Scuba divers frequently photograph sand tiger sharks circling shipwrecks off North Carolina, and a Duke University scholar says those photos have inadvertently proven an odd scientific fact.
Female sand tiger sharks have favorite shipwrecks in the “Graveyard of the Atlantic” where they like to hang out year after year — something researchers are calling “site fidelity.”
“We’re now trying to figure out why they return,” said a statement from Avery B. Paxton, lead author of the tiger shark study.
“They could be using the wrecks as rest stops along their migratory paths, but they could also be returning here for mating or possibly to give birth. There are all kinds of hypotheses our team is testing,” said Paxton in the report.
In the study, published April 22 in Science Daily, researchers credit scuba divers with supplying the evidence that led to the study’s conclusions.
Photos taken by the recreational divers and uploaded to the N.C. Aquarium’s Spot A Shark USA site revealed certain sharks were always at the same wrecks, the study says. The researchers made that discovery by “analyzing and comparing the spot patterns on sharks” in photos dating back 12 years, the study says.
The area of the Atlantic Ocean off North Carolina is called “The Graveyard of the Atlantic” because it is home to thousands of shipwrecks dating back to the 1500s, VisitNC.com reports on its website.
Duke researchers believe many of those wrecks have become important habitats for very specific female tiger sharks, but don’t yet understand the reason they’re so choosey, the report says.
“This is the first time we’ve been able to document site fidelity to habitats in offshore waters along the East Coast,” Paxton says the report.
“Previous studies have shown similar behavior patterns in Australia and Africa ... so what we are finding off North Carolina definitely fits into global patterns.”
Male sharks are also believed to be loyal to certain sites off the coast, but photos have not been able to prove it, Paxton says.
The Duke team says the study is important because sand tiger sharks experienced a 75 percent population drop in the 80s and 90s, the report says.
“We don’t know if (the population) has stabilized or is still declining, in large part because we’ve mostly had to rely on anecdotal sightings,” Paxton says in the report.
“Having photographic evidence that these wrecks form an important habitat the sharks... gives us a focal point for ongoing research so we can better understand how the species is faring,” she says.