Researchers use lasers and robots to study mysterious spotted sharks at NC shipwrecks
Sand tiger sharks swerve slowly, sinuously around a shipwreck among schools of hundreds of glittering silver fish, video gathered by a robot shows.
They don’t appear fazed by a swimming robot pointing laser beams in their direction.
Avery B. Paxton is the lead researcher on a project using marine robotics and lasers to study sand tigers — a species of shark not much is known about.
“There are so many mysteries surrounding sand tiger sharks,” Paxton said in an interview with The News & Observer. “By using this technology we’re able to get eyes underwater and start to learn a bit more to answer some of these longstanding mysteries.”
Paxton, who grew up diving with sharks at shipwrecks off the North Carolina coast, is a marine ecologist, postdoctoral fellow at the South-East Zoo Alliance for Reproduction & Conservation (SEZARC) and a visiting scholar at Duke University’s Marine Lab. She’s leading the research partnership between the National Oceanic and Atmospheric Administration, the Coastal Studies Institute Duke University, North Carolina Aquariums and the Sand Tiger Shark Consortium.
‘Like a video game controller’
The project began in July and uses a remotely operated marine robot to gather data on sand tiger sharks at eight World War I and World War II shipwrecks off the coast, Paxton said.
A crew of researchers travels by boat to the shipwrecks and launches a robot using joysticks “kind of like a video game controller,” she said.
The robot is outfitted with multiple cameras and sensors that record video, document temperature of the water every 10 seconds, track salinity of the water and pick up signals from acoustic tags placed on animals, Paxton said.
It also has lasers.
“There are two laser beams that shine into the water,” Paxton said. “When they shine on a shark, you can see the laser points on that shark.”
Researchers can use those laser beams to measure the sharks with minimal disturbance.
“It gets us our eyes underwater without having to physically touch the sharks or bring them up to the surface,” Paxton said. “We thought that was a really big benefit to this method. It gives us a great picture of what’s going on underwater.”
A ‘vulnerable’ species
Many types of large sharks are disappearing, Paxton said. Sand tiger sharks are among them.
“Sand tiger shark numbers declined by more than 75 percent in the ’80s and ’90s,” Paxton said, adding that overfishing contributed to their loss.
The International Union for Conservation of Nature has labeled sand tigers a “vulnerable” species.
Paxton and her team are hoping to learn more about the sharks to help with conservation efforts.
“They’re really easy to recognize,” Paxton said of sand tigers, which have “iconic ragged, toothy” grins and dark spots on their brown-gray bodies. Those spots are unique to each shark, like a human finger print, and help researchers ID them, she said.
Sand tigers can grow to be more than 10 feet long and are “a very docile shark species,” Paxton said.
Since they’re docile, the marine robot has little trouble getting close to the apex predators at the shipwrecks where they like to hang out. Researchers are trying to find out why.
“We’re trying to figure out what their numbers are now, where they’re located and what areas of coastal oceans they’re using for their homes,” Paxton said.
‘Graveyard of the Atlantic’
North Carolina’s coastal ocean is littered with hundreds of shipwrecks. It’s known as the “graveyard of the Atlantic,” Paxton said.
Those shipwrecks attract a huge variety of marine life, including sand tigers.
“You’ll see these incredible bait balls of silvery, glittery fish,” she said. “It’s really a dynamic and quick-paced environment underwater around these wrecks.”
Paxton and her team are studying sand tiger sharks at eight shipwrecks stretched north-to-south from Cape Lookout, she said.
Sand tiger sharks are believed to migrate from their summer homes near New England south to their winter homes near Florida.
But sand tigers congregate at shipwrecks off the coast of North Carolina, “right smack dab in the middle” of their migration route, Paxton said.
“North Carolina is a huge puzzle for us,” Paxton said, adding that while the overall population of sand tigers has declined sharply, North Carolina consistently hosts high numbers of sand tiger sharks..
“The thing that’s kind of puzzling is that we don’t understand why these sharks are here in North Carolina,” Paxton said.
The shipwrecks could be a clue.
“We’re seeing really unusually high numbers in shipwrecks right here in our backyard,” she said. “We can see 100 or more sharks around a single shipwreck. It’s really a remarkable sight.”
Paxton and her team are trying to discover if the sand tigers are making rest stops in North Carolina’s coastal waters at the wrecks or if some of them are making North Carolina their permanent homes, she said. They’ll be checking on the shipwrecks monthly for at least a year to track the sharks.
As Paxton and her team learn more about the sand tigers, track their numbers and find new clues about where they make their homes and why, they can help facilitate management decisions that could protect the species.
“Sand tiger sharks, along with other sharks, are important for the health of coastal oceans,” Paxton said. “These sharks often function as some of the top predators in the system, which really maintains the overall health of the ecosystem.”
Paxton said her team is hoping its laser-targeted research will add to conservation efforts to maintain a healthy ocean environment that creatures and people depend on.
“They’re mysterious,” Paxton said of the sand tigers. “We’re just trying to shed a little light where we can to learn more about them and hopefully protect them.”