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.
Habitat: 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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