The other piece, and it ties with Rich's comment, is that earliest returning fish tend to be age-1 smolts, of which a well-nutriented system produces naturally. Since they return earlier, they have less time to feed and would tend to neb smaller.

That would make the mainstem spawners later retuning, older as smolts, and larger as they fed longer. Also, it would a larger fish to spawn in a mainstem rather than a tributary.

The steelhead escapement goals were based on whole watershed rearing habitat. IF we are deliberately (at least in the past) removing the early tributary spawners and IF the choice of spawning area istied to return time then the escapement goals or management paradigm needs re-examining. My bet is that the goals will be examined before management.