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JonE said..
My guess, they're those AIS buoys they attach to their nets. The coloured vessels say "fishing", the rest are "unspecified vessel"
whats interesting is that theres something in that area recieving the AIS and pushing it out to the internet.
I've encountered this sailing off the East coast. There was a heap of AIS signals showing up along the edge of the continental shelf. They are unregistered AIS devices used by fishers to track nets. You can buy them in bulk for about $50-$100 each. So far as I am aware, they are illegal, which is why they tend to be used in international waters and not closer to shore. The MMSI numbers are generally not issued by a recognised authority. Another problem with them is that AIS uses just two frequencies and time division multiplexing, which means there is a limit to the number of signals that can be sent/received in proximity to each other in a given period of time. If this is exceeded, then signals clash and information is lost. As I understand it it is already the case that in busy areas such as the English Channel, there are so many vessels sending signals that signal clash occurs and vessel position information is lost. Proliferation in using AIS for fishing nets can adversely effect the original use of AIS, for safety of vessels at sea.