One of the problems, of many, with MSY is that when you fish (say) the salmon, herring, and whatever the herring eat at MSY you knock the spawning population down to about 20% of unexploited, on average. So, what eats herring and salmon now have a lot less to eat.

Then, we try and "recover" pinnipeds. Killer Whales, cormorants, terns, grizzlies, and all the other predators that eat salmon to historic numbers. Without the food base to support it.

It may make sense to fish the top of the food chain at MSY but the further down the food chain one goes, the less one can support at the upper levels.