Southern sea otter
FWS Focus

Overview

Southern sea otters, also known as California sea otters, can be found in nearshore areas along the central California coastline, including areas of high human activity, like harbors. As a keystone species, they play a fundamental role in the natural food web, and keep important elements of coastal ecosystems like kelp forests and seagrass beds in balance.  

Kelp forests provide numerous benefits, including habitat for hundreds of invertebrate and fish species, reductions in coastal erosion and carbon storage that can moderate  climate change climate change
Climate change includes both global warming driven by human-induced emissions of greenhouse gases and the resulting large-scale shifts in weather patterns. Though there have been previous periods of climatic change, since the mid-20th century humans have had an unprecedented impact on Earth's…

Learn more about climate change
 . Seagrasses also provide important benefits, like nursery habitat for many other species, shoreline protection and carbon sequestration. 

Unlike whales and seals, sea otters lack blubber. Instead, they rely on their dense fur coat and elevated metabolism to stay warm. The average adult sea otter must eat 20 to 30 percent of its body mass in food each day just to meet its energy requirements. Sea otters need to conserve energy, which means that uninterrupted rest is an important part their well-being. To minimize the potential for disturbance and harm to sea otters, people sharing sea otter habitat should: 

  • Maintain a safe distance - if a sea otter notices you, you are likely too close and should back away

  • Keep kayaks at least 60 feet (or five kayak lengths) away, passing by parallel rather than pointing directly at any animals and moving slowly but steadily past rather than stopping

  • Keep pets on a leash on and around docks and harbors and never allow interactions, even if the animals appear to be playing

  • Never feed sea otters, as they can become aggressive, which could result in their removal from the population

Like all sea otters along the North Pacific rim, southern sea otters were hunted to near extinction during the fur trade of the 1700s and 1800s. The subspecies survived because a few dozen animals eluded hunters off the rugged coast of Big Sur. Southern sea otters are now protected under the Endangered Species Act, Marine Mammal Protection Act and California state law. The southern sea otter population has grown slowly since receiving federal protections in the 1970s, fluctuating around 3,000 in recent years.

Learn more from the U.S. Geological Survey population survey for southern sea otters.

To support southern sea otter recovery, we translocated 140 sea otters from the central California coast to San Nicolas Island in the late 1980s to create a secondary population to buffer against the chance of extinction. Most sea otters immediately swam back to their home range or into other areas of California, and some died, but about a dozen stayed, forming a small core population that grew slowly for many years. One requirement of that translocation program was that sea otters entering a no-otter management zone, which extended throughout southern California except the translocation zone around San Nicolas Island, be removed by non-lethal means. Non-lethal removal proved impractical, expensive, harmful to the animals removed, and due to the strong homing impulse of sea otters, it also proved futile. We terminated the program and its associated zones in 2012. Now, more than three decades after the program was initiated, the population is growing more rapidly, though it remains small and represents less than five percent of the southern sea otter population overall. 

Range expansion is a key part of southern sea otter recovery and is critical to the restoration of ecosystems in which sea otters evolved as a keystone predator. Southern sea otters have reached carrying capacity in the central part of the mainland range, with mortality from shark bites at the range peripheries preventing range expansion from happening naturally. As a result of shark-bite mortality, no net range expansion has occurred in more than 20 years.  Under a directive from Congress, we worked with partners and stakeholders in 2021 to evaluate the feasibility of reintroducing sea otters to the West coast of the contiguous U.S., where sea otters historically thrived. Assessment of feasibility is the first step in any reintroduction effort, but it is not a reintroduction proposal. If reintroduction consideration continued, any reintroduction proposal would be developed with extensive input from a broad range of stakeholders.  We are currently reviewing the status of the southern sea otter under the Endangered Species Act. The species status assessment is based on the best available scientific and commercial data regarding the species, including population trends, distribution, demographics, genetics, habitat conditions, threats and conservation measures. By thoroughly reviewing the best available data, we will have a better understanding of all the factors influencing the sustainability of southern sea otters in the wild - now and into the future.  

Characteristics
Overview

Southern sea otters, also known as California sea otters, can be found in nearshore areas along the central California coastline, including areas of high human activity, like harbors. As a keystone species, they play a fundamental role in the natural food web, and keep important elements of coastal ecosystems like kelp forests and seagrass beds in balance.  

Kelp forests provide numerous benefits, including habitat for hundreds of invertebrate and fish species, reductions in coastal erosion and carbon storage that can moderate climate change climate change
Climate change includes both global warming driven by human-induced emissions of greenhouse gases and the resulting large-scale shifts in weather patterns. Though there have been previous periods of climatic change, since the mid-20th century humans have had an unprecedented impact on Earth's…

Learn more about climate change
. Seagrasses also provide important benefits, like nursery habitat for many other species, shoreline protection and carbon sequestration. 

Unlike whales and seals, sea otters lack blubber. Instead, they rely on their dense fur coat and elevated metabolism to stay warm. The average adult sea otter must eat 20 to 30 percent of its body mass in food each day just to meet its energy requirements. Sea otters need to conserve energy, which means that uninterrupted rest is an important part their well-being. To minimize the potential for disturbance and harm to sea otters, people sharing sea otter habitat should: 

  • Maintain a safe distance - if a sea otter notices you, you are likely too close and should back away

  • Keep kayaks at least 60 feet (or five kayak lengths) away, passing by parallel rather than pointing directly at any animals and moving slowly but steadily past rather than stopping

  • Keep pets on a leash on and around docks and harbors and never allow interactions, even if the animals appear to be playing

  • Never feed sea otters, as they can become aggressive, which could result in their removal from the population

Like all sea otters along the North Pacific rim, southern sea otters were hunted to near extinction during the fur trade of the 1700s and 1800s. The subspecies survived because a few dozen animals eluded hunters off the rugged coast of Big Sur. Southern sea otters are now protected under the Endangered Species Act, Marine Mammal Protection Act and California state law. The southern sea otter population has grown slowly since receiving federal protections in the 1970s, fluctuating around 3,000 in recent years.

Learn more from the U.S. Geological Survey population survey for southern sea otters.

To support southern sea otter recovery, we translocated 140 sea otters from the central California coast to San Nicolas Island in the late 1980s to create a secondary population to buffer against the chance of extinction. Most sea otters immediately swam back to their home range or into other areas of California, and some died, but about a dozen stayed, forming a small core population that grew slowly for many years. One requirement of that translocation program was that sea otters entering a no-otter management zone, which extended throughout southern California except the translocation zone around San Nicolas Island, be removed by non-lethal means. Non-lethal removal proved impractical, expensive, harmful to the animals removed, and due to the strong homing impulse of sea otters, it also proved futile. We terminated the program and its associated zones in 2012. Now, more than three decades after the program was initiated, the population is growing more rapidly, though it remains small and represents less than five percent of the southern sea otter population overall. 

Range expansion is a key part of southern sea otter recovery and is critical to the restoration of ecosystems in which sea otters evolved as a keystone predator. Southern sea otters have reached carrying capacity in the central part of the mainland range, with mortality from shark bites at the range peripheries preventing range expansion from happening naturally. As a result of shark-bite mortality, no net range expansion has occurred in more than 20 years.  Under a directive from Congress, we worked with partners and stakeholders in 2021 to evaluate the feasibility of reintroducing sea otters to the West coast of the contiguous U.S., where sea otters historically thrived. Assessment of feasibility is the first step in any reintroduction effort, but it is not a reintroduction proposal. If reintroduction consideration continued, any reintroduction proposal would be developed with extensive input from a broad range of stakeholders.  We are currently reviewing the status of the southern sea otter under the Endangered Species Act. The species status assessment is based on the best available scientific and commercial data regarding the species, including population trends, distribution, demographics, genetics, habitat conditions, threats and conservation measures. By thoroughly reviewing the best available data, we will have a better understanding of all the factors influencing the sustainability of southern sea otters in the wild - now and into the future.  

Scientific Name

Enhydra lutris nereis
Common Name
Southern sea otter
FWS Category
Mammals
Kingdom

Location in Taxonomic Tree

Identification Numbers

TSN:

Characteristics

Characteristic category

Lifecycle

Characteristics
Reproduction

Mating and pupping occur throughout the year, but on average across their range, a peak period of pupping occurs from October to January, with a secondary peak in March and April. Females typically give birth to a single pup, and solely provide care to the pup for approximately six months until weaning. Pup rearing and provisioning impose high energetic costs on females, which requires them to increase the amount of effort that they put into foraging. During this period, female parents are highly susceptible to stressors, like infections and aggression by males, that they may encounter when they come into estrus after weaning. 

Characteristic category

Similar Species

Characteristics
Similar Species

In the United States, there are two distinct sea otter subspecies, the northern sea otter and the southern sea otter, also known as the California sea otter. Northern sea otters live in the nearshore waters of Alaska, British Columbia and Washington state. A third sea otter subspecies, the Asian sea otter, occurs in northern Japan and the Russian far east. 

Characteristic category

Habitat

Characteristics
Habitat

Southern sea otters live and feed in marine coastal areas along the central California coastline, including rocky and sandy areas along the exposed outer coast and protected areas such as bays and estuaries. Because they are efficient predators and consume large quantities of marine invertebrates, sea otters play a significant role in the nearshore marine ecosystems of the Pacific Ocean, enhancing not only kelp forests but also seagrass beds.

Sea otters help maintain kelp by preying on sea urchins, which can clear-cut kelp forests when left unchecked. Sea otters enhance seagrass by preying on crabs, which eat sea slugs and isopods. By controlling the predators of these mid-size underwater grazers, sea otters allow the sea slugs and isopods to graze the algal epiphytes that can coat the seagrass blades, allowing sunlight to penetrate and the seagrass to flourish.

Sea otters help to mitigate  climate change climate change
Climate change includes both global warming driven by human-induced emissions of greenhouse gases and the resulting large-scale shifts in weather patterns. Though there have been previous periods of climatic change, since the mid-20th century humans have had an unprecedented impact on Earth's…

Learn more about climate change
 and some of its consequences through their kelp and seagrass work. Kelp and seagrass capture carbon dioxide from the atmosphere and transform it into organic carbon during growth. Some of this carbon is stored in their bodies, and some is sequestered in the deep ocean or in sediments where it is no longer cycling and contributing to climate change. Kelp and seagrass protect shorelines from erosion caused by sea level rise and increased storm intensity, and they locally reduce ocean acidification, which results from the ocean’s absorption of excess atmospheric carbon. Ocean acidification can be devastating to calcifying organisms, such as the shell-forming species that constitute much of sea otters’ prey.

Through these same effects on kelp and seagrass, sea otters indirectly enhance commercial, recreational and subsistence finfish fisheries through benefits to species like lingcod, kelp greenling, rockfish, Pacific herring and salmonids.

Marine

Having to do with water

Coastal
Urban
Characteristic category

Food

Characteristics
Food

Southern sea otters prey on a variety of bottom-dwelling invertebrates including clams, crabs, sea urchins and snails. Sea otters occasionally go as deep as 300 feet, but the vast majority of dives by southern sea otters are less than 80 feet deep. Sea otters primarily use their sensitive whiskers and paws to locate prey. 

Characteristic category

Behavior

Characteristics
Behavior

Sea otters are social animals and usually rest in groups. To keep from drifting while resting, they often wrap themselves up in kelp or seagrass, forming something that resembles a raft. 

Sea otters are well known for using tools, typically a rock that can be used as a hammer or anvil to break open hard-shelled prey. A loose patch of skin under their armpit serves as a pocket to store multiple prey items obtained on a dive.

Characteristic category

Physical Characteristics

Characteristics
Size & Shape

Sea otters are the smallest marine mammal. They depend on their dense fur for insulation instead of blubber like other marine mammals.

Weight

Southern sea otters are among the smallest of marine mammals, with adult females and males averaging 46 and 64 pounds, respectively. Unlike most other marine mammals, they have little subcutaneous fat, relying instead on their clean, dense, water resistant fur for insulation against the cold. Contamination of their fur by oily substances can destroy its insulating properties and lead to hypothermia and death. Sea otters also maintain a high level of internal heat production to compensate for their lack of blubber. As a result, their energetic requirements are high, and they consume an amount of food equivalent to about 25 percent of their body mass per day.

Geography

Characteristics
Range

Southern sea otters have reclaimed about 13 percent of their historical range, including the mainland coastline from San Mateo County to Santa Barbara County and San Nicolas Island, in Ventura County. Before the fur trade, sea otters as a species ranged more or less continuously along the North Pacific Rim from Hokkaido, Japan to Baja California, Mexico. The species was likely structured as a latitudinal cline, without strict demarcations between subspecies. Sea otters most closely resembling today’s southern sea otters occupied the southernmost portion of that range - from at least as far north as Oregon to the species’ southern limit at Punta Abreojos, Baja California.

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