Three separate attacks are the first confirmed blue whale deaths by killer whales

Researchers have discovered the first-ever record of killer whales hunting and killing the largest animal on earth – an adult blue whale.

In late March 2019, annual whale and dolphin research surveys led by WA’s Cetacean Research Centre (CETREC WA), along with Project ORCA, stumbled across the first-ever documented attack and eventual killing of a healthy adult blue whale (Balaenoptera musculus) by killer whales (Orcinus orca).

Reported in a paper just published in Marine Mammal Science, there were also two subsequent attacks on a blue whale calf and juvenile two weeks later and in 2021, respectively.

Killer whales are known to prey on a large variety of species – including whales – but had previously only been known to kill and feed on large whale calves, such as grey and humpback whales. They have previously been documented attacking and harassing blue whales, but these three events are the first confirmed kills.

“When we arrived about 14 killer whales were attacking the blue in 70m waters, with the female killer whales leading the attack,” says co-author Isabella Reeves, a Flinders University PhD candidate.

“At arrival we already noticed a substantial flesh wound on the top of its head with bone exposed. The dorsal fin was missing, no doubt bitten off by the killer whales. Tooth-rake marks were evident in front and behind where the dorsal once was and even all the way to the whale’s tail.”

“Soon after, there was large chunks of skin and blubber stripped off the sides of the whale, the blue was bleeding profusely and was weakening, evident by its slow speed,” says lead author and CETREC lead researcher, John Totterdell. “Coordinated attack by several killer whales resulted in some females ramming the side of the whale while others attacked the head.

“Close to the end, a female animal lunged headfirst into the blue’s mouth, presumably to feed on the tongue, the whale weakened more and we did not see the carcass again. After the whale carcass sunk, about 50 killer whales were in the area feasting and sharing around the blue’s flesh.”

These killer whale predatory behaviours have been seen in similar events with large whales. It’s a hunting strategy that results in tiring out and immobilising the whale, leaving them defenceless and an easy target.

Two populations of killer whales have been recently discovered in Australia, both found to feed at least in part on marine animals. The southwestern Australian population of over 140 animals is most often found seaward of the continental shelf in the Bremer sub-basin, where these attacks where documented.

“These guys are ferocious with a preference for squid, fish and beaked whales,” says Totterdell. “In recent years recordings of the number of beaked whales taken have increased, although they seem to also predate on humpback and minke.”

As the ocean’s apex predators, killer whales have a large influence on marine environments and understanding their role in the marine ecosystem is particularly important for monitoring prey species – especially for those that are still recovering from commercial whaling.

“It is suggested that killer whale predation has impeded grey whale population recovery in the Northwest Pacific, yet in Australia, with many whale species known to be targeted by killer whales, the impact of their predation on these populations remains unknown,” says Totterdell.

“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.”