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White shark detections off Cape Cod increased by 24 percent last year

But researchers are still tallying the numbers

Jon Dodd (left), executive director of the Atlantic Shark Institute, was on this boat last week deploying acoustic receivers that can detect tagged sharks in the waters off Block Island.Atlantic Shark Institute

More white sharks were detected in the waters off Massachusetts and Rhode Island in 2021 compared to previous years, according to data from two research organizations.

Detections of tagged white sharks have increased as the number of receivers deployed to detect them has gone up, according to Jon Dodd, executive director of the Rhode Island-based Atlantic Shark Institute.

“We see more detections, but we also have many more receivers,” Dodd said in a phone interview on Friday. “We know these sharks have been in this area for a long, long time...millions of years. We’re getting much better at detecting them now.”


The big question is, Dodd said, “What were the numbers before?”

White sharks, which were once hunted and considered a trophy catch, became a protected species in most federal waters in 1997 and in Massachusetts waters in 2005, according to the Cape Cod-based Atlantic White Shark Conservancy.

While white shark sightings and catch records suggest some level of population recovery in recent years, “stock status remains uncertain,” the organization’s website says.

By having more receivers in the water, researchers can get more detections, and that allows them to confirm not only which sharks are out there, but how they move around and at what pace, Dodd said.

The receivers can detect pings from tagged sharks within a range of 1,000 yards. Each tagged shark has a unique ping so researchers can determine its species, when it was tagged, and other information.

Dodd said the white sharks detected off the coast of Rhode Island don’t stick around; they appear to use those waters as a travel route to Cape Cod, where they can find an abundance of seals.

“They don’t even seem to pause,” said Dodd. “They’re literally passing through.”

According to the Atlantic White Shark Conservancy’s white shark logbook, 74 receivers recorded 136,135 white shark detections (of 117 individual sharks) off the coast of Massachusetts in 2020, compared to 169,198 detections (of 132 individual sharks) recorded from 65 receivers in 2021, and that number will only go up after all of the receivers have been accounted for.


Some receivers “have not yet been retrieved and downloaded, which is why the number of receivers currently reported for 2021 is lower than it was last year,” said Megan Winton, a research scientist with the Atlantic White Shark Conservancy, said in an e-mailed statement. “Detections from those receivers will be added once they are retrieved.”

Winton said 46 additional white sharks were tagged with acoustic transmitters last year. Each tag can last almost a decade before the battery dies.

“The greater number of detections logged in 2021 largely reflects the number of tagged sharks at liberty (swimming around the region),” she said.

Dodd said the Atlantic Shark Institute currently has 15 acoustic receivers in strategic locations in the waters off Rhode Island. (There are 11 receivers around Block Island; one at Scarborough Beach; one at the Center Wall in Galilee on Point Judith; one off Watch Hill in Westerly, at the southernmost tip of Rhode Island; and one off the coast of Fishers Island in New York, he said.)

In 2019, there were only three receivers in Rhode Island waters, and they detected three individual white sharks; in 2020 there were 10 receivers that detected 9 individual white sharks; and in 2021 there were 13 receivers that detected 11 individual white sharks, he said.


Emily Sweeney can be reached at Follow her @emilysweeney and on Instagram @emilysweeney22.