Scientists Identify Shark Species Using DNA From Tooth Found in Boy's Leg

Sand Tiger Shark
A sand tiger shark swims inside a tank at Madrid's Zoo Aquarium. There are only 29 records of unprovoked sand tiger bites and none of those ended with a person dying. ANDREA COMAS/REUTERS

In July, two swimming children were bitten near Fire Island, New York, spreading worries about great white sharks in the area. For the first time, a shark involved in a bite has been successfully identified using DNA.

Scientists from the University of Florida studied a shark tooth fragment left in one child's leg to determine how worried the public should be. Gavin Naylor, director of the Florida Program for Shark Research at the Florida Museum of Natural History, published the findings in Nature Communications last week.

The scientists extracted the sample from the tooth and compared it to DNA sequences of around 900 species of cartilaginous fish such as sharks, skates and rays.

"We're as close to 100 percent sure as we can get that this shark was a sand tiger," Naylor told the University of Florida

According to the Florida Museum of Natural History, a sand tiger shark is a slow-moving, large species and is often found near the coast. They're light brown but also have some dark spots.

The sand tiger shark often hunts invertebrates and fish near reefs, shallow bays and surf. While they are hunted and eaten in many parts of the world, the Atlantic Fishery Management Plan protect them in North American waters.

"If they really wanted to nobble you, they could," Naylor said. "Sand tigers can weigh 500 pounds and have very sharp teeth. They have the potential to do real damage to humans but don't, which underscores the fact that these bites are accidental. Sharks are not hunting humans."

Sand tiger sharks rarely attack humans except when provoked. There are only 29 records of unprovoked sand tiger bites and none of those ended with a person dying. The last time sand tigers bit people near New York was in 1988 and 1974, according to the International Shark Attack File at the Florida Museum of Natural History. However, in 2015 and 2017 there were attacks where they weren't able to identify the fish—70 percent of shark attacks are by unidentified species.

Naylor thinks that the sand tiger sharks may have mistaken the children as fish because of the turbulent surf, high light and schooling baitfish at Fire Island. The cases are rare because sand tiger sharks usually don't feed when the surf is up—even though they normally eat during the day.

"Perhaps incorrectly, I'm putting these in the bin of naïve young sharks," he said. "I'm sure the children who were bitten were petrified, but the sharks probably were, too."