Value of Information Analysis of Kuskokwim River Chinook Salmon Monitoring Projects

This project built on a previous review by an AYKSSI expert panel of the Kuskokwim River Chinook salmon run-reconstruction and stock recruitment models (Schindler et al. 2019). Schindler et al. (2019) used a simulation approach to assess the performance of the run-reconstruction model used by the Alaska Department of Fish & Game (ADFG) for estimating abundance of Chinook salmon in the Kuskokwim River, and recommended model improvements that were adopted by ADFG for the run reconstruction in 2019. These changes to the run-reconstruction model vastly improved its stability and performance for estimating Chinook salmon abundance in the Kuskokwim River. Schindler et al. (2019) also suggested additional simulation analyses to assess the value of information obtained from escapement monitoring projects for estimating the run size of Chinook salmon. Such a value of information approach was considered particularly timely because the various weir and aerial monitoring projects are at risk of becoming discontinued due to budget constraints, but there has been no systematic assessment of the consequences of reductions in sampling coverage for properly estimating Chinook salmon abundance in the Kuskokwim River.

In this project, a value of information analysis was conducted to evaluate the consequences of discontinuing weir and aerial surveys for enumerating Kuskokwim River Chinook salmon. Specifically, a simulation modeling approach to quantify the errors in estimating run size under various scenarios (number of operating weirs and aerial surveys) was used and its effects on the estimation of management reference points such as the escapement that produces maximum sustained yield (MSY). In addition, how periodic mark-recapture studies could alleviate some of the negative consequences of fewer weir and aerial escapement indices were analyzed. The results of this project are expected to inform future decisions on how limited funds should be allocated to ensure the best possible monitoring, given available resources, for estimating the run size of Kuskokwim River Chinook salmon. Preliminary analyses demonstrate that the ‘state-of-nature’ defined in the simulation model (e.g., the degree of coherence in the dynamics of sub-populations and the presence of regime shifts) have important effects on the sensitivity of run-reconstruction model performance to reductions in sampling intensity.

Reference: Schindler, D.E., T.E. Walsworth, M.D. Adkison, R.M. Peterman, and A.E. Punt. 2019. Kuskokwim River Chinook salmon run-reconstruction and stock recruitment models: a review by an independent expert panel. Arctic-Yukon-Kuskokwim Sustainable Salmon Initiative. Anchorage, AK. 164 pp.

In 2016 an Independent Review Panel on escapement quality of Chinook salmon was established by the AYK-SSI to synthesize the existing data and quantify the magnitude of changes in the demographic characteristics of Chinook salmon in the AYK region rivers. The intention was also to investigate the hypothesis that selective fishing and natural mortality have altered the genetic character of stocks and changed the expression of size, sex ratio, and composition of life history types that have contributed to declines in egg deposition in AYK Chinook salmon populations. The main concern, as stated by this hypothesis, is the contribution of declining trends in spawnermean age and size to reductions in population productivity and abundance of Chinook salmon in the AYK region. Further, a potential problem for managers is that changes in age-size structurecan introduce bias into run reconstruction and spawner-recruit models that form the basis for current fishery management in this region, i.e. development of appropriate escapement goals.

Specifically, the aim of the Expert Panel was to quantify how changes in population demographyhave resulted in changes in per capita fecundity and total egg mass in AYK rivers using the best data available. One of the original project objectives was to compile and organize an extensive open-source database on Chinook salmon age-sex-length (ASL) observations from fisheries and escapement projects across the AYK region. Yet, extensive efforts by AYK Region ADF&G Commercial Fish Division staff to collect and publish a comprehensive ASL database that includes most of the available data for Chinook salmon negated the need for development of an additional database. This has allowed the Expert Panel to shift the focus of the analytic work for this project from compiling and organizing data to the second core project objective: a detailed analysis to quantify changes in escapement quality of Chinook salmon in the AYK region.

The goals of the Expert Panel were to (i) understand historical changes in location-specific and drainage-wide age, sex, and length compositions, (ii) estimate potential effects of these changes on the average reproductive potential of the populations in terms of potential number of eggs in the gravel, and (iii) explore potential management implications of changes in escapement quality of Chinook salmon.

In addition to this report and as part of the objectives of the AYK SSI Expert Panel, a synthesis of trends in average length and reproductive potential for Chinook salmon in the Yukon River is currently under consideration for publication as a journal article.