A porbeagle shark shown here being hooked. Photo: Wikimedia Commons
In 2021, an 8-foot pregnant porbeagle shark was, apparently, eaten by another shark. The year before, researchers fitted her with a tag in order to learn more about her life and habitat, but they didn’t expect to find out about her death, too. Now, her story has been published in the journal Frontiers in Marine Science.
“This is the first documented predation event of a porbeagle shark anywhere in the world,” said lead study author Dr. Brooke Anderson, a marine fisheries biologist in the North Carolina Department of Environmental Quality, via an email to CNN.
Porbeagle sharks are relatively widespread. They call the Atlantic and South Pacific oceans and Mediterranean Sea home, and on occasion can grow to about 12 feet in length. They’re an elusive species, so we don’t actually know all that much about them.
Like many other sea-faring creatures, overfishing and fishing nets are killing far too many of them. They’re listed as vulnerable on the International Union for Conservation of Nature Red List of Threatened Species, and since they don’t reproduce all that frequently, the loss of a pregnant one is kind of a big deal.
“In one event, the population not only lost a reproductive female that could contribute to population growth, but it also lost all her developing babies,” Dr. Anderson continued. “If predation is more widespread than previously thought, there could be major impacts for the porbeagle shark population that is already suffering due to historic overfishing.”
Researchers suspect that whatever ate the porbeagle shark was either a great white shark or a mako. This particular porbeagle was tagged off Cape Cod with the hopes of figuring out where they go in order to ramp up protection efforts.
Tagging them certainly doesn’t sound like a pleasant experience for the shark, but it’s for the greater good. Using rods and reels, the scientists catch the sharks, bring them onto the vessel, stick a saltwater pump into their mouth so they can breathe, and then implant the tag.
“They actually calm down really well to make tagging easy,” Anderson said. “We’ve tagged dozens of porbeagle sharks in the past 10 years and are currently working on analyzing the data to determine the most important habitats for the population that can be prioritized for conservation and management directions.”
But about six months after watching this one, something weird happened. She had been spending nearly all over her time at depths of around 2,000 feet during the dat and 500 feet at night. The water temperatures down there are recorded by the tag. Suddenly, the tag began to register a constant temperature of 71.6 degrees Fahrenheit, which made no sense given the fluctuations of the water temperatures. Then, four days later, the tag floated to the surface.
This led the researchers to believe that the tag was ingested then pooped out.
“The first and most important data was the sudden spike in temperature recorded by the tag, even at 600 meters depth,” Anderson said. “This indicated right away that the tag was now inside the stomach of a warm-bodied predator such as a lamnid shark. There was also a slight change in the diving pattern recorded by the tag, which also indicated the tag was now tracking another animal (the predator).”
Although it is possible that the tag fell off the porbeagle early and was eaten by another shark, it’s unlikely.
“We often think of large sharks as being apex or top predators, but with technological advancements, we have started to discover that large predator interactions could be even more complex than previously thought,” Anderson explained. “It’s clear that we need to continue studying predator interactions, for example to estimate how often large sharks are hunting each other, and start to uncover what cascading impacts these interactions could have on the ecosystem.”
