Polar bears stand as remarkable apex predators within the challenging Arctic environment. These powerful animals exhibit unique adaptations that allow them to thrive amidst vast stretches of ice and frigid waters. Their ability to navigate and hunt beneath the surface of the ocean is a fascinating aspect of their survival in this icy domain.
Typical Underwater Breath-Hold
Polar bears hold their breath underwater for short durations, with many dives lasting around 30 seconds. They remain submerged for up to two minutes, allowing effective maneuvering beneath the ice. A record of three minutes and ten seconds has been observed, showing their potential for extended submersion. This dive was performed by a thin bear.
For most underwater activities, polar bears cruise at depths of three to 4.5 meters (10 to 15 feet). The record-setting bear also reached a depth of 45 to 50 meters (147 to 164 feet). Their everyday hunting and travel dives are much briefer, tailored to the immediate task.
Specialized Adaptations for Diving
Polar bears possess physical features enabling their underwater abilities. Their large, partially webbed paws function like paddles, providing powerful propulsion, with hind legs acting as rudders. A thick blubber layer, up to 11 centimeters (4.3 inches) thick, provides insulation and buoyancy, helping them float.
Their dense fur, with an insulating undercoat and water-repellent guard hairs, traps air, contributing to warmth and buoyancy. When submerged, polar bears close their nostrils to prevent water entry, and their eyes adapt for clear vision both above and below the surface. Their streamlined, tapered bodies reduce drag, allowing efficient movement through water.
Beyond external features, polar bears exhibit internal physiological adaptations for diving. They possess large lungs, approximately 165 liters in capacity. During dives, they significantly slow their heart rate, a process called bradycardia, from about 70 beats per minute to as low as 5-6 beats per minute, conserving oxygen. This allows them to direct blood flow efficiently to essential organs, ensuring sustained function while submerged.
Purpose of Underwater Activity
Polar bears engage in underwater activities for hunting and movement in their ice habitat. They employ an “aquatic stalking” technique, swimming stealthily beneath the surface to approach seals on ice floes or near breathing holes. This method allows them to surprise prey by bursting out of the water onto the ice.
Underwater foraging also extends to hunting seabirds or retrieving crabs and shellfish from the seafloor. Movement between ice floes is a reason for swimming and diving, especially as seasonal ice melts create more open water. They swim considerable distances, sometimes for days, to navigate their fragmented environment.
Occasionally, polar bears enter the water to cool down, as their substantial insulation can lead to overheating during physical activity or on warmer days. They may also dive to investigate submerged carcasses or seaweed. While strong swimmers, their primary hunting strategies leverage the ice surface, making underwater excursions a specialized tool in their Arctic survival.