A pregnant 7-foot porbeagle shark appeared to have been eaten by an even larger shark in what researchers believe is the first such evidence of the ocean hunter becoming the hunted.
Researchers captured the porbeagle shark near Cape Cod, Massachusetts, in late October 2020 and attached two tracker tags – one mounted on the shark’s dorsal fin to transmit its geolocation and a second tag, called a pop-off satellite archival tag (PSAT), that measures the temperature and shark’s depth in the ocean, scientists wrote in a paper published Tuesday in the journal Frontiers in Marine Science.
The PSAT is designed to detach from the shark after about a year, but in this case the device popped off after about five months near Bermuda.
"Something had gone very wrong," Brooke Anderson, one of the researchers, told NBC News.
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The data collected from the shark showed that in the days before the tag detached, its diving patterns had become erratic. Its temperature readings also increased despite swimming at a deep enough depth that would have made the readings much cooler, according to the study.
Using this data, researchers determined that the tag had spent several days in the stomach of another animal. Mammals like the orca were ruled out due to having warmer temperature readings, so the scientists focused on endothermic sharks.
"The data presented in this study is, to the best of our knowledge, the first evidence of predation on a porbeagle and provides novel insight into inter-specific interactions for this large, globally vulnerable shark species," the study states.
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The researchers surmised that the ocean apex predator had become prey for a bigger shark, of which they say only two are big enough to have eaten the pregnant 7-footer: the white shark and the shortfin mako.
James Sulikowski, director of the Coastal Oregon Marine Experiment Station at Oregon State University who also took part in the research, told USA Today that the study shows the ocean still contains many mysteries that scientists want to solve.
"It makes us want to study more and learn more about how susceptible other large sharks are to be eaten and who is the top dog out there," he said.
