Alternative harvest strategies to alleviate predation bottlenecks: a bioeconomic modeling approach to inform adaptive management

Thesis (Ph.D.)--University of Washington, 2016-06

There has been increasing emphasis on using ecosystem-based management to account for the effects of trophic interactions in fisheries. However, such approaches require knowledge of ecosystem structure and function often not available to managers. I studied the Chignik salmon fishery in Alaska to explore ways to manage predator-prey interactions when predator abundance data and knowledge of interaction strengths are limited. The Chignik salmon fishery primarily targets sockeye salmon for harvest. Coho salmon are not managed or subject to directed harvest at present, but prey heavily on sockeye salmon as juveniles in the watershed. Thus, a directed coho salmon harvest may reduce predation pressure and increase productivity of the sockeye salmon fishery. I used a Bayesian hierarchical modeling approach to estimate the annual abundance of coho salmon in the Chignik River from limited daily escapement counts, using information in years with more data to inform estimates in years with limited data. Using these estimates, I examined the relationship between sockeye salmon productivity and coho salmon escapement, and detected no strong evidence of a predation effect on sockeye salmon. Simulation models revealed that recruitment stochasticity and observation error mask even very strong predation effects and bias predation effect estimates towards zero. Simulations also revealed that active adaptive management strategies to reduce coho salmon abundance would take up to a decade before significant increases in sockeye salmon harvest were experienced by fishers, even when very strong predation effects are present. Commercial fisheries are not executed by a single stakeholder, and each stakeholder group has different perspectives, economic constraints, and incentives. I used simulation models to examine the ecological and economic conditions under which a directed coho salmon harvest would be beneficial to fishers and seafood processors. Differential economic constraints resulted in very different outlooks for the two stakeholder groups, with processors being more limited than fishers in terms of the scenarios in which a coho salmon fishery would be beneficial over the long-term. As trade-offs are inherent to natural resource management, it is critical to consider the economic constraints and incentives of different stakeholders for management actions.