Age and Length Composition of Columbia Basin Chinook, Sockeye, and Coho Salmon at Bonneville Dam in 1998

AUTHORS:	Rian C. Hooff  |  Jeff Fryer  |  John Netto
PUBLICATION DATE:	31 March 1999
REPORT #:	99-3

ABSTRACT:
Representative samples of adult 1998 Columbia Basin chinook (spring, summer, and fall) sockeye, and coho salmon populations were collected at Bonneville Dam. This was the twelfth year spring chinook salmon, the ninth year summer chinook salmon, and the fourteenth year sockeye salmon were sampled in this study. It was the first 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, five-year-old fish were estimated to comprise 46% of the spring chinook, 52% of the summer chinook, and 39% of the fall chinook salmon population. Four-year-old fish were estimated to comprise 50% of the spring chinook, 33% of the summer chinook, and 24% of the fall chinook population. Two-, three-, and six-year-old fish were estimated to comprise the remaining 4% of the spring chinook, 15% of the summer chinook and 36% of the fall chinook salmon population. The sockeye salmon population sampled at Bonneville was predominantly five-year-old fish (66%), and the coho population was almost entirely four-year-old fish (98%). Differences in age class returns over the past ten years were used to predict spring chinook population sizes for 1999.

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