A pair of orcas working in concert have been killing great whites along a stretch of South African coastline since at least 2017, plundering the sharks' nutrient-rich livers and discarding the rest.
Scientists have been trying to make sense of the hunting approach, which has driven the sharks away from some parts of the coast around Cape Town, and now research has revealed a startling new twist in the behavior that could offer clues on what it might mean for the wider marine ecosystem.
Scientists witnessed one of the hunters, a male orca known as Starboard, single-handedly kill a 2.5-meter (8.2-foot) juvenile white shark within a two-minute time frame last year.
"Over two decades of annual visits to South Africa, I've observed the profound impact these killer whales have on the local white shark population. Seeing Starboard carry a white shark's liver past our vessel is unforgettable," said Dr. Primo Micarelli, a marine biologist at Italy's Sharks Studies Centre and the University of Siena who was aboard one of two vessels from which researchers observed the attack.
"Despite my awe for these predators, I'm increasingly concerned about the coastal marine ecology balance," Micarelli said in a statement.
It's not unprecedented for orcas, highly intelligent and social animals, to hunt large animals individually. However, it's the first such occurrence involving what is one of the world's largest predators — the great white shark — the researchers reported in a study published Friday in the African Journal of Marine Science.
Starboard's kill is at odds with more widely observed cooperative hunting behavior among orcas, which can surround large prey, such as sea lions, seals and sharks, and use their combined intelligence and strength to attack, said lead author Alison Towner, a doctoral researcher at Rhodes University.
Previously observed attacks on great whites involved between two and six orcas and took up to two hours, according to the study.
"This sighting revealed evidence of solitary hunting by at least one killer whale, challenging conventional cooperative hunting behaviors known in the region," said Towner, who has studied great white sharks for 17 years, learning about their movement patterns through tagging data, in a statement.
"These are groundbreaking insights into the predatory behavior of this species," she said. "The presence of these shark-hunting killer whales possibly ties into broader ecosystem dynamics. Rapid developments in this phenomenon, make it challenging for science to keep pace."
Port and Starboard
The event detailed in the study took place on June 18, 2023, 800 meters (875 yards) offshore close to Seal Island near Mossel Bay — about 400 kilometers (250 miles) east of Cape Town — where people on two vessels were observing the orcas.
Less than an hour after arriving, a shark appeared near the surface, and researchers, tourists and others on board witnessed Starboard grip the left pectoral fin of a shark and "thrust forward with the shark several times before eventually eviscerating it" in less than two minutes, the study said.
Later Starboard was photographed from one of the vessels with a "bloody piece of peach-colored liver in its mouth," according to the study. Starboard's male companion, Port, was observed around 100 meters (328 feet) away while the kill took place and didn't get involved.
The duo is well-known among the study's authors and has been involved in hunting and killing great white sharks for many years. The orcas' dorsal fins are bent in opposite directions — the inspiration for their names.
The two travel huge distances along South Africa's eastern coastline up as far as Namibia. Researchers suspect they first started targeting great whites in 2015. It wasn't until 2022 that aerial footage first captured the orcas killing a great white shark, Towner said.
"While we don't have solid evidence on the specific drivers, the arrival of the killer whale pair could be linked to broader changes in the ecosystem," Towner said. "It's clear that human activities, such as climate change and industrial fishing, are stressing our oceans. To fully grasp these dynamics, additional research and funding are essential.
"There are still plenty of unanswered questions about these shark-hunting killer whales and where they came from."
The killer orcas are scaring off great white shark populations, but researchers don't know where the sharks are relocating. "As they relocate, they might end up overlapping with heavy commercial fisheries," Towner added.
The distinct smell of shark liver in the air and gulls diving toward a slick on the water's surface, as well as a second shark carcass measuring 3.55 meters (11.6 feet) discovered nearby, led onlookers to believe another great white might have been killed before the boats' arrival that day, the researchers said.
The kill by a lone orca might have been made possible by the prey's smaller size as a juvenile great white, according to the study. Adult great whites have a maximum length of 6.5 meters (21.3 feet) and mass of 2.5 tons.
The swiftness of the attack may reflect Starboard's skill and efficiency as a predator, which could be a response to the stress of spending time hunting close to shorelines in areas where humans are abundant, the study suggested.
"We cannot speculate that this killer whale has become more sophisticated but the rapid time frame he killed the shark in does show incredible skill and proficiency," Towner said via email.
The livers of great whites are huge organs, about a third of their body mass, and rich in lipids, and the orcas discard the rest of the carcass — selective feeding behavior that's known among other carnivores, such as harbor seals, brown bears and wolves, according to the study.
"The observations reported here add more layers to the fascinating story of these two killer whales and their capabilities," Dr. Simon Elwen, founding director and principal scientist at Sea Search Research & Conservation and a researcher at Stellenbosch University in South Africa, said in a statement.
"As smart, top predators, killer whales can rapidly learn new hunting techniques on their own or from others, so monitoring and understanding the behaviors used here and by other killer whales in South Africa is an important part of helping us understand more about these animals," added Elwen, who wasn't involved in the research.
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