The footage is impressive, and slightly unnerving. Several orcas, swimming abreast, approach an Antarctic ice floe on which is resting an unsuspecting seal. The whales dive just beneath the ice, generating a wave that cracks the floe and washes the seal into the water. Desperately, the seal clambers back on to the ice's remnants, only for the orcas to tip the slab over and dump their putative prey back into the ocean. Somehow, the pinniped evades capture and clambers out on to a larger floe; but, too exhausted by its desperate flight to drag itself away from the edge, it is powerless to resist as one of the whales grabs it by the tail and pulls it beneath the waves one last time.

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What is especially striking, and a little discomfiting, about the video is the obvious intelligence with which the whales pursue their victim: they judge the size of the initial wave perfectly, they confuse the seal with sideswipes of their tails that create underwater eddies, they work together to upend the sanctuary that their prey briefly secures.

The note that accompanies the clip – from Discovery Channel's outstanding 'Frozen Planet' series – on YouTube observes that it marks 'the first complete filming of killer whale 'wave washing' behavior.' And indeed, as far as I am aware, it does. If it has been filmed elsewhere, it assuredly has not been documented so impressively and beautifully.

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Certainly, in my times studying whales or sailing Antarctic waters I've never filmed that behavior. But I have seen it – or something that appeared remarkably close to it. In this instance, the would-be victims escaped unharmed. But they weren't seals, and they weren't on an ice floe. They were in a boat, and they were my friends.

It was February 1995. I was leading an expedition on board the MV Greenpeace, the primary objective of which was to locate and intercept the Japanese whaling fleet. We had also prepared some low-key but potentially valuable scientific studies for times when we were not with the whalers, which was the situation we found ourselves in now. 

We were in the Ross Sea – specifically, McMurdo Sound. We were about as far south as it was possible for a ship to go. Our captain nudged our bow into some fast ice to keep us safely anchored and we prepared to launch a rigid-hulled inflatable boat, carrying two researchers collecting plankton samples and another lowering a hydrophone over the side to record vocalizations of any whales that were nearby.

Three such whales appeared soon enough, their presence first advertised by the anxious squawking and scurrying of the emperor penguins that had taken up residence on the ice next to the ship. The whales were orcas, two females and a male, and we watched as they spy-hopped along the ice edge, presumably checking out the penguins. It didn't take long, however, before they apparently noticed something more interesting.

The team in the inflatable hooted in delight the first time the male swam directly and deliberately toward them before ducking under the hull, generating a small wave that caused the boat to rock slightly. When the whale returned shortly afterward, seemingly swimming with more purpose this time, and certainly slightly faster, the wave was larger, the boat rocked a bit more eagerly and the crew smiled a little more nervously.

There was a pause, and the orcas disappeared from view.

Suddenly, the male appeared again, like a finned torpedo cutting through the water's surface, diving below the waves at the last moment and this time tipping the boat noticeably over to one side. There, waiting with mouths partly open, were the two females.

Lena, the boat's driver, had seen enough. She fired up the engine – which, for the first time that day, started instantly – and took off as the scientists rapidly hauled up their equipment. As they sped toward the safety of the ship, they looked anxiously astern, not seeing the orca that spy-hopped just off their bow.

It is always important to use caution when interpreting other species' behavior. However, it was hard not to figure that the orcas had viewed the boat's crew as oversized, survival-suit clad penguins, and the boat as a peculiarly-shaped ice floe.

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What was especially chilling – and testament, like the 'Frozen Planet' footage, to orcas' intelligence and cooperative nature – was listening to the recordings made by the hydrophone. There were the clicks from the whales' echolocation as they found the boat; the excited squeaks between the whales before and after each of the males' first two passes beneath the inflatable; and then, before the final assault, one more burst of communication, followed by complete silence that was punctuated only by the whoosh of the wave hitting the side of the boat.

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Alas, I don't know what happened to the recording; I would like to track it down, and marry it with footage that our videographer happened to be taking from the deck of the ship. But I remember that day vividly – although, I suspect, rather less vividly than Lena and her crew. I recall that we chuckled, after everyone was safely back on board, at the irony of whales apparently attacking a Greenpeace crew.

And I remember also that, at least for a short while, a few of us subconsciously stopped referring to them as orcas, and instead started calling them killer whales. I remember above all being in awe of the strength and smarts of those whales, an awe that remains 17 years later and is only magnified by watching their more successful pursuit of that hapless seal.

Top photo: Orca (Orcinus orca) killer whales swimming together in group with dorsal fins showing, near rubber dinghy carrying tourists, Prospect Point, Antarctica. (Momatiuk – Eastcott/Corbis)

Bottom photo: Orca spyhopping amid sea ice. (NOAA)