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Age and Length Composition of Columbia Basin Chinook and Sockeye Salmon and Steelhead at Bonneville Dam in 2004

Mar 31, 2005


In continuation of the Stock Assessment Project, the Columbia River Inter-Tribal Fish Commission (CRITFC) conducted a field study at Bonneville Dam in 2004 to assess the age, length-at-age and stock composition of adult Pacific salmon migrating up the Columbia River, and to predict the 2005 Chinook Salmon run. Adult spring, summer and fall Chinook Salmon (Oncorhynchus tshawytscha), Sockeye Salmon (O. nerka) and summer-run steelhead (O. mykiss) were randomly collected, sampled for scales and additional biological data, revived and released. Caudal fin clips were also taken from Chinook Salmon and steelhead for later genetic analysis. Scales were examined to estimate age composition; the results contributed to an ongoing database for age class structure of Columbia Basin salmon populations. Based on scale pattern analysis of Chinook Salmon, five-year-old fish (from brood year [BY] 1999) comprised 6.0% of the spring Chinook, 46.4% of the summer Chinook, and 39.2% of the bright fall Chinook Salmon migration. Four-year-old fish (BY 2000) comprised 88.7% of the spring Chinook, 31.0% of the summer Chinook, and 24.7% of the bright fall Chinook Salmon migration. Three-year-old fish (BY 2001) comprised 5.1% of the spring Chinook, 17.0% of the summer Chinook and 32.6% of the bright fall Chinook. The largest proportion of the Sockeye Salmon migration through Bonneville Dam was four-year-old fish (97.7%). The steelhead migration consisted of 40.7% four-year-old fish and 39.7% three-year-old fish. Based on the combination of scale pattern analysis and fin marks for classification, the steelhead migration consisted of 74.1% hatchery and 25.9% wild steelhead. A-run steelhead, less than 78cm in length, comprised 87.3% of the steelhead run. B-run fish, equal to or greater than 78cm, comprised 12.7% of the run. The steelhead run consisted of 59.7% females and 40.3% males. A year-class regression over the past 16 years of data was used to predict spring, summer, and bright fall Chinook Salmon population sizes for 2005. The 2005 run size predictions should be used with caution; some of these predictions are beyond the range of previously observed data.



Donette, M.P., J. Whiteaker, and J. K. Fryer. 2005. Age and length composition of Columbia Basin Chinook, Sockeye, and Coho salmon at Bonneville Dam in 2004. Columbia River Inter-Tribal Fish Commission Technical Report 05-3. Portland, OR. 48p.



Report No.


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CRITFC Technical Report