Migration and Movement Patterns of Adult Chinook (Oncorhynchus tshawytscha) Above Wells Dam

To evaluate summer/fall Chinook (Oncorhynchus tshawytscha) migration and movement patterns as part of the planning process for the Colville Confederated Tribes’ planned Chief Joseph Hatchery, we radio tagged 291 adult Chinook that migrated above Wells Dam in 2005. The primary objectives of this study were to 1) identify whether the passage time of Chinook through the Wells Dam was related to spawning time and location, 2) if the proposed hatchery ladder was suitably placed to attract returning adults, and 3) identify areas where Chinook may be captured using selective fishing gears.

Both spawning location and spawning ground arrival date are related to passage date at Wells Dam but a relationship between spawning date and passage date at Wells was not observed. Earlier-arriving Chinook were more likely to migrate to the upper Okanogan and Similkameen rivers while later-arriving Chinook were more likely to migrate to the lower Okanogan River or remain in the mainstem Columbia River. Most radio tagged Chinook migrated up the Okanogan River when the temperature dropped below 20 degrees Celsius. However, there were tagged Chinook that migrated into the Okanogan River despite water temperatures of 20-25 degrees Celsius, temperatures typically considered lethal for salmonids. Data were collected so that in the future, genetic analysis can be used to further evaluate potential population differences.

Broodstock collection for the planned hatchery will use selective fishing methods. As a result, radio tag detections from fixed and mobile surveys were used to identify areas where fish aggregate. During 2005, suitable fishing gears were also identified. These gear/location combinations will be tested in the next two years for their ability to capture salmon with little harm and in good condition so that broodstock may be collected and species of concern, such as steelhead trout (O. mykiss) may be released with little harm.

Based on the results of this study, the ladder placement for the planned hatchery is suitable. Many Chinook hold at the base of Chief Joseph Dam and move back and forth between this area and the Colville Trout Hatchery, which is near the confluence of the Columbia and Okanogan Rivers. The proposed ladder position on the right side (north shore) of the Columbia River should draw in adults that hold in this area. Although 87.9% of the fish in this area spent time on both sides of the river, most fish (70.1%) were first detected on the right bank, indicating they moved into the area from the right bank (north shore) of the river. Further, although fish were found on both sides of the river throughout the study period, significantly more fish were found on the right bank. Once the hatchery is built and holds juvenile salmon, the ladder should provide additional incentive to adult Chinook as a chemical attractant.

Many radio tagged fish (41.8%) remained in the mainstem Columbia, indicating that deepwater spawning may be presently occurring in the area between Wells and Chief Joseph dams. Historic data describes spawning occurring in this area. As a result of this study, potential spawning areas have been identified for future investigation.