(Enhydra lutris)
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Geographic range: Nearctic: Originally from Hokkaido Island of Japan north through the Kuril Islands and eastern coast of Kamchatka, east through the Commander Islands and Aleutian archipelago, the southern coast of Alaska, and the west coast of North America to Baja California in Mexico.
Sea ice represents the limits of the northern range at about 57 degrees N latitude, and the distribution of kelp forests limits the southern range to about 22 degrees N latitude. Hunting during the 18th and 19th centuries greatly reduced the distribution for the sea otter.

Physical characteristics: The largest member of the family Mustelidae. Males weigh 22 to 45 kg and are 1.2 to 1.5 m in length. Females are slightly smaller, weighing 14 to 33 kg and measuring 1 to 1.4 m in length. The tail comprises less than a third of the body length. The body is brown or reddish brown. Sea otter fur is the densest of all mammals, with about 100,000 hairs per square centimeter. Since sea otters do not have any insulating fat, the fur is responsible for maintaining warmth. The hind legs are long and the paws are broad, flat, and webbed. The forelimbs are short and have retractable claws. The maximum estimated life span of sea otters is 23 years in the wild.

Food habits: Carnivorous. Almost any seafood is consumed (mussels, sea urchins (Strongylocentrotus sp.), snails, abalone, crabs, octopus, squid, sea stars, and fish. Otters need to consume 20-25% of their body weight each day. They obtain most of their water from prey but will drink seawater to satisfy thirst also.

Sea otters are a keystone species. They play a major role in the community by controlling of herbivorous invertebrates, mainly the sea urchin (Strongylocentrotus sp.), inhabiting kelp forests. Sea urchins graze on kelp. In coastal areas where otters are absent, sea urchins are abundant and the area is devoid of kelp forests. Where sea otters are present, the urchins are limited by otter predation and kelp forests are abundant. Kelp forests are dependent on sea otters for protection from grazers. The diversity of the sea otter diet reduces competition between benthic grazers and supports greater diversity in those species. The presence of sea otters is believed to be important in the evolution of kelp forest ecosystems.

Reproduction: Sea otters can reproduce year round. Delayed implantation causes varied gestation times. Pregnancy has been reported to be 4-12 months. Females usually give birth about once a year. Pups typically remain with their mother for 5 to 6 months after birth. Females reach sexual maturity at 4 years. Males reach sexual maturity at 5 to 6 years, but may not mate until much later. Sea otters have a polygynous mating system. Many males actively defend territories.

Behavior: Sea otters are solitary for the most part. Males congregate in groups when resting. Females tend to stay away from males except when mating. Sea otters can spend their whole life in the ocean but will rest on land when the population density is high. Swimming is performed using the hind limbs, tail, and vertical undulations of the body while the forelimbs are tucked into the chest. Otters can swim as fast as 9 km per hour under water. Sea otters are diurnal with crepuscular peaks in foraging activity. Foraging dives usually last 50-90 seconds, but otters can remain submerged for nearly 6 minutes.

Temperate coastal waters with rocky or soft sediment ocean bottoms less than 1 km from shore. Kelp forest ecosystems are characteristic of otter habitats.

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