California Sea Otter

Enhydra lutris nerei

Sea otters are frequently seen in the waters around Piedras Blancas, swimming or resting on their backs, foraging for food, or interacting. They are the smallest marine mammal of North America. Although it would be easy to think of them as ocean-going teddy bears they are actually members of the weasel family. They are the most recently evolved marine mammal; their ancestors probably entered the ocean around 5 million years ago and they have been in their present form for about 3 million years.

The sea otter played an important role in the development of the West and in California's history. The discovery of sea otters by Vitus Bering in 1741 led to the Russian colonization of the northwest coast of America. After the depletion of the California sea otter Russia lost interest in the settlement at Fort Ross and sold the property to an American named John Sutter. Sutter established a sawmill on the American River in order to raise money to pay for the property and it was there that gold was discovered in 1848.

Color: Their thick, luxurious fur ranges from shades of brown to almost black. With age, both males and females may develop a silver head as a result of the loss of hair pigmentation. Referred to as grizzling, this silvery appearance can extend onto the chest and abdomen. Pups are born with a fuzzy light brown or yellow natal pelage.

Weight and length: Healthy adult female California sea otters usually weigh between 40-50 pounds. Adult males weight between 55-90 pounds, averaging about 65 pounds. Pups are about 3-5 pounds at birth. (Brian Hatfield, USGS Wildlife Biologist based at Piedras Blancas, caught a record-breaking 111-pound male otter off Washington in the summer of 2002.) California sea otters can reach a length of 4-4.5 feet.

Shape: The front appendages of a sea otter are shaped like a cat's paw, with claws used for grabbing prey and for grooming. The rear appendages are large and webbed, like flippers, for effective movement through the water. The tail, which is broad and flattened, is useful for propulsion and steering. They have tiny rolled, external ears and excellent hearing.

The front paws are shaped like a cat's paw, but the rear appendages are webbed and flipper-like.

 
How do they keep warm? Sea otters are the only marine mammals that don't have blubber. Instead, they rely on their luxurious fur coats and a high metabolism to keep warm. Their incredibly lush, soft coat functions like a fuzzy dry suit, keeping their skin dry. Sea otters have a double layer of fur, which is the densest in the animal world, ranging from 1/4 million to a million hairs per square inch. Compare that to human beings that may only have 100,000 hairs on their entire body!

Grooming: Sea otters spend a considerable amount of time grooming. During the grooming process tiny air bubbles are trapped in the dense underfur to help maintain buoyancy and provide insulation that keeps the skin warm and dry. Grooming also distributes natural oils that aid in repelling water. If the fur becomes soiled water can penetrate to the skin and cause over-chilling. Grooming usually takes place before and after eating and resting. The four stages of the grooming process are 1) somersaulting and rolling, 2) rubbing the body, 3) licking the flippers and tail, 4) licking the paws, chest, and face. The skin is very loose so it can be pulled around for easy cleaning.

Breathing and diving: Sea otters usually dive in water that is less than 130 feet deep and within 1 1/2 miles of shore. However, they can dive deeper - up to 300 feet deep and they are occasionally seen farther from shore. Sea otters have a lung capacity of about 2.5 times that of a land mammal of similar size. Most dives are between 1-2 minutes or less. Increased lung size not only provides oxygen storage but also increases buoyancy.

Feeding: Sea otters must eat 20-30% of their body weight each day to maintain their high metabolism. That means a 40-pound otter would have to eat about 10 pounds of food each day. California sea otters feed on more than 60 different invertebrates, including crabs, clams, abalone, mussels, and sea urchins. Interestingly, otters show strong individual food preferences. One may prefer kelp crabs and squid, but another may prefer turban snails and mussels. The sea otter is one of the few tool users in the animal kingdom. Hard-shelled food is banged against a rock on the chest to crack it open. Listen closely for the tap-tap-tapping that occurs while otters are feeding. Frequently gulls can be seen in the vicinity of a foraging otter, waiting for scraps of food.

Sea otters have canine teeth for ripping and tearing food and large molars for crushing and grinding. Those otters that eat a lot of sea urchins develop a purple discoloration on their teeth and bones, referred to as echinochrome coloring.

In general, otters tend to feed about 3-4 times a day - early in the morning, in the late afternoon, and once or twice at night (although this pattern varies considerably).  They use touch and vision to find food. The sense of touch is very important because they often search for food in dark and murky water. Sensitive paws and whiskers are useful in searching for prey.

  Territorial males have been observed holding a pup hostage until the mother turns over food in exchange. A few otters have been observed eating seabirds.

Movement/Behavior: They usually swim on their backs about 2mph. Faster speeds are obtained by swimming on their stomachs; territorial males are seen patrolling their territories in this fashion.

The behavior in which the upper part of the body is thrust out of the water to get a good look around is called periscoping. Although sea otters are completely adapted to life at sea they are occasionally seen hauling out on rocks, even among harbor seals. Piedras Blancas is an area where sea otters are known to haul out. Young otters do a lot of playing. Pups have a distinctive dive with a jerky flip of the hindquarters.

 Although sea otters usually forage alone, with the exception of mothers with pups and male/female pair bonds, they come together in groups to rest and socialize. A group of otters is called a raft. Most rafts contain 2-12 animals but large groups of 40-50 or more may be seen. In Alaska, rafts of over 1000 sea otters have been reported.

Sounds: Sea otters make a variety of sounds including screams and whistles. They grunt and coo while eating yummy food. During courtship a male might coo or whine like a begging dog. When trapped they make a hissing or snarling noise. The sound you are most likely to hear is that of a pup or its mother - "EEEE."  Loud and piercing, it is designed to get them re-united, usually after foraging dives at night or in rough sea conditions.

Reproduction: Females are sexually mature around 3-4 years of age. Males probably can't hold a territory until around 8 years of age. When sea otters mate, the male grasps the female and bites her nose leaving wounds that result in scarring. If you see an otter with a pink or red nose it is likely a female that has recently mated. Although mating may occur any time of the year, in California it peaks in late summer and fall.  The male-female bond lasts for about 1-4 days. Gestation is about 4-6 months, including a period of delayed implantation.  Most pups are born between January-March, although a second pupping peak occurs from August-October. (This is because females who lose pups come into estrous soon thereafter.) Most pups are born in the water. A female otter comes into estrous within a few days of weaning her pup. California sea otter females usually give birth to a pup every year. There have been reports of twins but the mother will abandon one because she can't care for two pups.

The best way to tell a male from a female is to look for the genital bulges on the male and nose scarring on a female. Mature males are larger than females and they have a thicker neck area. Behavior is also a good indicator of sex. Males can also be identified by their aggressive behavior: stealing food, harassing other otters, and grabbing females and trying to mate.

Pups: Small sea otter pups are covered with a dense fur coat that keeps them buoyant so they bob around like fuzzy corks when mom is diving. Sometimes a mother otter wraps her pup in kelp so it doesn't float away while she's diving. Most of the time young pups are seen resting on their mother's chest or belly. The two nipples are located toward the lower part of the mother's abdomen. Sea otter milk contains 20-25% fat. At about 3-4 months of age the natal pelage is replaced by the regular coat and the pup can dive proficiently and look for food. Pups are weaned at about 6-8 months of age weighing 25-30 pounds.

Longevity: In the wild, females may live 15-20 years and males may live 12-15 years.

Distribution: At one time sea otters ranged all along the north Pacific coastline from Japan down to Baja California. (See illustration at end of this report.) Today there are three sub-species of sea otters recognized: Enhydra lutris nereis (California or southern sea otter), E. lutris lutris (Russian sea otter), and E. lutris kenyoni (Alaskan sea otter). The sub-species designations are based on differences in skull size and shape and on genetic differences.

Most of the California sea otter population is found between Point Conception and Half Moon Bay, although some travel outside that area. The males do a lot of travelling but most females remain within a 3-6 mile area. However, some females travel further.

Status: Sea otters were nearly hunted to extinction for their luxurious pelts. The otter trade began in 1741 and continued until 1911. Before the hunts the entire sea otter population was believed to be 150,000-300,000. The California population is believed to have been between 16,000-20,000. After the hunts there were about 1000 otters remaining in the Aleutians and less than 100 off California. In 1915 a remnant colony of 32 otters was observed off Big Sur but their presence was kept secret until 1938 when the coast highway was built.

The stretch of coastline between Cambria and Monterey is officially a "sea otter refuge," which was a source of protection before the Marine Mammal Protection Act of 1972. California sea otters are classified as "threatened" under the Endangered Species Act. The MMPA lists them as "depleted."
           
Importance: The sea otter is considered a "keystone species" because it is responsible for much of the structure of the ecosystem in which it lives. By keeping sea urchins (who feed on kelp) in check, giant kelp forests thrive, which in turn provides habitat for many creatures. Sea otters are also referred to as an "umbrella species" because protection for them and their habitat benefits a large variety of other species. The otter is maligned for damaging the abalone population, but abalone are part of the kelp forest ecosystem and survive in areas where there are otters by living in crevices beyond the reach of otters and human hunters. After the otter populations were decimated the abalone population reached unnatural highs, which allowed a commercial abalone fishery to develop. After otters repopulate an area the natural balance is re-established, where there are abalones but not enough to support a commercial fishery. Sea otters and abalone have been coexisting for millions of years.

Predators: Historically, man has been the sea otters greatest predator. The great white shark is responsible for some otter deaths in California, but it is believed that most strikes are a case of mistaken identity because the otters are not eaten. Great white sharks prefer to prey on blubber-rich seals and sea lions.

Other threats to sea otters include oil spills, pollution, disease, and drowning in fishing nets and traps.