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Division: Sport Fish
Title: Stock assessment of late-run Chinook salmon in the Kenai River, 1999–2006.
Author: McKinley, T. R., and S. Fleischman
Year: 2010
Report ID: Alaska Department of Fish and Game, Fishery Data Series No. 10-96, Anchorage.
Abstract: The status of late-run Chinook salmon Oncorhynchus tshawytscha in the Kenai River was assessed using information from creel surveys, an inriver sonar project, educational harvests, an inriver gillnetting project, personal use fishery harvests, commercial fishery harvests, and the Alaska Statewide Harvest Survey. This report updates stock assessment statistics with data from 1999 2006. The estimated total runs of late-run Kenai River Chinook salmon were 60,773 (SE = 778) in 1999, 50,770 (SE = 308) in 2000, 43,446 (SE = 640) in 2001, 54,668 (SE = 1,373) in 2002, 59,759 (SE = 459) in 2003, 84,262 (SE = 1,770) in 2004, 70,664 (SE = 1,397) in 2005, and 52,795 (SE = 891) in 2006. The commercial fishery in Cook Inlet harvested 17% of the run in 1999, 8% in 2000, 15% in 2001, 18% in 2002, 27% in 2003, 28% in 2004, 33% in 2005, and 18% in 2006. The estimated inriver sport fishery harvest was 22% of the run in 1999, 30% in 2000, 38% in 2001, 23% in 2002, 28% in 2003, 21% in 2004, 26% in 2005, and 30% in 2006. Spawning escapement estimates of late-run Chinook salmon were 34,962 (SE = 1,271) in 1999, 29,627 (SE = 1,048) in 2000, 17,947 (SE = 1,254) in 2001, 30,464 (SE = 1,551) in 2002, 23,736 (SE = 1,559) in 2003, 40,198 (SE = 2,055) in 2004, 26,046 (SE = 1,934) in 2005, 24,423 (SE = 1,175) in 2006. Spawning escapement estimates from 1999 through 2006 were all within or above the current biological escapement goal (BEG) of 17,800 35,700 fish. Hook-and-release mortality estimates for late-run Chinook salmon ranged from 499 (SE = 276; 2000) to 1,803 (SE = 978; 2003). Return-per-spawner estimates for all complete brood years (1986 1999) ranged from 1.00 (replacement; SE = 0.41) to 2.79 (SE = 0.12). Estimated sibling ratios averaged 1.78 (SD = 0.33) for age 5 to age 4, 3.22 (SD = 0.48) for age 6 to age 5, and 0.07 (SD = 0.02) for age 7 to age 6 Chinook salmon. In recent years there is a higher preponderance of age-1.2 fish in the run. The mean age estimates of both the escapement and the return for 1986 1999 (i.e., years with complete brood returns) are similar to the long-term average for this stock. Mean length-at-age estimates have not changed since 1986. Relative harvest selectivity is generally insignificant for this stock; age composition of the harvest is similar to the age composition of run and the resulting escapement. However, in recent years there is a higher preponderance of age-1.2 fish in the run than the harvest. The ratio of females in the run, harvest, and escapement is stable and generally between 40% and 50%. An age-structured Ricker spawner-recruit model was fit to the historical data using Markov Chain Monte Carlo methods. Results were consistent with the existing BEG for this stock (17,800 35,700). No change to the goal is recommended, except to re-designate it as a sustainable escapement goal (SEG) because of measurement error introduced by sonar assessment of the inriver run and escapement.
Keywords: Kenai River, Chinook salmon, total return, spawning escapement, sibling ratios, brood tables, spawner–recruit analysis, maximum sustained yield, Markov Chain Monte Carlo, Oncorhynchus tshawytscha.