Dear Mossman,
I was not there on the dive, all I could say was what I was told. One of the most respected old time Mexican dive authorities, Alberto Friescone, was along with three other highly experienced divers. They have seen perhaps more than thousands of Caribbean Reef sharks, and insist they are not that. And I have no idea how you can discern how blunt the head is from this photo. It is most likely the silky sheen of the skin, witnessed first hand by very experienced authorities, that caused them to suspect the species to be Silky Shark. The very small second dorsal fin is also an indicator.
But hell, I don't know, that is why I posted the photo in the first place…didn't want to start a fight. Welcome!
Dave Dillehay
Aldora Divers