Age and Length Composition of Columbia Basin Chinook and Sockeye Salmon and Steelhead at Bonneville Dam in 2007
The Columbia River Inter-Tribal Fish Commission conducted a field study at Bonneville Dam in 2007 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 2008 Chinook salmon run. Adult spring, summer and fall Chinook salmon (Oncorhynchus tshawytscha), sockeye salmon (O. nerka) and summer-run steelhead (O. mykiss) were 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 runs. Based on scale pattern analysis four-year-olds were the most abundant age group for both spring and fall Chinook salmon comprising 52.4% and 46.2% of their respective runs. Three-year-olds were the most abundant age class for summer Chinook making up 37.4% of the run. Three-year-olds were also the most abundant age group for sockeye salmon and steelhead comprising 39.9% and 59% of their respective runs. Based on fin marks for classification, the steelhead migration consisted of 81.9% hatchery- and 18.1% natural-origin steelhead. A-run steelhead, less than 78cm in length, comprised 88.9% of the steelhead run. B-run fish, equal to or greater than 78cm, comprised 11.1% of the run.
A year-class regression based on up to 20 years of data was used to predict spring, summer, and bright fall Chinook salmon population sizes for 2008. Based on three-year-old returns, the relationship predicts four-year-old returns of 251,100 (+/- 65,700, 90% predictive interval [PI]) spring Chinook, 58,300 (+/- 26,300, 90% PI) summer, and 90,000 (+/- 98,800, 90% PI) bright fall Chinook salmon for the 2008 runs. Based on four-year-old returns, the relationship predicts five-year-old returns of 16,300 (+/- 41,000, 90% PI) spring, 11,600 (+/- 9,000, 90% PI) summer, and 52,500 (+/- 41,300, 90% PI) bright fall Chinook salmon for the 2008 runs.
Whiteaker, J. and J.K. Fryer. 2008. Age and Length Composition of Columbia Basin Chinook and Sockeye Salmon and Steelhead at Bonneville Dam in 2008. Columbia River Inter-Tribal Fish Commission Report 08-04. 45p.