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Taxonomy/Description
The Sea Otter's scientific name is Enhydra
lutris, which means "otter that lives in the water". This
species is aptly named because sea otters rarely come
on land. This animal is the largest otter species by weight. Adults
range in weight from 50-100lbs and grow to 4-5ft from head to tail
tip.
Sea otters belong to the weasel family, Mustelidae, which they share
with minks and weasels.
photo M Noonan
Habitat/Diet
The sea otter can be found along the Pacific Coastline of North
America. We observed it's most southern population on the coast of
California. A separate population also exists along the Aleutian
Island chain of Alaska. Sea otters are specialist feeders who
primarily feed on mollusks and crustaceans. The type of mollusk
chosen by a given sea otter is strongly influenced by what he was
taught by observing his mother.
photo M Noonan Behavior/Reproduction
The fur of the sea otter is more dense than that of any other
mammal. In some places on its body it has as many as one million
hairs per square inch! To appreciate this, imagine all the hair
follicles from ten human heads compacted into one square inch. This
dense fur allows the sea Otter to keep warm in the cold waters of
the northern Pacific. They blow air bubbles into their fur to create
air pockets around the hair follicles and these air pockets act as
insulators which separate the sea otter's skin from the cold water.
This adaptation is critically necessary for the sea otter to survive
because it is the only marine mammal without blubber. Unfortunately,
the sea otter’s reliance on its dense fur makes it particularly
susceptible to oil spills. The oil clogs the otter’s fur limiting it
from maintaining the necessary insulating air pockets.
photo M Noonan
When feeding, sea otters can often be seen floating
on their backs. They characteristically dive to the bottom of the
ocean and pick up a mollusk and a rock. Back at the surface, they
then float on their backs placing the rock on their abdomens. The
otters then repeatedly hit the mollusk against the rock in order to
break open the hard shell and gain access to the meat inside. Some
otters keep the same stone throughout their entire lives, placing it
inside their armpit for later use. The practice of cracking open
mollusks with stones is a form of tool use.
Conservation
Sea otters were once hunted extensively for their dense pelts. When
this practice was discontinued in the mid 20th century, the Southern
population of sea otters made a wonderful recovery from near
extinction. However, the population of sea otter peaked around 1995
and now has been once again on the decline. The Southern population
is estimated at 2000 animals. It is counted twice per year with
approximately 200 sea otters dying between recent counts. Scientists
have begun to search for explanations for this decline and, at
first, it was believed that the otters were starving because their
bodies were very thin when discovered. However, researchers did not
find a decline in the main food sources for the otters. Instead,
studies of the dead otters did show parasites and protozoa,
particularly Toxoplasma, in levels higher than in healthy sea
otters. This suggests a weakened immune system is the cause. It has
been hypothesized that human pollutants in the water such as PCB’s,
DDT and tributylin, a substance found in boat paint, may be the
causes of the otters' weakened immune system. The rise and fall of
southern sea otter population is a perfect example of how human
activities can impact the lives of marine mammals.
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