Thanks to tracking equipment, experts have recorded for the first time a porbeagle shark being eaten by a predator, most likely a great white shark.
A team of scientists at Arizona State University attached tracking devices to porbeagle sharks (Lamna nasus) was pregnant and was suddenly discovered to have disappeared after a few months. It is likely that this 2.2-meter-long animal was attacked by a larger predator. The research results were published in the journal Frontiers in Marine Science September 3rd
“This is the first case of porbeagle sharks being hunted and eaten anywhere in the world,” said Brooke Anderson, lead author of the study and a former graduate student at Arizona State University. Anderson’s team had previously tagged porbeagle sharks off Cape Cod, Massachusetts, to study their migration patterns.
Each shark was fitted with two satellite devices: a transmitter mounted on its fin and a floating satellite storage device (PSAT). The fin-mounted device tracked location, while the PSAT measured depth and temperature. Interestingly, when separated from the shark, the PSAT would float to the surface and continue transmitting data.
The team was particularly interested in a pregnant shark that was tagged in October 2020. It was normally active in waters from the surface down to 100 meters deep. But in December 2020, the tag showed it began diving as deep as 800 meters during the day and about 200 meters at night. It continued this activity as it moved south, where it was tagged, to waters off Bermuda.
On March 24, 2021, the temperature patterns corresponding to the depth changed significantly. While the shark had previously moved through water with temperatures ranging from 6.4 to 23.52 degrees Celsius, that day the tracking device recorded temperatures of 16.4 to 24.72 degrees Celsius, even at the same depth range.
The team believes this change suggests the device was in the stomach of another shark, as the temperature was warmer than it would be at that depth. Based on the geographic range of sharks large enough to eat porbeagle sharks, they believe the predator was likely a great white shark (Carcharodon carcharias) or shortfin mako shark (Isurus oxyrhinchus). Great white sharks are more likely because the tracking device records a stable depth range after being swallowed, while mako sharks tend to dive deeper and then quickly surface.
The new research has important implications for porbeagle shark populations, which have been threatened by overfishing in the past. “We used to think of large sharks as apex predators. But with advances in technology, we’re starting to discover that the interactions between large predators may be more complex than previously thought,” Anderson said.