Based on this study the hatchery winter-run steelhead were about one half as effective as wild winter-run steelhead in naturally producing smolt offspring. In addition, hatchery winter-run steelhead were about one sixth as effective as wild winter-run fish in naturally producing adult offspring.
The reproductive success differential between hatchery and wild winter-run steelhead in the Kalama River may be similar to that previously estimated for Kalama summer-run steelhead. Such findings have serious implications regarding the potential genetic effects that interbreeding between hatchery and wild fish could have on wild populations.