Researchers from the Cetacean Research Centre in Western Australia spotted the orcas hunting and killing an adult blue whale while carrying out annual dolphin and whale research in 2019.
The 14 killer whales were savaging the adult blue, with female predators "leading the attack", Isabella Reeves, a Flinders University PhD candidate, said in a statement released by the university on Thursday.
Another blue whale calf was taken and killed by a group of orcas two weeks later, the researchers said.
They reported an additional event of orcas preying on a blue calf in 2021.
Killer whales are known to harass and attack blues, but the confirmed kill of a healthy adult blue whale is a world-first.
The animals are the apex predators of the ocean, and are known to prey on a wide variety of species, including the calves of humpback and grey whales.
However, it was not previously known if killer whales would target and kill the blue whale.
Their role in the ecosystem is key, and the species continues to recover from commercial whaling.
While many species are targeted by killer whales, it's not yet known what impact they have on other animal populations in Australian waters, CETREC lead researcher John Totterdell said.
In the northwest Pacific, it's believed killer whale attacks are impeding the recovery of the grey whale population.
"This study, combined with our recent research, highlights the need for increased understanding of killer whale population ecology so we can better determine their impact on the marine ecosystem in Australian waters."
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