A logical solution would be to restrict noisy activities to limited times or areas, and take steps to minimize the noise that routine activities make. However, it's important not to muffle boat noise too much: the natural shape of the boat already creates a "sound shadow" toward the front that causes whales to swim in front of it. Muffling the engines would mean really needing squealers on the front so cetaceans can perceive the danger and avoid the boat.
We could also promote less noisy activities such as surfboards over jetskis or sailboats over speedboats. While these are different hobbies, if the quiet ones were offered free while the noisy ones cost money, that would redirect a lot of traffic. Furthermore, a hefty noise tax on things like speedboats could be routed into cetacean care.