Sea otters
What is a sea otter?
Sea otters are the world’s smallest marine mammals. These members of the weasel family (Mustelidae) are the largest otter species, reaching up to 160 centimetres (60 inches) in length and weighing up to 40 kilograms (90 pounds).
Found in coastal waters of the Northern Hemisphere, sea otters are well-known for their habit of floating on their backs while eating food or carrying their young. They are extremely social animals, sleeping in groups of up to 1,000 individuals and engaging in playful behaviours at all ages. Sea otters are also highly energetic—they can eat as much as 30% of their body weight in one day and expend all of this energy diving, grooming, and playing.
Grooming, in particular, is an essential activity for sea otters because they cannot survive with an unkempt coat. Sea otter fur is the densest in the entire world—they have between 600,000 to 1,000,000 hair follicles per square inch of skin. To put that into perspective, humans typically have less than 100,000 hairs on our entire heads.
By massaging and grooming their fur, they create an insulating layer of air that keeps their skin both dry and warm. Sea otters don’t have a blubber layer like seals and other marine mammals, so their fur is the only thing that keeps them safe in cold waters. When you see a sea otter diving for food, you’ll notice they always massage their fur afterwards because diving underwater pushes some of the air out of their fur, meaning they need to replenish it frequently.
Sea otters are very good with their paws. They pick up shellfish from the sea floor, store them in their underarm pockets, and smash them to pieces with rocks to access the meat. They hold food in their paws to eat it while floating on their backs. They even use their paws to stay safe while sleeping, holding hands with other sea otters to keep from floating off with the tide.
Kelp forests are also perfect habitats for sea otters, as they wrap themselves in kelp to stay anchored while sleeping. Sea otters help keep these forests healthy by controlling the sea urchin populations that eat the kelp. Sea urchins are known for wiping out entire kelp forests without predators to keep them in check, so the sea otters’ role is essential. Kelp forests are also natural carbon sinks, absorbing significant amounts of carbon dioxide from the atmosphere, so keeping them healthy helps keep the planet healthier.
What is a sea otter’s scientific name?
The sea otter’s scientific name is Enhydra lutris, which comes from the Greek word for ‘in water’ and the Latin word for otter.
Are sea otters endangered?
The IUCN classes sea otters as endangered with a decreasing population. They suffered a massive population decline due to overhunting in the 1700s and 1800s and have also experienced large-scale decline in recent years. In the western parts of their range, the sea otter population has declined by over 50% in the past 30 years.
The current decline is caused by several factors, including disease, increased predation, pollution, and climate change.
Where do sea otters live?
Sea otters live in the coastal waters of the Pacific Ocean, in specific areas of North America and Asia. The largest sea otter populations are around the coasts of Alaska in the US and Kamchatka Krai in Russia. Individual otters are also frequently spotted in areas of the Mexican coast and off the shores of Erimo in Hokkaido, Japan, but these are not considered separate otter populations.
Sea otters live in near-shore environments and find the majority of their food in waters less than 30 metres (100 feet) deep and within a kilometre (0.6 miles) of the shore. Their preferred habitats include rocky coastlines, thick kelp forests, barrier reefs, and bays because they provide protection from ocean winds and swells.
Sea otters usually live within a small home range of just a few kilometres of coastal water and often stay within this range throughout the year. Adult males establish territories and patrol their borders, while female sea otters travel between male territories freely. Fighting is rare, even among males.
Threats
Today, sea otter populations are fragmented and unstable due to historical overhunting. They also face modern threats like climate change, pollution, and bycatch.
Hunting and trapping
Sea otters have the densest fur of all living mammals, and it’s the sole reason they can survive in their cold ocean habitat. This level of insulation was very valuable to humans a few centuries ago, as it allowed them to make fur clothes that could help them survive in cold areas like northern Russia.
However, otters could not repopulate fast enough to sustain the level of hunting. As a result, sea otters were nearly hunted to extinction.
In 1911, the United States, Great Britain, Japan, and Russia signed the North Pacific Sealing Convention of 1911, protecting sea otters and northern fur seals from hunting. This treaty helped sea otter numbers recover during the 20th century. Today, their populations remain separated and fragmented, covering only a fraction of their historical range.
Sea otters generally aren’t targeted for their fur today, but the lasting effects of historic overhunting may never fully go away.
Disease
Sea otters are susceptible to a range of infectious diseases, and 40% of modern sea otter deaths can be attributed to disease. Sea otter populations in California suffer from toxoplasmosis, and northern populations are often infected with phocine distemper and strep syndrome.
Because sea otter populations are small and fragmented, disease can significantly affect mortality and breeding, leading to population declines.
Pollution
Oil spills are incredibly dangerous for sea otters. If oil gets on a sea otter’s fur, it can no longer maintain the layer of insulating air that keeps them warm. Sea otters don’t have a layer of blubber, and their fur is the only thing that keeps them safe from the cold. During an oil spill, otters become hypothermic.
When they try to groom themselves to get rid of the oil, otters ingest it, which can cause gastrointestinal disorders and even death. Fumes from the oil can also cause lung damage. The Exxon Valdez oil spill in Alaska in 1989 killed an estimated 2,800 sea otters.
Because sea otters live in coastal waters, they can also be affected by pollutants that run off into the ocean.
Climate change
Just like all creatures that call the ocean home, sea otters are threatened by climate change. Rising sea temperatures may affect the kelp forests that sea otters live in and the abundance of the food they eat. Increasing carbon dioxide levels lead to ocean acidification, affecting the shellfish sea otters live on. Climate change also leads to more intense storms, which are dangerous for sea otter pups and their mothers during breeding season.
Sea otters also suffer from increased predation from killer whales, which is believed to be playing a significant role in population declines around Alaska. Killer whales usually prefer prey with blubber, such as northern fur seals, harbour seals, and steller sea lions—but population declines in these species appear to have forced the killer whales to switch to sea otters.
FAQs
Are sea otters mammals?
Sea otters are marine mammals, meaning their ancestors lived on land and then re-entered the sea. Sea otters spend almost their whole lives in the ocean, where they sleep, mate, and give birth. They can also walk on land, sometimes resting on shores or placing their young on rocks for safekeeping.
As mammals, sea otters can’t breathe underwater. Instead, they hold their breath for more than five minutes to dive to the seafloor (in shallow waters) and find food. To achieve this, they have a lung capacity two and a half times greater than land mammals their size.
What do sea otters eat?
Sea otters feed on a range of sea creatures in the coastal waters where they reside, including sea urchins, octopuses, squid, fish, crabs, clams, and abalone. To break open shellfish, they smash the shells on nearby rocks or use stones to hit the shells until they break open.
While swimming along the seafloor, sea otters will use the loose skin under their armpits to store the food they find—allowing them to keep searching until they need to come up for air. Then, when it’s time to eat, they float on their backs and take out bits of food as needed. They can grab new bits of food quickly, so to onlookers who don’t know about these ‘pockets’, it can look like otters produce an endless supply of food from thin air.
Where do sea otters live?
While sea otters used to be much more widespread, they now live in specific areas of the US, Canadia, and Russia, on the Pacific coasts. They can also be found on the northern coasts of Mexico and the coasts of Hokkaido, Japan’s northernmost island, but only in small groups that don’t count as full colonies. Sea otters stay in coastal waters and can often be seen around local ports in certain areas.
What is a group of sea otters called?
A group of sea otters is known as a raft. This comes from their habit of sleeping in groups and wrapping themselves in seaweed. This tactic helps them stay safe and ensures they wake up where they went to sleep.
Why are sea otters endangered?
The main reason sea otters are endangered today is that humans over-hunted them from the mid-1700s until the International Fur Seal Treaty was established in 1911, protecting sea otters by law. Since then, conservation and reintroduction efforts have replenished numbers to some extent, but it’s an ongoing effort. When the treaty was signed in 1911, the estimated population of sea otters had decreased from as many as 300,000 individuals to fewer than 2,000.
Conservation efforts have increased numbers since then, but many colonies haven’t been surveyed recently, so we don’t have an accurate population count. Estimates made between 2000 and 2018 suggest a worldwide population of around 128,000. Today, sea otters are threatened not by hunting but by disease, pollution, and climate change.
What’s the difference between a river otter and a sea otter?
River otters and sea otters are both members of the Mustelidae family, which includes around 62 species, including ferrets, badgers, weasels, and the wolverine. Sea otters are a single species, Enhydra lutris, while the term ‘river otter’ refers to a handful of different species.
Despite the relation and the common name, river otters and sea otters don’t look all that similar. If you put them next to each other, you’ll first notice how much larger sea otters are. The largest male individuals can reach 41 kilograms (90 pounds), while male river otters range from 4.5 to 15 kilograms (10 to 33 pounds), depending on the species.
The two also have different shaped faces. The easiest difference to spot is a river otter’s small round nose compared to a sea otter’s large, more triangular-shaped nose. Another thing that’s obvious at first glance is how much furrier sea otters are. River otters have a smoother coat compared to the fluffy fur sea otters have.
Sea otters spend almost all of their time in the water, often float on their backs, and carry their young on their stomachs. River otters, on the other hand, spend more time on land, don’t float on their backs, and keep their young beside them rather than carrying them.
If you see an otter in the wild, the best way to tell the difference is simply by taking note of where you are. If you’re next to a river, it’s a type of river otter. If you’re by the sea, it’s a sea otter.
Why do sea otters hold hands?
Sea otters often sleep in the ocean, which means they can easily get carried away by the water’s movement. To ensure they stay in the right place, they often sleep in groups and anchor themselves to one spot by wrapping themselves in seaweed. However, they also have a second tactic: holding paws with another individual. They might do this if there’s no seaweed around or if the waters are extra choppy and they want even more security than the seaweed can provide.
How can you help?
Marine mammals face many threats due to climate change and human activities like commercial shipping. You can help by supporting our Blue Speeds initiative to slow down shipping vessels and create a quieter and safer ocean for whales and all other marine mammals.
Learn more about IFAW’s marine conservation projects around the world.