Effect of Juvenile Length on Chinook Salmon Survivals at Four Hatcheries in Washington State

Abstract In 3 years at four Washington State hatcheries, a total of 10 groups of juvenile Chinook salmon Oncorhynchus tshawytscha were length-sorted and coded-wire-tagged before release via the AutoFish System (Northwest Marine Technology, Shaw Island, Washington). After tagging, the length-groups were combined at each hatchery and reared through spring release. The release groups comprised (1) lower Columbia River yearling spring Chinook salmon (four releases), (2) lower Columbia River fall Chinook salmon subyearlings (three releases), (3) mid-Columbia River fall Chinook salmon subyearlings (two releases), and (4) Puget Sound summer Chinook salmon subyearlings (one release). In three releases, large juveniles at tagging produced significantly more jack returns (recovered at the hatchery or on spawning grounds in the year of release or the following year) than did small juveniles, while in one release mid-sized and small juveniles each produced significantly more jack returns. In 7 of 10 releases, larger juveniles produced significantly more adult returns than smaller fish; there was no significant difference in 3 releases. If the smaller fish can be partitioned out and growth-accelerated as juveniles, and if they subsequently survive to adulthood at the same rate as their larger cohorts, there is potential to increase adult survival by about 33% at little additional cost. Received May 18, 2010; accepted September 22, 2010