In recent weeks, orca pods off the south coast of Western Australia have been spotted on two separate occasions hunting and killing blue whales – behaviour that's rarely been documented in the past.

A pod of orcas recently attacked a blue whale off the western coast of Australia. Image © Project Orca

On March 21, research assistant Ashleigh Roddick was on her way to observe orcas at a biodiversity "hotspot" in the Bremer Canyon off Australia's southern coast. Feeling a little ill, she decided to brave the stormy weather and sat outside on the deck in the hopes that the lightning and rain would provide a distraction. Through the haze, Roddick and another team member spotted several birds fluttering in the distance. Below the birds something big was splashing in the water.

By this stage, lead researcher at CETREC WA (Cetacean Research) John Totterdell was also on deck, initially with the intention to pick up some debris floating in the water. He, too, spotted the splashing. Before long, all eyes were fixed on the commotion in the distance as everyone on deck began to realise what they were witnessing: a blue whale was under siege by a pod of orcas.

Image © Project Orca
Image © Project Orca
Image © Project Orca

“In awe, we witnessed about 50 killer whales feed on their prize for the next 6 hours,” Totterdell wrote on Facebook. It was the first time that the predators had been recorded killing a pygmy blue whale off the Australian coast.

While it's a scenario that seems too extraordinary to be real, if any animals are capable of taking down the largest whales in the ocean, it's orcas. The black and white predators have been recorded eviscerating porpoises, tail-flinging turtles and even squeezing the livers out of great white sharks. They also actively hunt baleen whales – a group comprised of 14 species of whale including humpback, grey and blue – but they typically stick to juvenile and subadult individuals. Attacks on blue whales have only been recorded a handful of times.

The first dates back to 1979 and involved a subadult whale in Baja California. The attack lasted a couple of hours and, although the young whale escaped, it's likely that it later succumbed to its injuries. Then in 2003 researchers working in the Costa Rica Dome recorded orcas feasting on the fresh carcass of a blue whale calf that the predators had likely hunted down and killed. Another predation attempt off the coast of California a year later ended when an adult blue flicked its fluke and escaped. And in May 2017, drone footage from California's Monterey Bay showed a pod of orcas harassing a sizeable blue whale. The whale escaped by outpacing the orcas – a technique that they are known to employ.

Image © Project Orca
Image © Project Orca

According to Totterdell, the mammal targeted in the recent attack was a 20-metre pygmy blue whale (Balaenoptera musculus brevicauda) – a subspecies of blue whale found in the Indian and southern Pacific Oceans. They can reach a maximum length of about 24 metres, which would place this individual on the cusp of sexual maturity. "The thickness of its peduncle area, the body scarring and the amount of cookie cutter bites all indicate an older animal," Totterdell told us via email. 

Taking down a whale of this size is no small feat. The task requires a carefully synchronised attack. "Orcas are known as the wolves of the sea. They hunt in a pack with orchestrated precision," explains marine biologist and co-founder of the Centre for Whale Research Micheline Jenner. "The killer whales attack a whale in various places, by holding onto the dorsal fin area and the tail flukes, to slow and hold the whale down – to drown it." It took these orcas almost an hour to finally dispatch their massive prey.

Just two weeks after killer whales made history off Australia's coast, they struck again. This time the victim was a 15-metre pygmy blue whale. The attack took place on April 6 in perfect weather conditions allowing whale watchers and researchers to capture much of the action. Marine biologist Pia Markovic was on board a Naturaliste Charters vessel when the team spotted big splashes on the horizon. The ocean surface was bubbling as masses of pilot whales, at least 30 orcas, and a scatter of striped dolphins surged towards the melee, Markovic explained on the Naturaliste Charters blog

When they arrived at the scene, a group of about ten orcas were latched onto the whale as it pumped its tail in an attempt to escape. "They had already taken multiple large chunks of skin and blubber from its sides in an effort to try slow the enormous baleen whale down," Markovic wrote. For about half an hour, the orcas repeatedly forced the juvenile whale underwater while biting at its flanks. "As the blue flailed about, it was turned upside down with its tail flipping out of the water. This was one of the last times we saw it as the orcas drove it below the surface to end the ordeal."

"It is believed that the tongue is a favoured item in the predation of killer whales on baleen whales," Jenner explains. "Once the whale has been drowned, by holding it underwater, the mouth opens and the tongue is readily accessible … It is a source of high nutrition being solid protein, as compared with biting through the relatively thick blubber layer of the flank, to get to the muscle below." Image © Naturaliste Charters

With two successful attacks on blue whales in the same number of weeks it's tempting to conclude that Western Australia's orcas are developing a knack for "blue murder", but it's more likely that this sort of predation happens with greater frequency than the records reveal. "Even though this is the first recorded encounter (off Australia) of a large baleen whale succumbing to an attack, it's likely other large whales (including blues) often face the risk of predation from killer whales," Totterdell explains on Facebook.

A study published in 2014 reveals that humpback calves are a predictable and plentiful prey source for the apex predators for at least five months of the year when the whales migrate along the Australian coastline. Many adult humpbacks (and nearly every other large whales species) bear tooth rake marks on their flukes and flippers from altercations with orcas, suggesting that attacks may be fairly common. It's safe to assume that blue whales could feature regularly on the orcas' menu.

"Given the slow but steady increase in the SE Indian Ocean pygmy blue whale population (approximately 2,000 whales) … there is a possibility the killer whales of the Bremer Canyon are taking advantage of this population," Jenner explained to us via email. She suggests that an abundance of orca prey such as tuna and beaked whales – a species that killer whales have been targeting more frequently recently – may be linked to improved reproduction rates. More orcas means more demand for protein and blue whales offer plenty to go around.

Further research is needed, however, to get the full picture on orca predation. "This is a species [blue whales], that particularly in our location, we know very, very little about," Kirsty Alexander, the project coordinator for South Coast Cetaceans, told ABC. Alexander is currently working on a project that examines the distribution, abundance and habitat use of whale species along Australia's south coast to gain more insights into population numbers and behaviour.

Curt Jenner, a researcher who has spent over 30 years studying whales off Australia's south coast, agrees that further research is required and offers an interesting theory: perhaps juvenile blue whales could be drawing attention to themselves by making a racket. "Blue whales swim along making a lot of noise, they are probably the noisiest thing in the ocean, in fact, they have calls louder than a 747 taking off at the end of a runway," he explained to ABC. Perhaps the inexperienced whales are giving up their locations by calling loudly in the presence of orcas. "They're not street smart yet and they've suffered the consequences," he suggests. 

It's also possible that the orcas are just having a bit of fun. When a group of killer whales were captured on camera hounding a blue whale off the coast of California back in 2017, marine biologist Nancy Black told National Geographic that "they were probably doing it for the heck of it. They play with [whales] like cats play with their prey."

Top header image: timnutt, Flickr