Shark-on-shark crime: Unprecedented shark murder in Bermuda Triangle

By Stephen Beech via SWNS

Great white sharks are hunting and killing other large sharks , suggests new research.

The first known case of a porbeagle shark being eaten by another large apex predator has been discovered.

Marine scientists believe the pregnant porbeagle was killed by another shark species - with a great white being the most likely culprit - thanks to evidence provided by a swallowed tracking device.

Details of the astonishing high-tech version of Cluedo played out in the notorious Bermuda Triangle, were published in the journal Frontiers in Marine Science .

Lead author Dr. Brooke Anderson, of Arizona State University , said: “This is the first documented predation event of a porbeagle shark anywhere in the world.

“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.”

Porbeagles, classed as an "endangered" species, inhabit the Atlantic and South Pacific Oceans as well as the Mediterranean.

They are large and powerfully built – up to 3.7 meters (12 ft) long and weighing up to 230 kilos (36 stone) – and live for up to 65 years.

Dr. Anderson explained that females don’t reproduce until they are about 13 years of age, and then give birth to an average of four pups every one or two years, born live after a gestation period of between eight and nine months.

She said that because of their slow reproductive cycle, porbeagle populations can't recover quickly from persecution, recreational fishing, bycatch and habitat loss threats to which they currently are exposed.

Northwest Atlantic porbeagles are listed as "endangered" on the IUCN Red List of Threatened Species, while the Northeast Atlantic and Mediterranean populations are classed as "critically endangered".

As part of their research into shark migration , Dr. Anderson and her colleagues captured porbeagles off Cape Cod, Massachusetts, in 2020 and 2022.

Each porbeagle was equipped with two satellite tags, a fin-mount satellite transmitter and a pop-off satellite archival tag (PSAT), before being released.

Fin-mount tags send the current location to satellites whenever the shark’s fin rises above the surface.

PSATs continuously measure depth and temperature and store the data until the tag falls off, usually after a predetermined period, after which they float to the surface and transmit their stored data to satellites.

Among the tagged porbeagles was a 2.2-metre (7.2 ft) pregnant female.

Dr. Anderson and her team hoped to obtain data from the females to help identify important habitats for porbeagle mothers and their pups.

But, unexpectedly, the female’s PSAT started to transmit off Bermuda 158 days after its release, implying that it had popped off and was now floating on the surface.

Data then transmitted showed that the female had been cruising for five months at a depth between 100 and 200 meters (328 and 656 feet) at night and between 600 and 800 meters (1,968 and 2,635 ft) during the day, in waters with a temperature between 6.4 and 23.5 degrees Celcius.

During that period, the fin-mount tag was transmitted only once, confirming that the shark remained underwater most of the time.

But suddenly, from March 24, 2021, onwards over a period of four days, the temperature as measured by the PSAT remained at around 22C, at a depth between 150 and 600 meters (492 and 1,968 ft).

The research team said that only one explanation was possible: that day, the pregnant porbeagle had been hunted and eaten by a larger predator.

The PSAT must then have been excreted about four days later, starting to transmit.

Dr. Anderson said: “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 and shortfin mako."

Shortfin mako sharks are known to feed on octopus, bony fish, small sharks, porpoises, sea turtles, and seabirds, while great whites feast on whales, dolphins, seals, and rays.

Of the two candidates, the researchers say the great white is considered the more likely culprit, as shortfin mako typically make rapid oscillatory dives between the sea surface and deeper depths during the day while in the open ocean – a behavior not registered by the PSAT.

Dr. Anderson said: “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."

She added: “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.”

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