Wednesday, March 22, 2006

The Thresher

The rather poor quality profile shot below is my best image of one of the more unusual species of shark, the Pelagic Thresher (Alopias pelagicus). I've been lucky enough to dive with these sharks some 5 times even though they are only commonly seen by divers in a couple of locations around the world. This is an adult circling the cleaning station at Monad Shoal in the Philippines. Monad Shoal is a volcanic sea mount that rises from the depths and is home to many small wrasse who will clean the sharks as they pass by. You will also sometimes see giant Manta Rays taking advantage of this.
The threshers come up from the depths where they feed on squid in the early morning for a bit of a clean and scrub-up. No-one is certain of the evolutionary principle behind the thresher's long tail but some believe it to be used as a whip to confuse schools of small fish or squid. This second picture, looking down on a juvenile at Big Brother island in the red sea, shows the size of the thresher's pectoral fins. These are a good way to identify pelagic species - almost all offshore sharks have wing like pectorals for efficient gliding through the desert-like expanses of open water.

1 comment:

Pam in Tucson said...

My maiden name is Thresher - I always got teased as a child. I've never known anyone who's been that close to a Thresher shark. These are fantastic photos. What an amazing tail!