New Zealand researchers have captured stunning underwater video of a killer whale off the coast of Antarctica as part of their efforts to monitor the apex predator.

The incredibly rare footage was captured with an underwater 'Boxfish' drone, which has been carefully engineered to withstand water as cold as -1.8degC.

University of Canterbury scientist Dr Regina Eisert is using the footage, captured near New Zealand's Scott Base, to keep a careful eye on Type C 'Charley' killer whales as they feed in McMurdo Sound.

The whales flock to the area every summer to follow an icebreaker as it cuts a channel through the sea ice, allowing ships to get into the American base at Ross Island. That in turn opens new feeding grounds for the predators, allowing them to get to Antarctic toothfish deep under the ice.

This creates a unique setting: a 'Killer Whale Highway' that allows researchers to get up close and personal with dozens of whales in a narrow space every single day.

Dr Eisert, one of the world's leading whale scientists, follows them from on high in a helicopter and up close and personal with underwater cameras.

"We're trying to collect the baseline data for how many killer whales are there, what do they eat, where do they eat it, where do they go when they're not here," she says.

"Having this whale highway in front of Scott base with 150 whales going through the channel every day in super clear water is just a dream."

Her study has now been running for five years and indicates there are only around 300 killers in the area in any given summer, with many returning year after year.

The science will help to inform the effectiveness of a new marine protected area in the Ross Sea, designed to protect one of the killer whales main food sources, the Antarctic toothfish.

It's dangerous science with researchers required to land helicopters on the sea and work right out on the edge by freezing water. A specialist Antarctic field trainer, Tom Arnold, is on hand to make its safe at all times.

"It's a pretty harsh environment and you need to be on top of it," he says.

"We're wearing full immersion suits, these will keep us buoyant and afloat and also keep us warm, should the unlikely event that we end up in the water."

This year, the researchers have brought an underwater drone company - Boxfish - to deploy a $100,000 remote controlled floating camera to capture the creatures inside their own world.

Co-founder Ben King says the device has been in the works for three-and-a-half years and has to work hard to survive in the harsh conditions.

"From the cold affecting batteries to screens and other things, the brightness, the wind, the cold makes it difficult for us," he says.

"It's really deep and dark; once you get down below a few hundred metres, so being able to actually observe those animals at that depth is a major challenge."

Dr Eisert also takes biopsy samples from the tiny population at McMurdo Sound. She says there are only around 300 in the area and she's starting to recognise them.

"The first year they ignored us, and the second year they actually looked at us from a distance and the third year they came over and talked and blew bubbles at us and stuff," she says.

"So we recognise them, they're the same individuals over and over again, so that again suggests there aren't that many of them."

Her hope is that science will help to save these majestic creatures, and the harsh environment they call home.

Newshub.