Weeks before a porbeagle shark was due to give birth, one of two tracking tags that marine scientists had placed on the animal floated to the surface near Bermuda.
The team didn’t expect the tag to reappear for months. It had been attached to the 6-foot-long creature just 158 days earlier, after they hoisted the shark onto a boat off Cape Cod, Massachusetts, in October 2020 and gave it an ultrasound. The removable tag was designed to stay in place for about a year.
“Something had gone seriously wrong,” said Brooke Anderson, who was working as a shark researcher at Arizona State University at the time.
A second tag, designed to transmit a signal when the shark’s fin broke the sea’s surface, will never do so again.
The data from the recovered pop-off tag revealed a curious trend. For about five months, the depth and temperature information seemed normal for the species. Then everything fell apart.
“All of a sudden the temperature increased, even at 600 meters down, and remained elevated,” Anderson said.
The creature’s diving pattern has also become strange.
“All the data pointed to the same conclusion: She had been eaten,” Anderson said.
Researchers determined that the explanation for the tag’s abnormal readings was that the device had spent several days in the stomach of another animal.
Anderson and his fellow researchers presented their findings in a study published Tuesday morning in the journal Frontiers in Marine Science. It’s the first evidence that a porbeagle shark was eaten by something even bigger.
The study authors named a few potential killers. They narrowed the list of suspects based on their biology. The tag’s temperature readings didn’t fit the profile of a mammal like an orca, for example. So the scientists focused on endothermic sharks, which have some warm-blooded abilities.
“It had to be a shark that could raise its body temperature above that of the surrounding water. It had to be large enough to cause enough damage to the porbeagle, and it had to inhabit the area where the predation occurred,” Anderson said.
The researchers concluded that a great white shark or shortfin mako must have nibbled on their pregnant mako and temporarily ingested the tag.
“I’m guessing it was an adult female great white shark, probably over 15 feet,” Anderson said.
Before that, researchers didn’t even think it was possible that porbeagle sharks could be preyed upon by these animals, she added.
The team’s initial goal was to track pregnant porbeagle sharks throughout their pregnancies and determine where these creatures typically travel to give birth.
In total, they found and tagged 11 porbeagles over two seasons in the Atlantic, hauling each one into their boat, laying the creature on the deck, giving the shark a hose of aerated salt water, and covering its eyes with a damp towel.
“We work like a NASCAR pit crew,” Anderson said….
