While tracking porbeagle sharks recently, researchers made a horrifying discovery. One of their tags transmitted strange water depth and temperature readings, leading them to conclude that their subject had been eaten by a larger shark.
This is the first recorded incident of a shark preying on a porbeagle shark, an incident that could have dire consequences for a species already facing severe population declines.
Marine biologists, including former Arizona State University graduate student Brooke Anderson, caught porbeagle sharks in the waters southeast of Cape Cod in October 2020 and again in the same month two years later. After capture, researchers attached satellite-connected transmitters to the shark’s fins. The tag designs remain on the sharks for a year, after which they surface. Once there, they can transfer the collected data to Anderson and her colleagues.
In April 2021, while tracking sharks, they noticed that a seven-foot-long (2.2-meter) pregnant female shark was sending back some strange data. Just five months later, her launcher broke away near Bermuda, which was unusual. Even stranger were the readings from the week before the tag appeared. Temperatures measured during that time ranged from 61.5 degrees Fahrenheit (16.4 degrees Celsius) to 76 degrees Fahrenheit (24.7 degrees Celsius), much warmer than the water she was supposed to be swimming in. The shark fragments presumably ended up in the predator’s digestive system.
Porbeagle sharks are large, reaching lengths of up to 12 feet (3.7 meters) and weights of up to 500 pounds (230 kilograms), and can be found in the waters of the North and South Atlantic, Pacific and Indian Oceans. Research published in journal Frontiers of Marine ScienceAnderson and her team concluded that at this time of year, only two predators exist in the area of the Atlantic where porbeagle sharks are eaten – great white sharks and shortfin mako sharks, both of which are large sharks.
Anderson said in a press release that the discovery was “the first documented predation event of a porbeagle shark in the world.”
The incident is shocking because of what it could mean for the porbeagle shark community. These sharks are listed as endangered, and a 2016 National Oceanic and Atmospheric Administration report estimated that their numbers have declined by 90 percent due to fishing and habitat loss. Porbeagle sharks generally live to be around 30 years old (although some have been recorded as being as old as 65), but female porbeagle sharks don’t reach sexual maturity until around 13 years old. . This is a relatively slow reproductive cycle, which means that once the population begins to decline, it is difficult to rebound. Adding other sharks to the mix, especially pregnant females, only makes the situation even scarier.
“In one event, not only did people lose a fertile female that might have contributed to population growth, but they also lost all of their developing babies,” Anderson said. “If predation was more widespread than previously thought, “There could be significant impacts on porbeagle shark populations that are already suffering from historical overfishing.”
Finding a rare endangered shark eaten isn’t great news for marine biologists, but it could be significant. Now that researchers like Anderson know this happens, they can further study the phenomenon of large sharks eating each other. This could lead to new strategies to save these terrifying and awe-inspiring creatures while still having time.
