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Age
and Length Composition of Columbia Basin Chinook and Sockeye Salmon and
Steelhead at Bonneville Dam in 2006
Abstract |
The Columbia
River Inter-Tribal Fish Commission conducted a field study at Bonneville
Dam in 2006 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 2007 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 79.8% of the run. Five-year-olds
were the most abundant age class for summer and fall Chinook making
up 53.3% and 35.8% of their respective runs. Four-year-olds were the
most abundant age group for sockeye salmon comprising 65% of the run,
and three and four-year-old were the most abundant in steelhead comprising
39.7% and 35.4% respectively of the run. Based on fin marks for classification,
the steelhead migration consisted of 70% hatchery- and 30% natural-origin
steelhead. A-run steelhead, less than 78cm in length, comprised 71%
of the steelhead run. B-run fish, equal to or greater than 78cm, comprised
29% 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 2007. Based on three-year-old returns, the relationship
predicts four-year-old returns of 55,400 (±62,100, 90% predictive
interval [PI]) spring Chinook, 13,600 (±24,000, 90% PI) summer,
and 116,200 (±124,700, 90% PI) bright fall Chinook salmon for
the 2007 runs. Based on four-year-old returns, the relationship predicts
five-year-old returns of 13,700 (±49,800, 90% PI) spring, 21,700
(±9,200, 90% PI) summer, and 50,700 (±44,200, 90% PI)
bright fall Chinook salmon for the 2007 runs. |
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