A pair of working killer whales have been killing great white sharks along a stretch of the South African coastline since at least 2017, plundering the sharks' nutrient-rich livers and throwing away the rest.
Scientists have been trying to understand the hunting approach that 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.
Scientists last year witnessed one of the hunters, a male orca known as Starboard, single-handedly kill an 8-foot young white shark in the space of two minutes.
"During twenty years of annual visits to South Africa, I have seen the profound impact these killer whales have on the local white shark population. It is unforgettable to see Starboard carry the liver of a great white shark past our ship," said Dr. Primo Micarelli, a marine biologist at Italy's Sharks Studies Center and the University of Siena, who was aboard one of the two ships from which researchers observed the attack.
"Despite my awe for these predators, I am increasingly concerned about the balance in the marine ecology of coastal areas," Micarelli said in a statement.
It is not uncommon for killer whales, highly intelligent and social animals, to hunt large animals individually. However, this is the first occurrence involving 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 killing is at odds with the commonly observed cooperative hunting behavior among killer whales, which can encircle large prey, such as sea lions, seals and sharks, and use their combined intelligence and strength to attack, said lead author Alison Towner, a Ph.D. researcher at Rhodes University.
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Previously observed attacks on great whites have involved between two and six orcas and lasted up to two hours, according to the study.
"This observation revealed evidence of solitary hunting by at least one killer whale, challenging the conventional cooperative hunting behavior known in the region," said Towner, who has spent 17 years studying great white sharks and learning about their movement patterns through tagging data. rack.
"These are groundbreaking insights into the predatory behavior of this species," she says. "The presence of these shark-hunting killer whales may be related to broader ecosystem dynamics. The rapid developments in this phenomenon make it a challenge for science to keep pace."
Port and Starboard
The event described in the study occurred on June 18, 2023, 800 meters offshore, close to Seal Island near Mossel Bay - about 400 kilometers (250 miles) east of Cape Town - where people on two ships observed the orcas. .
Less than an hour after arriving, a shark appeared on the surface, and researchers, tourists and others on board witnessed Starboard grab a shark's left pectoral fin and "push the shark forward several times before finally releasing it eviscerated" in less than two hours. minutes, the study said.
Later, Starboard was photographed from one of the ships with a "bloody piece of peach-colored liver in its mouth," the investigation said. Starboard's male companion, Port, was observed about 100 yards away as the murder occurred, but did not become involved.
The duo are well-known among the study's authors and have been involved in hunting and killing great white sharks for years. The killer whales' dorsal fins are curved in opposite directions - the inspiration for their names.
The two travel enormous distances along the east coast of South Africa, all the way to Namibia. Researchers suspect they first started targeting great white sharks in 2015. It wasn't until 2022 that aerial footage of the orcas killing a great white shark was captured for the first time, Towner said.
"While we don't have solid evidence on the specific causes, the arrival of the orca pair could be linked 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."
The deadly killer whales are scaring populations of great white sharks, but researchers don't know where the sharks are moving. "If they move, they could end up overlapping with heavy commercial fishing," Towner added.
The distinct smell of shark liver in the air and seagulls diving for a smooth spot on the water's surface, as well as a second 3.55-meter (11.6-foot) shark carcass discovered nearby, led onlookers to believe that another great white might be there shark had been killed before the arrival of boats that day, the researchers said.
The kill by a lone killer whale may have been made possible by the smaller size of the prey as a juvenile great white, according to the study. Adult white sharks have a maximum length of 6.5 meters (21.3 feet) and a mass of 2.5 tons.
The speed of the attack could reflect Starboard's skill and efficiency as a predator, which could be a response to the stress associated with spending time hunting close to shore in areas where humans are plentiful, suggested the study.
"We cannot speculate that this orca has become more advanced, but the rapid time frame in which it killed the shark does demonstrate incredible skill and skill," Towner said via email.
The livers of great whites are enormous organs, about a third of their body weight, and rich in lipids, and the killer whales discard the rest of the carcass - selective feeding behavior known to other carnivores, such as harbor seals, brown bears and wolves. , the study said.
"The observations reported here add more layers to the fascinating story of these two killer whales and their abilities," said Dr. Simon Elwen, founder and chief scientist at Sea Search Research & Conservation and researcher at Stellenbosch University in South Africa. a statement.
"As smart, apex predators, killer whales can quickly learn new hunting techniques, alone 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 learn more about these animals to understand. " added Elwen, who was not involved in the research.
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