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Age and Length Composition of Columbia Basin Chinook, Sockeye, and Coho Salmon at Bonneville Dam in 1999

Dec 14, 1999


Representative samples of adult 1999 Columbia Basin Chinook (spring, summer, and fall), Sockeye, and Coho Salmon populations were collected at Bonneville Dam. This was the thirteenth year spring Chinook Salmon, the tenth year summer Chinook Salmon, and the fifteenth year Sockeye Salmon were sampled in this study. It was the second year for sampling fall Chinook and Coho. Fish were trapped, anesthetized, sampled for scales and biological data, allowed to revive, and then released. The scales were examined to estimate age composition. The results of this project contribute to an ongoing database collection of Columbia Basin salmonid populations age class structure.

Based on scale analysis, four-year-old fish (from brood year 1995) were estimated to comprise 70% of the spring Chinook, 39% of the summer Chinook, and 62% of the fall Chinook Salmon population. Five-year-old fish (BY 1994) were estimated to comprise 7% of the spring Chinook, 37% of the summer Chinook, and 8% of the fall Chinook population. Three-year-old fish were estimated to comprise 23% of the spring Chinook, 21% of the summer Chinook and 28% of the fall Chinook Salmon population. Two and six-year-olds accounted for the remaining 1% of spring Chinook, 3% of summer Chinook, and 2% of the fall Chinook runs. The Sockeye Salmon population sampled at Bonneville was predominantly four-year-old fish (83%), and the Coho population was entirely three-year-old fish (age 1.1).

Differences in age class returns over the past ten years were used to predict spring and summer Chinook population sizes for 2000. Based on a regression with three-year-old returns, the relationship predicts four-year-old returns of 95,800 spring Chinook and 14,900 summer Chinook.



Hooff, R.C., A. Ritchie, J. Fryer, and J. Whiteaker. 1999. Age and length composition of Columbia Basin Chinook, Sockeye, and Coho Salmon at Bonneville Dam in 1999. Columbia River Inter-Tribal Fish Commission Technical Report 99-4. Portland, OR. 45p.



Report No.


Media Type

CRITFC Technical Report