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Age and Length Composition of Columbia Basin Chinook, Sockeye, and Coho
Salmon at Bonneville Dam in 2004
Abstract |
| In continuation of the Stock Assessment Project, the
Columbia River Inter-Tribal Fish Commission (CRITFC) conducted a field
study at Bonneville Dam in 2004 to assess the age, length-at-age and
stock composition of adult Pacific salmon migrating up the Columbia
River, and to predict the 2005 Chinook salmon run. Adult spring, summer
and fall Chinook salmon (Oncorhynchus tshawytscha), sockeye
salmon (O. nerka) and summer-run steelhead (O. mykiss)
were randomly 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 class structure of Columbia Basin salmon
populations. Based on scale pattern analysis of Chinook salmon, five-year-old
fish (from brood year [BY] 1999) comprised 6.0% of the spring Chinook,
46.4% of the summer Chinook, and 39.2% of the bright fall Chinook
salmon migration. Four-year-old fish (BY 2000) comprised 88.7% of
the spring Chinook, 31.0% of the summer Chinook, and 24.7% of the
bright fall Chinook salmon migration. Three-year-old fish (BY 2001)
comprised 5.1% of the spring Chinook, 17.0% of the summer Chinook
and 32.6% of the bright fall Chinook. The largest proportion of the
sockeye salmon migration through Bonneville Dam was four-year-old
fish (97.7%). The steelhead migration consisted of 40.7% four-year-old
fish and 39.7% three-year-old fish. Based on the combination of scale
pattern analysis and fin marks for classification, the steelhead migration
consisted of 74.1% hatchery and 25.9% wild steelhead. A-run steelhead,
less than 78cm in length, comprised 87.3% of the steelhead run. B-run
fish, equal to or greater than 78cm, comprised 12.7% of the run. The
steelhead run consisted of 59.7% females and 40.3% males. A year-class
regression over the past 16 years of data was used to predict spring,
summer, and bright fall Chinook salmon population sizes for 2005.
Based on three-year-old returns, the relationship predicts four-year-old
returns 118,000 (± 63,700, 90% predictive interval [PI]) spring
Chinook, 58,200 (± 26,200, 90% PI) summer, and 256,500 (±
147,600, 90% PI) bright fall Chinook salmon for the 2005 runs. Based
on four-year-old returns, the relationship predicts five-year-old
returns of 39,000 (± 43,700, 90% PI) spring, 31,400 (±
8,200, 90% PI) summer, and 57,400 (± 45,400, 90% PI) bright
fall Chinook salmon for the 2005 runs. The 2005 run size predictions
should be used with caution; some of these predictions are beyond
the range of previously observed data. |
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