|Beamish, R.; Neville, C.; Riddell, B.
|Gulf of Alaska
|ocean winter habitat, scale annulus
Relevance of the Catches of Steelhead in the Study of the Ocean Ecology of Pacific Salmon in the Gulf of Alaska in the Winter of 2022
There were 57 steelhead caught in a study of the winter ecology of Pacific salmon in the Gulf of Alaska from February 25 to March 25, 2022. The study used experimental gillnets and baited longlines to capture Pacific salmon with steelhead only captured in gillnets. Steelhead catches were the largest of all Pacific salmon catches with most steelhead caught in the top 4 m of the gillnet that was set at the surface and all steelhead were caught in the top 6 m. These catches and a review of published studies indicated that steelhead spend virtually all of their life in the open ocean in the surface few meters. There were 34 ocean age 1 and 21 ocean age 2 steelhead with 9 of these fish mature. DNA identification of these mature steelhead indicated they were returning to the Columbia River, Puget Sound, West Coast of Vancouver Island and the Nass River area. These fish would arrive in rivers after the calendar winter and would be expected to spawn quickly. There were 45 other fish identified to their spawning location using DNA, but the spawning location assignments of all steelhead are tentative because of the limited baseline data base. There were no ocean age 2 fish that had a second annulus and 16 of 33 ocean age 1 fish had an annulus. The circuli on the scales of ocean age 1 fish that formed after the annulus ranged from 2 to 7 indicating that annuli on the scales of all steelhead form over a protracted period. Steelhead were caught at some stations where surface temperatures exceeded the upper thermal limit published for steelhead in the winter. The inherited requirement to live at the ocean surface and the continued ocean warming that includes recent marine heat events, identify the urgent need to better understand the ocean ecology of steelhead, particularly in the winter.