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Sea Otter: Facts and Info

The author is a research enthusiast. She studied botany and zoology as major subjects in her bachelor's program.

Read on to learn facts and info about sea otters, a truly intriguing marine mammal. The photo above shows a Russian Sea Otter rubbing its face.

Read on to learn facts and info about sea otters, a truly intriguing marine mammal. The photo above shows a Russian Sea Otter rubbing its face.

Sea Otter, the Smallest Marine Mammal

Sea otters, a marine mammal species, are the only living members of the genus Enhydra. They are the smallest marine mammals that lack blubber. There are 13 living species of sea otters. The life span for males is 10 to 15 years, and females can live for approximately 15 to 20 years. In this article, you'll find the following facts about sea otters:

  • Subspecies of sea otter
  • Physical description
  • Adaptation to the marine environment
  • Importance of sea otter
  • Fast facts

Subspecies of Sea Otter

Based on geographic distribution, there are three subspecies of sea otters:

  • Russian Sea Otters
  • Northern Sea Otters
  • Southern Sea Otters

Russian sea otters are distributed from Japan through the Kuril Islands and the Kamchatka Peninsula to the Commander Islands of Russia. Northern sea otters (also known as Alaskans) range from the Aleutian Islands to Prince William Sound and along the Pacific coast of Canada and Washington state.

In the 1980s, a rapid population decline of the Northern Sea otters occurred because of the Killer whale (Orcinus orca). Southern sea otters have a small range along the central California coast.

Physical Description

Although an otter is the smallest mammal, it is also the heaviest mustelid. Males weigh between 22 and 45 kg, and females are smaller, weighing around 14 to 33 kg. The color of the fur is brown with silver stripes. The ears are small, and the tail is short and flattened.

Diet and Behavior

Sea otters feed on marine invertebrates such as mollusks, sea urchins, and some fish species. Their favorite food is sea urchins, and the way they consume sea urchins is very interesting. They take a rock as a "plate," balance it on their stomach, and use another rock to smash the urchin.

Using rocks as a tool makes them one of the few mammal species to use tools. They spend most of their time grooming themselves, including blowing air into their fur, cleaning their fur, removing loose fur, and straightening their fur.

Sea Otters Using Rocks as a Tool


They are polygynous, which means males copulate with multiple female partners. Females give birth to a single pup. Males become sexually mature at the age of 5 to 6 years, and females reach puberty at 4 to 5 years.

Sexual behavior is quite violent in otters. Sometimes, females become extremely injured and stressed after breeding activities. Mothers' behavior is very loyal towards their children. They lick and cradle their babies for hours after birth

Mama Sea otter playing with her pup

Mama Sea otter playing with her pup

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Adaptations for Survival in the Marine Environment

Over the years, the sea otter's body has developed to get used to living in the water. It has evolved a suite of modifications for life in cold coastal waters that include limb modifications, high tactile sensitivity, dense bones, increased blood volume, and thick protecting fur. We will discuss the following three adaptations that helped sea otters survive in the cold marine environment:

  1. Swimming feet with webbed soles
  2. Extra-thick fur to reduce heat loss
  3. Kidneys with high osmoregulation efficiency
Two Sea Otters floating on the surface of the water

Two Sea Otters floating on the surface of the water

1. Swimming Feet With Webbed Soles

Its web-like feet make swimming more manageable and smoother. They help them pick up speed in the water. Their feet contain areas of heat loss. When the water temperature is too hot, they extend their feet into the water to reduce the heat. In cold temperatures, they float on their backs, keeping their feet out of the water to minimize heat loss.

2. Extra-Thick Fur to Reduce Heat Loss

Sea otters lack blubber and rely on a thick fur coat to keep them warm in a cold marine environment. They have the densest fur, containing 150,000 strands of hair per square centimeter. The fur consists of "guard hairs," which are the outer layer of the fur coat.

An air compartment is present between the fur and the skin. The air is trapped here and heated by the body. This helps in reducing heat loss. Sea otters' backs, sides, and stomachs contain the longest hairs.

3. Kidneys With High Osmoregulation Efficiency

Sea otters have specialized kidneys that allow them to inhabit environments with a broad salinity range. The kidneys are the principal organs for water and electrolyte regulation. The kidneys comprise hundreds of individual lobes, and each lobe contains discrete cortical tissue.

Sea otters can concentrate their urine above the concentration of seawater. Otters can produce urine concentrations that are similar to those in seawater. This adaptation makes it possible to drink seawater and not lose freshwater.

Importance of Sea Otters

Sea otters have a significant role in maintaining the ecosystem of their environment. They indirectly help to reduce the level of atmospheric carbon dioxide by protecting healthy kelp forests. Here, we will discuss the following two elements that make sea otters a notable species:

  1. Sea otters as a keystone species
  2. Sea otters as a sentinel species

1. Sea Otters as a Keystone Species

Devic (2003) defined keystone species as "strongly interacting species whose top-down impact on the ecological community is large relative to their biomass dominance within a functional group." As a keystone species, it controls the population of sea urchins. Sea otters affect rocky ecosystems dominated by mussel beds by removing mussels from rocks. This allows space for competing species and increases species diversity.

In the 1900s, the sea otter population almost went extinct due to killer whales. Sea otters disappeared utterly, and sea urchins took over that area. Due to this, kelp began to disappear, and many animals lost their habitat. Sea otters were re-introduced there, and the sea urchin population was put back under control.

2. Sea Otters as a Sentinel Species

Sentinel species are used to detect dangers to humans. Plants and animals can both be used for this purpose. For example, a "Domestic Canary" detects gas in coal mines. Sea otters have a unique biology that makes them excellent sentinel species. They eat 25% of their body weight per day in shellfish and other invertebrates.

Shellfish are also harvested as human food. Shellfish serve as an intermediary for some infections and cause disease and the death of sea otters. These infections are potentially dangerous for humans.

Fast Facts

  • Sea otters float in groups that are called rafts. The rafts are gender-based, meaning male sea otters gather together and females like to hang out together.
  • The pups are born with buoyant fur that is called lanugo. Lanugo helps them float on the top of the water.
  • Unlike other mammals, sea otters lack blubber and have a high metabolic rate.
  • It is a keystone species and plays a crucial role in maintaining the hierarchy of the ecological community.
  • They can eat up to 25% of their body weight per day.
  • They wrap themselves in kelp when resting and eating to avoid drifting out to sea.
  • Sea otters have long whiskers growing from their muzzles. These whiskers help them detect vibrations caused by fish’s tails.
  • Sea otters and seals are the only carnivorous species with two pairs of lower incisors.
  • They are known for using rocks as anvils to facilitate access to hard-to-reach prey.


This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2022 EK Jadoon

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