'We snuck up on sharks.' Scientists estimate hundreds off Cape Cod

Armed with underwater GoPro cameras and guided by a spotter pilot, a team of shark scientists spent four years patrolling coastal waters in search of the holy grail: a number.

Their effort to track the movement and turnover of great white sharks led to a conclusion that was less than surprising. After all, scientists had always assumed that Cape Cod is the country's most frequented destination for sharks. But now, for the first time, a true estimate points to how many predators are roaming the North Atlantic at any given time.

An estimated 800 sharks came through the region between 2015 and 2018, according to a new study by the Atlantic White Shark Conservancy, UMass Dartmouth's School for Marine Science and Technology, and the Division of Marine Fisheries.

The number confirms that the species is returning to the ecosystem following a steep population decline due to overfishing, said Megan Winton, the study's lead author.

The population estimate relied on repeated surveys and thousands of videos captured during more than 100 trips at sea. Scientists were able to tell the sharks apart based on markings and notches in their dorsal fins.

Not all 800 sharks were here at the same time.

"One of the tricky things about white sharks is that they move so much—they're constantly moving into and out of the area," Winton said.

That turnover underscores the need to monitor the population and reinforce public safety, she said. It also has scientists curious: Are sharks hunting at certain times of day? And when are they likely to be close to shore?

Sharks are often hunting for seals in depths less than 15 feet, Winton said, but the risk of encountering a great white is low.

"They are very cautious predators," Winton said. "But the increased presence and number of white sharks off the Cape really drives home the need for ongoing research."