Concentration of private (commercial?) sea-going vessels?
Edit: although, I keep being drawn to the cluster around Normandy - something to do with D-Day? Though what the load around Land's End would have to do with that stumps me.
I don't think they're wrecks or there would be more of a concentration around headlands like the Lizard. I'd love to say whale or dolphin sightings bu they go a long way up the Thames
huge numbers off the Cornish coast - jellyfish? but again wouldn't be up the Thames. dunno
oh it is shipwrecks. Oh well there you go. That was my first thought before being too clever about it.
I'm intrigued why so many are out in the sea outside Mount's Bay but less on the rocks of the Lizard or Cape Cornwall itself. But thats maybe because all the dots superimpose