<P> In some areas, this is a protected species, and some places have otter sanctuaries that help sick and injured otters to recover . </P> <P> Sea otters (Enhydra lutris) are classified as marine mammals and live along the Pacific coast of North America . Their historic range included shallow waters of the Bering Strait and Kamchatka, and as far south as Japan . Sea otters have about 26,000 to 165,000 hairs per square centimeters of skin, a rich fur for which humans hunted them almost to extinction . By the time the 1911 Fur Seal Treaty gave them protection, so few sea otters remained that the fur trade had become unprofitable . Sea otters eat shellfish and other invertebrates (especially clams, abalone, and sea urchins). Otter populations are affected by the density of prey they hunt . Because the otter food source is easier to excavate from rocky - bottom habitats, as opposed to soft - bottom habitats, more otters tend to live in waters with rocky bottoms with access to shallow - burrowing prey . They frequently carry a rock in a pouch under their forearm and use this to smash open shells, making them one of the relatively small number of animals that use tools . They grow to 1.0 to 1.5 m (3.3 to 4.9 ft) in length and weigh 30 kg (66 lb). Although once near extinction, they have begun to spread again, from remnant populations in California and Alaska . </P> <P> Unlike most marine mammals (such as seals or whales), sea otters do not have a layer of insulating blubber . As with other species of otter, they rely on a layer of air trapped in their fur, which they keep topped up by blowing into the fur from their mouths . They spend most of their time in the water, whereas other otters spend much of their time on land . </P> <P> The giant otter (Pteronura brasiliensis) inhabits South America, especially the Amazon river basin, but is becoming increasingly rare due to poaching, habitat loss, and the use of mercury and other toxins in illegal alluvial gold mining . This gregarious animal grows to a length of up to 1.8 m (5.9 ft), and is more aquatic than most other otters . </P>

How long can otters stay out of water
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