Both members of the Mustelidae family, sea and river otters are among some of the most adored creatures on the planet, living both in fresh water and in the ocean. There are thirteen different species of otter, of which only one belongs to the ocean.

Although ocean and river otters may appear the same at first glance, they have multiple differences, such as their physical appearance, diet, lifespan, and of course, habitat.

Let’s take a look at how the sea and river otters compare.

A river otter
Sea otter (left) vs river otter (right)

Main Differences Between Sea Otter vs River Otter

  • Appearance: Sea otters are 2 to 3 times larger than river otters. They have thicker, fluffier fur and a thicker, shorter tail.
  • Habitat: Sea otters spend the majority of their life in the ocean, close to the shore, in shallow waters. River otters, on the other hand, spend most of their life on land, yet around freshwater bodies such as lakes, rivers, and some marine environments such as estuaries.
  • Reproduction: Sea otters have long gestation periods and only reproduce every 2 years. River otters, on the other hand, go through a full gestation cycle in less than three months.
  • Diet: Sea otters diet mostly on hard-shelled mollusks, and fish, while river otters favor softer prey such as fish, amphibians, and snakes.
  • Predators: River otters are preyed on a few animals but are hunted by wolves, birds, and reptiles. Sea otters, for the most part, fall prey to sea lions, sharks, and killer whales.
  • Species diversity: There are 12 species of river otter and only one species of sea otter.

We’ll explore the differences and facts about these two animals below.

Sea Otter

The sea otter is a marine mammal that is found in coastal areas (predominantly at sea) of the north and east sides of the North Pacific Ocean. Although otters found on either side of the coast are often considered to be two different species, they are, in fact, the same and only species of sea otter.


Sea otters are small mammals that are covered in dense dark brown fur. These cute sea animals typically weigh between 16 – 40 kg and reach lengths of 100 – 170 cm.

Sea otters have long, streamlined bodies with small ears, rounded heads, and large eyes.

Sea otters have furry and sleek bodies, with a flattened head, small ears, and round snout
Sea otters have furry and sleek bodies, with a flattened head, small ears, and round snout

The tail of the otter is thick at the base and tapers off near the tip, which, along with their webbed feet, assists with swimming.

Sea otters’ teeth are specially adapted for the food they eat. They have 32 teeth with fewer incisors which makes breaking open their hard meals an easy task.

Habitat and Distribution

Sea otters feel most at home in shallow waters near the shore (usually less than a half mile). These areas offer an abundance of food and shelter for these aquatic mammals. Sea otters can often be seen playing or hunting among kept forests, barrier reefs, and protected rocky areas.

With a range spanning the North Pacific Ocean, sea otters can be found in California, Washington, Canada, Alaska, and all the way to Russia and Japan.


Sea otters are carnivores and feed entirely on ocean creatures, specifically those with a shell.

Sea urchins, clams, mussels, crabs, snails, and urchins are all common snacks for sea otters, but they also often enjoy prey such as fish, octopus, and a variety of other marine invertebrates.

Sea otters can eat up to 25% of their body weight per day, which mostly consists of hard-shelled invertebrates. These furry animals can often be seen floating on their back, hitting to open the shells of their prey with a rock.


Female sea otters reach sexual maturity at around four years, while their male counterparts only become capable of breeding after the age of five. That said, male sea otters often remain inactive breeders until later on in life.

Sea otter pups are born helpless and rely on their mother for warmth and nourishment from her milk
Sea otter pups are born helpless and rely on their mother for warmth and nourishment from her milk

Sea otters breed throughout the year, with the males often taking more than a single breeding partner.

The pregnancy period of the sea otter is six months, with the cycle continuing only every year or two. Sea otters only give birth to a single pup at a time; however, twins are possible, although rare.

Predators and Threats

Although sea otters are a cornerstone in the shallow coastline predatory ecology, they are still preyed on by multiple aquatic and non-aquatic species, some of which include:

  • Eagles
  • Sea lions
  • Killer whales
  • Sharks
  • Seals
  • Sharks
  • Grizzly bears
  • Coyotes
  • Bobcats

Although sea otters have a large list of predators, nothing threatens their population as humans do.

Through hunting, overfishing, fishing gear entanglement, boat collisions, oil spills, disease, and loss of habitat, humans are drastically impacting the population of sea otters.

River Otter

Twelve species of freshwater otters can be found distributed around the globe. River otters spend most of their time on land, only using water for transport, hunting, and protection. These species are smaller and faster than their ocean counterparts. Unlike sea otters, river otters swim belly down.


As mentioned, river otters are noticeably smaller than ocean otters. Adult river otters weigh between 4.5 – 15 kg and reach lengths between 76 and 152 cm long (depending on the species).

River otters have a full set of mammalian teeth. This includes incisors, canines, premolars, and molars. River otters typically have 36 teeth (four more than ocean otters).

The fur on a river otter is short and sleek, while sea otters have a thicker coat for protection from the cold. Unlike sea otters, river otters’ legs are adapted to walk on land. The tail of a river otter is long and pointed, which aids in navigating along rivers and in between reeds.

Habitat and Distribution

River otters can be found vastly distributed around the world’s riverways, inhabiting all continents except for Australia and Antarctica.

River otters inhabit a variety of waterways, both marine and freshwater. These habitats include rivers, estuaries, lakes, creeks, marine coves, and rocky sea shores.

River otters can be found throughout North America, including the United States, Canada, and Mexico
River otters can be found throughout North America, including the United States, Canada, and Mexico

Some river otters, such as the Cape clawless otter, are found inhabiting a wide range of habitats, from rainforests to semi-arid zones and coastal plains.

River otters can be found both at sea level as well as at higher altitudes.


Eating almost anything they can get their little paws on, river otters are considered to be generalist carnivores.

Although they will eat most things (besides plants), river otters tend to favor fish, crabs, frogs, turtles, snakes, small birds, and eggs.

River otters are opportunistic feeders and consume a variety of prey
River otters are opportunistic feeders and consume a variety of prey

That said, the diet of river otters depends greatly on their environment and species. In the Amazon, river otters hunt in groups which means larger prey such as piranha and caiman are an option.

The Asian small-clawed otter (the smallest otter species) regularly feeds on mollusks, small fish, and insects.


Because of the diversity of species, exact measurements may differ slightly, but on average, male and female river otters reach sexual maturity in their second or third year; however, successful reproduction is rarely seen until their fifth to seventh year.

For most species of river otter, the gestation period lasts between 62 and 86 days. Female river otters carry between 1 – 3 pups at a time, with 2 – 3 being the most common.

The mating period of the year also differs with river otters. Some Eurasian otters mate all through the year, while others mate in late winter and early spring.

North American otters tend to mate during winter and spring.

Predators and Threats

Healthy adult river otters have few predators, as they are swift, agile, and happily turn to aggression when threatened.

That said, river otters are not at the top of their respected food chain and are commonly preyed on by wolves, birds of prey, alligators, and large snakes.

Once again, humans disrupting the natural environment of river otters, as well as hunting for their fur, has posed a large risk to their population.

The main threats to river otters are habitat destruction, pollution, hunting and trapping, and roadkill incidents
The main threats to river otters are habitat destruction, pollution, hunting and trapping, and roadkill incidents


Are river otters as aggressive as sea otters?

Sea otters are known to form tighter bonds than river otters. Male river otters are extremely territorial, which promotes more aggression than sea otters. That said, both sea otters and river otters will turn to aggression when needed.

Do river otters or sea otters live longer?

In a natural environment, river otters typically live between 12 and 15 years, while sea otters live between 15 and 20 years. That said, river otters have been known to live up to 20 years and more in captivity.

How long can river otters hold their breath when compared to sea otters?

Both sea otters and river otters can hold their breath for a significant amount of time. River otters can hold their breath for the longest, at an impressive 8 minutes vs a sea otter’s 5-minute breath hold.

Do both sea otters and river otters dig burrows?

Both sea otters and river otters dig burrows for protection from predators and weather. That said, ocean otters spend the majority of their lives at sea, while river otters make more use of their burrows.

About Ocean Info

At Ocean Info, we dive deep into ocean-related topics such as sealife, exploration of the sea, rivers, areas of geographical importance, sailing, and more.

We achieve this by having the best team create content - this ranges from marine experts, trained scuba divers, marine-related enthusiasts, and more.

Sea Anemone with Clownfish

Dive into more, the ocean is more than just a surface view

Shrimp vs prawn: Main differences

Shrimp vs Prawn

While these two animals look similar, there are notable main differences between shrimp and prawns, from their appearance and taste to their habitat. Read on to learn more.

Share to...