The polar bear, Ursus maritimus, is a highly capable swimmer, distinguishing it as the most aquatic of all bear species. Its classification as a marine mammal highlights its dependence on the ocean and sea ice for survival. The ability to navigate and endure the frigid Arctic waters is fundamental to its biology and lifestyle.
Physiological Adaptations for Aquatic Life
The polar bear’s body is engineered to withstand the extreme cold and perform efficiently in the water. An insulating layer of fat, or blubber, can be up to 11 centimeters (4.3 inches) thick, providing warmth and buoyancy in the icy ocean. This layer helps maintain a core body temperature of about 37°C (98.6°F), even when submerged in near-freezing water.
The bear’s coat features dense, water-repellent fur that minimizes heat loss and prevents the skin from becoming wet. The outer guard hairs are hollow, which aids in insulation and contributes to the bear’s overall buoyancy.
For propulsion, the polar bear possesses large, slightly webbed front paws that function like powerful paddles. These paws can measure up to 30 centimeters (12 inches) wide, providing a large surface area to push against the water. Their body shape is also slightly tapered, featuring a long neck and smaller shoulders, which creates a more streamlined profile for moving through the water.
Mechanics of Swimming and Diving
Polar bears propel themselves through the water primarily using a dog-paddle style stroke with their powerful front limbs. The front paws are the main source of forward thrust, pulling the bear through the water with each stroke. The hind legs and feet are held relatively flat and used as rudders to steer and maintain stability, rather than contributing to forward momentum.
When diving, the polar bear has specialized physiological controls that allow it to operate underwater. The nostrils close tightly to prevent water entry, and they may also close their eyes or use a transparent inner eyelid for protection. They primarily make shallow dives, usually between 3 to 4.5 meters (10 to 15 feet), for stalking prey or navigating ice floes. Although dives are typically shallow, they can remain submerged for over a minute, with the longest documented breath-hold lasting 3 minutes and 10 seconds.
Endurance and Long-Distance Capability
The polar bear’s swimming performance is marked by speed and stamina. They can achieve a cruising speed of about 6 kilometers per hour (3.7 miles per hour), with top speeds reaching up to 10 kilometers per hour (6.2 miles per hour) in short bursts. This sustained speed is supported by high fat reserves, which act as a concentrated energy source to fuel prolonged activity and maintain core body temperature.
These animals are capable of aquatic endurance, often swimming for several hours without rest. Documented instances show that polar bears can travel continuously for multiple days, with one study finding an average sustained swim duration of 3.4 days. The longest recorded continuous swim by a female polar bear lasted for nine days, covering a distance of 687 kilometers (426 miles) across open water.
The Role of Swimming in Hunting and Survival
Swimming is integral to the polar bear’s life cycle, enabling essential movements and hunting strategies across the Arctic environment. They use this ability to travel between separated ice floes, cross open water leads, and reach distant land masses, especially when sea ice retreats during the summer months. This capacity allows them to follow the shifting sea ice and access new hunting grounds.
While most hunting occurs on the ice, swimming is sometimes employed to ambush prey, particularly seals resting near the edge of an ice floe or at breathing holes. The bear can discreetly approach its target from the water, using the element of surprise to secure a meal. However, the increasing necessity of long-distance swimming due to receding sea ice is now presenting a significant survival challenge. Longer, more frequent swims deplete energy reserves and increase mortality risk, especially for cubs.