Fig. 1.

Illustration of steelhead run-timing and study design. Broodstock fish were first collected from the wild and spawned in captivity. The F1 offspring were reared in a hatchery until becoming juveniles; at that time, they were released into the wild near spawning grounds. F1 juveniles went out to sea and subsequently returned to spawn as adults in the wild. All returning adult fish were sampled at the Powerdale Dam en route to their spawning grounds. Broodstock reproductive success was measured as the number of returning adult F1 offspring assigned to broodstock with parentage analysis. The reproductive success of F1 fish was measured by assigning F2 fish back to their F1 parents. F2 fish spent their entire lives in the wild. Each F1 hatchery run-year consists of fish from multiple brood-years. In run-years 1995–1999, a small number of returning F1 hatchery fish were used as broodstock. Notice that hatchery fish return, on average, 1 y earlier than wild-born fish owing to accelerated growth in the freshwater phase of the life cycle (1 y in the hatchery vs. an average of 2 y in the wild).