There are plenty of stories of cetaceans saving humans. Indeed, Jonah was rescued by a whale when he was thrown overboard, and there have been tales of dolphins assisting swimmers in distress or shielding them from circling sharks.

Killer whales, however — themselves a species of dolphin — didn't get their name for nothing. Early Basque whalers called them whale killers when they saw them attacking other whales. Hunting like a pack of wolves, orca know no fear. They'll tear the throats from grey whale calves, and have even been known to take chunks out of sperm whales — the largest predators that ever lived.

But here's a sight to gladden the eye. Earlier this year, Californian scientists Robert L Pitman and John W Durban sailed to the Antarctic in search of killer whales. They were looking for a possible new species, known to hunt Weddell seals — one of the plumpest of the pinnipeds (the suborder that includes seals and sea lions) — by washing them off ice floes with their wake.

That's what was happening here — until a group of humpback whales arrived on the scene. Unlike orca, which are odontocetes or toothed whales, humpbacks are mysticetes, harmless leviathans with only baleen plates in their mouths.

Doubtless open-mouthed themselves, Pitman and Durban — along with a film crew from the BBC Natural History unit — watched as one seal, swept into the water by the orca, swam towards the humpbacks.

As the killer whales moved in, the plucky pinniped leapt on to the vast ribbed belly of a humpback, and nestled in the animal's armpit. Not only that, but when a wave threatened to return the seal to danger, the humpback used its massive flipper (at five metres, the longest in the animal kingdom) to nudge it back on.

"Moments later the seal scrambled off and swam to the safety of a nearby ice floe," wrote the scientists. They believe the seal triggered a maternal defence mechanism in the humpbacks. Whatever the truth, it's a heartening tale. But spare a thought for the orca. They've got kids to feed, too.