Identification of Columbia Basin Sockeye Salmon Stocks in 2005
In 2005, samples of adult Columbia Basin Sockeye Salmon Oncorhynchus nerka were collected at Bonneville Dam on the Columbia River as well as at Tumwater Dam on the Wenatchee River, and Wells Dam in the mid-Columbia River downstream of the Okanogan River. Tumwater and Wells dams were chosen to provide samples of Sockeye Salmon from the two principal stocks of Columbia Basin Sockeye Salmon, which originate from the Wenatchee and Okanogan basins. Age composition was estimated from the sampled Sockeye Salmon passing the three dams. Four-year-old fish were estimated to comprise 89% of the mixed-stock Sockeye Salmon migrating past Bonneville Dam, 89% of the Okanogan stock migrating past Wells Dam, and 78% of the Wenatchee stock migrating past Tumwater Dam. Five-year-old fish were estimated to comprise 8% of the Bonneville Dam mixed-stock, 6% of the Okanogan stock, and 22% of the Wenatchee stock. Three-year-old fish were estimated to comprise 1% of the Bonneville Dam mixed-stock, 1% of the Okanogan stock and none of the Wenatchee stock. Scale pattern analysis techniques were used to estimate that 32% of the Sockeye Salmon passing Bonneville Dam were of Okanogan origin, 61% were of Wenatchee stock, with the remaining 7% of unknown origin. This estimate differed substantially from that derived from fish counts at mainstem dams of 78% Okanogan and 22% Wenatchee stock. Low known-stock classification accuracy (66%) due to the similarity of scale patterns on Okanogan and Wenatchee Age 1.2 Sockeye Salmon is likely responsible for this difference.
Fryer, J.K. 2006. Identification of Columbia Basin Sockeye Salmon stocks in 2005. Columbia River Inter-Tribal Fish Commission Technical Report 06-4. Portland, OR. 33p.