Scratching the Bottom (Trawlers)?

It has been obvious for sometime, that the protection offered by being designated a 'Marine Protected Area' (MPA) by the UK, is fairly minimal. Most (74/76) of such areas off the UK coast, are still open or partly open to destructive fishing. One of the most destructive techniques is 'bottom trawling', where weighted nets are dragged along the seabed. What they don't catch, they destroy. Patrols of MPAs are few and severe penalties for inappropriate actions are hardly ever incurred. Greenpeace are now taking direct action (https://guernseypress.com/news/uk-news/2021/02/26/greenpeace-builds-boulder-barrier-to-protect-marine-site-from-fishing/). The organisation is dropping huge granite boulders (adorned with the names of celebrities) from their ship (Esperanza) into the sea along the margins of MPAs. The intention is to make bottom trawling in such areas mechanically impossible. Esperanza has done this off the Dogger Bank in the North Sea and is continuing the activity off the coast of Brighton. The fishermen are, predictably, unhappy, describing the action as 'illegal and dangerous'.