What is the Difference Between
a River Otter and a Sea Otter?
26 September 1997
The river otter and sea otter are both members
of the family of animals called mustelidae
that includes badgers, weasels, minks, wolverines,
and skunks. The primary difference between the two
species has more to do with where they live than
actual physical differences.
Sea otters are true marine mammals, found only
in the ocean and rarely seen on land. They are really
quite clumsy on land and are perfectly capable of
spending their entire lives at sea. River otters
are land mammals that inhabit fresh water lakes,
rivers, and streams.
otters, like this
one, are better suited for life on land than their
cousins, sea otters. North Carolina river
otters can be found primarily in the coastal and
central sections of the state.
They are amphibious creatures that are well adapted to
a life in water and on land. Their strong legs enable them
to move quickly on land; in fact, over a short distance
a river otter can outrun a man.
In North America, sea otters can only be found in the shallow
waters of the Pacific Ocean along
the coast of California and Alaska. River otters can be
found in waterways throughout North America (except extreme
northern Canada and the desert areas of the southwest).
In North Carolina, river otters are found chiefly in the
coastal and central portions of the state. A relocation
program instituted by the North
Carolina Wildlife Resources Commission in the early
'90s reintroduced otters to the river systems of western
Physically, the two species are quite similar -- both have
streamlined bodies that are well suited to swimming and
diving; dark, dense fur coats consisting of two layers that
serve to insulate and waterproof; webbed feet; and long,
muscular tails. The river otter is smaller than the sea
otter, weighing from 10 to 30 pounds and measuring three
to four feet in length from the tip of its nose to the end
of its tail. Its tail is longer than its cousin's, approximately
two-thirds the length of its head and body. Sea otters average
50 to 90 pounds and reach lengths of up to five feet. Their
tails are roughly 1/3 the length of their head and body.
Seeing an otter in the water is one of the best ways to
tell the difference between the two species. At the surface,
river otters swim belly-down and expose very little of their
back, while sea otters swim belly-up and float high in the
water due to their air-filled fur. Both are strong swimmers
and divers; river otters swim at a rate of up to seven miles
per hour while sea otters can dive to depths of up to 180
Because sea otters are true ocean-dwelling creatures, their
hind limbs are paddle-shaped and are webbed to the tips
of their toes to aid in swimming. River otters have smaller,
more circular shaped webbed paws because they are adapted
to land travel.
Both species are known for their playful behavior and acrobatic
stunts in water. Sea otters, however, are more social, living
in large groups (called rafts) while river otters rarely
are seen in groups larger than a single family (mother plus
three to four young).
Whether ocean or river dwellers, otters in North America
are threatened by pollution, habitat degradation, hunting
and trapping. Wildlife protection legislation and programs
are in existence in many states to protect and preserve
these acrobats of the water.