From catching sea lions on beaches to stunning fish with a flick of their tails, killer whales are renowned for their highly specialized hunting techniques passed down from generation to generation. Now, for the first time, killer whales have been recorded hunting the planet’s largest animal – the blue whale – in coordinated and brutal attacks.
Pods of female-led killer whales, also known as orcas, have been recorded killing and eating blue whales in three separate attacks off the Australian coast since 2019, according to to a paper published in Marine Mammal Science.
Previously, there were reports of these apex predators “chasing” blue whales – which are up to 33 meters long – but authenticated attacks are extremely rare. This research is the first to officially document these kills, including details of how orcas swim into the blue whale’s mouth 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,” the researchers wrote in the paper. “Notably, the first whale captured appeared to be a healthy adult.”
All of the attacks occurred off Bremer Bay in Western Australia, less than 60km from shore, and were observed from commercial whale watching vessels. Many individual women were involved in all three attacks. The March 2019 attack targeted a healthy adult whale, measuring between 18 and 22 meters in length. It was coordinated by at least 12 killer whales, led by eight adult females and one male, with the younger ones watching.
By the time observers reached the site, large chunks of skin and blubber had been torn from 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 the side, pushing it underwater, while two others attacked its head. The last one swam into his mouth and started eating his tongue, which is nutritionally dense.
Over the next six hours another 50 killer whales joined in the feeding, along with 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. “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 seabed,” the researchers wrote. . The killer whales were not seen again on the spot.
The next attack a few weeks later involved a blue whale calf measuring between 10 and 12 meters in length. It was led by 25 killer whales, including 22 females, about 25 miles from the first attack. Toward the end of the attack, an adult female again put her head in the blue whale’s mouth to feed on its tongue.
For the next three and a half hours, about 50 killer whales fed on the carcass, bringing large chunks of flesh to the surface, which were torn off and fed by various members of the pod. There was no evidence of aggression or binge eating, the researchers said.
The third attack was on a yearling, about 12-14 meters long, who was chased 15 miles for 90 minutes. The kill involved the same strategy of lining up and pushing the whale below the surface, while also attacking its mouth. The attack was launched by 12 killer whales, including six females. At least 50 showed up to feed on the carcass.
Killer whale pods are matriarchies, led by the oldest female, and all male offspring are descendants of the matriarch. Previously, it was assumed that for killer whale attacks on large whales to be successful, adult males had to be involved, but all three attacks were carried out by females, which are about 20% smaller. Females need to feed the young and may need to feed more often than males, possibly making them more likely to trigger attacks, the researchers said.
Killer whales are known to hunt large prey, similar to wolf packs, successfully preying on gray whales, sea lions, dolphins and even great white sharks. This study adds the largest creature on the planet to this list, suggesting that the only baleen whale impervious to attack from these apex predators is the adult humpback whale.
Most killer whale populations specialize 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 opportunistic when it comes to feeding on mammals, said one of the authors, Robert Pitman of Oregon State University, so this could be a return to normal as populations of blue whales are recovering after centuries of whaling. “Maybe what we’re starting to see now is how the ocean was before we wiped out most of the big whales…While some of these populations continue to recover, we have a better chance to see how normal marine ecosystems work,” he said.
Scientists say these findings are important for understanding how killer whales shape marine communities, and also how they may affect blue whale populations recovering from historic whaling. It was estimated that there were 300,000 blue whales before the whaling and now there could be 15,000 to 20,000, and their numbers are thought to be increasing.
Whale and Dolphin Conservation researcher Erich Hoyt said the “excellent” paper confirmed what was known about killer whales and how they attacked, including the tongue, which has been recorded on other species of whales. “But the excellent photographs in the article and the extraordinary detail provided by the scientists give us a real insight into how this happens.
“This paper is the first to truly confirm the death of a blue whale and at the same time it provides firm confirmation that killer whales will prey on even mature, healthy blue whales,” he said.
The behavior of orcas of feeding on large whales has been observed in other parts of the world, such as the North Pacific, but this is not common and most killer whale pods would not view large whales as food, Hoyt said. “These particular killer whales off South Australia feed on an unusually diverse diet,” he said. “It’s weird because elsewhere in the world, killer whales are picky eaters and tend to learn from their pod how to grab food, and what the food is, and they stay with that, whether it’s salmon around Vancouver Island or baby sea lions in 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 killer whale prey species. However, the small sample size limits the information we can take. This behavior may have been going on for centuries on the high seas where it is difficult to study.