Researchers Delve Into Unheard-of Shark Attack

Shark attacks on humans remain exceedingly rare, but a deadly incident off the coast of Hadera, Israel, in April involving dusky sharks has sparked new questions about what triggers shark "feeding frenzies"—and whether human behavior is increasing the risk. The event, which left only the victim's clothes behind, puzzled researchers because dusky sharks are not known to attack humans; the Global Shark Attack File lists no other fatal dusky shark attacks on record, and a press release explains the large creatures most typically eat small fish and crustaceans. Marine biologists Eric Clua and Kristian Parton analyzed witness accounts and video footage from the attack to arrive at findings that have been published in the journal Ethology.

They concluded that the incident likely began with an exploratory or accidental bite, possibly triggered by the electromagnetic signal emitted from the victim's GoPro camera—a type of signal sharks are able to detect in the water, per Smithsonian. In this case, sharks in the area may have already been accustomed to humans as a source of food due to the local practice of hand-feeding sharks from the shore, the researchers write. Once one shark bit the swimmer, the resulting commotion and the sounds of biting and chewing—Chua says sound travels five times faster in water and is typically a quicker draw than blood in the water —likely triggered a competitive feeding frenzy among others nearby.

The study notes the 40-year-old victim was, according to witnesses, snorkeling about 300 feet off the shore in order to observe the sharks. Per the study, "Should the local authorities decide to maintain shark-watching tourism while making it safer," their main objective should be "to eliminate the begging behavior in sharks, and this can only be achieved by establishing and enforcing a complete and total ban on all artificial feeding of sharks by the public, as well as spearfishing in the area, which can often fuel the impulse in sharks to obtain food from humans. Any other measure could be complementary, but undeniably less relevant than this approach."