The polar bear, Ursus maritimus, is an apex predator of the Arctic, classified as a marine mammal due to its dependence on the ocean environment. These large carnivores inhabit the circumpolar Arctic, relying almost entirely on sea ice for survival. Sea ice serves as the primary platform from which they hunt seals, their main source of high-fat nutrition, and as a resting and breeding ground. Exploring the polar bear’s ability to navigate open water reveals its physical capabilities and the environmental pressures currently reshaping its existence in the rapidly warming Arctic habitat.
The Mechanics of Polar Bear Swimming
Polar bears possess specific physiological and anatomical features that make them formidable, though not necessarily efficient, swimmers. Their swimming style is a powerful dog-paddle, driven primarily by their large, slightly webbed front paws, which act as powerful paddles for propulsion. The hind legs are trailed behind the body and used more like rudders to help steer and stabilize their path through the water.
A thick layer of blubber, which can measure up to 11 centimeters deep, provides insulation against the frigid Arctic waters and significant buoyancy. This natural flotation device helps the bear conserve energy by keeping its body higher in the water. The bear’s dense coat of fur is also water-repellent, offering protection against heat loss in the marine environment.
These adaptations allow polar bears to maintain a steady swimming speed, reaching up to 10 kilometers per hour (6.2 miles per hour) in short bursts. When submerged, the polar bear can close its nostrils to prevent water intake, demonstrating its semi-aquatic nature. While they are built for the water, their primary mode of travel and hunting remains walking on the ice, making swimming an energetically demanding alternative.
Documented Swimming Distances and Records
Scientific tracking has revealed the extraordinary endurance of polar bears, showing they are capable of continuous aquatic journeys far beyond previous estimates. Researchers use satellite-linked telemetry devices, often attached to GPS collars on adult female bears, to map their movements on ice and in open water. These studies define “long-distance swims” as continuous aquatic travel exceeding 50 kilometers (30 miles).
Analysis of tracking data from bears in the Beaufort Sea identified over 50 long-distance swimming events between 2004 and 2009, with the average distance covered in a single event being approximately 153 kilometers (95 miles). The most extreme documented feat of endurance involved an adult female bear that completed a continuous swim of 687 kilometers (426 miles). This marathon swim took place over a period of 9.67 days in the frigid waters of the Beaufort Sea.
This record-setting movement demonstrated the upper limits of the bear’s capability to traverse the open ocean. The tracking data confirmed that the bear was in the water for nearly 232 continuous hours as it searched for a stable ice floe or land.
Why Increased Swimming Distances Matter
The necessity of undertaking these increasingly long swims carries biological and ecological consequences for the species. Prolonged swimming drains a polar bear’s energy reserves, demanding a caloric expenditure that is three to five times greater than walking the same distance on ice. This high metabolic cost forces the bears to burn through fat stores quickly, which are essential for surviving the long fasting periods of the summer.
The female bear that completed the 687-kilometer swim, for instance, lost 22 percent of her body mass during the journey, illustrating the severe energetic toll. This rapid depletion of fat reserves impacts their overall body condition and reproductive fitness, making successful hunting upon reaching their destination even more urgent. The risk of mortality is also substantially higher, particularly for cubs, who are less equipped to handle the energetic demands and thermal challenges of the open water.
Young cubs have less insulating blubber, making them highly susceptible to hypothermia. The record-setting female’s yearling cub did not survive the prolonged swim, highlighting the vulnerability of the younger generation. The primary driver behind the increase in these strenuous aquatic journeys is the accelerating retreat and fragmentation of the sea ice across the Arctic.
As the ice melts earlier in the spring and freezes later in the autumn, the distance between the remaining ice edge and the shore grows, creating vast stretches of open water. Bears are forced to cross these gaps to reach their traditional foraging grounds or to get to land for the ice-free season. This changing habitat structure transforms a normally terrestrial movement into a lengthy, high-risk aquatic one, directly challenging the survival mechanisms of this ice-dependent Arctic species.