Bremer Canyon’s famous orcas documented killing blue whales for the first time in a new scientific paper

Bremer Canyon’s famous orcas are the focus of a groundbreaking scientific publication documenting the first known recordings of orcas killing the world’s biggest animal, blue whales. Observations of two killings witnessed by orca-watching boat tour guides in 2019, and one in 2021, were published in the scientific journal Marine Mammal Science on January 21. Marine biologist and lead tour guide at Naturaliste Charters Pia Markovic contributed her first-hand accounts to the paper, which she said had “international relevance” for marine biologists worldwide. “It has never been recorded ever, in the entire world, in the history of people looking at this sort of stuff,” she said. From January to mid-April each year there are about 200 orcas that appear near the 5000m deep Bremer Canyon, about 70km off the coast of Bremer Bay. Orcas are most abundant in colder waters, especially those surrounding Antarctica, Alaska and Norway. Ms Markovic hopes the paper will prompt scientists and orca watchers in other areas across the globe to be more observant for signs of blue whale attacks, now that this has been officially recorded. “We used to say on the vessel that blue whales were the only animal that were not eaten by orcas, because of their speed,” she said. The first time Ms Markovic and other tour guides witnessed orcas killing a blue whale was on a dark and stormy day in March 2019, as reported in the Advertiser at the time. On the second occasion, the very next month, the ocean conditions were much calmer, and they were better prepared for the experience. “There was a big oil slick that was coming out from up ahead of where we were, and oil on the surface is pretty indicative that there’s prey that’s been injured,” Ms Markovic said. “We knew that they had something and they weren’t just trying to chase it down, they actually already had it. “And then we saw the big blue whale.” About 70 orcas from at least seven different families worked together to kill the ocean giant. “As they’re swimming along with the blue, they’re holding on to the outside of it to stop it from swimming because the blue whale can take off and they’re quite fast, a bit faster than a killer whale,” she said. “That’s the whale’s only way to get away from the orca, they can’t dive deep, they can’t jump out and slap their tail around because they’re so big.” The orcas were observed targeting the peduncle part of the whale’s tail where there is an artery and vein in an attempt to further slow down the whale. As the whale became weaker, the orcas drove their bodies into the whale and pushed it under the water. They then worked together to slowly bring the whale to the surface, with one orca reaching inside the whale’s mouth to eat its large tongue, a post-hunt behaviour that signalled the end of the attack. “The tongue is a very nutritious part of the whale, it’s got no bones and it would be super soft,” Ms Markovic said. There “were a few tears” from the passengers onboard as “everyone just processed what was going on”, Ms Markovic said. Ms Markovic estimates Bremer Bay tours have had fewer than 10 encounters with blue whales near the Bremer Canyon over, compared with the “hundreds” they had seen over many years working on whale tours in Dunsborough. Sightings of the endangered blue whales off Bremer Bay could indicate that their population numbers are increasing, but Ms Markovic also cautioned that “if we lose that species, and that’s a huge food source for the orcas, then it’s a snowball effect”. She said the passengers on the tour boats helped made their scientific discoveries possible. “If there are no passengers, we’re not going out there and we’re not seeing it,” Ms Markovic said. “Every passenger, every day, is paying for science which is really, really cool I think.”