By popular demand, this week we’re discussing sea otters, the smallest marine mammal.
Native to the northern Pacific Ocean from Russia to southern California, this charismatic critter was seriously overhunted for its fur – almost to extinction. It has been protected by international law since 1911 and its population is starting to rebound, but it is still considered endangered. Now 90% of sea otters live off the coast of Alaska. Sea otters can sometimes be found in large groups of either males or females, known as rafts.
The sea otter can spend its entire life in the ocean, including sleeping anchored to kelp beds to keep from drifting away. Because it spends so much time in cold water and has no insulating fat, it relies on its fur, which is the densest of any mammal, to stay warm. It blows bubbles of air into this coat, with 100,000 hairs per square centimeter, to keep water from penetrating to its skin.
The pictures you’ve seen are probably of sea otters floating at the surface, but they are highly adapted to life in the water. Sea otters have a large tail to steer and large hind feet that act as flippers. Sea otters can swim as fast as 9 kilometers per hour and stay underwater for almost six minutes while diving.
Sea otters also eat in the water, hunting invertebrates like mussels, snails and crabs. Otters often become "specialists" in one type of prey, depending on their skills and what is available. The otter stores its prey in skin pouches under its forearms while it returns to the surface, where it uses its chest as a table and pounds frees its tasty morsel using a rock. This makes it one of only a couple of non-primate mammals known to use tools. Sea otters often keep using the same rock for multiple dives, and have been observed washing their prey. Males are known to steal food from females.
Sea otters have voracious appetites; in fact, their hunger can be crucial to maintaining healthy ecosystems. In some areas, otters act as ‘keystone species,’ which means that they keep populations of their prey, such as sea urchins, strictly under control. Without sea otters present, urchin populations could grow rapidly and eat entire kelp forests; with sea otters present, kelp can live long enough to form forests.
Threats to sea otters include oil spills, killer whale predation, which is increasing as other prey options are becoming scarcer; infectious diseases, particularly toxoplasma; and being caught as bycatch, particularly in fisheries that use gill nets.
Learn more about the sea otter and other fascinating animals at Oceana’s marine life encyclopedia.