The polar bear, Ursus maritimus, is classified as a marine mammal uniquely adapted to the harsh, ice-covered environment of the Arctic. Their existence is fundamentally tied to the presence of sea ice, which serves as their primary platform for hunting seals, mating, and travel. While they are powerful swimmers, extended swims were historically considered an occasional necessity rather than a regular occurrence. The increasing frequency and distance of these aquatic journeys now provide scientists with a new measure of the bear’s extraordinary physical limits.
The Mechanics of Polar Bear Swimming
The ability of a polar bear to sustain long periods in frigid water is supported by physical and physiological adaptations. A thick layer of blubber, which can measure up to 11 centimeters (4.3 inches), provides significant insulation against the near-freezing Arctic water and aids in flotation. This blubber layer is so effective that overheating, not hypothermia, is often a concern for bears on land.
The bear’s fur consists of a dense undercoat and long guard hairs that are water-repellent, minimizing heat loss upon exiting the water. Their massive, slightly webbed front paws function as powerful paddles, providing the main source of propulsion in a modified doggy-paddle style. The smaller hind legs serve as rudders to steer the bear, contributing to a swimming speed that can reach up to 10 kilometers per hour (6.2 mph) for short bursts.
Record-Breaking Swims: Duration and Distance
Documented evidence confirms the polar bear’s capacity for extreme aquatic endurance. In 2008, researchers tracked one adult female that swam continuously for 232 hours (over 9.6 days) through the frigid waters of the Beaufort Sea. During this marathon effort, the bear covered a straight-line distance of 687 kilometers (426 miles), demonstrating the species’ physiological reserve.
The bear moved at an average pace of approximately 3 kilometers per hour, indicative of sustained endurance travel rather than short-distance hunting. While most swimming events observed in tracking studies are much shorter, this multi-day swim establishes the maximum known limit of their continuous aquatic travel. Such lengthy efforts are not typical behavior for a healthy bear on stable ice and are considered rare responses to environmental pressures.
The Environmental Driver: Why Swims are Getting Longer
The observed increase in extreme swimming events is directly linked to the rapid retreat and fragmentation of Arctic sea ice. Polar bears rely on the ice as a stable platform from which to hunt seals, their primary food source. As global temperatures rise, the summer sea ice melts earlier and refreezes later, forcing the bears to travel farther to find suitable hunting grounds or to reach mainland denning sites.
The expanding distance between the continental shelf, where seals are most abundant, and the remaining permanent ice edge is a major issue. When the open water gap becomes too wide, bears are compelled to swim across the expanse to access necessary resources. This necessity for long-distance aquatic travel has become a pattern in regions like the Beaufort Sea, where the proportion of bears undertaking swims over 50 kilometers has significantly increased since the early 2000s.
The Cost of Endurance: Risks of Extended Swimming
While adult polar bears are physically built for aquatic travel, prolonged swims extract a high physiological price. The energy expenditure is immense, rapidly burning through the bear’s stored fat reserves, which are necessary for survival during periods of food scarcity. The female bear that completed the record-breaking swim, for instance, lost 22 percent of her body mass during her nine-day journey.
The greatest survival risk falls on the young, as cubs lack the thick blubber layer and physical conditioning of the adults. Their smaller body size makes them more susceptible to hypothermia in the cold water, and they do not possess the necessary endurance to keep pace with their mothers. Research shows that mothers who undertake long-distance swims face a significantly higher cub mortality rate, suggesting these extreme efforts compromise future generations.