In the matter of fishing, for example, what would be effective is to use the totalitarian power of the state to forbid all fishing in the sea for the next hundred years, and to blow any fishing boat out of the water if it attempts to contravene the prohibition.
It would take measures that strong in order to have the oceans regain their former productive equilibrium --- though so much damage has been done already, it is doubtful that it would be the same equilibrium they had before. Some things are lost forever, and cannot be regained.
What is quite certain is that the longer we wait to use totalitarian force to restore the oceans, the worse the final outcome will be.
Florida has had considerable luck since the mid 19th century leasing areas of ocean bottom for oyster production. The state has also had some fair success with the totalitarian approach when the net ban went into effect on the west coast. No one had to be "blown out of the water" to enforce the new regulations and commercial fishermen found other means to take various species from the gulf for profit. The Redfish and Speckled Trout numbers increased drastically within a very short span of time.