The answer is all of the above. In some watersheds it is habitat; in some commercial overharvest; in some it is hydro. But it is a fact we will NEVER bring back the wild fish without habitat improvments. And don't be fooled by the fact that you think the rivers you see are fine spawning habitat. I used to think the Tolt was perfect habitat until I saw a report that there were many many obstacles to upper tributaries, where the steelhead typically spawn, including bad culverts and excessive braiding due to poor looging practices.

In other cases the damage may not be visable to the untrained eye. I have a lot on the Tahuya River. We used to have a tiny seasonal stream thet crossed the property. Hundreds, if not thousands, of tiiny coho used that tiny stream every year. The kids used to love watching them. A development across thr road diverted the stream into a ditch. No more habitat. No more coho. That story has been repeated thousands of times in Puget Sound area.

It is easy to balme gillnetters, and I have NO love for them either, but fish will not make a comeback unless they can spawn and then have a good environment to live in.
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No huevos no pollo.