Adult Return of Fingerling Coho Salmon Outplanted in the Upper Elwha River

摘要

Fingerling Elwha coho salmon were coded-wire-tagged and outplanted above the Elwha dams to evaluate adult return. This work was undertaken to evaluated outplanting strategies for restoring coho to the upper Elwha River. Adults survival was compared to Elhwa hatchery production and to pre-smolt outplanting conducted elsewhere. In these comparisons, survival data from previous Elwha fish studies were used to estimate the outplant's passage loss through the Elwha dams and its smolt-to-adult survival. Estimated fingerling-to-adult survival of the outplant ranges from 0.71% to 0.87%, which is higher than values reported from Washington Coast, but lower than values reported from Puget Sound. Estimated smolt-to-adult survival of the outplant ranged from 2.16% to 2.61%, which compared favorably to Elwha hatchery smolt-to-adult survival from the same brood (2.40%) and nine other broods (mean=1.36%, range=0.17% to 3.23%). Several factors suggested that adult survival of the outplant was underestimated, however. Catch distribution of the outplant was not significantly different than that of tagged hatchery production of the same brood, but 29% fewer rack recoveries were observed (compared to tagged hatchery production of the same brood). Adult lengths of the outplant were similar to Elwha River hatchery production.