The long-anticipated revelation that orcas, the world’s largest predator, are capable of killing adult blue whales, potentially the largest animals ever known, has finally come to light. Credible accounts of attacks go back at least to the 1970s.
But it has only been confirmed, in detail that is at once coolly scientific and compellingly dramatic, in a paper by John Totterdell and others in Marine Mammal Science late last year (DOI:10.1111/mms.12906). They tell of the remarkable, highly co-ordinated social behaviour of groups of orcas hunting down, killing and eating an adult and two calves, in three separate incidents, off Bremer Bay in southwest Australia.
Their account of the adult blue whale’s demise concludes like this:
“After approximately 20 min of continuous attack by the killer whales, the blue whale slowed and began swimming in a circle with a radius of about 200 m. By 09:20, large chunks of skin and blubber had been stripped off the whale’s flanks behind the dorsal fin; it was bleeding profusely and appeared to be weakening as it continued to reduce its swim speed.
“A few minutes later, three adult female killer whales lined up, side-by-side, perpendicular to the blue whale . . . and rammed headlong into its flank, pushing it through the water and then forcing it under. At the same time, two other killer whales were attacking the blue whale’s head, and its forward movement stopped. Moments later, at approximately 09:30, while it was still alive, an adult female killer whale put its head inside the blue whale’s mouth and began feeding on its tongue.”
Gripping – and grim – as this spectacular narrative is, the authors are keen to point beyond it to the questions it raises, both about the social organisation of orcas, and the larger implications of such predation for the marine food web.
Co-author Robert Pitman is a marine ecologist and one of the world’s most experienced observers of whales and dolphins. He has studied orca predation on half a dozen species of whale, and in a 2015 article in the same journal documented the systematic predation by orcas on the calves of Humpback whales, also in the Bremmer area, which he argues has altered the migration pattern of this huge whale.
He thinks it is certainly significant that predation on an adult blue whale has now been proven, but he wonders whether this behaviour is really as exceptional as it might seem from current statistics. He takes a much longer view.
“Those of us alive today,” he told The Irish Times this week from his office in Oregon State University, “have never experienced an ocean that wasn’t largely depleted due to commercial whaling. We don’t know how things really were. And as we give protection to whales and they increase, we are going to see conditions we have never seen before. We are in for some surprises.”
He also draws attention to how the blue whale attacks reveal a very similar hunting pattern by orcas to that observed previously, albeit this time on larger prey.
He stresses that orca social groups (pods) are matriarchies, led by a single dominant female, who is generally related to all other members of the group. While there are adult males in a pod, it is the adult females who do almost all of the serious hunting work in attacking whales. He is not sure why this is, but offers a couple of possibilities:
“Females need to feed more often, to support their young, so they are more likely to initiate these attacks. But it is also true that females are better adapted for hunting than males.” There may also be some commonality with land-based predators, like lions, where females do most of the hunting
The male is larger and has a larger dorsal fin, which seems to be sexually attractive to females. But the very size of males, he continues, makes them too slow to be effective hunters of whales, which often require long pursuits at speed; the female’s body size and shape is ideally adapted for this activity.
He agrees there may also be some commonality with land-based predators, such as lions, where females do most of the hunting.
The recent Marine Mammal Science paper also notes that, while many orcas, including adult males not in the hunting pod, joined in shortly afterwards to feed on the blue whales, no aggression was observed between any of them. Again, Pitman is unsure why, but suggests that it may be simply because so much food was available.
But he adds that orcas need to mate outside their pods, so the gathering to feed on the whale may be a welcome opportunity to socialise with potential partners.
Whale behaviour is so complex, he says, that it makes a very exciting field for young people to enter “because so much is still unknown”.
Another curious aspect of orcas is that the feeding preferences of one population group, and sometimes even of one pod within that group, may be radically different from another’s.
“You could say the pod is like a personality cult in which everyone does what Mom says is the best thing.”
Simon Berrow, chief science officer of the Irish Whale and Dolphin Group, says that in the north Atlantic one orca population, or “ecotype”, eats only fish, while another preys solely on mammals. Human behaviour has divergent impacts here. Because whales are now protected, the mammal-eating ecotype is doing well.
But since salmon has been critically overfished in the area, the fish-eating population is struggling to maintain itself.
Berrow says that orca predation on whales has not been observed in Irish waters, but is not surprised that the killing of blue whales has been confirmed, given that whales are being observed more closely and widely than ever before.This may affect fertility, so that the future of this predator could itself be in doubt
He gives credence to Pitman’s theory that it could also occur more frequently in future, if populations of both species increase, but enters a caveat: a 2019 paper (https://doi.org/10.1016/j.marpolbul.2019.110699) he co-authored shows that orcas found dead on Irish shores have high concentrations of persistent organic pollutants. This may affect fertility, so the future of this predator could itself be in doubt. Like all ecosystems, the marine food web has many variables, each of which affects many of the others.
Both scientists agree that the tendency of popular media reports on the orca-blue whale story to attach words such as “vicious” and “brutal” to the orca’s hunting and feeding techniques is misplaced.
“These words imply that they are capable of malice,” says Pitman. “But they are just doing what they need to do to stay alive. Only humans can be cruel.”
Berrow says a converse notion, that bottlenose dolphins, such as Fungie, have a “smiling” face and therefore a benevolent nature, sometimes has to be countered when he is talking to schoolchildren. “It doesn’t make me popular,” he says. “But I do remind them that bottlenose dolphins can batter porpoises to death.”
Perhaps this tricky issue of comparing human and animal behaviours is best captured by the Nobel Prize-winning poet Wislawa Szyborska, in her ironic In Praise of Feeling Bad About Yourself. She suggests it is precisely our capacity to feel guilty that makes us human, remarking along the way that:
“Though hearts of killer whales may weigh a tonIn every other way they’re light.”