Growth performance of Rainbow Trout in reservoir tributaries and implications for steelhead growth potential above Skagit River dams.

This article focuses on evaluating the freshwater growth potential of juvenile Rainbow Trout (Oncorhynchus mykiss) in tributaries above the impassable Gorge, Diablo, and Ross dams in the Skagit River basin, Washington, USA, as part of assessing the feasibility of introducing anadromous steelhead (anadromous Rainbow Trout) upstream of these dams. Using empirical data on fish size, diet, invertebrate prey availability, and stream temperature combined with bioenergetics modeling, the study found that growth of juvenile Rainbow Trout in eight of nine tributaries generally did not meet size thresholds associated with successful smolt survival observed in wild steelhead below the dams. Cooler thermal scenarios improved growth potential, but prey availability appeared to be the primary limiting factor for growth in these tributaries. These findings provide important context for managers considering steelhead introductions and highlight the need to address food resource limitations and consider alternative rearing habitats or strategies.