The objectives of this report are to: 1) describe the productivity and capacity of the Kuskokwim River Chinook salmon stock, as quantified from stock-recruit analyses, 2) recommend a drainage-wide escapement goal based on this information, and 3) revise escapement goals for selected tributaries.
An age-structured state-space spawner–recruit model was fit to estimates of relative and absolute abundance, harvest, and age composition for Copper River Chinook salmon (Oncorhynchus tshawytscha) from 1980 to 2016. Bayesian statistical methods were employed to assess uncertainty in the presence of measurement error, serial correlation, and missing data. Ricker stock-recruit parameters and management reference points were estimated, including the escapement that provides for maximum sustained yield (SMSY). It is recommended that a sustainable escapement goal range of 18,500 to 33,000 fish be adopted for Copper River Chinook salmon. Escapement is evaluated by subtracting estimates of inriver harvest from estimates of inriver abundance. Escapements within this range have a high probability of producing sustainable yields.
Age-structured state-space spawner-recruit models were fit to 1986-2015 data on abundance, harvest, and age composition for early and late runs of Kenai River Chinook salmon (Oncorhynchus tshawytscha), 75 cm mid eye to tail fork (METF) and longer. Historical annual run abundance, stock recruitment parameters, and fishery management reference points were estimated from these models. Sustainable Escapement Goals of 2,800-5,600 (early run) and 13,500-27,000 (late run) Chinook salmon 75 cm METF and longer are recommended, and their attributes and limitations discussed. Fish 75 cm METF (approximately 33.3 in total length) and longer can be assessed directly by imaging sonar in the Kenai River at river mile 13.7.
Historical escapement and run size of fall chum salmon Oncorhynchus keta was reconstructed from incomplete sonar, weir, counting tower, mark-recapture, aerial survey, and foot survey data of varying precision from 1974 to 2007. The resulting estimates of drainage-wide escapement were fitted to an age-structured Ricker spawner-recruit model. Bayesian statistical methods were employed, which allowed for realistic assessment of uncertainty in the presence of measurement error, serial correlation, and missing data.
The current sustainable escapement goal (700,000–1,200,000) for Kenai River late-run sockeye salmon was established in 2011. For this escapement goal review, the escapement time series and production data were updated through 2018. The fit of 6 spawner–recruit models to data from brood years 1968–2012 and brood years 1979–2012 was examined. Although the classic Ricker model was determined the most appropriate to use given the data, all brood years were estimated to have replaced themselves, which compromised obtaining accurate and precise estimates of most model parameter estimates and biological reference points, including a scientifically defensible estimate of maximum sustained yield. Markov-type yield tables were constructed to evaluate yields at different levels of escapement. We recommend the sustainable escapement goal for Kenai River late-run sockeye salmon be revised to 750,000–1,300,000 fish because the analyses indicated escapements in this range will likely provide better yields.
Quantitative modeling methods have become a central tool in the management of harvested fish populations. This book examines how these modeling methods work, why they sometimes fail, and how they might be improved by incorporating larger ecological interactions. Fisheries Ecology and Management provides a broad introduction to the concepts and quantitative models needed to successfully manage fisheries. Walters and Martell develop models that account for key ecological dynamics such as trophic interactions, food webs, multi-species dynamics, risk-avoidance behavior, habitat selection and density-dependence. They treat fisheries policy development as a two-stage process, first identifying strategies for varying harvest in relation to changes in abundance, then finding ways to implement such strategies in terms of monitoring and regulatory procedures. This book provides a general framework for developing assessment models in terms of state-observation dynamics hypotheses, and points out that most fisheries assessment failures have been due to inappropriate observation model hypotheses rather than faulty models for ecological dynamics. Intended as a text in upper division and graduate classes on fisheries assessment and management, this useful guide will also be widely read by ecologists and fisheries scientists.
