Great White Sharks: Underwater Drone Captures First Recordings Of Ambush Attack
Great white sharks appear to lurk in the darkness before ambushing their prey, according to researchers from the Woods Hole Oceanographic Institute (WHOI). During a recent expedition, the institute's underwater drone called the "REMUS SharkCam" was attacked nine times by four sharks, providing researchers with the first-ever footage of great white predatory behavior.
"Most of what we know about white shark predatory behavior comes from surface observations. We have all seen pictures or footage of sharks surging out of the water to capture a seal," lead author Greg Skomal, a biologist with the Massachusetts Division of Marine Fisheries, explained in a news release. "But we wanted to find out what was happening at depth--when the sharks swam into the deep, how were these animals behaving? Were they hunting? The REMUS AUV was the perfect tool to do this."
During a 2013 expedition in the waters off Guadalupe, an island off Mexico where Pacific white sharks congregate to hunt seals, the autonomous underwater vehicle (AUV), REMUS SharkCam, recorded 13 hours of footage, from which scientists were able to dissect every move a great white makes when hunting prey: The sharks will remain secluded in deeper, dark waters and stalk their prey from below. When the moment is right, they will burst out of the darkness and seize their prey in their jaws.
"This SharkCam groundbreaking technology offers a new and innovative tool for scientists to better understand the fine-scale behavior of marine animals," WHOI engineer Amy Kukulya, one of REMUS SharkCam's principal investigators, said in a statement. "There is currently no other method in the world that can get imagery of white sharks at depth in the open ocean. Not only do we get to see what they are doing, but we also know exactly where they are and collect data about the physical environmental in which they live."
In total, the expedition team conducted six AUV missions over a period of seven days in November 2013. During that time the team tagged and tracked four sharks, including one male and three female great whites. The sharks - one of which was the famous 21-foot-long Deep Blue - were followed to depths of 100 meters. (Scroll to read more...)
The behaviors filmed by REMUS SharkCam ranged from simple approaches to bumping the vehicle and, on several occasions, aggressive bites. A shark nudging the vehicle with its snout was deemed aggressive or even defensive, but bites were interpreted as predatory because it meant the sharks were committed to an attack. The behaviors caught on tape support the idea that white sharks dive to great depths in order to use light to their advantage.
"If the shark hangs down at a great depth, in the darkness, then its prey swims above it silhouetted and the shark reduces its own likelihood of detection," Skomal told the Guardian. "The remarkable new observations indicate that [my colleagues'] hypothesis is correct, and the sharks ambush from the darkness."
While the SharkCam provided a snapshot of a shark's daily life under the sea, researchers say there is still much to learn. In the future, the team hopes to create a deeper diving REMUS that can swim for longer periods of time.
"They're arguably the most charismatic, if not the most well-known species on the planet," Skomal continued, "and it's still one we know remarkably little about some of its most basic natural history."
Their findings were recently published in the Journal of Fish Biology.
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