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Swallowed tag suggests large sharks are chowing down on one another, study shows
Researchers from the US have been perplexed over the mystery of a dead shark, only to discover that it might have been eaten by another of its own kind.
Despite it being more likely that you’d be killed by a cow than a shark, the world is obsessed with the toothy predators. Still, they are deadly creatures and expert warnings should be heeded in case of an encounter.
Turns out sharks can be cannibals
It’s been a busy few months in the world of sharks, with numerous firsts popping up after scientists captured the first recorded instance of a boat hitting a shark.
In a new study published this week in the Frontiers in Marine Science, scientists found another first following an intense game of cat and mouse. They initially set out to discover what happened to a tagged pregnant porbeagle shark, only to discover it met a grizzly end.
This is the first documented predation event of a porbeagle shark anywhere in the world, said lead author Dr Brooke Anderson from Arizona University. In one event, the population not only lost a reproductive female that could contribute to population growth, but it also lost all her developing babies. If predation is more widespread than previously thought, there could be major impacts for the porbeagle shark population that is already suffering due to historic overfishing.
Porbeagle sharks are native to the Atlantic, South Pacific, and Mediterranean oceans where they grow to around 3.7 meters long (15 feet) and 230kg.
Though they can live to the grand age of 65, porbeagle sharks have an extremely slow reproductive cycle which has led them to be placed on the endangered species list thanks to years of environmental stresses, fishing, and pollution.
While conducting research on the species between 2020 and 2022, researchers tagged a 2.2-meter-long pregnant female. Just 158 days after its release, the shark’s tag popped off.
The scientists put on their detective caps
The scientists soon realized that their porbeagle shark had been eaten by a larger predator, but what is ferocious enough to eat a shark? Another shark, of course.
Two endothermic predator candidates large enough to predate upon mature porbeagles and located within the vicinity and at the time of year of the predation event include the white shark Carcharodon carcharias and shortfin mako Isurus oxyrhinchus, wrote the authors.
By analyzing the data the tracker provided before its, for lack of a better term, release, the researchers theorized that a Great White Shark was the criminal they were hunting. Mako’s typically prefer smaller prey and move at a rate not registered by the tracker.
The predation of one of our pregnant porbeagles was an unexpected discovery. 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, said Anderson.
We need to continue studying predator interactions, to estimate how often large sharks hunt each other. This will help us uncover what cascading impacts these interactions could have on the ecosystem.
