The truth is that there is no single reason our salmon and steelhead returns are tanking. Steelhead and salmon are supposed to spend anywhere from one to five years in their natal stream with the exception of pinks and chum. Side note is that these are the runs that have been doing better than the rest, until recently.
While in that stream the fry eat plankton and gradually move up to insects and other small invertebrates. I'm no scientist but if the fry have nothing to eat because our streams have become nutrient deserts, they are starting life out at a deficit. It might be interesting to see what lies under the rocks of our streams these days.
So in nature (question if this applies to hatchery fish) these fish remain in their natal streams up to five years for steelhead. So they're starving, does that force them to the estuaries early? From there it's a whole new game as it is a hostile environment of birds and a population of seals and sea lions that have exceeded that natural populations. So, question number one, are there any studies to see how many smolts actually survive this stage?
After that the smolts finally make to the salt. At that point I'll stop because that has become another toxic sludge of hazards lately. Food for though, think about the normally reliable runs of chum that failed to arrive this year. That should be a red flag for what might have happened to our other runs of salmon and steelhead.