Dan O, I will try to answer it is pretty complex though. Starting in about 1982 there has been a repetitive and extremely damaging series of heavy rainfall and early snow melts resulting in catastrophic Riparian zone shifts and gravel recruitment. This has been accelerating and if you fish the Hoh much you have seen the evidence of these floods. The worst damage is in the areas that have been logged but by no means is the areas in the park immune to these events.
River course changes of the magnitude that are occuring on the Hoh are devastating to all spieces. In a lot of cases the water just simply moves away from where fish have spawned before the eggs get out of the gravel. In other instances the rearing areas for the fry and parr are filled in with the excessive sand and gravel thereby limiting the carrying capacity of the stream.
In a lot of the Hoh there is a lack of the larger woody debris that forms log jams which create stability to the banks and the course of the river. Too the log jams are important to the fry and parr in diferent stages of there various life historys.
I'm sure that you know all these things but its a pretty short list compared to all that is wrong with the Hoh.
I'm quite certain that the Hoh needs to be managed very carefuly by all the managers involved Native Tribe, National Park, Timber companys, the State, and us as individuals.
Hope that helps Dan O, I am headed out the door to do a bit of angling.