they aren't all pot buoys - the black or nearly black ones have been there 'sometime'..........

most of them are actually leisure boaters dropping the odd single pot on their way out - to be picked up on the way back. Some are even active Scuttlebutt members ie yachts

I am thinking particualliry about the 4 set around Lobster rock - in a straight line between Poole Harbour Entrance and the Solent.

Those on Christchurch ledge are seasonal but mainly nets

Those closer into the bay are nets and cuttle traps

Outside a line from old harry to the needles you will find very few such problems - they will be pot buffs but if the tide is running they will be hard on the bottom and even at slack they will be few and far between.