How Far Can Polar Bears Swim? Long-Distance Swimming Facts

The longest recorded polar bear swim

The record swim was tracked with a GPS collar on an adult female in the Beaufort Sea north of Alaska. She swam continuously for about nine days, covering roughly 687 km (427 mi) before reaching sea ice. Afterward she kept walking and swimming over the ice, and by the end of the journey she had lost about 22% of her body weight.

She did not finish the trip unharmed. She had started out with a yearling cub, and the cub was no longer with her when she came out of the water. This single case became a well-known example of how a warming Arctic can push polar bears to their limits.

How often do polar bears swim long distances?

The same research team studied GPS-collared females in the Beaufort and Chukchi seas between 2004 and 2009. They recorded 50 long-distance swims of more than 50 km (31 mi), made by 20 different bears. These swims averaged about 154 km (96 mi) and lasted about 3.4 days.

Long swims were most common in years when the summer sea ice retreated far from the coast, leaving wide areas of open water between the ice edge and land. In other words, bears swim long distances mainly when they have to, not by choice. For the polar bear, the ice is a hunting platform, and when it moves far away the bear must either swim to it or wait on land without seals to eat.

How do polar bears swim?

Polar bears swim like a powerful dog paddle. The huge front paws, up to about 30 cm (12 in) across and slightly webbed between the toes, do the work, pulling the bear through the water. The hind legs trail behind and act like rudders for steering. The bear keeps its head above water, with its eyes and nose high on the skull, so it can breathe easily while swimming at the surface.

Several features help it stay warm and afloat:

• Blubber. A fat layer up to about 10 cm (4 in) thick insulates the body and makes the bear more buoyant.
• Oily, water-shedding fur. The long guard hairs shed water quickly when the bear climbs out, so the fur insulates again soon after a swim. See are polar bears really white? for how the coat works.
• Large body size. A big body loses heat more slowly than a small one, an important advantage in near-freezing water.

How fast and how deep can polar bears swim?

Polar bears are steady rather than fast swimmers. Their top swimming speed is about 6 km/h (3.7 mph), and on long trips they often average around 2–3 km/h (1–2 mph). That is slow compared with seals, which is why polar bears rarely catch seals in open water and instead hunt them at breathing holes or on the ice.

Polar bears can also dive. They swim underwater with their eyes open and nostrils closed, and sometimes stalk seals or seabirds resting on ice floes by approaching underwater. Most dives last well under a minute. The longest dive ever recorded, filmed in Svalbard in 2014, lasted about 3 minutes and 10 seconds, as a bear approached seals resting on the ice.

Why long swims are dangerous for cubs

Swimming is costly even for an adult. A bear on a long swim burns fat it cannot replace, because it cannot hunt in open water. Adults have large fat reserves to cover this cost, but young cubs have little body fat and lose heat much faster.

In the Beaufort and Chukchi seas study, mothers that made long-distance swims were roughly twice as likely to lose their cubs as mothers that did not. Cubs sometimes climb onto their mother’s back in the water, but on long journeys this is not always enough. Storms and rough seas add further risk, and young bears and cubs are the most likely to drown.

Are polar bears marine mammals?

Yes. Although they walk on land and ice, polar bears are generally classed as marine mammals, together with seals, sea lions, walruses, whales and sea otters. Their scientific name, Ursus maritimus, means “sea bear”. Almost all their food comes from the ocean, mainly seals, as explained in what do polar bears eat?

In the United States, polar bears are protected under the Marine Mammal Protection Act of 1972, and the US Fish and Wildlife Service manages them along with walruses and sea otters. They are the only bears that rely on the sea in this way.

Swimming and climate change

Because Arctic summer sea ice now retreats farther and earlier than it did a few decades ago, many polar bears face longer gaps between land and ice. Some respond by swimming more, others by staying ashore for longer. Both choices cost them energy, since they cannot hunt seals in either situation.

Scientists therefore use swimming behavior, along with body condition and cub survival, as one sign of how polar bears are coping with sea ice loss. For the bigger picture of where numbers are falling, see how many polar bears are left?