The Effect of Hatchery Spawning Protocols on Coho Salmon Return Timing in the Cowlitz River, Washington

Abstract We compared the pre- and posthatchery return times of adult coho salmon Oncorhynchus kisutch on the Cowlitz River, Washington, after 30 years of hatchery operation. In addition, at the Cowlitz Salmon Hatchery in fall 1998, 1999, and 2000, we differentially tagged juveniles for release in 1999, 2000, and 2001 that were produced from broodstock originating from early (August to mid-October), middle (mid-October through November), and late (December and thereafter) time arrival windows to determine the fidelity of adult return time distribution to the window of origin. We found that posthatchery mean and median coho salmon adult return times were delayed about 2 weeks compared with prehatchery conditions, that October–November returns increased from 46% to 81% after hatchery operation, that a mean of 57% of 3-year-old adult fish returned in the return time window of origin, and that many of the early- and late-origin fish returned in the middle time period. A mean of 70.4% of 2-year-old jacks from all releases returned in the middle return window. Much of the increase in October–November returns was probably due to a hatchery production emphasis of the middle-returning fish. We recommend that broodstock be accumulated at historically proportional rates with respect to run timing, which may require additional adult holding ponds at the hatchery.