Pregnant shark that disappeared could have been eaten by one other shark

A pregnant porbeagle shark could have been eaten by an awesome white shark close to Bermuda, within the first recorded incident of its sort.

In October 2020, Brooke Anderson, then at Arizona State College, and her colleagues tagged a pregnant porbeagle shark (Lamna nasus) south-east of Cape Cod in Massachusetts as a part of analysis into pregnant shark migration.

The researchers used pop-off tags, which constantly measure the depth and temperature of the shark. When the tag detaches from the shark and floats to the floor, the saved knowledge is pinged again to shore.

5 months after the pregnant shark was tagged, the tag resurfaced south-west of Bermuda and the researchers acquired knowledge on its current actions.

The shark had spent 5 months cruising via waters at a depth of 600 to 800 metres throughout the day and 100 to 200 metres at evening, with water temperatures various from 6.4 to 23.5°C (43.5 to 74.3°F), based on the tracker.

However from 24 March 2021, one thing modified. The ambient temperature across the pregnant shark remained between 16.4°C and 24.7°C (61.5°F and 76.5°F), regardless of it swimming at the same depth to earlier than. In addition to the change in temperature, there was a shift in diving patterns.

It suggests the tag – and the connected shark – was eaten, says Anderson, who now works at North Carolina Division of Marine Fisheries. “All our evidence points to the same conclusion,” she says. “It’s clear that our porbeagle shark was eaten by another shark.”

An important white shark (Carcharodon carcharias) is the almost certainly offender, the crew concluded, as it’s the solely predator within the space giant sufficient to mount such an assault. The diving patterns and physique temperature of an awesome white additionally match the info collected by the tag.

“This was a big female shark that got eaten,” says crew member James Sulikowski at Oregon State College. “So something probably larger than it had to have attacked it.”

Anderson says the assault was almost certainly opportunistic. “The predation occurred about 300 meters deep in the open ocean where there may be sporadic pulses of prey available for predators,” she says. “In this scenario, if you can pull it off, a large pregnant porbeagle shark would be a lot of bang for your buck in terms of a meal.”

Porbeagle sharks, that are endangered, are discovered within the Atlantic Ocean, the South Pacific Ocean and the Mediterranean Sea. They develop as much as 3.7 metres lengthy, can weigh as much as 230 kilograms and stay for as much as 65 years.

Feminine porbeagle sharks don’t begin breeding till they’re about 13 years outdated, and provides delivery to round 4 pups each one or two years, with a gestation interval of 8 to 9 months.

Shark-on-shark predation is comparatively widespread, says Sulikowski, however it’s uncommon for a shark to focus on one other giant shark in deep water. That is the primary documented case of a porbeagle being eaten by one other shark.

Whether it is taking place extra extensively, it might be a fear for conservationists, says Anderson. “In one instant, the population not only lost one of these important reproductive females, but also all of her babies,” she says. “While predation is a natural event, this discovery highlights the need to continue studying predation of porbeagle sharks and to determine how often it really occurs.”

Nevertheless, Chris Lowe at California State College, Lengthy Seaside, says the paper doesn’t show it was a shark that ate the porbeagle. There have been situations of orcas consuming giant sharks, he factors out. “There was clearly some predation event, but [I’m] not sure without seeing the data that I could be convinced that it was limited to lamnid sharks,” he says.

A 12 months later, one other shark tagged by the group additionally died at the same depth, in the identical space close to Bermuda, says Sulikowski. In that case, although, the shark sank to the underside of the ocean. Sulikowski believes this was a case the place the shark was attacked and will have solely partially been eaten.