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Division: Sport Fish
Title: Assessment of coho salmon from the Kenai River, Alaska, 2005.
Author: Massengill, R.
Year: 2007
Report ID: Alaska Department of Fish and Game, Fishery Data Series No. 07-91, Anchorage.
Abstract: Wild coho salmon Oncorhynchus kisutch smolt were captured in the Kenai River drainage in spring 2004, marked with an adipose finclip and injected with a coded wire tag (CWT). These were recovered as adults in 2005 from selected commercial fisheries in Upper Cook Inlet (UCI), Alaska, and from within the Kenai River drainage. There were 224,657 coho salmon harvested among all UCI commercial fisheries and 47,132 (21%) were examined for marks. There were 7,548 fish examined that could not be assigned to a fishery strata and were excluded from commercial harvest calculations. There were 269 adipose finclipped fish observed, 268 were recovered, 216 had a readable CWT, and 65 were from the Kenai River drainage. Temporal variation in the tagged proportion of returning adults sampled inriver precluded an accurate estimate of the commercial harvest of Kenai River-bound coho salmon. However, minimum, maximum, and overall 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 assessment and planning purposes, but must be qualified for addressing allocation issues. In 2005, 432 of 5,517 adult coho salmon captured in the Kenai River by fish wheels and examined were missing an adipose fin. Kenai River CWTs were found in 431 of these, resulting in an overall tagged proportion estimate of 0.078. Based on this proportion, a qualified estimate of 3,310 (SE = 681) coho salmon of Kenai River origin were harvested by the Central District eastside set gillnet fishery; 1,533 (SE = 617) by the Central District drift gillnet fishery; and 176 (SE = 51) by the Northern District eastside set gillnet fishery for a total of 5,019 (SE = 921). Qualified harvest estimates represented 17.0% of the total eastside set gillnet coho salmon harvest, 1.1% of the drift gillnet harvest, and 1.6% of the Northern District eastside set gillnet harvest. There were 83,674 live coho salmon smolt released with an adipose finclip at the Moose River in 2004. Based on the number of returning adults (5,517) from this cohort examined from the Kenai River in 2005 and the number missing an adipose fin (432), there were an estimated 1,066,324 (SE = 49,009) coho salmon smolt that emigrated from the Kenai River in 2004. An index of inriver adult Kenai River coho salmon abundance was developed using natural-log transformed fish wheel CPUE to periodically predict end-of-season abundance arriving at river kilometer 45. The index was classified into one of three levels (<50,000 [low], >50,000 and <120,000 [medium], >120,000 [high]). The final end-of-season log-transformed cumulative CPUE value for the period from August 1 through September 30, 2005, was 5.46 and classified as “medium” which was consistent with the inseason predictions.
Keywords: coho salmon, Oncorhynchus kisutch, population assessment, sustained yield, fish wheel, adult abundance, index, contribution, commercial harvest, coded wire tag, Kenai River, smolt abundance, wild.