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Division: Sport Fish
Title: Optimal Production of Chinook Salmon from the Taku River Through the 2001 Year Class
Author: McPherson, S. A., E. L. Jones III, S. J. Fleischman and I. M. Boyce
Year: 2010
Report ID: Alaska Department of Fish and Game, Fishery Manuscript Series No. 10-03, Anchorage.
Abstract: The biological escapement goal for Chinook salmon Oncorhynchus tshawytscha from the Taku River was investigated with information from a stock assessment program (1973–2007), and catch sampling programs of the Canadian inriver gillnet fishery, U.S. commercial gillnet fishery in Taku Inlet, and troll fishery in Southeast Alaska, and the U.S. recreational fishery near Juneau. Stock assessment was based on aerial surveys and mark–recapture experiments to estimate abundance of large (=660 mm MEF, mostly age-1.3 and age-1.4 fish) salmon on the spawning grounds. Relative age composition was estimated from 1973 through 2007 at a carcass weir on the Nakina River, and during mark–recapture experiments (1989, 1990 and 1995–2007) on other tributaries. Additional mark–recapture experiments using coded wire tags provided estimates of harvest in fisheries and abundance of emigrating smolts. Spawning abundance that would produce maximum sustained yield (NMSY) was estimated at 25,075 large Chinook salmon using the traditional Ricker exponential stock-recruit model fit to the production data for the 1983–2001 year classes, and at 25,686 fit to production data from the 1973–2001 year classes. From simulations of the production data incorporating measurement error from a Bayesian age-structured Ricker analysis, we estimated a 90% confidence interval of 18,470 to 36,530 around the point estimate of 25,075 above. No autocorrelation among residuals was detected in fitting these data sets. For the 1983–2001 year classes, the estimated range that will produce, on average, 95% of NMSY is 18,675 to 32,094 large spawners, and that which will produce 90% of NMSY is 16,178 to 35,203 large spawners. Results were corroborated by the Bayesian Markov chain Monte Carlo analysis, a Beverton-Holt model fit to the smolt production data, a Parken habitat model utilizing watershed characteristics, and Ricker models that included smaller, age-1.2 fish. We recommend that the Alaska Department of Fish and Game and the Department of Fisheries and Oceans (Canada) adopt a biological escapement goal range of 19,000 to 36,000 fish, with a point goal of 25,500 large spawning Chinook salmon, for management purposes for this Chinook salmon stock, as estimated from mark–recapture methods. We also make recommendations regarding continuation or modification of several stock assessment components to manage this stock.
Keywords: Chinook salmon, Oncorhynchus tshawytscha, Taku River, smolt abundance, spawning abundance, mark–recapture, age, sex and length composition, escapement goal, stock-recruit analysis, measurement error, Ricker, Beverton-Holt, Parken.