Age and Length Composition of Columbia Basin Chinook and Sockeye Salmon and Steelhead at Bonneville Dam in 2008
The Columbia River Inter-Tribal Fish Commission (CRITFC) conducted a field study at Bonneville Dam in 2008 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 2009 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 spring Chinook salmon comprising 75.1% of the run. Three-year-olds were the most abundant age class for fall Chinook and four-year-olds were the most abundant for the summer Chinook making up 50.9% and 58.6% of their respective runs. Four-year-olds were the most abundant age group for sockeye salmon comprising 89.1% of the run, and three and four-year-old were the most abundant in steelhead comprising 40.4% and 44.6% respectively of the run. Based on fin marks for classification, the steelhead migration consisted of 71.7% hatchery- and 28.3% natural-origin steelhead. A-run steelhead, less than 78cm in length, comprised 73% of the steelhead run. B-run fish, equal to or greater than 78cm, comprised 27% of the run.
A year-class regression based on up to 19 years of data was used to predict spring, summer, and bright fall Chinook salmon population sizes for 2009. Based on three-year-old returns, the relationship predicts four-year-old returns of 259,500 (+/- 88,200, 90% predictive interval [PI]) spring Chinook, 58,700 (+/- 24,700, 90% PI) summer, and 218,600 (+/- 67,200, 90% PI) bright fall Chinook salmon for the 2009 runs. Based on four-year-old returns, the relationship predicts five-year-old returns of 26,100 (+/- 38,900, 90% PI) spring 49,700 (+/- 9,300, 90% PI) summer, and 37,200 (+/- 46,000, 90% PI) bright fall Chinook salmon for the 2009 runs.
Torbek, C., J. Mainord, J. Whiteaker, and J.K. Fryer. 2009. 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 reference #09-05, Portland, Oregon.