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Fish FISH DIVISION
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Evaluation of Fall Chinook and Chum Salmon Spawning Below Bonneville Dam

chumPacific salmon stocks have declined dramatically over the past century due to a variety of human impacts. Historically, runs of chum salmon in the Columbia River numbered over one million fish. They had the widest distribution of Pacific salmon and comprised up to 50% of the biomass of returning spawners. Despite restoration efforts, chum salmon populations have remained depressed for the past several decades, and were listed as a threatened species in 1999. Conversely, late-spawning bright fall Chinook salmon populations have remained relatively healthy. In recent years, agencies documented extensive spawning of both species in areas directly downstream from Columbia River dams.

The Oregon Department of Fish and Wildlife takes part in a multi-agency project involved with research and monitoring of fall Chinook and chum salmon spawning in the mainstem Columbia River below Bonneville, The Dalles, John Day and McNary dams. Our role is to monitor adult spawning and juvenile rearing of these fish below Bonneville Dam.

Adult surveys are carried out in the fall and juvenile surveys in the spring of the following year. We document spawning below Bonneville Dam along the shorelines of Pierce and Ives islands, and the shorelines of the Columbia River adjacent to the islands. We estimate the date of peak spawning activity, run timing, residence time of spawning adults, and the number of spawning fish. We collect biological samples from carcasses to describe vital statistics such as age, size, and gender. We also count and map Chinook and chum salmon redds to identify important habitat and provide real-time updates of spawning activity. This ensures that hydrosystem operations can be managed to protect these fish during spawning, incubation, hatching, and rearing. In the spring we seine for juvenile fish to corroborate emergence timing estimates, provide relative density estimates, and describe rearing and outmigration.

In spring 2001 we began using coded-wire tags (CWT) to mark juvenile fall Chinook salmon produced in the study area. These tags are recovered in salmon fisheries or from carcasses retrieved from the spawning grounds, allowing us to estimate survival to adulthood. Except for 2002, we have tagged more than 10,000 fish each year, including more than 30,000 in 2005. In fall 2005 we recovered the first returning adults that we tagged as juveniles. Three were caught in ocean troll fisheries off of Alaska and Canada and six were collected in the Columbia River. Of those returning to the Columbia, four were caught in sport and commercial fisheries and two were collected on the spawning grounds. Survival estimates are pending.

The Columbia River directly below Bonneville Dam provides important spawning and rearing habitat for threatened chum salmon, and fall Chinook salmon produced in this area contribute to several important fisheries. We plan to continue our monitoring activities, and address additional topics, such as quantifying the production of juvenile chum salmon.

The Fall chinook and chum project is funded by the Bonneville Power Administration. The project leader is Tom Friesen.

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