The difference between sea and river otters

Sea otters, as the name suggests, are marine animals, and they live just off the coasts of the Northern and Eastern Pacific Ocean.  These animals spend most of the time in the water, but they can move around on the land also.  These animals are the smallest of marine animals, and they were once hunted almost to the point of extinction.

The otters belong to the weasel family Mustelidae.  They weigh between 30 and 100 pounds.  They are covered with thick fur which is predominantly dark brown, but it can sometimes be black or a silvery gray. The coloring of adult sea otters tends to be lighter on their heads, throats, and chests

Sea Otters have fully webbed, long, flat hind feet which they use to swim.  Their front paws are used to find prey in the dark murky water, with their whiskers helping them with this task.  Their muscular tails, which are short and thick, steer them like a rudder when swimming and help with balance on land.

The health of many other species is determined by the health of the sea otter population, making them a keystone species.  Their diet consists mostly of shellfish and other marine invertebrates like mussels, clams, snails, abalone, and sea urchins.

Sea otters did not have the thick layer of blubber common to most other marine mammals and needed for insulation against the cold waters.  Instead, they have very thick fur coats.  In fact, this fur is the most abundant among all animals on earth. The fur has long waterproof hairs which lie over a layer of short underfur which insulates the sea otters body. The condition and cleanliness of this fur are essential to ensure warmth, and therefore sea otters are meticulous about grooming. To facilitate this they have loose skin, and they are flexible and supple so they can reach the fur on all parts of their bodies.

Sea otters are strong and seasoned swimmers, and they maneuver themselves with ease in the water, using their feet and tails expertly. Sea otters are streamlined and sleek and can reach speeds of up to six miles per hour.

When they are on the surface of the water, sea otters like to float on their backs,  swishing their tails and feet from side to side in order to move about. The air trapped within the thick fur of their coats coupled with an incredible lung capacity (about 2.5 times more than any other mammals of the same size) makes the sea otter very buoyant.

As already mentioned, sea otters and river otters are members of the weasel family which, perhaps surprisingly, also includes badgers, minks, wolverines, skunks, and, of course, weasels.  Sea otters spend most of their time in the water, only occasionally climbing onto land, but river otters stay on land for the majority of the time and go swimming in order to find prey. The gait of sea otters on land is somewhat clumsy, but river otters can sprint short distances at high speed.

Sea otters live in large colonies, but river otters tend to stay in small family groups. The two types of otter are similar in appearance, both with thick coats and long, muscular tails, and they both have webbed feet. The sure way to differentiate between the two is the fact that on the surface of the water river otters swim with their belly facing downwards,  their bodies almost submerged, but sea otters do backstroke while floating fairly high above the surface of the water.

In the years from about the 1740s and the early 1900s, the population of sea otters plummeted from about 200,000 animals to just about 2000 due to their being extensively hunted and killed for their thick fur.  In recent years there has been much effort put into returning sea otter populations to previous numbers with conservation programs and re-introduction projects. The sea otter is, however, still an endangered species and their health is constantly monitored.

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