Smolt production and harvest of coho salmon from the Situk River, 1992-1993

Description

We estimated the abundance and age composition of coho salmon Oncorhynchus kisutch smolt leaving the Situk River in 1992 and estimated their harvest as returning adults in marine fisheries in 1993. Smolt abundance was estimated using two separate mark-recapture experiments; these two methods yielded very different estimates of abundance. In the first experiment to estimate smolt, two 8-ft-diameter rotary screw traps were fished on the upper and lower Situk River during spring 1992. Eighteen thousand eight hundred eleven (18,811) emigrating smolt were captured at the upper trap, marked with a shallow caudal finclip, and released. At the lower trap, 22,659 smolt were captured and inspected for marks, and 766 finclipped fish were recaptured. Because complete mixing did not occur between sampling events, a Darroch estimator was used to estimate abundance at 612,034 (SE = 43,927) coho salmon smolt leaving the Situk River in 1992. In a second experiment, 37,656 smolt that had been captured in both traps and marked with coded wire tags/adipose finclips in 1992 were used as the marked event. In 1993, 1,239 adults were sampled in the Situk River, and, of these, 38 fish were missing adipose fins. Chapmans modification of the Petersen method was used to estimate that 1,197,298 (SE = 186,212) coho salmon smolt emigrated from the Situk River in 1992. We examined potential biases in each method and concluded that the smolt/adult method provided the best estimate of abundance. The estimate of smolt age composition was stratified by three seasonal periods to account for differing sample rates over the different strata. The age composition of smolt was 68.3% (SE = 2.6%) age 1.0, 28.6% (SE = 2.5%) age 2.0, and 3.2% (SE = 1.1%) age 3.0. The harvest of Situk River coho salmon was estimated through recoveries of coded wire tags in marine fisheries. We estimated that 49,800 (SE = 4,269) Situk River coho salmon were harvested in commercial, sport, and subsistence fisheries during 1993. Most (62.1%) of the harvest was taken in the commercial set gillnet fishery in the Situk-Ahrnklin Lagoon. The commercial troll fishery in the Northwest Quadrant and the Situk River sport fishery took 25.1% and 3.7%, respectively, of the estimated harvest. The remainder of the harvest occurred in the subsistence fishery off the mouth of the river (0.6%), Prince William Sound gillnet fisheries (2.9%), and other Yakutat gillnet fisheries (5.6%).

Subjects

Series Statement

• Fishery data series -- no. 97-26.

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