How to stop overfishing

I read a short item in The Ecologist this month (October issue) about Greenpeace dumping 3 tonne blocks of granite in the German North Sea to foul the fishing tackle of bottom trawlers. It struck me as a very neat way of enforcing fishing controls, and one that governments could do well to endorse. Dumping large objects in the sea could be a very simple way of enforcing no fishing zones -- at least as far as the highly destructive bottom trawlers are concerned. It reminds me of the proposal to decontaminate the decommissioned North Sea oil platforms, and sink them. This would have been far cheaper for the oil companies than towing them back to land for dismantling, but was unfortunately opposed by Greenpeace and other environmentalists at the time.