Sea otters wear densest fur and smash shells with tools
The sea otter (Enhydra lutris) is a North Pacific coastal mammal. Adults weigh fourteen to forty-five kilograms—heaviest of the weasel family yet among the smallest marine mammals. Instead of blubber they rely on the densest fur in the animal kingdom and can live entirely at sea.
They dive to forage mostly on urchins, mollusks, crustaceans, and some fish. Rocks pry and crack prey, making them one of few tool-using mammals. As a keystone predator they curb urchins that would otherwise clear kelp forests. Fur hunting from seventeen forty-one to nineteen eleven crashed numbers from an estimated one hundred fifty to three hundred thousand down to one to two thousand; bans, conservation, and reintroductions restored occupancy to about two-thirds of the historic range.
Unique among mustelids, they lack functional anal scent glands and can complete life without leaving water—so odd that as late as nineteen eighty-two some scientists doubted the placement. Fossils show the Enhydra line isolated in the North Pacific about two million years ago; modern otters arose in northern Hokkaidō and Russia before spreading to the Aleutians, Alaska, and down the American coast.
A raft of otters cracking lunch on their chests is ecology in miniature: fashion nearly erased them, kelp needs them, and a rock in the paws still marks one of mammal life’s rare tool kits.
Staying warm without blubber is expensive. Up to 150,000 hairs crowd each square centimetre, with long waterproof guard hairs shielding a short underfur that holds a layer of body-warmed air; the catch is that diving squeezes that layer thin just when the otter forages. Its metabolism runs two to three times faster than that of land mammals of similar size, so it must eat between a quarter and nearly two-fifths of its own weight every day, and a meal can pass through in about three hours. Unlike most marine mammals it also drinks seawater, relying on large kidneys to extract fresh water. An urchin-heavy diet can even stain its teeth and bones purple.
Source: Sea otter
