From snatching sea lions off beaches to stunning fish with a strike of their tails, orcas are renowned for their highly specialised hunting techniques passed down over generations. Now, for the first time, killer whales have been recorded hunting the planet’s largest animal – the blue whale – in coordinated and brutal attacks.
Female-led pods of killer whales, also known as orcas, have been recorded killing and eating blue whales in three separate attacks off the coast of Australia since 2019, according to a paper published in Marine Mammal Science.
Previously there were reports of these apex predators “chasing” blue whales – which grow up to 33 metres long – but authenticated attacks are extremely rare. This research is the first to officially document these killings, including details about how orcas swim inside the mouth of the blue whale to eat its tongue just before it dies.
“Here we provide the first documentation of killer whales killing and eating blue whales: two individuals killed, 16 days apart in 2019, and a third in 2021,” researchers wrote in the paper. “Notably, the first whale taken appeared to be a healthy adult.”
All the attacks happened off Bremer Bay in Western Australia, within 40 miles (60km) of the shore, and were observed from commercial whale-watching vessels. Many individual females were involved in all three attacks. The attack in March 2019 was on a healthy adult whale, between 18 and 22 metres long. It was coordinated by at least 12 orcas, led by eight adult females and one male, with younger ones watching.
By the time observers reached the site, large chunks of skin and blubber had been stripped off the adult blue whale and most of the dorsal fin had been bitten off. After an hour of relentless attacks, three female killer whales lined up side-by-side and rammed the blue whale on its side, pushing it underwater, while two others attacked its head. The last one swam inside its mouth and started eating its tongue, which is nutritionally dense.
In the next six hours, 50 more orcas joined in the feeding, as well as at least 200 flesh-footed shearwaters, more than 20 storm petrels and at least one albatross. Several dozen birds continued to feed on scraps for days afterwards. “We visited the kill site for six days after the attack, and for the first few days there was a large slick on the surface where oil was emanating from the carcass on the seafloor,” the researchers wrote. The killer whales were not seen on site again.
The next attack a few weeks later was on a blue whale calf between 10 and 12 metres long. It was led by 25 orcas, including 22 females, around 25 miles from the first attack. Towards the end of the attack, an adult female again put her head inside the blue whale’s mouth to feed on its tongue.
For the next three and a half hours, about 50 killer whales fed off the carcass, bringing large chunks of flesh to the surface, which were torn apart and fed on by various members of the group. There was no evidence of aggression or frenzied feeding, researchers said.
The third attack was on a yearling, about 12 to 14 metres long, which was chased for 15 miles for 90 minutes. The killing involved the same strategy of lining up and pushing the whale below the surface, while also attacking its mouth. The attack was started by 12 orcas, including six females. At least 50 turned up to feed on the carcass.
Killer whale pods are matriarchies, led by the oldest female, and any male offspring are descendants of the matriarch. Previously, it had been assumed that for killer whale attacks on large whales to be successful, adult males need to be involved, but all three of these attacks were led by females, which are about 20% smaller. Females need to feed young and may need to feed more often than males, which possibly makes them more likely to initiate attacks, researchers said.
Killer whales are known for hunting down large prey, similar to wolf packs, successfully predating on gray whales, sea lions, dolphins and even great white sharks. This study adds the planet’s largest creature to that list, suggesting the only baleen whale impervious to attack from these apex predators is the adult humpback.
Most killer whale populations specialise in a certain type of prey, but killer whales off Bremer Bay have a particularly diverse diet. They have also been observed attacking deep-diving beaked whales, Antarctic minke whales and yearling humpback whales, using similar pack strategies to hunt.
Killer whales tend to be opportunists when it comes to feeding on mammals, said one of the authors, Robert Pitman from Oregon State University, so this could be a return to normal as blue whale populations recover after centuries of whaling. “Maybe what we’re starting to see now is how the ocean used to be before we took out most of the large whales … As some of these populations continue to recover, we have a better chance to see how normal marine ecosystems function,” he said.
Scientists say these discoveries are important for understanding how killer whales shape marine communities, and also how they may affect blue whale populations recovering from historical whaling. There were estimated to have been 300,000 blue whales before whaling and now there may be 15,000 to 20,000, with numbers believed to be increasing.
Erich Hoyt, a research fellow at Whale and Dolphin Conservation, said the “excellent” paper confirmed what was known about killer whales and how they attacked, including going for the tongue, which has been recorded on other whale species. “But the excellent photographs in the paper and the extraordinary detail provided by the scientists give us a real insight into how it happens.
“This paper is the first to really confirm a blue whale kill and at the same time it provides firm confirmation that killer whales will even go after mature healthy blue whales,” he said.
The orca behaviour of feeding on large whales has been found in other parts of the world such as the north Pacific but it is not common, and most killer whale pods would not see large whales as food, said Hoyt. “These particular orcas off South Australia subsist on an unusually diverse diet,” he said. “This is strange because elsewhere in the world, killer whales are fussy eaters and tend to learn from their pod how to catch food, and what is food, and they stay with that, whether it’s salmon around Vancouver Island or sea lion pups at Punta Norte in southern Argentina.”
Dr Peter Richardson, head of ocean recovery at the Marine Conservation Society UK, said: “This fascinating paper expands our knowledge of the prey species of orca. However, the small sample size limits the insights we can take. This behaviour has perhaps been going on for centuries out in the open ocean where it’s difficult to study.”