Fisheries, Subsistence, and Habitat
Publications Searchable Database

Search Again
Division: Sport Fish
Title: Stock assessment of early-run Chinook salmon in the Kenai River, 2002-2006
Author: McKinley, T. R., and S. J. Fleischman
Year: 2010
Report ID: Alaska Department of Fish and Game, Fishery Data Series No. 10-19, Anchorage
Abstract: The status and escapement goal of early-run Chinook salmon Oncorhynchus tshawytscha in the Kenai River was assessed using information from creel surveys, an inriver sonar project, an age-structure spawner-recruit analysis, educational harvests, an inriver gillnetting project, and Alaska Statewide Harvest Surveys. This report updates stock assessment statistics with data from 2002–2006. The estimated total runs of early-run Kenai River Chinook salmon were 7,226 (SE = 169) in 2002, 13,371 (SE = 199) in 2003, 15,587 (SE = 261) in 2004, 20,526 (SE = 295) in 2005, and 23,401 (SE = 394) in 2006. The estimated inriver sport fishery harvest was 12% of the run in 2002, 21% in 2003, 22% in 2004, 19% in 2005, and 20% in 2006. Spawning escapement estimates of early-run Chinook salmon were 6,185 fish (SE = 221) in 2002, 10,097 (SE = 540) in 2003, 11,855 (SE = 487) in 2004, 16,387 (SE = 412) in 2005, and 18,428 (SE = 495) in 2006. Spawning escapement estimates for 2002–2006 were all within or above the current optimal escapement goal of 5,300–9,000 Chinook salmon. Hook-and-release mortality estimates for early-run Kenai River Chinook salmon ranged from 78 (SE = 54; 2002) to 389 (SE = 276; 2003). Return-per-spawner estimates ranged from 0.53 (SE = 0.28) to 3.89 (SE = 0.71). Estimated sibling ratios averaged 4.27 (SD = 2.67) for age 5 to age 4, 2.27 (SD = 1.16) for age 6 to age 5, and 0.06 (SD = 0.04) for age 7 to age 6. Results suggest there is an increasing trend in the runs of ocean-age-2 fish. The mean age estimates of the escapement from the last two complete brood returns (1998 and 1999) were the lowest in the last 20 years; however, the mean age estimates of the return from 1998 were above average and 1999 were average. Mean length-at-age estimates have not changed since 1986. A slot limit imposed in 2003 decreased the selective harvest for ocean-age-4 and ocean-age-5 fish, and increased the selective harvest for ocean-age-3 fish. However, because of low harvest rates, the slot limit has not substantially affected the age composition of the escapement. Estimated runs of ocean-age-5 fish from 2002–2006 ranged from 129 (SE = 49; 2003) to 865 (SE = 284; 2006). Based on an age-structured Bayesian spawner-recruit analysis, spawning escapement at maximum sustained yield SMSY is, with 95% probability, between 3,592 and 6,073 (posterior median = 4,579). Spawning escapement at maximum return SMAX is, with 95% probability, between 4,443 and 9,755 (posterior median = 6,189). Active research is underway to develop improved sonar estimates of inriver run. Preliminary results indicate that the current published estimates are subject to substantial measurement error. No immediate change is recommended to the current optimal escapement goal of 5,300–9,000 fish.
Keywords: Kenai River, Chinook salmon, total run, spawning escapement, sibling ratios, brood tables, slot limit, spawner-recruit analysis, maximum sustained yield, Bayesian statistics, Markov Chain Monte Carlo, Oncorhynchus tshawytscha.