Great white sharks on the hunt for seals typically attack at dawn and dusk, when the dim light lets them sneak up on their prey. But at the Dyer Island Marine Reserve off the west coast of South Africa, great whites display a different behavior, hovering around thick kelp forests that the seals frequent throughout the day. Scientists observing the animals were puzzled: Surely, they thought, great whites are too large to venture into these dense seaweed growths. But as JoAnna Klein reports for the New York Times, a new study has revealed that the hulking marine predators can and do maneuver through kelp forests in pursuit of a tasty meal.
Researchers working in the area have previously had a hard time following the sharks’ movements underwater. They tried tracking the animals with acoustic tags, but the signals often faded out near the kelp forests. For the new study, published in Biology Letters, the researchers implemented a different method: they lured great whites to the surface of the water with chum—pieces of cut up fish—and a seal decoy, and then used a rod to clamp a camera and motion sensor onto the sharks’ dorsal fins. The instruments were designed to pop off of the sharks after a number of hours, so they could be collected at the water’s surface.
The scientists managed to tag eight sharks in this way, and ultimately collected 28 hours of footage. Their efforts have yielded what is believed to be the first documented evidence of “extensive and repeated use of kelp forests by white sharks,” the study authors write. Kelp was seen, to varying degrees, in footage from all of the sharks. Seven repeatedly moved into areas of dense kelp coverage, contradicting previous hypotheses about the protective power of kelp forests.
“A previous study found Cape fur seals were taking refuge from the white sharks in kelp forest,” Oliver Jewell, lead study author and marine biologist at Australia’s Murdoch University, tells Roni Dengler of Discover. “What we found is that the white sharks go into the kelp forest after them and are more than capable of navigating through and foraging within and through dense kelp.”
Indeed, the scientists documented ten interactions with seals—all made by a single shark. When they caught sight of the predator moving in their midst, the seals deployed defensive tactics: they blew bubbles at it, swam deeper into the kelp or hunkered down on the seafloor.
These findings, the study authors write, suggest that “future research should reevaluate the role of kelp forest in the foraging ecology of white sharks rather than presume it to be a habitat they avoid.” It is possible—though not yet proven—that great whites could be engaging in similar hunting behaviors around kelp forests off the coasts of California and Australia, Jewell notes. Speaking to Klein of the Times, Jewell says that the study’s findings also refute the perception of sharks as “mindless killing machines.”
“They’re very calm and they’re also curious animals,” he explains, “and they’re just there doing their own thing.
Kelp forests may not be the shark-less sanctuaries that scientists previously assumed, but this marine environment still appears to offer some refuge to seals. The researchers observed seals hiding in kelp fronds and successfully evading their pursuers. In fact, the footage they collected did not document a single instance of a shark successfully preying on a seal—“unfortunately,” the researchers opine, though the seals may have a different perspective on the matter.