A group of orcas has been documented attacking and taking down a blue whale off the southern coast of Western Australia, according to a post by Kristy Brown of Naturaliste Charters. The incident occurred over the Bremer Canyon system, a network of submarine trenches that are associated with significant marine productivity.

The Bremer system is well-known for major congregations of cetaceans, including orcas that often gather here during the austral summer and fall – the largest-known seasonal orca get-together in Australian waters.

Based on Brown’s report, the Naturaliste Charters whale-watching vessel came across orcas on the morning of March 16. The action started slow, but eventually, they realised that the orcas were working on a blue whale, estimated at about 16 metres long.

More and more orcas arrived on the scene, including “at least six big males from different pods”. Ultimately, the observers estimated that anywhere between 50 and 70 killer whales were taking part.

Orcas relentlessly attacked the blue’s jaw, a common strategy when the predators hunt large whales. The attack lasted for hours before the blue finally gave out in the afternoon.

Even if the Bremer Canyon blue whale was a juvenile of the larger subspecies, it was still much bigger than the orcas that dined on it.

This – and the sheer number of killer whales involved – makes the incident noteworthy. This is not the first such incident, as several recent attacks on similarly sized blue whales have been reported in this orca hotspot.

In March 2019, orcas killed a 20-metre-long pygmy blue whale here with upwards of 50 killer whales digging into the carcass. A mere two weeks later, a 15-metre pygmy blue also fell to orcas.

Some experts believe attacks such as these could be more frequent than previously appreciated. “Given the slow but steady increase in the Southeast 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,” says Micheline Jenner of the Centre for Whale Research.

Moreover, an older observation of an orca attack on a blue whale off Cabo San Lucas in Baja California in the late 1970s involved an 18-metre juvenile blue, harried by close to 40 orcas.