in abundance and demographics of these stocks have fostered concern over the future sustainability of Kuskokwim salmon fisheries.



Scientific understanding of the reasons for changes in Kuskokwim Chinook salmon stocks remains weak in this remote and vast watershed, where biological and environmental data are scarce and highly uncertain. In particular, how future climate change will affect the stock productivity remains unknown. Concomitant declines in the ages and body sizes of spawners also remain largely unexplained but highlight changes to the demographic potential of this stock in terms of declining fecundity and egg size.



This combination of declining socio-economic performance in the fisheries, poor understanding of its causes, and cognizance of ongoing climate change has focused scrutiny on whether current management approaches provide the most effective basis for achieving sustainability. Further, it is unclear whether the diverse range of values held by the variety of stakeholders of this resource are satisfied equally by different management approaches. We propose to engage stakeholders, resource managers, and scientists in a formal collaborative assessment process known as Management Strategy Evaluation (MSE) to co-develop a common understanding of trade-offs among alternative management strategies for satisfying diverse objectives, given the inevitable uncertainties about the future conditions in the ecosystem and how these will impact Kuskokwim River salmon populations.