Just weeks before a porbeagle pup was expected to be born, one of two trackers that marine scientists had attached to the animal surfaced near Bermuda.
The team didn’t expect the tag to resurface for months. They attached it to the 7-foot creature just 158 days ago, after lifting the shark onto a boat off the coast of Cape Cod, Massachusetts, in October 2020 and giving it an ultrasound. The removable tag was designed to stay in place for about a year.
“Something went wrong,” said Brooke Anderson, who was a shark researcher at Arizona State University at the time.
The second tag, which was designed to transmit a signal when a shark's fin broke the surface of the sea, will never do so again.
The data from the recovered “dropout” tag showed a curious pattern. For about five months, the depth and temperature information seemed normal for the species. Then it went awry.
“Suddenly the temperature jumped sharply, even at a depth of 600 meters, and remained high,” Anderson said.
The creature's diving habits also became strange.
“All the evidence points to the same conclusion: she was eaten,” Anderson said.
The researchers determined that the tag's abnormal readings were due to the device spending several days in another animal's stomach.
Anderson and her fellow researchers outlined their findings in a study published Tuesday morning in the journal Frontiers in Marine Science. It's the first evidence that the porbeagle shark was eaten by something even bigger.
The study's authors named several possible killers. They narrowed the pool of suspects based on their biology. The tag's temperature readings didn't match the profile of a mammal, such as a killer whale. So the scientists focused on endothermic sharks, which have some warm-blooded capabilities.
“It had to be a shark that could raise its body temperature above the surrounding water temperature. It had to be large enough to cause enough damage to the porbeagle, and it had to be in the area where the predation occurred,” Anderson said.
The researchers concluded that a great white or shortfin mako shark must have eaten a pregnant female porbeagle and temporarily swallowed the tag.
“I'm guessing it was an adult female great white shark, probably over 15 feet long,” Anderson said.
She added that before this, researchers did not even consider it possible that herring sharks could become an object of hunting.
The team's initial goal was to follow pregnant porbeagle sharks throughout their pregnancy and find out where the creatures typically go to give birth.
In just two seasons in the Atlantic, they found and tagged 11 porbeagles by lifting each one into their boat, laying the creature on the deck, dousing the shark with a hose filled with aerated salt water and covering its eyes with a wet towel.
“We operate like a NASCAR pit crew,” Anderson said. Eight of the sharks were pregnant.
Her team had no idea that they would be about to uncover a deep-sea murder mystery.
Matt Davis, a marine resource specialist with the Maine Department of Marine Resources who was not involved in the study, said the new study's findings “definitely ring true.”
Davis added that the incident shows that scientists still have much to learn about the lives and relationships of predators and prey in the mid-ocean depths.
The porbeagle shark is listed as vulnerable International Union for Conservation of Nature because they have been overfished since the 1960s. By 2001, the species' population was estimated to have declined by 75 to 80 percent, Anderson said.
The species is recovering thanks to fishing regulations, but recovery will take decades, if not longer, as porbeagle sharks can live in the Atlantic for 30 to 40 years and produce relatively few pups compared to other species.
“We need to continue to tag and track these sharks to see how often this is happening,” Anderson said of the predation. “In one fell swoop, this already depleted species has lost not only an important reproductive female, but all of her developing young. We need to better understand how often this is happening and what impact it may have on the population.”
In the Atlantic, where sharks eat sharks, their research could ultimately help restore the species to health.
This article was originally published on NBCNews.com