A hungry polar bear has been witnessed diving and swimming underwater for more than three minutes without coming up for air, smashing a previous record of 72 seconds.

The feat, described in the journal Polar Biology, may illustrate the desperate measures polar bears must take to survive as climate change melts away their traditional hunting grounds on the sea ice of the Arctic Ocean, says one of the authors of the study.

The new record was witnessed by veteran Arctic guide Rinie van Meurs last August. He had been taking a family out by boat to see polar bears near the Svalbard archipelago in northern Norway, when they spotted a "very, very skinny" adult male polar bear, he recalled in an interview with CBC's As It Happens.

An Arctic guide witnesses the longest-known polar bear dive, but says the feat was an act of desperation made necessary by shrinking sea ice. 6:28

As they watched and filmed it on video, the polar bear began to stalk three bearded seals on a large ice floe on the other side of a large channel of open water, beyond the boat.

Tourist Petrina Steains films an emaciated polar bear in a record-breaking dive 3:38

Polar bears rely on sea ice as a habitat for hunting seals, but as the Arctic gets warmer as a result of climate change, there is less and less sea ice, especially in the summer.

Nowhere to hide

Normally, van Meurs said, when polar bears stalk seals on ice floes, they hide behind other ice floes "but in this case, there was nothing" to hide behind.

Instead, the bear hid underwater, diving when it was about 40 metres away from the first seal. When that seal escaped into the water, the polar bear changed course toward the second seal without coming up for air.

He went to the extreme to make this work. - Rinie van Meurs, Arctic guide

Three minutes and 10 seconds later, the bear "exploded out of the water at the floe edge and propelled itself halfway onto the ice immediately in front of the second seal," wrote van Meurs and Canadian polar bear researcher Ian Stirling, from the University of Alberta, in their research paper.

"The seal got away," van Meurs recalled, "but he was very, very close."

In this case, he added, the scrawny bear looked very desperate for food.

"He went to the extreme to make this work," van Meurs said.

But the success rate for polar bears in this kind of hunt is very low, the researchers noted in their paper. Because of that, they said, they don't think polar bears can evolve better diving abilities fast enough to compensate for the rapidly melting sea ice.

Previously, the longest dive ever recorded for a polar bear was 72 seconds, according to Stirling, who witnessed the 72-second dive in 1973.

This isn't the first record set by a desperate polar bear – in 2011, a female polar bear swam for nearly 700 kilometres over nine days in search of ice floes to hunt on.

As the ice melts, van Meurs said, polar bears may push themselves to the limits of their abilities to dive, swim, walk and fast in order to survive. But even that won't help when the sea ice completely disappears during the summer months.

"Then, simply, bears can't make a living anymore."