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Monday Mustelid - Enhydra lutris Edition

I’ve been waiting until it was time to post this one!

The Sea Otter (Enhydra lutris) is one of the world’s smallest marine mammals, and is unique among them in that they do not rely on a layer of blubber to provide insulation in the water. Instead, they have the most dense fur coat of any mammal in the world, with 100,000 to 150,000 hairs per square centimeter of coat. Sea Otters naturally produce oils that help seal the coat, making it relatively waterproof. They were heavily hunted for this fur between the 1700 and 1900s, to the point that their population dropped down to only 1,000 individuals. Conservation efforts and legal protection have allowed the Sea Otter to regain parts of its historic range in the northern Pacific coasts, and it can now be found along the west coast of North America and the east coasts of Russia and Japan.


There are currently three recognized subspecies of Sea Otter:

  • Enhydra lutris lutris (western Pacific coasts)
  • Enhydra lutris nereis (California coast)
  • Enhydra lutris kenyoni (Alaskan and surrounding coasts)

Adult Sea Otters can grow to almost 5 feet (1.5 meters) in body length, and can weigh up to 99 pounds (45 kg). Males are usually larger than females by about 20 pounds (9 kg). This makes them the heaviest of all otters. While the Giant Otter is longer, its build is much slimmer. Sea Otters have a number of adaptations that allow them to live comfortably in the ocean, the most fully aquatic of all otter species. Their eyes and ears can close when they go underwater, and their long, flat hind feet act as rudders and paddles in the water. They do not often go ashore, and they do not dig or give birth in burrows or dens. Their coats vary in color, from gray to deep brown to a tawny color. Adults usually have paler color on their heads and chests.


Sea Otters tend to live in or near kelp forests, which contain a lot of the types of animals they eat. They forage by making short dives, often all the way to the sea floor. They can hold their breath for up to five minutes, but the average dive time is around one minute. They retrieve animals like snails, clams, sea urchins, sea stars and other kinds of shellfish. They are only marine mammal that grabs prey items with its paws rather than its teeth, and they have loose folds of skin that form pouches under their forepaws. They will stock these pouches during a dive and return to the surface to eat. Sometimes they will also retrieve rocks, which they use to crack open shells. They also use rocks to hammer at abalones, which are extremely difficult to remove from the underwater rocks to which they are attached.


When Sea Otters are old enough to be independent, they forage on their own. But same-sex groups of Sea Otters often rest together, holding paws and anchoring themselves with kelp to keep everyone from drifting apart and floating away. Sea Otter pups are born year-round, so there’s no rigid breeding season, but the births seem to peak between January and March in the southern parts of the range, and between May and June in the northern parts of the range. Usually only single pups are born, but there are twins on rare occasions. The females will spend a lot of time grooming and fluffing up their pups, which fills their coats with air and allows them to float on top of the water. Females with pups are incredibly devoted, and they have even been observed to take on orphaned pups. Pups get their adult fur at about 13 weeks, and they become independent at around eight months.


Sea Otters are what are known as a keystone species, which means that their presence is crucial to the health and survival of their ecosystems. Kelp forests depend on Sea Otters to keep the population of sea urchins in check, because the urchins graze on the connecting parts of the stems of kelp forests. Kelp forests without Sea Otters often turn into urchin barrens, a bare expanse of sea floor with plenty of sea urchins but no kelp. While the Sea Otter does have natural predators, it is not often purposefully hunted, as many predators find the taste of the scent glands not to their liking. They are susceptible to pollution and other contaminants that run off into the ocean, including diseases from the feces of domestic animals. Sea Otters are considered to be an endangered species by the IUCN.

Source for all images used in this post.

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