Reply #32: Sounds like a stingray

[ForrestGump]

Mantas are pelagic -- they don't bury themselves in the sand like other rays do. Stingrays are a favorite food of some sharks (hammerheads tend to hunt them down) and tigers will pretty much eat anything if it's handy. Of course, it might not have been a tiger shark, either -- tigers aren't seen all that often, even on the GBR, and any helicopter pilot who'd claim a large stingray is a manta is probably working up a leopard shark or something simialrly innocuous into a tiger. :D

Can't trust those damned Australians, you know...