Unlike seals, whales, and other such marine mammals, sea otters do not have blubber (a thick layer of subcutaneous fat) to keep themselves warm in cold ocean waters. Instead, sea otters are insulated by a remarkable coat of fur. At 150,000 strands of hair for each square centimeter of skin, the sea otter’s fur is the densest of any animal in the world, and keeps cold water from even touching the animal’s skin. The fur must be kept scrupulously clean in order to retain its insulating properties, and so sea otters spend a great deal of their time grooming and washing. Their skin is so loose that the otter can easily reach and groom every square inch of its body. The fur will also trap air bubbles between the outer “guard” layer and the undercoat, which not only helps keep the otter warm but will aid in buoyancy. In fact, a newborn sea otter’s fur will retain so much air that, after careful grooming by its mother, the baby literally cannot sink; it bobs in the water like a cork.
Sea otters are extraordinarily devoted mothers. Female sea otters will carry their pups on their chests, constantly grooming their fur to make sure the pup stays warm and buoyant. She will leave her baby only to find food, and will wrap the pup in kelp to make sure it stays safe and in one place. Her milk, rich in fat like that of whales or seals, sustains her baby for up to six months in southern populations, or up to a year in northern areas. If the pup dies, the mother will continue to carry the little corpse for days following its death. Female sea otters have also been recorded adopting orphaned pups.
On the other extreme, however, if conditions become particularly harsh a mother sea otter may abandon her pup. In particular, on the rare occasion that a sea otter gives birth to twins, the weaker pup may be abandoned to ensure the survival of its sibling.