Fishyologist -
While I agree the ocean tends to be an equalizer when it comes to survival the fact remains for species like steelhead and coho who spend considerable time in freshwater their freshwater survival "skills" are hugely important.

For wild coho and steelhead it is typcially for only 1 to 5 % of the eggs to survive the freshwater enivrnoment. Once a steelhead reaches the parr stage over winter survival (fall to spring) to the smolt stage is typcially in the 30 to 50% range. I think you would agree that is a lot of selective pressure for particular set of survival skills. Because the freshwater and marine waters survival skills are so different - one example for much of the freshwater stage a steelhead to be has to defend feeding areas and finding cover in a relatively small area but once it moves to the ocean to be successful it must be more or less constantly on the move searching for food -the overall survival success of a particualr fish is dependent onits adpatability to both the freshwater and marine water envirnoments.

There a number of studies showing how unproductive first generation hatchery steelhead and coho are in the wild.

The fact that a fish can adapt in a new envirnoment, especially in lack of competition from other anadromous fish does not in itself mean that when they are mixed with local adapted wild populations they will be as "fit" as those wild fish. This would be doublely so if there is a constant infusion of fish adapted to the hatchery envirnoment.

Tight lines
S malma