I have to agree with Todd 99.8%.Nets are diffinitely killers,but steelhead are in low numbers,even on ,somewhat virgin streams.Ocean survival through predation and diseases,I believe ,play a large roll.Also ,on some of these'virgin'streams,I believe during the 70's and 80's,meat anglers(maybe at the time,they just weren't educated to the fact that this is NOT an endless resource)were taking large hacks at these somewhat lesser known streams.No doubt the local rednecks going to catch dinner.(jk).
I voted habitat.pollution,over logging,development.
All the choices,except the nets,have a common thread,and can actually be tied together.
That's my .02% of a loonie.