Whale-watching tourists off western Australia saw more than they expected – and perhaps more than many of them wanted – last week. As two boats of observers took in the action, a humpback whale mother desperately and vainly tried to protect a calf from four predatory orcas.

The video below, shot from a light aircraft that circled overhead as the action unfolded, isn’t always easy to make out, but it shows the orcas circling as the humpback attempts to protect the calf by lifting it on to her back. (If you pause the video at about 12 seconds, you can see the whale more or less center of the screen, and the lighter-colored calf just above it.)

According to witnesses, the humpback was spotted with two calves, but the orcas swiftly came on the attack taking one. The mother only succeeded in protecting her second calf for about three-quarters of an hour before it, too, succumbed to the ambush:

“I’ve been diving for three years and I’ve never seen anything like it,” said Tamar Melen, who watched the 45-minute spectacle unfold metres from the boat. Sadly, the killer whales made off with both calves. Ms Melen, 31, said they grabbed the first in seconds, but the attack on the second lasted half an hour. “It was quite impressive,” Ms Melen said. “The first hit was so quick, but then they took their time with the second. It was agonising to watch the mother humpback trying to protect her calf.

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Not all orcas eat other whales, or even other marine mammals. Generally speaking, scientists agree that there are at least three ‘types’ of orcas: residents, which exhibit strong family bonds, eat primarily fish and live in coastal waters; offshore orcas, which also eat fish but may also eat marine mammals and sharks; and transients, which travel in smaller packs and appear to prey on marine mammals almost exclusively. The orcas that ate the two humpback calves showed behavior typical of transients.

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It is for their habit of hunting whales that are they named, and for which they developed, particularly among early observers, a fearsome reputation. For example, in his Natural History, the Roman writer Pliny the Elder described the species as ‘the enemy of other whales”, asserting that they would “bite and mangle the females and their calves” and “charge and pierce them like warships ramming.”

Orca attacks on other whales are rarely observed, but in recent years there have been documented instances of orcas preying on blue, gray, and sperm whales. Although the report of the humpback calves’ demise was headlined “Nature Turns Nasty,” it might more accurately be dubbed, “Nature Being Nature.”

Photograph by Captain Budd Christman/NOAA Photo Library