It was difficult to tell for sure. I managed to step on one at one point whilest walking backwards. One evening we were sitting on the balcony looking at the beach and saw a HUGE outline of a manta ray (or whatever kind of ray it was). I would estimate that it's wingspan was about 4 or 5 times larger than the ones I have taken pictures of - probably 12 to 15 feet. It was amazingly huge. Sadly, I didn't have the camera handy, and it never appeared again.