What Killed and Ate a Really Big Shark? An Even Bigger Shark, Scientists Say

When marine biologist James A. Sulikowski began monitoring the migration and mating habits of porbeagle sharks, he didn’t expect to find himself investigating a crime.

But when Penelope, an 8-foot-long porbeagle, disappeared from his research team’s radar, he and his colleagues eventually concluded that she had suffered a gruesome fate when she became someone’s dinner.

Their prime suspect? Another, even bigger shark.

“Penelope was a big shark, and the thought of something big eating her is terrifying,” said Sulikowski, director of the Big Fish Lab at Oregon State University. As it happens host Nil Köksal.

“The fact that this happened … is mind-blowing to us.”

Sulikowski and his colleagues published a study in the journal Frontiers in Marine Science presenting the first evidence that porbeagle sharks have natural predators, as well as a rare case of one large adult shark preying on another.

Scientists who were not involved in the study say the study’s conclusions are plausible, but more research is needed to definitively conclude that Penelope was the victim of a shark attack on another shark.

“Something really weird happened”

Sulikowski says porbeagle sharks are fast-moving sharks that can regulate their own body temperature, allowing them to survive in both cold and temperate waters. They can grow to 12 feet long and were previously thought to have no natural predators.

However, they are hunted by humans for their meat, and sometimes end up as bycatch from long-distance boats fishing for tuna and swordfish. They are listed as a globally vulnerable species by the International Union for Conservation of Nature.

That’s why Sulikowski and his colleagues are catching, tagging and tracking porbeagle sharks, especially pregnant females, to better understand their mating and migration routes, as part of conservation planning for the species.

They tagged and released Penelope off Cape Cod in 2020. The satellite tags, which measure depth and temperature, are designed to last for a year, Sulikowski said. But Penelope unhooked herself after just five months.

“They don’t usually just throw something out there without warning,” he said. “When we started analyzing the data, it was like, wow, something really weird happened.”

The data showed Penelope was swimming 600 metres below the surface when the temperature suddenly rose from 15°C to 27°C. She stayed that way for several days, while “cycling up and down in the water,” he said.

This means the device most likely landed “in the belly of a predator,” Sulikowski said.

That predator, he said, would have to be larger than Penelope. Given the depth and the location of the marker, only two reasonable suspects remain: a great white shark or a shortfin mako shark.

“Another murder”

Shark biologist Alison Towner, who was not involved in the research, told CBC the study’s conclusions are “not only intriguing, but also quite plausible.”

“White sharks have a varied diet, and although satellite data often show patterns such as oscillatory diving in open ocean environments, it is not always clear what they are preying on,” Towner, a research associate at the South African International Maritime Institute, said in an email.

“In this case, the observed temperature increase fits well with what would be expected from a white shark predation event.”

Not everyone is convinced. Megan Winton of the Atlantic White Shark Conservancy in Chatham, Mass., told Science News it’s possible another shark ate the tag, but not Penelope.

Sulikowski thinks this is unlikely.

“When a shark goes to eat, it doesn’t bite. It takes a big piece,” he said. “The tag she was wearing was halfway down her body. So that event probably tore her in half or tore off a piece of her body.”

Moreover, he added that “another murder” occurred in the same place a year after Penelope.

In this case, he says, another porbeagle they were tracking suddenly dove to the ocean floor, suggesting it was killed, and what was left of its body sank — along with the transmitter.

“When you put those two things together, you probably conclude that something ate both sharks,” he said.

Sharks eat sharks, not people.

If the authors are correct, it would not be the first time a shark has preyed on another shark, says Toby S. Daly-Engel, director of the Florida Tech Shark Conservation Lab.

She said large sharks are known to prey on smaller shark species and even smaller members of their own species.

Still, Daly-Engel, who was not involved in the study, said: “The study is cool.”

“What’s novel about this is that the shark that was eaten was an adult, so it had to be something big,” she told CBC.

Asked if the gruesome discoveries cast a negative image on the sharks he is trying to protect, Sulikowski said it is actually good news for those who fear being swallowed by the sea.

“Sharks are on the shark menu, OK? We, as human beings, are not on the shark menu. If we were, there would definitely be a lot more people in the ocean,” he said.

“We’re a lot slower than porbeagle sharks and we like to splash around… so we’d be easy prey.”