In my experience, and in the literature, most escapement estimates are significant underestimates of the real number. Then, you need good age data, annually. The catch, especially for non-terminal areas, has to be divided amongst the stocks. This, too, varies annually but normally averages are used. And, as with escapement you need the ages. Annually.

Keep in mind, though, that MSY management has absolutely nothing to do with biology or ecology. It is simply and economic analysis that asks "What is the minimum amount I have to invest (spawners) to maximize my return (catch)?"

As WH1A said, we need to manage from the rivers out. For all stocks. If they all have harvestable fish, above the in-river needs, then outside fisheries might be possible.

Or, we can just fish the stocks into economic extinction and move on to some other resource to rape.

What was that bumper snicker? "Earth First. We'll Log the Other Planets Later"