Well, Sustainable means sustainable, but not for humans, for the ecosystem. Ecosystem must remain (relatively) stable. To keep its stability the ecosystem must

Well, Sustainable means sustainable, but not for humans, for the ecosystem. Ecosystem must remain (relatively) stable. To keep its stability the ecosystem must be allowed to grow diverse and awfully complex. That the fish populations do not decline is not enough. All economically valuable species of fishes populations are depleted. In all parts of the planet. They must increase ASAP. And there must be something left for the fish predators and other parts of the ecosystem. If not, there is a serious risk of collapse of the entire house by a waterfall of collateral damages. If you remove predators, there will be consequences in prey populations, that range from displacement of key species to extinction of the preys. Marine Mammal's bycatch is a waste and not a desired outcome in fisheries management, but moral reasons are the wrong reasons here. They should not be wasted because we want and need fishes in the sea. We don't want oceans filled with unedible jellyfishes.