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Identification
of Columbia Basin Sockeye Salmon Stocks in 2004
Abstract |
| 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. |
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