There’s no honor among thieves—or thieving sharks, according to new research. In the warm waters off of French Polynesia, gangs of hundreds of gray reef sharks have been seen stealing the hard-won prey of whitetip reef sharks—in some cases, right out of their mouths. The new study, with accompanying video, is the first to show one species of sharks habitually “bumming” food off another shark species.
Getting the footage wasn’t easy, says Johann Mourier, a behavioral ecologist with the French Institute of Research for Development and one of the co-authors of the new study. He was part of an expedition that visited the islands every year from 2014 to 2018, and he made countless night dives near the southern pass of the Fakarava Atoll, a rectangular coral reef enclosing a small lagoon. The reef, which is part of the largest shark sanctuary in the world, is inhabited by a school of 900 reef sharks that feast every evening on groupers, parrotfish, and unicornfish.
“It’s amazing—in the beginning, it was a bit scary,” Mourier says. The scientists were often in the middle of the hunting fray—at one point a 4-meter-long great hammerhead burst through the dive team as it chased after gray sharks. And when grays caught prey they couldn’t immediately swallow, they would often corkscrew toward the surface in an effort to finish their meal—as opportunistic thieves gave chase. “Sometimes [the sharks] are coming right at you,” Mourier adds. But the fish never bit the researchers, and only occasionally bumped into them.
To better understand the lightning-quick action, the team made recordings with high-speed cameras. When researchers slowed down the footage, the hunting ritual became clear. As 50 whitetip reef sharks (Triaenodon obesus) used their small snouts to dig sleeping and hiding fish from the nooks and crannies of the reef, nearly 700 gray reef sharks (Carcharhinus amblyrhynchos) waited nearby. The grays, which spend much of their time hunting in the open waters of the Indo-Pacific, are too big—and too slow—to rustle up fish from the reef this way.
But whenever a whitetail had trouble with its prey, the gray sharks sprang into action (above). Cameras caught them stealing fish from the whitetails at least 11 times. Sometimes they took fish—or pieces of fish—right out of the whitetips’ mouths when the smaller sharks weren’t fast enough to swallow.
Further analysis showed gray sharks were more successful at getting a meal when they shadowed the whitetips and stole their prey than when they hunted alone or only with other gray sharks, the researchers report online in Ecology. But scientists don’t know how prevalent this hunting technique is, as it has never before been observed by a scientific study. But it’s probably common, Mourier says, because of the opportunistic nature of sharks.
The research shows how much we can still learn about animal behavior through direct observation, says Grace Casselberry, a Ph.D. candidate in marine science and technology at the University of Massachusetts, Amherst, who was not involved in the study. “Natural history studies,” she says, “remain a valuable tool for ecologists.”