There is another aspect that goes the other way. That is, the resource has different stability levels.

Say, originally, Skagit steelhead were stable with run of and an escapement of 150000-pre-human removals and all the salmon.

During tribal times the run was 130K with 10K removed along with some of the salmon.

Now, we are to about 10K more or less along with a few salmon.

Each time the fishery, or habitat destruction, changes productivity the steelhead adopt a new level. They are relatively stable at that level so long as the rest of the conditions such as salmon, stream temp, flows, ocean temps, estuarial quality remain rather constant.

One of the lessons that I learned early, but fought against for a long time, was that there is no single MSY, or optimum population, or even optimum escapement goal because there are so many conditions that go into it. Unfortunately, our fish find themselves in a very unstable situation where the only constant is kill as many as we think we can today.