Bob -
I think I understand your question.

First the an escapement at MSH would not fill all the habitat; rather the fish would likley being using the most productive habitat with the result being on the average that escapement would produce the largest "harvestable" surplus. If the goal was to manage at carry capacity there would be no "harvestable" surplus including no room for even a CnR fish thus no fishing.

If I understand correctly the habitat has changed with the river becoming shorter and the gravel less stable - in short the carrying capacity has likely been reduced.

Typical such factors leading to reduced carry capacity as cause reduced productivity of the spawners. The result is analysis of the spawner/recruit curve would result in a change in the estimate of the MSY escapement goal. It would be lowered.

Frankly I'm surprised that you have an interest in moving management in that direction however if you wish a less conservative management with the accompanying lowering of the escapement goal feel free to lobby for such actions but hope you don't mind that I'm not interest in joining you in that effort.

Happy Holidays and may the New Year bring you all tight lines.
S malma