Situk River steelhead trout studies, 1994

Description

The Situk River produces the largest run of steelhead Oncorhynchus mykis in Southeast Alaska. Steelhead were counted and sampled at a weir as they emigrated from the river and counted above the weir by boat. Counts of spawning steelhead obtained with float surveys were compared to counts of steelhead obtained at the weir. In another study, we measured the time it took emigrating steelhead to transit the Situk/Ahrnklin River estuary - information useful in reducing the incidental harvest of steelhead in commercial setnet salmon fisheries. Between May 21 and July 20, 1994, 7,854 steelhead were counted at a weir as they emigrated from the Situk River and 907 were captured and sampled for age and length.. Seventy four percent of the fish were from the 1987 and 1988 parent years and 51% were repeat spawners. Of the sampled fish, 5.8% were > 36 inches total length and by expansion, 459 (SE=58) fish (based on the emigrant count) were available for harvest under current regulations. Eleven float surveys were conducted to count steelhead and a maximum count of 4,702 steelhead was obtained on May 21. This count was 60% of the number of fish subsequently counted at the Situk River weir. In separate trials in 1992 and 1994, a total of nineteen steelhead implanted with sonic transmitters were tracked as they transited the Situk/Arhnklin River estuary, the site of a commercial set net fishery. Twelve of the 19 steelhead exited the estuary within twelve hours of passing downstream through the Situk River weir. These fish took an average of 13.7 hrs. (SE = 3.1, range = 2.75 to 53.75 hours) to pass from the weir through the estuary. All fish tracked or automatically recorded, emigrated from the estuary during an ebb tide, with 74% leaving within 3 hours following the onset of an ebb tide between midnight and 0600 hours. When high rates of steelhead emigration coincide with commercial fishery set net openings, incidental harvest of emigrating steelhead can be significantly reduced. According to findings on estuarine transit times, detaining steelhead above the weir and/or curtailing the set net fishery during the first three hours of the ebb tides between midnight and 0600 hours would be effective in reducing incidental harvest of steelhead.

Subjects

Series Statement

• Fishery data series -- no. 96-1.

Links

• URL