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Scientific Report

Age and Length Composition of Columbia Basin Chinook, Sockeye, and Coho Salmon at Bonneville Dam in 2003

Abstract

In continuation of the Stock Assessment Project, the Columbia River Inter-Tribal Fish Commission (CRITFC) conducted a field study at Bonneville Dam in 2003 to assess the age, length-at-age and stock composition of Pacific salmon migrating up the Columbia River, and to predict the 2004 Chinook salmon run. Adult spring, summer and fall Chinook salmon (Oncorhynchus tshawytscha), sockeye salmon (O. nerka) and coho salmon (O. kisutch) were randomly collected, sampled for scales and additional biological data, revived and released. Caudal fin clips were also taken from Chinook salmon 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 analysis of Chinook salmon, five-year-old fish (from brood year [BY] 1998) comprised 53.9% of the spring Chinook, 50.5% of the summer Chinook, and 26.9% of the bright fall Chinook salmon migration. Fouryear- old fish (BY 1999) comprised 38.5% of the spring Chinook, 32.5% of the summer Chinook, and 60.4% of the bright fall Chinook salmon migration. The largest proportion of the sockeye salmon migration through Bonneville Dam was four-year-old fish (38.4%). The coho salmon migration consisted of 93.1% three-year-old fish. A year-class regression over the past 14 years of data was used to predict spring, summer, and bright fall Chinook salmon population sizes for 2004. Based on three-year-old returns, the relationship predicts four-year-old returns of 191,300 (+ 67,400, 90% predictive interval [PI]) spring Chinook, 60,400 (+ 23,400, 90% PI) summer, and 98,200 (+ 149,400, 90% PI) bright fall Chinook salmon for the 2004 runs. Based on four-yearold returns, the relationship predicts five-year-old returns of 25,600 (+ 44,100, 90% PI) spring, 38,400 (+ 7,000, 90% PI) summer, and 182,900 (+ 89,600, 90% PI) bright fall Chinook salmon for the 2004 runs. The 2004 run size predictions should be used with caution; some of these predictions are well beyond the range of previously observed data.

Authors

Citation

Donette, M.P., J. Whiteaker, and J. K. Fryer. 2004. Age and Length Composition of Columbia Basin Chinook, Sockeye, and Coho Salmon at Bonneville Dam in 2003. Columbia River Inter-Tribal Fish Commission Report reference #04-02, Portland, Oregon.

Date

Mar 31st, 2004

Report No.

04-02

Media Type

CRITFC Technical Report

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