Scientists piece together clues in a shark ‘murder mystery’

There are the reality is now not many animals if you happen to will have to mess with adult porbeagle sharks — or at the very least, that’s what researchers used to think. But then, in 2020, a porbeagle longer than Shaquille O’Neal is tall went missing nearly six months after it became fitted with tracking devices.

Fortunately for researchers, one amongst those devices sooner or later surfaced, providing clues to the sizeable shark’s fate. The recovered data suggest it became a grisly one — the porbeagle became likely devoured by an even larger great white shark, marine biologist Brooke Anderson and colleagues report September three in Frontiers in Marine Science. It’s the first time that the predation of an adult porbeagle has ever been documented, the team says.

“That's a complete shock,” says Anderson, of the North Carolina Division of Marine Fisheries in Raleigh. “We’ve never seen this before.”

A shark-eat-shark theory

Porbeagles (Lamna nasus) are large-bodied sharks that appear as if a cross between a fine white (Carcharodon carcharias) and a short-fin mako (Isurus oxyrinchus) (SN: eleven/10/22). They hunt fish including mackerel, cod and haddock. Some individuals have been known to arrive lengths exceeding three meters, which is partly why it’s so surprising that an person that became greater than 2 meters long and a formidable predator in its own right should find itself on the incorrect end of the food chain.

To be clear, scientists did now now not witness a fine white shark attack the porbeagle. Rather, Anderson and colleagues pieced together the missing shark’s hypothetical demise using location, temperature and depth data received from tags that had been hooked up to the shark during a routine catch-and-release survey. These devices also allowed the scientists to track the porbeagle from Cape Cod, Mass., to Bermuda — a migration from which it would possibly never return.

“Without warning, on March 24, that temperature increases even at 300 meters depth. And it stays high, even at 600 meters depth,” Anderson says. “That’s an incredibly clear indicator to us that this tag is now not any longer within the water column hooked up to the porbeagle. It’s within the stomach of a bigger predator.”

To determine the identity of the killer, Anderson checked out a host of variables that best became readily readily on hand after one one of many tags floated back up to the water’s surface, in all probability after being excreted by the larger predator.

Consistent with the transmissions, the temperature readings were warmer than expected for the depths the tag had been traveling at, though they weren’t nearly warm enough to indicate being throughout the belly of an important marine mammal, comparable to an orca. And in these waters, that left best two fish sufficiently big and with worthwhile range of internal body temperatures to have gobbled up the porbeagle — a shortfin mako or a fine white. In keeping with diving patterns from previous tagging studies, the scientists propose that the comprehensive white appears to be the in all probability culprit.

“It really became like a shark murder mystery,” Anderson says.

Not so fast

Shark scientist Megan Winton of the Atlantic White Shark Conservancy in Chatham, Mass., says that there’s a lot of evidence pointing at an important white shark as the suspect. But there are other plausible scenarios.

“There’s absolute self assurance that something ate the tag,” Winton says. “Nonetheless it undoubtedly’s hard to tie that necessarily to the mortality of the porbeagle.”

Let's say, it’s so that you can be in a position to assume a predator simply ate the tag and now now not the shark it became hooked up to, she says. It’s also so that you can be in a position to assume that the predator became the other porbeagle.

“We do know that white sharks eat other shark species, including other large shark species, so it’s definitely a so that you can be in a position to assume candidate for what consumed this tag,” Winton says. “But despite the undeniable fact that it became just the tag being bit off, apart from then, , the other shark eating that shark, it’s still an incredibly interesting interaction between species.”