Keta,
Perhaps this doesn't directly address your question, but a few months back I heard some comments by Curt Kraemer. His contention was that steelhead in the Skagit and Sauk basins had evolved to produce some of the latest spawning winter steelhead in Washington state. He felt that this was due to the Skagit and Sauk Rivers' headwaters being in higher mountain terrain which, in turn, kept the waters of these rivers high into the late spring and early summer. The late spawning of the winter fish (in some cases not until June or even July) assured that the eggs would not hatch until the spring runoff had declined enough that the newly hatched fry would have a more benign environment in which to grow. He also felt that diking and the drainage ("reclamation") of sloughs and oxbows had significantly reduced the available rearing area for steelhead parr and smolts, further reducing the carrying capacity of the system.