What seems to fly-by folks is that MSY escapement is on the order of (say) 20% of what it was pre-Euro-American fisheries commenced. Now, if you harvest one resource down that far, it may work. But if you remember from the ecology the transfer of energy from one level to the next is like 10%. Now, we harvest the lower levels of the food chain (crabs, shrimp, clams, herring sardines, anchovies) down and then are surprised when the system supports fewer predators (salmon).
Then, to muck it up more, we try to "restore" the salmon predators like whales, seals, and birds.
Simply put, if you want a lot of salmon you will have to have enough food to seed them and the appropriate number of predators to eat them. You can't manage a single species by ignoring all the others. Well, actually you can because that is what we are doing so successfully.