The king of the Arctic has a wide range of different food sources. Due to the vastness of the area and its unforgiving climate, polar bears need a high energy-rich diet, mostly consisting of seals with their thick layer of blubber. But seals are not the only polar inhabitant with a delicious fat layer around them to protect them from the cold. Also other marine mammals, especially whales and dolphins rely on this form of insulation. But how should a polar bear hunt a purely aquatic animal? A group of Norwegian researchers coincidentally found an answer and some previously unknown behavior.

Polar bears lead a very difficult lifestyle in the regions of the High Arctic. They rely on a high energy-rich diet to maintain their body functions. And in the Arctic, layers of fat are the best way to store energy and get some protection from the cold and harsh environment. Thus, polar bears are constantly on the search for prey with a big layer of blubber. Their search usually takes them along the edge of the Arctic sea ice where they are looking for seals, their main prey. On the archipelago of Svalbard, however, polar bears also move along the ice-covered northern and eastern coasts on their search for food.

The polar bear encountered by Aars and his team was an old male and clearly undernourished as seen by the visible ribs. The dolphin carcass was still almost intact, only the valuable fat layer had been consumed by the bear already.
The polar bear encountered by Aars and his team was an old male and clearly undernourished as seen by the visible ribs. The dolphin carcass was still almost intact, only the valuable fat layer had been consumed by the bear already.

This behavior also makes them easier to spot for researchers who are trying to assess the ecology of polar bears by tagging the animals and later re-catching them to find out about their wandering routes and growth. In Svalbard, this survey is conducted annually by researchers of the Norwegian Polar Institute by means of ships and helicopters. On one of these survey trips, a team of researchers with Jon Aars came across a previously unknown behavior of Svalbard polar bears: the hunt of white-beaked dolphins, a small dolphin species which is found mostly along the west coast of Svalbard. 

Aars and his team found a presumably old and undernourished polar bear on the ice edge of a frozen fjord in the North of Svalbard. When getting closer, they saw that the bear had been just feeding on a small carcass which turned out to be the remains of white-beaked dolphin. The carcass was placed just next to a hole in the ice and the bear was in the process of covering the carcass with snow, another rare behavior of polar bears. The scientists couldn’t find another opening in the ice and thus concluded that it must have been a breathing hole kept open by the dolphins. A bit further away, the team found another carcass almost entirely consumed already.

Approximately 3’000 polar bears roam the area of Svalbard and the Northern Barents Sea. Although they are found almost anywhere on the islands, most bears are wandering along the coast, always on the lookout for food. Picture: Michael Wenger
Approximately 3’000 polar bears roam the area of Svalbard and the Northern Barents Sea. Although they are found almost anywhere on the islands, most bears are wandering along the coast, always on the lookout for food. Picture: Michael Wenger

The polar bear was immobilized and examined by the team. From their findings on both bear and dolphin, Aars and his team concluded that the bear had killed the dolphins and had dragged them onto the ice for consumption. Only very rarely, polar bears have been observed to hunt small cetaceans at their breathing holes after they had been trapped by fast incoming sea ice.

Polar bears usually feed on the fat layers first before consuming other parts. Interestingly, the meat of the muscles is eaten last as its digestion uses a lot of energy in form of heat. Once a polar bear has filled its belly, it sometimes covers the leftovers to protect it from being scavenged by other predators.
Polar bears usually feed on the fat layers first before consuming other parts. Interestingly, the meat of the muscles is eaten last as its digestion uses a lot of energy in form of heat. Once a polar bear has filled its belly, it sometimes covers the leftovers to protect it from being scavenged by other predators.

Jon Aars states that polar bears have not been reported before to hunt dolphins as the latter are rarely found that far north and are not ice-adapted. Additionally, dolphins are very fast swimmers and very agile and thus hard to catch even at a small breathing hole. More carcasses were found during the course of the summer in the vicinity of the fjord and Aars concluded that one or more pods of dolphins must have been trapped by the ice, then drowned or suffocated and gotten washed ashore where the remains were found by polar bears and other scavengers. “Dolphins may provide a significant source of food for some bears locally over a longer period of time after such an incident”, he states. “White beaked dolphins may offer a new prey or carrion food source to bears in an environment where access to ringed seals and bearded seals may decline in future years.”

Source: Polar Research (2015) No. 34