Sea Otter

Common Name: a 

Class: Mammalia

Order: Carnivora

Family: Mustelidae

Genus: Enhydra

Species: Enhydra lutris



Sea otters belong to the weasel family, Mustelidae, which they share with minks, weasels, badgers, wolverines, and other otter species, in the Mammalian Order Carnivora.  Its scientific name is Enhydra lutris, which means "otter that lives in the water".  Although all otters species spend time in the water, the sea otter rarely comes on land.  It is the smallest species of Marine Mammal.


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.



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.


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.  The sea otter is the only non-primate mammal to display tool use.


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.


Content provided by Canisius College students under the direction of Michael Noonan, PhD.