In the spirit of World Otter Day (May 25) let’s celebrate the unsung heroes of the pacific coastline – sea otters! Sea otters are best known for their adorable appearance and playful behavior; however, they are much more than just a pretty face.  Sea otters are a keystone species and play a crucial role in maintaining a healthy ocean ecosystem. Shockingly, sea otters are also one of the most endangered species in the Pacific, as they were nearly hunted to extinction in the early 1900’s.  Imagine a world without a picture of those cute, little guys to brighten up your day?  Exactly, that would be terrible. Help protect endangered sea otters from extinction by learning more about this fascinating animal!

California Sea Otter

California Sea Otter


Sea otters are the smallest marine mammal in North America, but one of the largest members of the weasel family.  An adult sea otter is about 4 feet long and females can weigh up to 50 pounds, whereas males can weigh closer to 70 pounds.  There are 3 known subspecies of sea otters: one off the coast of Japan and Russia, one in  Gulf of Alaska, and one off the California coast.  All subspecies look very similar, the only difference is their size as Northern sea otters tend to be larger than California sea otters.  The main physical characteristic of sea otters that differs from the majority of marine mammals is their lack of insulating blubber.  Instead of having blubber to keep them warm in the frigid Pacific ocean, sea otters have a dual layer coat of fur that is the densest of any marine mammal.  Sea otters have approximately 1 million hair per square inch, compared to only about 100,000 hairs on a human’s entire head!  All that hair requires a lot of maintenance and sea otters can often be observed grooming their coat.  They use their paws to brush through their coat, drawing their skin’s natural oil over their fur while also “fluffing” their fur to create air pockets.  The oils ensure that their fur is waterproof, while the air bubbles provide much needed insulation.  An interesting physical characteristic of sea otters are their built in pockets under their forearms that serve as a place to stash prey while diving so they can maximize their catch.


Sea otters live almost exclusively in the Northern Pacific kelp forests, relatively close to the coastline.  Their historic range is nearly all of the West coast of the U.S. up into Canada, Alaska, Russia and just south of Japan.  However, due to being hunted so heavily in the early 20th century their current range is: San Mateo County to Santa Barbara, California, the Gulf of Alaska, Aleutian Islands to Prince William Sound, and just north of Japan. The kelp forests are crucial to their survival because they not only provide a safe place to birth young, but also a steady food supply and constant shelter.  Sea otters are often seen either individually or in large groups, wrapped in kelp and floating on the water’s surface.  Sea otters wrap themselves in kelp in order to anchor them to an immobile object and avoid drifting off with the current while they rest or nap.  The rocky bottom and lush kelp bed environment that the otters inhabit have largely determined how they adapted and specialized in the ocean ecosystem.

Diet and Behavior:

Sea otter using a rock to eat his hard-shelled prey

Sea otter using a rock to eat his hard-shelled prey

Sea otter’s diet consists almost entirely of marine invertebrates with some of their favorite menu items including: sea urchins, crabs, snails, and mussels.  They are adept hunters as they are excellent swimmers and can dive for up to 5 minutes! Additionally, their strong paws and sharp teeth coupled with their intelligence enable them to hunt for prey efficiently. Due to sea otter’s unusually high metabolism, an adult consumes about 25% of its body weight every day! Sea otters eat while floating on their back as their underside serves as a personal dinner table and they are the only marine mammal known to use tools in order to eat hard-shelled prey.  Individuals are often seen smashing rocks against clams or mussels when floating on their back, in order to use minimal effort to eat the soft bodied invertebrates inside the shell.  Their ingenuity is one of the reasons sea otters have survived the many challenges that humans and the environment have imposed on them.

Sea otter raft

Sea otter raft


Sea otters are complex social animals who are rarely territorial due to their need for social interaction with other otters.  In order to keep warm during cold days, large groups of sea otters are seen holding hands while lying on their backs, forming what looks like a sea otter raft.  They are dedicated mothers who give birth to one pup per year and spend the whole year teaching their pups how to live like sea otters.

Sea Otter’s Role in Ecosystem:

Kelp forests are frequently plagued by overwhelming numbers of sea urchins who eat away at the kelp’s holdfast (part that attaches to ocean floor) and kill the kelp as it is no longer anchored to the seafloor.  Luckily for kelp forests, sea otter’s favorite meal is sea urchins.  Sea otters are the primary predator of sea urchins and are solely sea otters and kelpresponsible for keeping their population in check and preserving the kelp forests.  They are the keystone species of the Pacific kelp forest ecosystem as  they keep the entire ecosystem in check and are needed in order to maintain balance.

Conservation Status and History:

Sea otter populations used to thrive all the way from Baja California to the Pacific Rim, but were heavily hunted for the lucrative fur trade. Beginning in the 1700’s and lasting into the early 1900’s sea otters were hunted to near extinction for their beautiful pelts that were traded by Europeans and Americans in Asian markets. Wearing a sea otter pelt symbolized wealth and power in many Asian countries, and therefore the demand for pelts remained high until the 1900’s.  After depleting the sea otter species to only a couple thousand and shrinking their range and distribution, the hunting finally came to the end after the 1911 Northern Fur Seal Treaty; in addition, in the 1970’s sea otter protections were strengthened with the Endangered Species Act.  In 1938 only 50 sea otters remained off the California coast, but they have steadily made a comeback as a result of additional protections and scientific research – today they number nearly 3,000.  

The IUCN Red List has listed sea otters as an endangered species since 2000 and their current population status is decreasing.  Ranging from climate change, to oil spills, to pollution there are many threats that have hindered sea otters from being more prosperous and being upgraded from endangered to threatened.  Although sea otters have recovered from the devastating effects of the fur trade, the greatest threat to sea otters is oil spills.  As more and more offshore oil drilling is taking place it increases the likelihood of oil spills, which could wipe out thousands of sea otters. For example, the Exxon oil spill in Valdez, Alaska killed several thousand sea otters.  When oil spills into the water, it coats the sea otter’s fur and blocks their fur’s natural waterproofing ability.  This results in their fur losing its insulating properties and rendering the sea otter unable to keep warm.

If humans are more conscious of how their actions impact the unique animals we share the planet with, more species like the sea otter would not be endangered and at risk for extinction due to human interference.

Quiz Time!

Test your sea otter knowledge with this quiz!



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