Evidence Suggests Large Sharks May Be Hunting One Another, Researchers Say

In the intricate web of the ocean’s food chain, large sharks have typically few adversaries aside from orcas. However, a recent study has unveiled a startling revelation: these apex predators may now have to be vigilant of threats from their own kind.

Researchers have documented the first known instance of a porbeagle shark, which can reach lengths of up to 12 feet and weigh around 500 pounds, being killed by a larger shark predator. This significant finding was published in the biology journal Frontiers in Marine Science.

This is not the first documented case of “shark cannibalism.” According to Jon Dodd, executive director of the Atlantic Shark Institute, which contributed to the study, larger sharks consuming smaller individuals is a frequent occurrence. He explained, “In the open ocean, size matters, but there is always something bigger out there.”

Instances of sharks consuming their own species are also not uncommon, with bull sharks, mako sharks, and baby sand tiger sharks known to exhibit this behavior. However, cases involving larger sharks preying on others of similar size are notably rare, as highlighted by lead author Dr. Brooke Anderson, a marine biologist with the North Carolina Department of Environmental Quality.

The death of the female porbeagle raises important questions about potential shifts in behavior among large predators. Anderson commented, “With advancements in technology, we may discover that such occurrences happen more frequently than we have previously realized.”

The true scale of sharks consumed by other sharks remains elusive, but Dodd suggests that observations at the Atlantic Shark Institute indicate it might be more common than the scientific community perceives.

A coalition of researchers from various institutions across the United States made this alarming discovery while undertaking a satellite tracking project in the Northwestern Atlantic. The project aimed to deepen understanding of porbeagle sharks, particularly focusing on their locations, behaviors, and environmental preferences.

Researchers were particularly interested in female porbeagles, known for their extensive oceanic journeys to give birth. “We were eager to understand the habitats utilized by pregnant females and pinpoint potential birthing sites,” Anderson explained.

The shark at the center of this investigation, affectionately named Penelope, was one of eleven sharks tracked after being tagged off the coast of Cape Cod between 2020 and 2022. Researchers affixed tracking devices to the dorsal fins of the sharks, designed to record important data such as water temperature and depth. These devices stored data until they naturally detached from the sharks, sending the information back to researchers via satellite upon detachment.

Initially, the tracking devices were expected to remain attached for a year. However, just five months into the study, data from Penelope began to raise alarm bells. “As soon as I received the information from that tag, something didn’t seem right,” Anderson recalled.

Days before Penelope’s tagging device was dislodged off Bermuda’s coast, researchers noted an unusual spike in water temperature. This abnormal high temperature persisted, even reaching profound depths of 600 meters underwater, an observation Anderson described as “very unusual.”

From this data, the authors surmised the grim fate of the porbeagle: she had likely been hunted and consumed by a larger sea predator. Anderson stated, “The only rational explanation for that data is that this tag is now within the stomach of a predator.”

While researchers cannot identify the exact predator responsible for the attack, they noted that the diving patterns indicated by the tag’s data closely resembled those of white sharks they had tracked previously. “Based on that information, I would guess it was a mature female white shark,” Anderson opined.

Traditionally, porbeagle sharks have faced overfishing, leading to their classification as endangered in specific regions of the world. The loss of pregnant females and their pups, given their vulnerable status, raises serious concerns for their survival. Anderson emphasized that this loss could be devastating for the population.

Moreover, the ramifications of this shift are likely not limited to sharks alone. As vital components of the marine ecosystem, healthy shark populations play critical roles in maintaining balance by regulating smaller predator species and enriching nutrient availability in shallow waters.

Anderson concluded, “Human societies greatly depend on oceans for food and various resources, which makes it essential to sustain healthy shark populations.”