Sharks are supposed to be the apex predators of the ocean, so how could a 2.2-metre-long pregnant shark seemingly get killed and eaten off the coast of Bermuda?
That is the question a team of US scientists was faced with when the porbeagle shark’s tracking device suddenly popped to the ocean’s surface off the coast of Bermuda 158 days after it was put on.
Former Arizona State University graduate Dr Brooke Anderson and her research team had been tracking a group of porbeagle sharks – an endangered species – off Cape Cod in Massachusetts between 2020 and 2022.
Porbeagle sharks are active, large and powerfully built predators growing up to 3.7 metres long and typically living for 30 years or more.
They are smaller cousins of the great white shark, but overfishing and habitat loss have left them vulnerable to extinction.
Data collected from the tag device showed that the shark had been mostly underwater in the five months since her release, only rising to the surface once.
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However, during one four-day period in March 2021, the tag’s temperature was at a steady 22 degrees, despite being at least 150 metres underwater.
The researchers could come up with only one explanation: the unfortunate porbeagle had been eaten by a larger predator and spent four days being digested, before the tagging device was excreted and rose to the ocean’s surface.
“This is the first documented predation event of a porbeagle shark anywhere in the world,” Anderson said.
The only two marine predators who produce internal body heat and are large enough to prey on an adult porbeagle shark in that part of the ocean were the great white shark and the shortfin mako.
Shortfin mako are known to eat smaller sharks, porpoises and sea turtles while great whites have been documented eating whales, dolphins and seals – but neither has previously been captured preying on a shark as large as the porbeagle.
“We often think of large sharks as being apex predators, but with technological advancements, we have started to discover that large predator interactions could be even more complex than previously thought,” Anderson said.
