Shark Behavior Study Suggests Predators May Tell Which Direction Divers Face, Choose To ‘Swim Up From Behind’

on December 17 2013 3:52 PM
shark-diver
In one controlled study, sharks passed behind divers 80 percent of the time. Reuters

Sharks, those fearsome predators of the deep blue sea, often strike fear in the hearts of amateur divers and beachgoers alike. Well, here’s another reason to worry: A new study confirms that sharks prefer to pass divers from behind – in other words, where we can’t see them.

Researchers from Shark Research Institute in Florida wanted to document the phenomenon many divers and shark experts have previously witnessed but never really studied scientifically. Scientists conducted an experiment in which they had volunteer divers kneel on the seafloor with their gaze straight ahead, so as not give the sharks any clues that would indicate the divers’ body orientations.

The volunteers remained in that position for hours while researchers filmed their interactions with Caribbean reef sharks. Researchers confirmed that about 80 percent of the time, sharks passed behind the divers. Their study, published in December in the journal Animal Cognition, concludes that sharks may have figured out how to tell which way a person is facing, and choose to pass out of view.

"They truly do swim up from behind, be it that they want to sneak up or they don't want to be seen," Erich Ritter, a scientist at the Shark Research Institute, told LiveScience. "It doesn't mean they sneak up in a way of having a vicious thought; mainly, they are curious but at the same time cautious."

How do sharks tell which way humans are facing? It’s unclear, but scientists guess it’s partly due to sharks’ previous interactions with divers. Others say they may recognize divers’ goggles as eyes, similar in shape to the eyes of the fish they hunt.

The research may explain why it is that most shark attacks occur from the rear, or why some divers report times they’ve turned around, only to find themselves face to face with great white sharks.

Florida is often cited as one of the most dangers places in the world for shark attacks. Since 1882, investigators have confirmed 663 unprovoked shark attacks off the Florida coast, 11 of which were fatal.

In 2007, of the 71 shark attacks that occurred worldwide, almost half of them were in Florida. Most of Florida’s shark attacks took place along the eastern shores of the state, specifically in Volusia, Brevard and Palm Beach counties – all popular spots for tourists.

“Pre-attack behavior by most sharks is moderately predictable,” rescuediver.org reports. “They start by swimming with an exaggerated motion, and their pectoral fins point down instead of out. Swimming in decreasing-size circles around its intended prey. As a rule divers should believe an attack may be imminent if a shark assumes an unnatural posture. Sharks have attacked without any pre-attack behavior.”

While shark behavior is often marred by stories of fatal or gruesome shark attacks, it’s important to keep in mind that shark attacks are extremely rare. Every year, there are only about 10 fatal shark attacks worldwide.

As California Academy of Sciences notes, in California the number of shark attacks is “much less than the numerous drownings, bee stings and lightning strikes that cause fatalities each year.”

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