Scientists have documented the first three instances of orcas successfully hunting and killing the largest animals on Earth, blue whales, findings that shed more light on the roles these mammals play in marine ecosystems.
While previous research has documented orcas – also known as killer whales – attacking and harassing blue whales, the three predation events reported in the new study, published recently in the journal Marine Mammal Science, are the first confirmed kills.
Killer whales – which despite their name belong to the dolphin family – are the apex predators in many ocean ecosystems and have a large influence on marine environments, preying on a large variety of species, including whales, say the researchers, from Flinders University in Australia.
Earlier studies have documented orcas preying on large whale calves globally, however, until now it was unknown whether they hunted and killed the largest whale, the blue whale.
The findings of the new study, according to the researchers, can help scientists better understand the role played by orcas in the marine ecosystem, particularly for monitoring their prey species — including blue whales — that are still recovering from commercial whaling.
“These guys are ferocious with a preference for squid, fish and beaked whales. In recent years recordings of the number of beaked whales taken have increased, in this region they are known to also predate on humpback and minke,” John Totterdell, lead author of the study from the Cetacean Research Centre (CETREC), said in a statement.
In 2019, CETREC researchers, who were running their annual whale and dolphin surveys off the coast of Australia, stumbled across the first-ever documented event of killer whales attacking and killing a healthy adult blue whale.
Then last year, they recorded an additional event of another blue whale calf predation.
“When we arrived about 14 killer whales were attacking the blue in 70m waters, with the female killer whales leading the attack, Isabella Reeves, a Flinders University PhD candidate and co-author of the study, said on the 2019 event.
“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,” Ms Reeves added.
In this coordinated attack on the blue whale by several orcas, some female killer whales rammed the side of the blue whale while others attacked the head, researchers said.
“Soon after, there were 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,” Ms Reeves said.
Towards the end of the targeted attack, the researchers say a female orca lunged head first into the blue’s mouth, likely to feed on the tongue.
“After the whale carcass sunk, about 50 killer whales were in the area feasting and sharing around the blue’s flesh,” Dr Totterdell added.
In the subsequent recorded events of orcas killing blue whales, scientists say similar strategies were on display, but with male killer whales also being active and calves involved in the third attack.
In all three events, researchers say at least 16 of the same animals participated in the attacks, and multiple orcas were active in two events.
They say that if the hunting strategy is successful it results in tiring out the blue whale, rendering it defenceless.
“It is suggested that killer whale predation has impeded gray 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,” Dr Totterdell noted.
“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,” he added.
