A new study has confirmed for the first time that killer whales have successfully hunted the world’s largest mammal, the blue whale, off the coast of Western Australia.
The three separate killings, documented in the journal Marine Mammal Science, took place in March and April 2019 and in March 2020, off Bremer Bay. They are the first recorded instances where blue whales have been lethally preyed upon by another wild animal.
A killer whale in the process of hunting the blue whale off the coast of Western Australia.Credit:Jade Sharp
John Totterdell, lead researcher at Cetacean WA and lead author of the study, described the attacks as the largest predation event in recorded history.
There have been cases where killer whales, also known as orcas, have attacked and harassed blue whales. There has never been a confirmed kill of either an adult or calf until now.
Hunting and killing the largest animal in the world is no easy feat.
The adult blue whale that was hunted in the first attack was around 20 to 22 metres, making it nearly four times the length of a standard killer whale, which can grow between up to seven metres.
Shortly after the death of the young blue whale in the second attack, a killer whale inserted its head into the whale’s mouth to feed on the tongue.Credit:John Daw
It is common for a group of killer whales to be involved in an attack, as they live and hunt in close-knit family pods, interchangeably attacking their prey and swapping roles throughout the kill.
“Everything they do is family-oriented,” Mr Totterdell said.
Teamwork and coordination are essential in a killer whale hunt.
In the second event, the study described five to six killer whales that were actively engaged in the attack on the blue whale calf at any one time, while another 10 to 15 lingered on the periphery, all frequently rotating roles.
A pod of killer whales in the first attack hunting and feeding on an adult blue whale.Credit:CETREC WA & Project ORCA
In the third attack, a minimum of 20 killer whales were involved at one time.
“There was no bite or hit that was fatal,” Mr Totterdell said. “[Instead], what they do with these larger animals is just wear them down [and] inhibit their movement. They come under it; they don’t let it dive.”
Researcher and PhD candidate Isabella Reeves, who studies evolutionary ecology, said that killer whales could be “opportunistic” and learned strategic behaviours from the females in their families.
“[Killer whales] have matrilineal societies, which means they basically travel in these female-driven groups. Quite often the grandma leads these [kills],” Ms Reeves said.
The study showed that each of the attacks were located further north from the Bremer sub-basin and canyons where killer whales often preside.
“For the killer whales, shallow water is better, so once they kill the animal, especially that big, it can just sink and they can just dive down and grab chunks [of it].”
Although this is considered to be the first time that humans have witnessed and documented killer whales attacking and successfully killing a blue whale, it may not be the first time it has happened.
“It could well indicate that prior to commercial whaling, this was the normal. This was what killer whales did,” Mr Totterdell said.
Now that blue whale numbers are steadily increasing, it is possible that killer whales are switching back to an old food source.
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