Among the most titanic of predatory events possible here on Planet Earth—and one that’s only been witnessed a handful of times—played out off the southwestern coast of Western Australia on April 7: a “superpod” of orcas—likely more than 60 of them—taking down a pygmy blue whale. A local whalewatching company, Naturaliste Charters, documented the attack:
“We witnessed an incredible and rare event yesterday as multiple pods of orcas successfully hunted a blue whale in Bremer Canyon,” Naturaliste Charters posted to Facebook. “The intense ordeal lasted less than 40 minutes from when we first saw the blue at the surface to when the battle was over.”
Offshore from Bremer Bay, the submarine Bremer Canyon is part of a regional network of underwater chasms—the Albany Canyons—gouged in the continental shelf and slope between Cape Leeuwin and the Esperance area. Funneling nutrient-rich Southern Ocean currents, the shelf-incising Bremer Canyon is a hotspot of biological productivity and diversity—and, in summer and fall, host to the greatest seasonal gathering of orcas documented in the Southern Hemisphere.
While the several hundred orcas hunting here commonly target such prey as beaked whales, tuna, and squid, pygmy blue whales—part of a rejuvenating Indian Ocean stock—sometimes land on the menu, as multiple Bremer Canyon predation events in recent years attests.
While pygmy blues are the smallest of the four blue-whale subspecies, they’re still enormous animals, reaching lengths of some 24 metres (79 feet). The victim in this most recent event was reckoned at 18 metres (59 feet). In 2021, Naturaliste Charters photographed some 50 to 70 orcas over Bremer Canyon kill an estimated 16-metre (52-foot) blue whale after an hours-long attack. And as Ian Dickinson wrote about here at Earth Touch News, Bremer Canyon orcas killed two pygmy blues—one of them 20 metres (66 feet) long—in the space of a couple of weeks in 2019.
These ambitious attacks on pygmy blues involve dozens of orcas, which, among other areas of the blue’s body, commonly target the jaws—the tongue apparently being a prized delicacy.
It’s unclear the degree to which orcas might attempt to kill a full-grown blue whale of the larger subspecies, which are the biggest of all beasts: Antarctic blues may exceed 30 metres (100 feet) and weigh 180 metric tons. In 2017, drone footage captured a pod of orcas charging an adult blue in California’s Monterey Bay, but this didn’t appear to be a serious predatory attempt, and the blue speedily exited the scene.
Indeed, except in the case of the small minke whale, successful orca strikes on mature baleen whales haven’t been documented very often. Patterns of rake marks seen on baleen species suggest most are primarily vulnerable to killer whales as calves or juveniles.
But given some populations and ecotypes of orcas commonly hunt whale calves—and may opportunistically make a go at older individuals—the threat of killer-whale predation likely helps shape the lifeways of baleen whales. In response to that threat, these ocean giants tend to follow either a “fight” or “flight” strategy.
Earlier this year, a study published in Marine Mammal Science showed that most whale species that customarily flee from orcas—which include blue whales as well as such close cousins as the fin, sei, Bryde’s, and minke—sing at a frequency too low to be detected at distance by killer whales: an example, perhaps, of “acoustic crypsis,” allowing these rorquals to communicate with one another without advertising themselves to their primary predator.
By contrast, baleen-whale species that fight back against orcas—among them humpbacks, bowheads, grey whales, and right whales—generally sing at higher frequencies above 1,500 Hz, clearly audible to killer whales. These offence-makes-the-best-defence species also tend to be slower and more manoeuvrable than their “flight” counterparts, which are slender, streamlined, and impressively nimble.
The study also notes that the “fight” species usually give birth, and frequently migrate, in coastal waters—relatively shallow nearshore environments where they can often stage successful group defence against persecuting orcas—whereas the “flight” types often breed and travel out in the open ocean. That deep, bluewater realm may improve their ability to outpace killer whales.
In a University of Washington press release about the research, faculty member and study author Trevor Branch said, “It just never occurred to me that some whales sing low to avoid killer whales, but the more I looked at this, the more I realized that every aspect of their behavior is influenced by the fear of predation.”
Top header image: timnutt, Flickr
Predator vs Prey
Whales and Dolphins
Predator vs Prey
