Scientists didn't expect a shark chomper stuck inside a human body for a quarter century to yield viable DNA. They were wrong.
In 1994, Jeff Weakley was paddling on a surfboard off Florida's Flagler Beach when a shark bit his foot, leaving him with lacerations and joint damage. At the time, he didn't know what kind of creature had latched onto him from behind, but he does a quarter of a century later, thanks to analysis of DNA from a tooth fragment left buried in his body all these years.
Weakley found the tiny bit of tooth after spotting a blister-like bulge in his right foot and digging in with a pair of tweezers last summer. At first he planned to turn the dental detritus into a pendant, but then he heard scientists from the Florida Museum of Natural History had used DNA from a tooth left in a more recent shark attack victim to determine the culprit's identity.
He was in.
"I was … a little bit hesitant to send the tooth in because for a minute I thought they would come back and tell me I'd been bitten by a mackerel or a houndfish -- something really humiliating," Weakley, editor of Florida Sportsman magazine, joked in a statement.
At first, the scientists didn't think they'd be able to extract viable DNA from a tooth that had been hiding in Weakley's foot for as long as Justin Bieber's been alive. But after carefully cleaning the tooth of contaminants, removing part of its enamel and scraping pulp tissue from the cavity, they were able to identify the attacker as a blacktip.
Blacktip sharks, Carcharhinus limbatus, are common to coastal tropical and subtropical waters, and though they don't hunt humans, they're frequently responsible for bites in Florida caused by cases of mistaken identity. The researchers detail their findings in the journal Wilderness and Environmental Medicine.
"It is surprising that the shark's DNA would persist intact for such a long period of time at mammalian physiological temperatures and in the presence of enzymes and an immune system optimized to target and break down foreign tissue," the study says.
While shark attacks are rare, they have long been the subject of fascination, thanks in no small part to movies like Jaws. Researcher Lei Yang of the Florida Program for Shark Research, which focuses on biodiversity and conservation, says he understands Weakley's curiosity. "If I was bitten by a shark, I would want to know what it was," he said.
But the DNA discovery does more than satisfy questioning minds, according to the scientists. It contributes to the understanding of shark bites and could help prevent them.
"The aftermath of an attack has the potential to influence public attitudes toward sharks and policy decisions surrounding shark attack mitigation and conservation," the study says.
Meanwhile, Weakley, who was 21 and an experienced surfer at the time of the attack, still surfs weekly.
"I certainly don't have a hatred of sharks or any feeling of vindictiveness toward them," he said. "They're part of our natural world."