New Study Reveals Dusky Sharks Preying On Seals For First Time Off Nantucket

A new study confirms what scientists have known for years: dusky sharks are eating seals off the coast of Nantucket.

There are few known predators of seals in the Atlantic Ocean, but scientists can add one more to the list after a team of researchers captured what is believed to be the first aerial video showing a dusky shark killing and eating a grey seal near Nantucket.

“It's one of the most exciting things I've been involved with as a shark scientist because it really changes the way we see this species,” said Megan Winton, a senior scientist at the Atlantic White Shark Conservancy and the lead author of the study.

Two years ago, in July of 2023, boaters and beachgoers took photos and videos of sharks preying on seals off Great Point, and scientists later confirmed that the sharks in question were dusky sharks, not white sharks, as initially thought. This was notable because, until then, there was no evidence that dusky sharks ate seals.

One study from South Africa had found a seal in the stomach of a dusky shark, but at the time, scientists thought it was the result of a scavenging event, rather than part of the shark’s usual diet.

Now, the evidence is irrefutable. A team of scientists from the Atlantic White Shark Conservancy, the New England Aquarium, and the Massachusetts Division of Marine Fisheries published a study in the scientific journal Environmental Biology of Fishes, providing evidence that changes the existing understanding of the diet and ecological role of the dusky shark.

“Though the observations we’re reporting are preliminary, they have changed our understanding of the feeding ecology of dusky sharks, which are considered endangered on a global scale, as well as predatory interactions between sharks and seals in the waters off Massachusetts,” Winton said. “This footage provides us valuable insight into understanding the behavior of a shark species that experienced steep population declines in the mid-20th century but now seems to be recovering and reassuming an important ecological role.”

Though dusky sharks hadn’t been observed preying on seals before, scientists don’t think the behavior is new. Instead, they think it’s more likely that as populations of sharks and seals have rebounded dramatically in recent decades, the species are returning to old ecological niches and behavioral patterns that were once common before human intervention disrupted their populations. Those behavior patterns were never observed before because by the time the relevant science began to develop, the populations had already collapsed.

“It seems likely this was a historically important predator-prey relationship,” Winton said. “I think we're going to keep seeing some of these ecological surprises as some of these species make a comeback.”

“This work opens a new chapter in our understanding of how recovering shark populations in the US Atlantic may influence the ecological structure of coastal ecosystems,” said co-author Dr. Gregory Skomal, Senior Fisheries Biologist at Massachusetts Division of Marine Fisheries and Director of the Massachusetts Shark Research Program. “These incredible observations, a first for this species, raise important questions about how these predators may impact both wildlife management and public safety as they return to their historic habitats.”

It’s another piece of evidence supporting the effectiveness of conservation efforts, including the Marine Mammal Protection Act, which is currently under threat from Congress.

“We don't really know what the waters around Cape Cod and the Islands are supposed to look like. We don't know,” Winton said. “There's a part of me that does worry history will repeat itself, just as we're starting to get a glimpse into what these ecosystems should look like.”

It’s also an example of the power of public engagement. Scientists were initially alerted to the possibility that dusky sharks are preying on seals because of photos and videos taken by members of the public, highlighting how public interest and the proliferation of high-quality cameras have impacted scientific efforts in recent years.

“That is one of my favorite things about this story is that members of the public first documented this,” Winton said. “It's a great example of the role members of the public and citizen scientists can play in exciting science.”