River Otter Vs. Sea Otter: 10 Fundamentals Keys

feature image - sea otter vs river otter

The otter is a carnivorous mammal whose life expectancy can be 5 to 10 years, depending on its living conditions.

Different species of otter are found but based on their natural habitat; the otter is categorized into river otter and sea otter.

River and sea otters generally have common characteristics, and as the name suggests, the sea otter lives in the sea, and river otters are found in freshwater. Apart from the natural habitat, the river and sea otters vary in different aspects. 

Below the distinctive characteristics of the sea and river otter have been explained so you can easily distinguish between these two cutest animals. 

1. Distinctive Features

River otter 

Thick and lustrous, the coat of the river otter is dark brown and thins out on the belly. Its paws are webbed, and it has a long, pointed tail that thickens at the base. 

Generally, the female is usually smaller in size than the male. Adult males are on average 120 centimeters long, including the tail, and weigh between 9 and 13 kilograms.

Adult females are slightly smaller and sometimes mistaken for their marine cousins. River specimens can travel long distances over land.

River otters love to play on slippery rocks or snowy shores; sometimes, you can even see grooves from their bodies in the snow. 

Sea otter

He has an elongated cylindrical body with a tail occupying 1/3 of the body, a short thick neck, and a rounded head with dark shiny eyes.

Small ears with auditory canals-slits are almost invisible on a neat head, which closes when the animal is immersed in water.

The shortened forelimbs are adapted to grip sea urchins, the favorite dish of the sea otter. The thick paw is united by a dense skin sac, beyond which the fingers with strong claws protrude slightly. 

The hind limbs are laid back, and the enlarged feet resemble flippers, where the toes are clothed in a woolly swimming membrane to the last phalanges.

Hair is not exceptionally long, about 2–3 cm throughout the body, but grows so densely that it does not allow water to reach the skin at all. 

The general color tone is usually dark brown, with a light coat on the head and chest. The older the sea otter, the grayer it has in its color – a characteristic silvery coating.

Sea otter reaches a length of 180 centimeters in size and weighs up to 36 kilograms. Sea otters are adapted to saltwater, and they swim to the shore only for rare rest and procreation. 

The male sea otter is gigantic and heavier than the female sea otter. The male sea otter weighs 22 to 45 kg and measures 1.2 to 1.5 m in length. The female sea otter weighs 14 to 33 kg and stretches up to 1.0 to 1.4 m. 

2. Lifestyle and Behavior

Giant River Otter. Copyright: James Wolfe

River otter

The river otter is highly secretive. It is seduced by various aquatic habitats, from small streams to large rivers, alpine lakes, coastal lagoons, and sandy beaches. 

Individual otters tend to mark their territory. The otter can have several resting places, called holts, which can be located at a considerable distance (up to 1 km) from the river. 

Otters don’t build nests. They occupy abandoned beaver burrows or secluded nooks under rocks and tree roots. River otters are alert and have well-developed hearing and sense of smell, but they are rather short-sighted. They will not be able to notice the observer if he is motionless.

Sea Otter

Sea otters quickly get along with other animals (fur seals and sea lions ), neighboring them on the rocky coasts. Sea otters unite in small (10–15 individuals) groups; less often, they rally into large (up to 300 individuals) communities with no clear hierarchy. 

The sea otter has no decisive territory, so they don’t need to defend it. Sea otters do not migrate; in the summer, they feed and spend the night in the thickets of seaweed. They hold the seaweed to their paws or wrap themselves in seaweed so as not to be carried away into the ocean.

The sea otter swims like a seal, pulling back the hind limbs and making them oscillate up and down along with the waist. Sea otters rarely come ashore: for short-term rest or childbirth.

The sea otter has a disgusting sense of smell, mediocre vision, and poorly developed hearing, reacting only to vital sounds. The definition of touch is best developed – sensitive vibrissae help quickly find mollusks and sea urchins in the pitch underwater.

3. Sexual dimorphism

River Otter

Female and male otters look almost the same, but they are different in size. The male otters are usually more giant than the female.

Sea Otter

Female sea otters are shorter (by 10%) and lighter (by 35%) than males. With an average length of an animal of 1–1.3 m, females rarely weigh more than 35 kg, while males gain up to 45 kg.

4. Species

River Otter

There are 12 types of river otters. There were 13 of them until the Japanese River Otter was declared extinct in 2012. 

These animals are found everywhere except in Australia and Antarctica. Some are aquatic, and some spend half of their time on land.

The smallest otter is the Eastern or Asian small-haired otter. This otter is a beautiful, expressive little animal weighing no more than 4.5 kilograms. 

They are found in wetlands along the shores of lakes and rivers in southern Asia, but their numbers decline as their natural habitat is lost.

The European otter, also known as the Eurasian or common otter, is the most common species. They can be found throughout Europe, in many regions of Asia, and parts of North Africa. These otters are primarily solitary. 

The giant otter is the longest species, reaching 214 centimeters, excluding the tail and 39 kilograms in weight. These otters are the most social species and have a somewhat wolf-like lifestyle. 

Sea Otter

The modern classification divides sea otters into three subspecies:

  • Enhydra lutris lutris (Asian sea otter) – settled on the east coast of Kamchatka, and the Commander and Kuril Islands.
  • Enhydra lutris nereis (California sea otter, or southern sea otter) – found off the coast of central California.
  • Enhydra lutris kenyoni (Northern sea otter) – inhabits south Alaska and the Aleutian Islands.

5. Habitat

River Otter

River otter territories can stretch for several kilometers. The total length of the range depends on the availability of food. The domain of males, as a rule, is more significant than that of females. 

They occupy natural rock crevices, nooks, and crannies at the roots of trees growing along the banks of rivers and lakes. 

These natural nests have multiple exits invisible from the outside to ensure the safety of the animal. Otters do not build nests, but they can occupy abandoned dwellings of rabbits or beavers. The otter also has spare housing – located remotely in dense vegetation away from water. 

Sea Otter

Sea otters once lived in the North Pacific Ocean, forming a continuous arc along the coast. Now the range of the species has noticeably narrowed and occupies island ridges and the shores of the mainland. 

A narrow arc of the modern range begins from Hokkaido, further capturing the Kuril Ridge, the Aleutian / Commander Islands, and extends along the entire Pacific coast of North America, ending in California. 

The sea otter usually settles in barrier reefs, steep rocky shores, stones with thickets of kelp, and alaria. Sea otters avoid flat beaches (sandy and pebbles) and love to live in a quieter place away from human habitat. 

6. Diet

sea otter in the snow- river otter vs sea otter
Sea otter biting fish in the snow (source)

River Otter

River otters are opportunists, feeding on a wide variety of foods, but mostly fish. They usually eat small, slow-moving fish such as carp, mud minnows. Nevertheless, otters actively seek out spawning salmon, following long distances.

River otters also eat freshwater mussels, crayfish, amphibians, meaty water beetles, birds (mostly injured or swimming ducks and geese), bird eggs, fish eggs, and small mammals ( muskrats, mice, young beavers). 

Sea Otter

Sea otters feed mainly during daylight hours, but sometimes they go hunting at night if a storm rages on the sea during the day. The sea otter primarily feeds on sea urchins, bivalves/gastropods, medium-sized fish, crabs, and octopuses.

Due to the thickening on the front legs and movable toes, the sea otter picks up sea urchins, mollusks, and crabs from the bottom, easily splitting their shells using improvised tools (usually stones). 

Ascending, the sea otter holds a stone on its chest and knocks on it with its trophy. Under natural conditions, the sea otter does not feel thirsty and does not drink, getting enough moisture from seafood.

7. Reproduction

River Otter

Generally, otters can breed at any time of the year, but spring or early summer is a perfect time. The female, using aromatic tags, signals to the males that she is ready to mate.

Pregnancy lasts about two months, after which a litter of pups is born. They usually give birth to two or three babies, but there have been cases of five too.

For two months, the mother drags the babies between dwellings. Young otters remain in the family group for about six months or longer before dispersing to form their families.

Sea Otter

Sea otters are polygamous and do not live in families, the male mates sexually mature females that wander into its restrictive territory. 

In addition, the breeding of sea otters is not confined to a specific season; however, childbirth more often occurs in the spring than during the harsh stormy months.

The female gives birth to two babies on land, but she brings only one baby as the mother can raise the only offspring. The baby spends the first hours and days with his mother, lying on the shore or her stomach when she enters the sea. 

He starts independent swimming (first on the back) after two weeks, and already at the 4th week, he tries to roll over and swim next to his mother. 

Although the grown sea otter stops drinking breast milk, it still keeps near the mother, catching bottom-living creatures or taking food from her. A full-fledged independent life begins in late autumn when young animals join the herd of adult sea otters.

8. Natural Enemy

Sea otter fighting for existence. Copyright: BBC Earth

River otter

River Otter is vulnerable while on land. Predators ( coyotes, wild dogs, cougars, and bears ) attack mainly young animals.

Also, people catch river otters to control fish populations in private ponds and commercial fish farms to prevent damage to exclusive property. 

The most significant impacts on otter populations include a deterioration in water quality due to chemical pollution and soil erosion, and changes in riverbank habitats.

Sea Otter

The list of natural enemies of the sea otter is headed by the killer whale, a giant toothed whale from the dolphin family. 

The list of enemies also includes the polar shark. The skin of the sea otter, being sensitive, dies from minor scratches, where infections can quickly manifest.

The Far Eastern seal is considered a food competitor of the sea otter, which infringes on its favorite prey and displaces the sea otter from its habitual rookeries.

Among the enemies of the sea otter is also the human population who ruthlessly exterminated him for the sake of fabulous fur, which has incomparable beauty and durability.

9. Life span

River Otter

In the wild, otters live up to ten years. When kept correctly in captivity, their lifespan is extended.

Sea Otter

The sea otter can live up to 8 to 11 years in the sea. In captivity, they can live up to 20 years if proper care is provided. 

10. Population

otters at zoo - river otter vs sea otter
Asian short-clawed river otters at Newquay zoo (source)

River Otter

There are about 3,000 California sea otters and 168,000 Alaskan and Russian sea otters in the wild. The Irish otter population has been stable in Europe.

Sea Otter

Before the large-scale destruction of the sea otter, there were hundreds of thousands reduced to 1 million animals. The early period of the 20th century saw a drop in the otter population to 2 thousand. 

After a declining number of otters, the United States law prohibited their hunting in 1911 and the USSR in 1924. The official counts in 2000-2005 allowed the species to be listed in the IUCN as endangered. Today the population of the sea otter is estimated to be 2962. 

Conclusion

Both the river and sea otters are magnificent creatures important for the ecosystem. Some characters they show have helped the human race discover new inventions such as building dams with simple materials available in nature.

Every creature deserves respect, and we should protect them as well as their habitat. Because of the hunting for personal gain, otters’ numbers are declining.

We need to save them; if we don’t take the appropriate measures on time, they will soon be categorized as endangered species and other fascinating animals.