Yukon River Chinook Salmon MSE

This project was funded with FY 2014 and FY 2015 funds. Phase 1 of the project utilized FY 14 funds to carry out objectives 1, 2, and 3:

Objective 1. In consultation with Yukon River salmon managers and biologists, the project identifed important management objectives and issues of concern for Yukon River Chinook Salmon,
Objective 2. The project reviewed, updated, and documented the Canadian-origin Yukon River Chinook Salmon run-reconstruction and Bayesian state-space stock-recruitment model, and
Objective 3. The project developed and applied an MSE model that incorporates the results of the revised stock-recruitment analysis, to examine trade-offs among management objectives identified through completion of objective 1.

Phase II of the project utilized FY 15 funds and carried out objective 4:

Objective 4. Engaged biologists and managers throughout the project (1) to ensure an appropriate set of management objectives guides our analysis, and (2) to inform them of the MSE process, including – as appropriate – training of biologists in the analytical methods used. The project was extended from May 2017 to December 2017 to accommodate an in-person meeting with fisheries managers and biologists at the Joint Technical Committee of the Yukon River Panel during Fall 2017.

After engaging with members of the Yukon River Panel Joint Technical Committee, we updated a state-space run-reconstruction and stock-recruitment model and developed a Management Strategy Evaluation (MSE) model for this population and its associated fisheries. We developed two models, one using traditional methods that do not consider the effect of changes in population structure on effective escapement (escapement quantity model), and a second that explicitly considered age, sex, and length dynamics in modeling escapement (escapement quality model). The two modeling approaches resulted in similar run reconstructions, but moderately different stock-recruitment relationships – the escapement quality model exhibited a larger escapement associated with maximum recruitment. However, the uncertainty associated with parameter estimates for both models was large relative to the differences on point estimate values. The MSE models revealed very limited differences in outcomes and trade-offs among management objectives between the two stock-recruitment models. Several notable trade-offs were made evident from the MSE model analysis, including trade-offs between US commercial harvest and outcomes for escapement, Canadian commercial harvest, and Canadian subsistence harvest. In general, lower harvest rates and higher escapement targets were favored for these three up-river outcomes, than would be optimal for US harvest. On the other hand, moderate US commercial harvests were achievable with policies that would be preferred for up-river stakeholders. Finally, MSE simulations demonstrated lower harvest rates and/or higher escapement targets are needed when using large mesh (e.g., 7.5”) gillnets for the fisheries rather than smaller mesh (e.g., 5.25”) gear. Future use of the evaluation tools described in this report will have greater impact if they are employed in an open, transparent manner that engages key stakeholders.

A couple of weeks extension was requested by the PI to enable co-PIs time to comment on and approve the final report after the PI had made some changes.

The models we develop will implicitly represent (uncertain) hypotheses about salmon recruitment dynamics, run timing, trends in stock productivity, and how management actions affect the quality and quantity of fish harvested.
Objective 1. In consultation with Yukon River salmon managers and biologists, identify important management objectives and issues of concern for Yukon River Chinook Salmon.
Objective 2. Review, update, and document the Canadian-origin Yukon River Chinook Salmon run reconstruction and Bayesian state-space stock-recruitment model.
Objective 3. Develop and apply an MSE model that incorporates the results of the revised stock-recruitment analysis, to examine trade-offs among management objectives identified through completion of objective 1.
Objective 4. Engage biologists and managers throughout the project (1) to ensure an appropriate set of management objectives guides our analysis, and (2) to inform them of the MSE process, including – as appropriate – training of biologists in the analytical methods used.

Earlier versions of the state-space run-reconstruction and MSE models described here were developed for Canadian-origin Yukon River Chinook Salmon in prior projects (S. Fleischman, ADF&F unpublished analysis; Jones et al. 2012). The consultation and engagement activities that occurred at the beginning and the end of this project led to significant revisions to these models that increased the salience of the analyses and facilitated greater understanding of the purpose of the work and its strengths and limitations. In our view, it is difficult to overstate the value of this type of engagement for modeling projects whose purpose is to develop tools to assist decision-making.

If the parties responsible for determining future management strategies for Yukon River Chinook Salmon decide that the technical methods described in this report could play a useful role in future deliberations on border passage goals or other such matters, we urge them to also consider embedding the MSE work in an open, transparent process that engages representatives from all key stakeholder groups. Experience with other contentious fisheries (Jones et al. 2016) has illustrated the critical importance of engagement in the development of a well-informed management strategy.