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A pair of killer whales working together have been killing white sharks along a stretch of the South African coast 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 surprising new twist in behavior that could offer clues about what it could mean for the wider marine ecosystem.
The scientists witnessed one of the hunters.A male killer whale known as Starboard single-handedly killed a 2.5-meter (8.2-foot) juvenile great white shark over a two-minute period last year.
“Over two decades of annual visits to South Africa, I have observed the profound impact these killer whales have on the local great white shark population. Watching Starboard pass the liver of a great white shark past our boat is unforgettable,” said Dr. Primo Micarelli, a marine biologist at the Center for Shark Studies in Italy and the University of Siena, who was aboard one of the two ships from which investigators observed the attack.
“Despite my fear of these predators, I am increasingly concerned about the balance of coastal marine ecology,” Micarelli said in a statement.
It is not unprecedented for orcas, highly intelligent and social animals, to hunt large animals individually. However, it is the first event of its kind involving one of the world’s largest predators, the great white shark, researchers reported in a study published on Friday in the African Journal of Marine Sciences.
Starboard’s killing 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. , doctoral researcher at Rhodes University.
According to the study, previously observed attacks on white sharks involved between two and six killer whales and lasted up to two hours.
“This sighting revealed evidence of solitary hunting by at least one orca, 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 of labeling data, in a declaration.
“These are groundbreaking insights into the predatory behavior of this species,” he said. “The presence of these shark-hunting killer whales is possibly related to broader ecosystem dynamics. Rapid advances in this phenomenon make it difficult 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 near Seal Island, near Mossel Bay, about 400 kilometers (250 miles) east of Cape Town. where people aboard two boats observed the orcas. .
Less than an hour after arriving, a shark appeared near the surface, and researchers, tourists and others on board witnessed Starboard grab a shark’s left pectoral fin and “push forward with the shark several times before finally gut it” in less than two minutes, according to the study.
Starboard was later photographed from one of the ships with a “bloody peach-colored piece of liver in his mouth,” according to the studio. Starboard’s male companion, Port, was observed about 100 meters (328 feet) away as the killing occurred and did not become involved.
Christiaan Stopforth/Drone Fanatics SA
A second white shark carcass washes ashore in June near Hartenbos, South Africa.
the duo is well known among the authors of the study and has been involved in hunting and killing great white sharks for many years. Orcas’ dorsal fins are bent in opposite directions: the inspiration for their names.
The two travel enormous distances along the eastern coast of South Africa until they reach Namibia. Researchers suspect they first began targeting large whites in 2015. It wasn’t until 2022 that aerial footage first captured orcas killing a great white shark, Towner said.
“While we don’t have strong evidence about specific factors, the arrival of the killer whale pair could be related to broader changes in the ecosystem,” Towner said. “It is clear that human activities, such as climate change and industrial fishing, are putting pressure on our oceans. To fully understand these dynamics, additional research and funding are essential.
“There are still many unanswered questions about these shark-hunting orcas and where they come from.”
Killer whales are driving away great white shark populations, but researchers don’t know where the sharks are relocating. “As they relocate, they could end up overlapping intense commercial fisheries,” Towner added.
The distinct smell of shark liver in the air and the seagulls diving towards a spot on the water’s surface, as well as the second shark carcass. Measuring 3.55 meters (11.6 feet) discovered nearby, it led onlookers to believe another white shark may have died before the boats arrived that day, researchers said.
According to the study, the killing by a lone killer whale may have been possible thanks to the prey’s smaller size when it was a juvenile white shark. Adult white sharks have a maximum length of 6.5 meters (21.3 ft) and a mass of 2.5 tons.
The rapidity 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 near shorelines in areas where humans are abundant, the study suggested.
“We cannot speculate that this orca has become more sophisticated, but the rapid period in which it killed the shark shows incredible skill and competence,” Towner said by email.
White sharks’ livers are huge organs, about a third of their body mass, and rich in lipids, and the orcas discard the rest of the carcass, a selective feeding behavior that is known among other carnivores, such as seals, brown bears and wolves, according to the study.
“The observations reported here add more layers to the fascinating story of these two orcas and their capabilities,” said Dr. Simon Elwen, founding director and senior scientist at Sea Search Research & Conservation and a researcher at Stellenbosch University in South Africa. a declaration.
“As intelligent, top predators, killer whales can quickly 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 was not involved in the investigation.