This is the first estimate of abundance for great white sharks (Carcharodon carcharias) in the western North Atlantic Ocean, the researchers said. The finding “suggests that Cape Cod is among the larger aggregation sites worldwide,” the authors wrote.
So why are these apex predators gathering off Cape Cod’s coasts? Because that’s where their favorite meal resides, explained study co-author Megan Winton.
“Over the course of the past 10 years, white sharks have come back to Cape Cod to feed on the recovering seal population,” Winton, a marine researcher and member of the nonprofit organization Atlantic White Shark Conservancy, told The Inertia.
Humans hunted gray and harbor seals to the brink of extinction in the 1960s, but their populations have dramatically increased since 1972 when the U.S. Marine Mammal Protection Act was passed, which makes it illegal to catch or kill marine mammals without a permit. Now, there are roughly 30,000 to 50,000 gray and harbor seals in southeastern Massachusetts, according to a 2016 estimate. As a result, the number of great white sharks in this area has also been steadily rising, the new study found.
To track their numbers, the researchers identified individual sharks by analyzing tagging data and recording their unique coloration patterns using underwater GoPro cameras. After more than 130 research trips over three years, they identified 393 individual great white sharks from 2015 to 2018.
However, the researchers also wanted to account for the sharks’ migratory behavior, so they developed a model to calculate how many sharks were moving in and out of the area, and estimated that roughly 800 sharks aggregated in this region over the three-year period.
In the 1980s, great white shark populations i