July 11, 2013
Thresher Sharks Take Down Prey With Whip-Like Tail
Brett Smith for redOrbit.com - Your Universe Online
Named after its long whip-like tail, the thresher shark uses its eponymous feature not only to swim, but also to strike at prey.
Shot in the tropical waters off the coast of the Philippines, the videos show pelagic thresher sharks accelerating toward schools of fish and throwing their pectoral fins forward to quickly decelerate. This braking method pushes the shark's back end up so it can unleash a blinding tail strike on the school in an attempt to stun and kill fish.
The marine biologists examined 25 filmed attacks taken between June and October 2010. The scientists watched as 22 of the attacks included overhead tail strikes and the rest included sideways tail flicks.
According to report co-author Simon Oliver, these new videos are the first clear evidence that "thresher sharks really do hunt with their tails."
A marine biologist at The Thresher Shark Research and Conservation Project in the Philippines, Oliver noted that the speed of the whip attack was difficult to visually track.
"It's a cross between a bull whip and a medieval war machine - it's extremely violent, extremely quick and it's incredible to observe," he told Victoria Gill of BBC News.
After breaking down the video, the team was able to understand the entire event in greater detail.
"The interesting thing about it was that these tail slaps were only successful about 60 percent of the time," Oliver said, "but when they were successful they managed to kill more than one prey item."
"So it seems the strategy is efficient in that the shark is able to consume more than one fish at a time to balance out the times when it wasn't successful," he added.
Oliver said the speed of the attack was so fast -- more than 50 mph -- the shark's tail essentially created shock waves in the water.
"We saw bubbles coming out of the water at the apex of the tail whip; an explanation for that is that it's caused by pressure differentials [that create] an explosion in the water [and] break down water molecules,â he said.
With a tail about half their body length, pelagic (open water) threshers grow to almost 13 feet long. Other species of thresher shark can reach almost 20 feet in length.
David Sims, deputy director at the UK's Marine Biological Association, said that the discovery expanded on previous research of common thresher sharks, which used a "sideways slap." He added that "this species [the pelagic thresher shark] does an impressive overhead kick with its tail fin."
"This team has really nailed it in terms of showing not only that the sharks do this, but that it leads to prey capture,â said Sims.
According to Oliver, learning about the feeding habits of thresher sharks will help with conservation efforts. The sharks' populations have dropped around 75 percent over the past ten years as a target of fisheries or victim of by-catch.