Polar Bears - Data, Pictures and Videos

[sanjay]

Question from Jonas: How can polar bears survive swimming in ice cold water when humans can't?

Answer from Dr. Thea Bechshoft: The answer can be summed up in one wobbly little word: fat!
Polar bears are exceptionally well adapted to the cold Arctic environment, and are able to stay toasty and keep up their 37° C body core temperature even when the snow storm is raging in the middle of the polar night. What keeps the bear from freezing when it’s above water is it’s fur – but when it’s under water, the hair no longer offers much isolation and the bear must instead rely on the fat layer it has accumulated under its skin to stay warm. This fat layer can be up to 11 cm thick, and is especially prominent on the back haunches (rump). How thick this layer becomes obviously depends on how successful of a hunter the individual bear is – the more seals, the fatter the bear. And as I’ve said before, a fat polar bear is a happy polar bear! On a side note, a good layer of fat also helps keep the bear naturally buoyant in the water.
Polar bears are very good swimmers, and long distance swims are common in adults that roam the ice alone. Females with cubs on the other hands tend to avoid swimming too much if at all possible; the cubs are not yet very well isolated, and may ultimately die if they are too cold for too long as would happen during a lengthy swim. Some polar bear mothers solve this by giving their cubs a piggyback ride when crossing the water between ice floes (as you can see an example of in the picture I’ve attached).
The most extreme polar bear swim on record is that of an adult female who swam for nine days straight, a total of 687 km. Very impressive! Unfortunately, it also cost her her cub and 22% of her body fat, which tells you that although this swim was physically possible for her, it was not without cost.
Humans on the other hand are very poorly insulated (even when you may feel that your bathroom scale is trying to tell you something else!). Compared to polar bears we have almost no fat layer under our skin, which is the main reason we don’t last very long in cold water. Some long-distance swimmers cover themselves in grease before an extensive open-water swim (e.g. lanolin, petrolatum, lard), partly to protect themselves against the cold, partly to protect themselves against jellyfish stings.

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