The great white sharks patrolling the Beaufort County, South Carolina and Georgia coasts aren't just passing tourists.
They're starting families here in what has become the prime birthing location of the north Atlantic Ocean, according to some marine scientists who study the ancient predators.
Fishermen and scientists are closely watching Mary Lee -- a 16-foot, 3,450-pound great white who is pregnant and appears to be headed toward Hilton Head Island, presumably to give birth, said Chris Fischer, founder of OCEARCH, a nonprofit group that tracks and studies the animals.
"When I look at (Mary Lee's) track, it appears to me that (the) region is likely to be part of that birthing, breeding-site puzzle," Fischer said Friday. "She's an old, mature shark who knows where she's going."
Fischer's group tagged Mary Lee in 2012 off Cape Cod with a device that "pings" her location each time she breaches the surface. For more than a year and a half, they've watched her swim up and down the East Coast. Her recent movements are consistent with the patterns of pregnant sharks, he said.
Earlier this year, she cruised the waters off Beaufort County and Savannah before settling in one location about 40 miles offshore, according to the tracker. Late last month, she left that area and bee-lined toward Hilton Head.
"I suspect she was making that move to drop off her pups somewhere," Fischer said. "We know how prolifically vibrant the Port Royal Sound is, and it appears to be a hugely important hot spot for sharks in the Atlantic. If you're a big shark, all of the estuary, inshore coastal area is just fabulous to drop off your baby shark, so it can gorge on (all the sea life)."
Mary Lee hasn't pinged since June 23. Fischer and other scientists suspect she had her pups near Beaufort County and is likely headed north to Cape Cod, where she was first tagged.
"I suspect the next time we hear from her, she'll be on her way to Cape Cod," Fischer said. "If she gets up there, she'll confirm that's the breeding site."
The research begins to put hard data behind what fishermen and scientists have only been able to estimate and is something of a milestone for the project, Fischer said.
Great whites aren't the only sharks being tracked.
The group is also following dozens of other sharks of varying age, size and species all over the world.
But because Beaufort County waters are so rich with marine life, OCEARCH has focused on the Port Royal Sound this summer to tag and study local tiger sharks.
With the help of Hilton Head fisherman Chip Michalove and Bryan Frazier, a marine biologist with the S.C. Department of Natural Resources, the group is following the movements of seven tigers on its online map.
"We're doing some groundbreaking work, there's no doubt about that," Michalove said. "To have OCEARCH in our own backyard, this is major."
The data already collected from the tigers have revealed how far they travel. One pinged off the coast of New Jersey, Michalove said.
Overall, the data help shape marine scientists understanding of how sharks navigate the large swaths of ocean they cover in mere days and where they breed and give birth.
"It all makes sense when you can see systems unfolding around the world, and they all sync up," Fischer said. "It's been amazing to be a part of it."
Follow reporter Zach Murdock at twitter.com/IPBG_Zach.