DNA nails source of New Yorkers’ shark bites

It’s a tourism board’s nightmare come true. In mid-July, two teenagers were bitten within minutes of each other while wading off beaches on Fire Island, a barrier island along the south shore of New York’s Long Island. There, thousands of locals and tourists sit blanket-to-blanket every day enjoying the surf and sun—and trying not to think about the movie Jaws.

Great whites were mentioned as possible attackers, as they are often found off the end of Long Island. But when lifeguards dug out a chunk of tooth from one of the teen’s wounds, officials decided to send it out for identification to the International Shark Attack File at the Florida Museum of Natural History in Gainesville, which has tracked shark bites since 1958.

The sliver wasn’t quite big enough to compare to other teeth, so researchers there cleaned it and took a DNA sample from its interior. They then sequenced a small section and compared it to the same stretch of DNA from 900 shark species around the world. The match: a sand tiger shark (Carcharias taurus), researchers report today in Nature . The second teen was likely bitten by the same kind of shark.

Despite its name, the 200-kilogram, 3-meter-long fish isn’t much of a tiger. Over 60 years, just 15 human bites have been reported to the International Shark Attack File, none of them fatal. Instead, scientists say, the sand tiger shark likely bites unintentionally when it pursues schools of fish into shallow water crowded with people.

This is a rare instance in which rescuers have saved shark teeth shards for further analysis; nearly 70% of bites in the attack file are unidentified. If more rescuers bagged the debris from shark bite wounds instead of tossing it, say scientists, DNA studies could easily bring that percentage down—and lead to a better understanding of which sharks are the most dangerous and why.