During a recent effort to track porbeagle sharks, researchers made a sad discovery. One of their signs showed strange water depths and unusual temperature readings, leading them to conclude that their subject had been eaten by a large shark.
This is the first recorded incident of sharks eating porbeagles, a development that could have dire consequences for a species that is already facing severe population declines.
Marine biologists, including former Arizona State University graduate student Brooke Anderson, went fishing for porbeagle sharks in the waters southeast of Cape Cod in October 2020, and again the same month, two years later. After being caught, researchers attached satellite-connected devices to the shark’s fins. The tags were designed to last on sharks for one year, after which they would go up. Once there, they can relay the data they’ve collected to Anderson and his colleagues.
In April 2021, while following sharks, they noticed that one pregnant female—about 2.2 feet long—was sending strange data. His transmitter had shut down near Bermuda after only five months, which was unusual enough. Even anonymity was the lesson of the week before the tag appeared. Temperatures measured during that time ranged between 61.5 degrees Fahrenheit (16.4 degrees C) and 76 degrees Fahrenheit (24.7 degrees C), much hotter than the water they were supposed to swim in. There can be only one reason: During that week, the tracker, and probably the pieces of the shark it was attached to, was in the digestive system of a predator.
Large porbeagles, growing up to 3.7 feet long and weighing up to 230 pounds, can be found lurking in the waters of the northern and southern Atlantic, Pacific, and Indian oceans. In the study, published in the journal Frontiers of Marine ScienceAnderson and his team concluded that only two predators would have been present in the part of the Atlantic where the porbeagle was eaten at that time of year—great whites and shortfin makos, both large sharks.
The discovery is “the first documented occurrence of a porbeagle shark attack anywhere in the world,” Anderson said in a press release.
This incident is scary because it can mean porbeagle sharks. Sharks are classified as endangered, with a 2016 National Oceanic and Atmospheric Administration report estimating that the stock has declined by nearly 90 percent due to overfishing and habitat loss. Porbeagles typically live up to 30 years of age (although some have been recorded as 65), but females reach sexual maturity around 13 years of age. Females give birth to an average of four cubs every year or two. That’s a slow reproductive cycle, which means the population has a hard time bouncing back once it starts to decline. Adding other sharks to the dangers, especially to pregnant women, makes the situation even more difficult.
“In one incident, people not only lost a woman giving birth that would have contributed to the increase in the population, but they also lost all the children who are still growing,” said Anderson. “If predation is more widespread than previously thought, it could have a major impact on the porbeagle shark which is already suffering from historic overfishing.”
Finding out that a rare, endangered shark has been eaten isn’t exactly welcome news in marine biology, but it may seem important. Now that researchers like Anderson know it’s happening, they can learn more about the story of giant sharks eating each other. That could lead to new strategies to save these terrifying, terrifying creatures while we still exist.
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