<P> Brown bears tend to dominate polar bears in disputes over carcasses, and dead polar bear cubs have been found in brown bear dens . Wolves are rarely encountered by polar bears, though there are two records of Arctic wolf (Canis lupus arctos) packs killing polar bear cubs . A rather unlikely killer of a grown polar bear has reportedly included a wolverine (Gulo gulo), anecedotely reported to have suffocated a bear in a zoo with a bite to the throat during a conflict . Polar bears are sometimes the host of arctic mites such as Alaskozetes antarcticus . </P> <P> Researchers tracked 52 sows in the southern Beaufort Sea off Alaska with GPS system collars; no boars were involved in the study due to males' necks being too thick for the GPS - equipped collars . Fifty long - distance swims were recorded; the longest at 354 kilometres (220 mi), with an average of 155 kilometres (96 mi). The length of these swims ranged from most of a day to ten days . Ten of the sows had a cub swim with them and after a year, six cubs survived . The study did not determine if the others lost their cubs before, during, or some time after their long swims . Researchers do not know whether or not this is a new behaviour; before polar ice shrinkage, they opined that there was probably neither the need nor opportunity to swim such long distances . </P> <P> The polar bear may swim underwater for up to three minutes to approach seals on shore or on ice floes . </P> <P> Polar bears have long provided important raw materials for Arctic peoples, including the Inuit, Yupik, Chukchi, Nenets, Russian Pomors and others . Hunters commonly used teams of dogs to distract the bear, allowing the hunter to spear the bear or shoot it with arrows at closer range . Almost all parts of captured animals had a use . The fur was used in particular to make trousers and, by the Nenets, to make galoshes - like outer footwear called tobok; the meat is edible, despite some risk of trichinosis; the fat was used in food and as a fuel for lighting homes, alongside seal and whale blubber; sinews were used as thread for sewing clothes; the gallbladder and sometimes heart were dried and powdered for medicinal purposes; the large canine teeth were highly valued as talismans . Only the liver was not used, as its high concentration of vitamin A is poisonous . Hunters make sure to either toss the liver into the sea or bury it in order to spare their dogs from potential poisoning . Traditional subsistence hunting was on a small enough scale to not significantly affect polar bear populations, mostly because of the sparseness of the human population in polar bear habitat . </P>

How do polar bears adapt to their environment wikipedia