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That's a very expensive operation.  Any sort of electronics that has to sit on the ocean floor requires constant maintenance.
I would propose a simpler solution:
Issue letters of marque for illegal fishing.
Faster, EU. At that speed there won't be any biodiversity left by the time the ban comes into effect. >

What we need are mines that prevent bottom trawling. They could sit harmlessly just off the ocean floor, but if a trawler snags them they are triggered by pressure sensor just as they are hauled on board. Their presence in an area should be loudly declared to operators and insurance companies, as their purpose would be to make it too expensive to illegally fish an area. No people ever need to be actually harmed.