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The polar bear or the sea/ice bear are the world's largest land predators.  They can be found in the Artic, the U.S. (Alaska), Canada, Russia, Denmark (Greenland), and Norway.  Each of these countries either banned hunting or established rules for how many polar bears could be hunted within its own boundaries. These rules help keep polar bear populations stable. Today, 25,000 to 40,000 polar bears roam the Arctic.

Researchers tracked 52 [bears] in the southern Beaufort Sea off Alaska with GPS system collars [...] Fifty long-distance swims were recorded; the longest at 354 kilometres, with an average of 155 kilometres. The length of these swims ranged from most of a day to ten days.

Fur. Polar bears' fur consists of a dense, insulating underfur topped by guard hairs of various lengths. It is not actually white—it just looks that way.

Each hair shaft is pigment-free and transparent with a hollow core that scatters and reflects visible light, much like what happens with ice and snow.

Polar bears look whitest when they are clean and in high angle sunlight, especially just after the molt period, which usually begins in spring and is complete by late summer. Before molting, accumulated oils in their fur from the seals they eat can make them look yellow.

EITHER
"The polar bear or the sea/ice bear is the world's largest land predator.  Polar bears can be found in the Arctic, the U.S. (Alaska), Canada, Russia, Denmark (Greenland), and Norway."
  OR
"Polar bears or sea/ice bears are the world's largest land predators.  They can be found in the Arctic, the U.S. (Alaska), Canada, Russia, Denmark (Greenland), and Norway."

You can use the singular (the polar bear representing all polar bears) or the plural, but you mustn't mix them up in the same sentence, or refer to "The polar bear" as "they" in the next sentence.