|
Authors
Denise A. Kelsey
Jeffrey Fryer
Report Reference
#02-1
Publication Date
31 Jan 2002
|
 |
Age and Length Composition of Columbia Basin Chinook, Sockeye, and Coho Salmon
at Bonneville Dam in 2001
Abstract |
| In 2001, representative samples of adult Columbia Basin chinook
(Oncorhynchus tshawytscha), sockeye (O. nerka), and coho salmon
(O. kisutch) populations at Bonneville Dam were collected. Fish were
trapped, anesthetized, sampled for scales and biological data, revived,
and then released adult migrating salmonids. 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 analysis
of chinook salmon, fouryear- old fish (from brood year [BY] 1997) comprised
88% of the spring chinook, 67% of the summer chinook, and 42% of the Bright
fall chinook salmon population. Five-year-old fish (BY 1996) comprised 9%
of the spring chinook, 14% of the summer chinook, and 9% of the fall chinook
salmon population. The sockeye salmon population at Bonneville was predominantly
four-year-old fish (81%), with 18% returning as five-year-olds in 2001.
The coho salmon population was 96% three-year-old fish (Age 1.1). Length
analysis of the 2001 returns indicated that chinook salmon with a stream-type
life history are larger (mean length) than the chinook salmon with an ocean-type
life history. Trends in mean length over the sampling period for returning
2001 chinook salmon were analyzed. Chinook salmon of age classes 0.2 and
1.3 show a significant increase in mean length over time. Age classes 0.1,
0.3, 0.4, 1.1, 1.2, and 1.4 show no significant change over time. A year
class regression over the past 12 years of data was used to predict spring,
summer, and Bright fall chinook salmon population sizes for 2002. Based
on three-year-old returns, the relationship predicts four-year-old returns
of 132,600 (±46,300, 90% predictive interval [PI]) spring chinook and 44,200
(±11,700, 90% PI) summer chinook salmon for the 2002 runs. Based on four-year-old
returns, the relationship predicts five-year-old returns of 87,800 (±54,500,
90% PI) spring, 33,500 (±11,500, 90% PI) summer, and 77,100 (±25,800,
90% PI) Bright fall chinook salmon for the 2002 runs. The 2002 run size
predictions should be used with caution; some of these predictions are well
beyond the range of previously observed data. |
|
|
(580 kB)