A large predatory shark swimming
near Bermuda was gobbled up by an even bigger shark even swallowing the
tracking device that was attached to it in what scientists say is the
first recorded case of its kind. Porbeagle sharks (Lamna nasus) can grow to about
12 feet (3.6 meters) long. These large sharks patrol the Northern Atlantic Ocean as well as
parts of the oceans of the Southern Hemisphere, ranging into the Antarctic. Their muscular,
streamlined forms and angled, spear-like teeth make them formidable predators. But the porbeagle,
it seems, is not immune to predation itself. In a paper published Tuesday (September 3)
in the journal Frontiers in Marine Science, researchers describe the likely predation of a
porbeagle shark by one of its larger relatives. This is the first documented predation event
of a porbeagle shark anywhere in the world, study lead author Brooke Anderson, marine
fisheries biologist with the North Carolina Department of Environmental
Quality said in a statement. The pregnant female shark was tagged
in October 2020 using both a satellite transmitter and a pop-off satellite
archival tag (PSAT) near Cape Cod. Data from these devices was meant to track
the shark's depth and geographic range over time. While satellite transmitters are
permanent, the PSAT tags are designed to detach from the animal after a year,
having recorded data on its movements. The porbeagles follow their prey, changing
position in the water column throughout the day. Their depth is calculated using pressure
and temperature data from the PSAT tags. Anomalies in pressure and temperature
indicate that the animal has died, or the tag has somehow detached prematurely. In this case, the shark ranged between the
surface and 328 feet (100 meters) down until December 2020, when it began diving to
depths of up to 2,600 feet (800 meters) during the day and hovering around 650 feet
(200 meters) at night. It maintained that pattern as it moved south from where it was
tagged to waters off the shore of Bermuda. On March 24, 2021, the temperature patterns
that correlated to its recorded depth changed drastically. While the shark had previously
been moving through waters that ranged from 43.5 to 74.3 degrees Fahrenheit to
–(6.4 to 23.52 degrees Celsius), on that day the tag recorded temperatures
between 61.5 to 76.5 Fahrenheit (16.4 Celsius to 24.72 Celsius) despite
remaining at a similar depth range. The researchers believe this shift meant the tag
was inside the stomach of another shark at the time as temperatures were warmer than they
would have otherwise been at those depths. Based on the geographical ranges of sharks large
enough to eat a porbeagle, the predator was likely either a white shark (Carcharodon carcharias)
or a shortfin mako (Isurus oxyrhinchus), the authors said. A white shark seems more
likely given the more stable depth range of the tag while it was ingested makos tend to
make deeper dives and then rapidly ascend. The team said the finding has implications
for the porbeagle population a species already under threat from historic overfishing. It is
listed as vulnerable by the IUCN. The predation of one of our pregnant porbeagles was an
unexpected discovery, Anderson said. 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.