A team of researchers spotted a great white shark Saturday about a quarter-mile off Nauset Beach in Orleans, the first sighting off the east coast of Cape Cod this year.
"She was incredible, very, very slowly moving across the water," said Cynthia Wigren, president of the Atlantic White Shark Conservancy , who was on a boat that followed the shark for about an hour. "It was easy to stay with her."
A spotter pilot, Wayne Davis , first saw the 14-foot-long female shark from his plane and called to the four-person boat, Wigren said. A scientist on the boat then got footage of the shark's identifying markings.
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"Sharks have a unique pattern along their lateral line, where the white of their body turns into a gray," Wigren said.
Researchers with the conservancy have just started a three- to five-year study, in partnership with the state's Division of Marine Fisheries, to determine the size of the local great white shark population, and to see how many return from year to year.
The Atlantic White Shark Conservancy, a volunteer organization, will be looking for the sharks from June through mid-October along the eastern coast of Cape Cod, between Truro and the southern tip of Monomoy Island.
Sharks tend to avoid humans, Wigren said, which makes them difficult to study and count.
"It's not easy to study them, which has been a huge issue historically. Within the last five years, Cape Cod has become an aggregate site for them, so scientists finally have predictable access," Wigren said.
As the multiyear study goes on, researchers will compare markings to see whether the sharks have visited waters near the Cape before.
A National Oceanic and Atmospheric Administration study published this month says the great white shark population has grown in the western North Atlantic, thanks in part to efforts to conserve sharks and their prey. Locally, sharks often prey on seals, whose population have grown significantly in the past two decades.
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But the shark that Wigren's group spotted did not seem to be after food at that moment.
"Where the shark was, I think we saw one random seal, shortly after we lost sight of the shark. The seal activity was quiet," she said.
Sharks rarely attack humans and sightings are nothing to be concerned about, said Greg Skomal, a senior biologist with the Division of Marine Fisheries. Anyone who sees a fin in the water should call the local harbormaster, who will alert researchers and other local authorities.
"This is common this time of year, as sharks start to move into the area to take advantage of the seal population," he said.
Gal Tziperman Lotan
can be reached at gal.lotan@globe.com.