Aha, yes, if it was lurking in a cave on the sand, then a reefie it most likely was. Length of fins is awfully hard to assess from a single photo as the fin can be inclined to the camera.
I thought it would be much more exciting though if you could say it was a whaler. Here is one of a silver tip monstering a diver. It shows the smaller dorsal fin.
http://www.photographersdirect.com/b...imageid=977463
Cheers