A sea otter has a loose pouch of skin under each foreleg where it can store food as it’s collected. When the otter returns to the surface, it can rest on its back and leisurely retrieve one piece of food after another from its pouch. In addition to food, the sea otter also stores a rock in one of its pouches. The otter may use the rock under water to pry loose mussels or other attached bivalves or to dislodge sea urchins wedged in crevices. When floating on the surface, the otter places the rock on its chest and pounds crabs, snails, clams, and other prey against the rock to break through the tough shells. Sea otters are one of the few animals other than humans known to use tools.
Mating can occur at any time of the year for sea otters, and while the young may be born in any season, most pups in Alaska are born in the spring. As with bears, when a sea otter becomes pregnant, the implantation and development of the embryo often stops, and the embryo may not implant for several months. Scientists believe the purpose of delayed implantation in sea otters is to allow for the birth of pups when environmental conditions and food supplies are most favorable. Sea otters are pregnant for four months, but because the length of the delayed implantation varies so greatly, the gestation period may last from four to twelve months.
Sea otter mothers are normally very attentive, affectionate, and protective of their pups. A pup spends most of its time riding on its mother’s belly, and even pups six-months of age or older and nearly as large as their mother will climb on her stomach as she appears to struggle to keep her head above water.
In addition to cradling her pup on her chest to keep him warm, a mother meticulously grooms her pup’s fur until the pup is three to four months old and able to groom himself. At this age, the pup is also able to swim on his back and dive with ease. The mother teaches the pup how to catch and eat prey, and by the time the pup is six months old, he can capture and break open his own prey. Sea otter pups remain with their mothers anywhere from three to twelve months.
Sea otters often float together in large groups called rafts. Except for territorial males who rest with female groups, most rafts are comprised of individuals of the same sex, and mothers with pups often rest together in nursery groups. Rafts usually consist of between ten and more than one-hundred otters, but in Alaska, rafts with 2000 individuals have been reported.
Sea otters are considered a “Keystone” species, meaning that they effect the ecosystem to a much greater degree than their numbers would suggest. Sea otters protect kelp forests by eating herbivores such as sea urchins that graze on the kelp. In turn, the kelp forests provide food and cover for many other species of animals, and kelp forests play an important role in capturing carbon and reducing atmospheric carbon dioxide levels.