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Division: Sport Fish
Title: Assessment of coho salmon from the Kenai River, Alaska, 2003
Author: Massengill, R. and J. A. Carlon
Year: 2007
Report ID: Alaska Department of Fish and Game, Fishery Data Series No. 07-38, Anchorage
Abstract: Wild coho salmon Oncorhynchus kisutch smolt were captured within the Kenai River drainage in the spring of 2002, marked with an adipose finclip and coded wire tag (CWT), and recovered as adults in 2003. Marked adults were recovered from selected commercial fisheries of Upper Cook Inlet (UCI), Alaska, and from within the Kenai River drainage. Data collected during this smolt-to-adult (marking-recovery) cycle were used to estimate the UCI commercial harvest of Kenai River-bound coho salmon in selected fisheries in 2003 and smolt abundance in 2002. Estimates of commercial harvest in 2003 were based on the proportion of each fishery harvest examined, the number of tagged coho salmon recovered, and the tag-bearing proportion of the return passing through marine commercial fisheries. The estimate of smolt abundance in 2002 was based on the number of smolt marked with adipose finclips in 2002, the number of returning adults sampled inriver for finclips in 2003, and the number of finclipped adults detected. Commercial harvest and smolt abundance estimates represent the eleventh consecutive set of annual estimates available for the Kenai River population. Of 101,677 coho salmon that were harvested among all UCI commercial fisheries, a total of 44,922 (44%) were examined. Most fishing periods were sampled. A total of 6,880 (15% of the sample) could not be positively assigned to fishery strata and were excluded from calculations of commercial harvest. Of the remaining 38,042, a total of 36,529 was examined as follows: 16,146 (67% of the harvest) were examined from Northern District harvests, 18,060 (34%) were examined from Central District drift gillnet harvests, and 2,323 (23%) were examined from Central District eastside set gillnet harvests. Among these fisheries, a total of 930 adipose-finclipped fish were observed, of which 912 were recovered, 795 bore a decodable CWT, and 146 were identified as being of Kenai River origin. Significant and substantial temporal variation in the tag-bearing proportion measured at all inriver sampling locations precluded an accurate estimate of the tag-bearing proportion passing through marine commercial fisheries; accurate estimates of commercial harvest of Kenai River-bound coho salmon were therefore not possible. However, a point estimate of the overall tagged proportion of the return ( =0.172; SE( )=0.008; =5.8; SE( )=0.259) was generated from a subset of inriver data, as were estimates of the potential minimum ( =0.164; SE( )=0.008; =6.1; SE( )=0.290) and maximum ( =0.246; SE( )=0.0280; =4.1; SE( )=0.486). Three resulting sets of harvest estimates were compared to evaluate the practical impact of the temporal variation on commercial harvest estimates. The evaluation indicated that harvest estimates based on the overall tagged proportion are practical for general research, assessment, and planning purposes, but must be qualified by the evaluation for addressing allocation issues. A total of 2,475 coho salmon were captured within the Kenai River by fish wheels in 2003 and examined for adipose finclips and 428 were found with an adipose finclip. Of these, 422 were estimated as bearing a Kenai River coded wire tag and six with no tag, resulting in an overall estimated tagged proportion of 0.172. Based on this subset of inriver data, a qualified estimate of 2,122 (SE = 252) coho salmon of Kenai River origin were harvested by the Central District eastside set gillnet fishery, 330 (SE = 65) by the Central District drift gillnet fishery, and 126 (SE = 39) by all Northern District set gillnet fisheries for a total of 2,578 (SE = 263). Qualified harvest estimates represented 21% of the total eastside set gillnet harvest of coho salmon, 0.6% of the drift gillnet harvest, and 0.5% of the Northern District set gillnet harvest. Based on the number of live smolt released with an adipose finclip at the Moose River in 2002 (108,520), the number of adult coho salmon examined for adipose fin status in the Kenai River fish wheel samples in 2003 (2,475), and the number of adults in the sample that had an adipose finclip (428), an estimated 626,335 (SE = 27,409) smolt emigrated from the Kenai River in 2002.
Keywords: coho salmon, Oncorhynchus kisutch, population assessment, sustained yield, contribution, commercial harvest, coded wire tag, Kenai River, smolt abundance, wild, fresh water, marine.