Identification of Columbia Basin Sockeye Salmon Stocks in 2004
In 2004, samples of adult Columbia Basin sockeye salmon, Oncorhynchus nerka, were collected at Bonneville Dam 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 principle 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 98% of the mixed-stock sockeye salmon migrating past Bonneville Dam, 95% of the Okanogan stock migrating past Wells Dam, and 98% of the Wenatchee stock migrating past Tumwater Dam. Three-year-old fish were estimated to comprise 1% of the Bonneville Dam mixed-stock, 2% of the Okanogan stock and none of the Wenatchee stock. Five-year-old fish were estimated to comprise 1% of the Bonneville Dam mixed-stock, 3% of the Okanogan stock, and 2% of the Wenatchee stock. Scale pattern analysis techniques were used to estimate that 94% of the sockeye salmon passing Bonneville Dam were of Okanogan origin, 5% were of Wenatchee stock, with the remaining 1% of unknown origin. This estimate differed from that derived from fish counts at mainstem dams of 77% Okanogan and 23% Wenatchee stock. Additional scales were measured to investigate the reasons for this difference and it was concluded that it was concluded that low known-stock classification accuracy (73%) is likely responsible.
Fryer, J. 2005. Identification of Columbia Basin Sockeye Salmon Stocks in 2004. Columbia River Inter-Tribal Fish Commission Report reference #05-02, Portland, Oregon.