Age and Length Composition of Columbia Basin Chinook and Sockeye Salmon and Steelhead at Bonneville Dam in 2005
In continuation of the Stock Assessment Project, the Columbia River Inter-Tribal Fish Commission (CRITFC) conducted a field study at Bonneville Dam in 2005 to assess the age, length-at-age and stock composition of adult Pacific salmon migrating up the Columbia River. These data were then used to predict the 2006 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 structure of Columbia Basin salmon populations. Based on scale pattern analysis four-year-olds (from the 2001 brood year [BY]) were the most abundant age group for all three races of Chinook salmon, comprising 74.2% of the spring Chinook migration, 57.6% of the summer Chinook migration, and 55.4% of the fall Chinook migration. Five-year-old fish (2000 BY) were second most abundant, comprising 15.7% of the spring Chinook, 31.7% of the summer Chinook, and 36.3% of the fall Chinook. Three-year-old fish (2002 BY) were third most abundant, comprising 5.6% of the spring Chinook migration, 7.7% of the summer Chinook migration, and 5.7% of the fall Chinook migration. The largest proportion of the sockeye salmon migration through Bonneville Dam was four-year-old fish 89.9%. The steelhead migration consisted of 33.4% four-year-old fish and 25.9% three-year-old fish. Based on fin marks for classification, the steelhead migration consisted of 86.9% hatchery- and 13.1% natural-origin steelhead. A-run steelhead, less than 78cm in length, comprised 70.1% of the steelhead run. B-run fish, equal to or greater than 78cm, comprised 29.9% of the run. A year-class regression over the past 17 years of data was used to predict spring, summer, and bright fall Chinook salmon population sizes for 2006. Based on three-year-old returns, the relationship predicts four-year-old returns of 75,700 (+/- 63,700, 90% predictive interval [PI]) spring Chinook, 13,200 (+/- 32,600, 90% PI) summer, and 80,700 (+/- 126,400, 90% PI) bright fall Chinook salmon for the 2006 runs. Based on four-year-old returns, the relationship predicts five-year-old returns of 23,900 (+/- 42,700, 90% PI) spring, 31,000 (+/- 8,500, 90% PI) summer, and 105,700 (+/- 48,500, 90% PI) bright fall Chinook salmon for the 2006 runs.
Whiteaker, J., J.K. Fryer, and J. Doyle. 2006. Age and Length Composition of Columbia Basin Chinook and Sockeye Salmon and Steelhead at Bonneville Dam in 2005. Columbia River Inter-Tribal Fish Commission Report Technical Report 06-02, Portland, Oregon. 47p.