I've encountered them twice while fishing for cod. What we were doing was jigging cod and reeling them to the surface slowly. This attractts the sharks for they probably wait for the small cod and so on to swim down and ambush them. We then use a whole mackeral and suspend it about eight feet from the bottom. We do the same at the surface, mid depth and twenty feet off bottom. While drifting, we continued to jig cod and eventually the ballon disappered. Hope this helps. They were a good change to reeling small cod up from the depths all day (1 porbeagle and 8 legals caught, all released.)