Scientists Tag 7-Foot Shark with Tracker, Realize Something's Wrong When Strange Readings Come Back
Researchers tracking a large shark may have stumbled on a disturbing first-of-its-kind discovery after recovering one of the tags.
The apex predator, a 7-foot pregnant porbeagle shark, was caught by scientists off the coast of Massachusetts in October of 2020 and tagged with two tracking devices.
One of the devices affixed to the fish’s fin was designed to transmit a signal when it broke the surface of the water. The other, called a pop-off tag, pops off after roughly a year and floats to the surface, providing scientists with critical data.
The tags and tracking program aim to discover more about the shark species’ reproductive cycle and to pinpoint where the mothers give birth.
According to NBC News, those watching the shark realized something wasn’t right when the pop-off tag floated to the surface only 158 days after being attached to the shark.
The device held a disturbing record.
Data on the tag reveals the first months were normal, showing depth and temperature readings expected from an active shark. Then, the record took a shocking turn.
“Something had gone very wrong,” Arizona State University shark researcher Brooke Anderson told NBC.
“All of a sudden, the temperature spiked, even at 600 meters depth, and stayed elevated.”
Typically, water grows colder as depth increases. The increase in depth coupled with the relatively high and consistent temperature pointed to a potential reality nobody expected.
The other tag, designed to stay attached to the shark and transmit at the ocean’s surface, has been completely silent.
“All of the data pointed to the same conclusion,” Anderson said. “She had been eaten.”
This is the first report of a porbeagle shark of this size being turned into prey, a feat that seemingly can only be accomplished by a much larger animal.
Researchers published the discovery in the Frontiers in Marine Science journal.
“Given the location of predation and elevated temperature at depth recorded by the pregnant porbeagle’s tag, potential predators include endothermic shark species such as the white shark Carcharodon carcharias and shortfin mako Isurus oxyrhinchus,” the article states.
“This is the first evidence of predation on a porbeagle globally and provides novel insight into inter-specific interactions for this large, threatened shark species.”
Scientists dismissed the possibility that a predatory marine mammal such as the orca had anything to do with the shark’s apparent disappearance.
“Large marine mammals,” the article explains, “such as odontocete whales (e.g., Orcas Orcinus orca) maintain much higher internal temperatures (close to 40°C; Whittow et al., 1974; Strøm et al., 2019) and so were not considered as a potential predator in this instance.”
Anderson’s educated guess is that the porbeagle’s predator is a mature female great white shark, “probably 15-feet plus.”
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