Two year-olds, mostly jacks (males) and a few jills (females), typically make up only a small proportion of the spawning run for all four races of Chinook in the Valley. I have heard that two year-olds are commonly found in higher proportions in the Klamath Basin, but I don't have much experience with the Klamath....
Most of the Chinook age reconstruction in the Central Valley comes from coded wire tag recoveries. Coded wire tags are essentially a hatchery salmon's birth certificate. They age a salmon with certainty. Most of the coded wire tagged hatchery Chinook in the Central Valley come back at three to four years of age....
However, (there are few holes for round pegs in fisheries science!) the last two years there have been unusually high numbers of two year old salmon returning to the hatcheries. Go figure? This has been verified through coded wire tag analysis.
Age analysis of naturally produced Chinook in the Central Valley is currently in active data collection and analysis mode and is based on scale reading. I am unaware of any results so far....
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