In the ocean food chain, large sharks generally only have to worry about sustaining themselves orcas from a distance — but a new study suggests that predators at the top of the food chain may need to be wary of themselves.
Researchers have discovered evidence that suggests the first known case of a porbeagle shark, which can grow up to 12 feet (3.6 meters) long and weigh 500 pounds (227 kilograms), being killed by a large predator. The findings were published Tuesday in the biology journal Frontiers in Marine Science.
This is not the first case of “shark cannibalism.” Jon Dodd, executive director of the Atlantic Shark Institute, who helped lead the study, said large sharks eating smaller sharks is a common occurrence. “In the open ocean, size matters, but there’s always something bigger,” he said.
In some cases, bull sharks, mako sharks and baby sand tiger sharksfor example, sharks even eat their own species.
But cases of large sharks eating other large sharks, the subject of this study, are rare, said lead author Dr. Brooke Anderson, a marine biologist with the North Carolina Department of Environmental Quality.
The death of the female porbeagle raises questions about whether this incident represents a broader trend among large predators, Anderson said. “With advances in technology, it’s possible that this is happening more frequently than we’ve just discovered,” Anderson said.
It’s impossible to know how many sharks are being eaten by other sharks, Dodd said, adding, “but if our experiments at the Atlantic Shark Institute are any indicator, there may be more than we think.”
A group of scientific researchers from across the United States discovered the porbeagle’s death while conducting a satellite tracking project in the Northwest Atlantic to better understand the shark species’ location, behaviors and environmental preferences. They were particularly curious about female porbeagles, which are known to cross long stretches of water to give birth to their young.
“We were really looking to understand the habitats that pregnant females use and try to determine where they might give birth,” Anderson said.
The victim of the attack, nicknamed Penelope by researchers, was one of 11 sharks that scientists tagged off Cape Cod in 2020 and 2022. Tracking tags were placed on the sharks’ dorsal fins and used to collect information about water depth and temperature. The tags stored the data until they fell off the sharks, at which point the data was transmitted to researchers via satellite.
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The tracking devices were designed to stay in place for a year, but five months into the experiment, Penelope’s data had already arrived. “As soon as I got the data from that tag, I knew immediately that something strange had happened,” Anderson said.
A few days before Penelope’s beacon was removed along the Bermuda coast, the water temperature The water level suddenly rose. It remained relatively high, even when it reached 600 meters below sea level, which is “very unusual,” Anderson said.
Anderson and his colleagues came to a heartbreaking conclusion: The porbeagle had been hunted and eaten by another ocean behemoth. “The only explanation for this data is that this tab is now in the stomach of a predator,” Anderson told CBS News.
The researchers aren’t 100 percent sure who the culprit was, but the predator’s diving pattern, which the researchers tracked by examining depth data collected by the tag, was similar to that of white sharks they’ve monitored in the past. “Based on that, it was probably, I would guess, an adult female white shark,” Anderson said.
Porbeagle sharks, which have historically been overfished, are considered an endangered species in some parts of the world. Given that they are already endangered, Anderson said the loss of pregnant females and their babies could be devastating to the population.
Sharks aren’t the only ones feeling the effects of this change. The masters of the deep maintain the balance of the underwater ecosystem by controlling small predator populations and adding essential nutrients to shallow waters.
“Humans rely heavily on the oceans for food and many other things, and the oceans need healthy shark populations,” Anderson said.
