Shark’s Tail Is A Deadly Weapon (If You’re A Sardine)

threshershark

As if sharks weren’t scary enough, now there’s definitive proof that pelagic thresher sharks (Alopias pelagicus, above) can hunt with their tails, not just their teeth. Even worse, they’ve got two ways of thrashing their tail around, so you’d never know from where death was coming.

But don’t worry. These shark tails are only dangers to sardines.

There had been rumors for years that pelagic threshers could kill small fish with their tails (even the flickr page of the image above mentions it). So a team from the Thresher Shark Research and Conservation Project in the Philippines and Bangor University in Wales set out, armed with underwater video cameras and SCUBA gear, to get the action on film and find out how the sharks accomplished their kills. The results of their study appear in PLOS One.

The researchers dove into the waters off the small coral island of Pescador in the Phillippines many times from June to October 2010, eventually capturing 25 shark hunting events, 22 in which the shark swung its tail overhead and three sideways.

Here’s how an overhead strike works: A shark lunges toward a school of sardines then draws its pectoral fins down, which changes the shark’s pitch and stalls its movement forward. The tail whips overhead, all the way to the shark’s snout, striking at the sardines. Finally, the shark turns a full 180 degrees and chomps up the stunned fish. All this happens in just a few seconds, and the shark’s tail reaches speeds as fast as 48 miles per hour.

The sideways tail-slap takes a little longer, but it’s more of a follow-up weapon. The sharks observed carrying out this move had already completed a successful overhead strike.

The tail-slap worked about a third of the time, but it had the added advantage of being able to catch a shark more than one fish in just one move. That’s a definite advantage; the researchers note that carnivorous ocean-dwelling sharks usually only pursue one piece of prey at a time (perhaps this should make swimmers feel slightly safer after a shark has gone after one of their fellow beachgoers).

Bigger sharks are faster tail-slappers, the scientists found. That’s likely because their longer tails make better whips.

Image courtesy of flickr user Rafn Ingi Finnsson