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Emigration and Survival of Hatchery-Reared Coho Salmon Released as Parr and Smolts in a Reintroduction Program

Bill Bosch, Shubha Pandit, Todd Newsome, Andrew Matala, Chris Frederiksen, Zack Mays, David Lind, Mark Johnston

Yakama Nation, 760 Pence Road, Yakima, WA 98908

Many hatchery programs and operations are being reformed and modernized to better serve conservation and harvest purposes. Releasing fish at varied life stages has the potential to increase the number and diversity of returning adults. Since the mid-1990s, Columbia River tribes have been working to reintroduce extirpated populations of Coho Salmon to areas upstream of McNary Dam. In the Yakima River Basin, this effort has included the release of hatchery-origin fish at both the parr and smolt life stages. In this study, we evaluated releases of parr and smolts that were tagged with passive integrated transponders over eleven brood years. We assessed emigration timing, fish survival (juvenile emigration, release-to-adult, smolt-to-adult return), and age-at-return for the two release groups. Emigrating juveniles that were released as smolts had higher survival and arrived to McNary and Bonneville Dams 6 to 15 days earlier than fish released as parr. Survival from Yakima Basin release locations to adult return to Bonneville Dam did not significantly differ for the two release groups. However, we observed a difference in apparent marine survival as fish released as parr had mean juvenile to adult return rates (evaluated at Bonneville Dam) greater than that of fish released as smolts. Parr releases also tended to return at older age (greater proportion of age-3 returns) than did smolt releases. Our results indicate that, while smolt releases have several advantages, implementing practices to reduce homogenization of hatchery releases may produce survival and diversity benefits as fish mature to later life stages. Given the rapid ecosystem changes Pacific Salmon are experiencing throughout their life cycles, varied release strategies may have increasing utility and import.