All About Sea Otters

The scientific name for sea otter is “Enhydra lutris“.

Sea otters are carnivorous aquatic/marine mammals from the Mustelidae family. Other mustelids are weasels, mink, wolverines, badgers, martens, and fishers. However, the relatives of the sea otter that I just mentioned are all terrestrial, while the sea otter is mainly aquatic. In its various sub-species forms, the river otter is the closest relative to the sea otter. However, river otters are only semi-aquatic.

Sea otters are a unique mustelid in that they perform the vast majority of their daily activities, including sleeping in the waters of the Pacific Ocean. They’re also unique in that they’re the heaviest member of the Mustelidae family while at the same time being the smallest marine mammal.

What Do Sea Otters Look Like?

Sea otters are most similar in body structure to river otters. Mustelidae family members with similarly shaped bodies are weasels, fishers, mink, and martins. Sea otters have proportionately long bodies with short legs and muscular tails that are flat from top to bottom like a paddle. Their feet are webbed. Additionally, their hind feet are larger than their forefeet, and they’re flattened out to serve as flippers to propel them through the water. Sea otters also have flaps of loose skin behind each of their forelegs that extend to their chests forming pockets. Sea otters store food and tools in these pockets.

Their fur is dark brown to reddish-brown on their backs and sides and lighter fawn-colored underneath. Older animals become grizzled around their heads. As they age further, the fur around their head and shoulders becomes almost white.

How Big Are Sea Otters?

Male Sea otters reach lengths up to 5.5 feet “167 cm” and weigh up to 100 pounds “45 kg”. Females can be up to 4.60 feet “140 cm” long and weigh up to 72 pounds “32.5” kg.

How Do Sea Otters Stay Warm?

Sea otters have an extremely high metabolism. They burn through calories at three times the expected rate for an animal their size. Here’s part of the reason this is so. Mitochondria are the powerplants that generate energy to an animal’s muscles on a cellular level. Sea otters have leaky mitochondria. In other words, their mitochondria leak energy to generate heat. That’s why sea otters eat so much. They consume 25% of their body weight each day to generate enough heat to stay warm. Source

Sea otters also have the densest fur around for insulation. The sea otter holds the distinction of having denser fur than any other mammal. They have between six hundred thousand and one million hairs per square inch. Their fur consists of a layer of coarse waterproof guard hairs over a layer of dense, fine fur.

While other marine mammals rely on their blubber layer to keep them warm, the insulating qualities of a sea otter’s fur is what keeps it protected and warm in the cold waters of the Pacific Ocean. They spend a portion of each day preening and conditioning their fur. This helps to trap a layer of air next to their skin If their fur becomes soiled or compimised by something like an oil spill, it will lose its insulating capability. Sea otters are covered with fur all over, except for on the pad of their nose, the inside s of their ears, and the bottoms of their feet.

Sea Otter vs River Otter

North American river otters sometimes inhabit marine environments along the Pacific coasts of the United States and Canada. Consequentially, people sometimes mistake them for sea otters and vice versa. However, sea otters are larger and have stouter bodies than river otters. From the section above, we see that sea otters can weigh up to 100 pounds. On the other hand, we learn from “North American River Otter” that North American river otters have a top weight of 33 pounds. Sea otters also have shorter, differently constructed tails than do river otters.

One more way to tell the difference between river otters and sea otters is the way that they swim. River otters only swim belly down while sea otters spend a good deal of time floating and swimming on their backs.

Sea Otter Range

Where do sea otters live? Sea otters live in remnant groups of their former populations around the northern pacific rim. In former times the sea otter population is thought to have numbered between 150,000 and 300,000 animals. Their luxurious pelts proved to be their undoing.

In the 1800s fur traders hunted sea otters to near extinction. By the turn of the 20th century sea otters were expatriated from much of their native range. In 1911, the United States, Great Britain, Russia and Japan formed an agreement called the International Fur Seal Treaty. It banned the hunting of fur bearing sea mammals. In the United States additional conservation efforts were extended to sea otters and other marine mammals through the Marine Mammal Protection Act of 1972. It paced a moratorium on importing, exporting, or selling of any marine mammal, or any marine mammal part or product within the U.S.

Today sea otter populations have largely recovered in some areas while they still struggle in others. Even though they are no longer hunted by humans, sea otter mortality still comes via other causes such as parasitic diseases and predation. Killer whales, great white sharks, and sea lions are all predators of sea otters.

Today they live in fragmented populations in their historic range from northern Japan to Russia. From Russia, their range extends across the Bearing straights to Alaska and down the eastern Pacific coast through British Columbia, Washington state, California, and Baja California.

Sea Otter Habitat

Sea otters prefer nearshore marine ecosystems. They generally stay in coastal waters, within 2/3 0f a mile “1 kilometer” of the shore. Additionally, they generally prefer sheltered coves.

They spend most of their time in areas with forests of giant kelp or seagrass bottoms.

What Do Sea Otters Eat?

They eat gastropods such as abalone and sea snails, crustations like crabs and barnacles, echinoderms like sea urchins, sea stars and sea cucumbers, cephalopods like octopus and squid, mollusks like clams and oysters, and various fish.

Do Sea Otters Eat Kelp?

No sea otters don’t eat kelp. They actually help kelp by eating the sea urchins that graze on it. Sea urchins will eat through the lower stems of kelp, allowing it to drift away and die.

How Do Sea Otters Help The Ecosystem?

Sea otters help to promote healthy kelp beds by feeding on marine herbivores such as sea urchins that feed on kelp. In turn, kelp forests sequester over 170 million metric tons of carbon from the atmosphere each year and provide roughly 70% of our oxygen. “A metric ton is equal to 1,000 kilograms or 2204.62 pounds.”

Are Sea Otters Secondary Consumers?

Yes, sea otters are secondary consumers in the kelp forests when they feed on primary consumers such as sea urchins, which graze on the kelp forests. They also feed on other primary consumers, such as abalone and sea snails. When they eat fish, they become tertiary consumers. Tertiary consumers eat secondary consumers.

Why Are Sea Otters A Keystone Species?

A keystone species is a species whose absence from a given ecosystem will create a cascading effect in which many other species will be adversely affected or lost. Sea otters are a keystone species because they help keep the kelp forests healthy and intact.

Sea otters eat the marine herbivores, particularly sea urchins that graze on kelp forests. Kelp forests provide shelter and nutrients for many other types of marine life.

There was a time when sea otter populations were seriously depleted due to overhunting. When sea otters disappeared from the Pacific coast of North America, sea urchin populations were left to overpopulate. In places where sea urchin populations are not kept in balance by sea otters, they can create areas referred to as urchin barrens devoid of kelp and any of the forms of marine life that depend on kelp for their sustenance.

Sea Otter Behavior

Sea otters spend the vast majority of their time in the waters of the Pacific Ocean. At times they will come out on land. When they do, they walk or bound sideways with a cumbersome gate. They move awkwardly when they’re out of the water. Their physical adaptations make them mainly aquatic animals. They carry out all their life’s activities such as eating, sleeping, and even mating and giving birth in the ocean.

How Sea Otters Sleep?

Sea otters sleep as they float on their backs in the water. They sometimes entangle themselves in kelp so that they’re anchored as they sleep. They also sleep side by side and hold hands sometimes to keep from drifting apart.

How Do Sea Otters Eat?

Sea otters eat fish and cephalopods, but they also eat sea urchins and various hard-shelled inebriates such as crustations and mollusks. Sea otters are the only marine mammals besides dolphins to use tools. When they eat hard-shelled animals, they have to break open their shells somehow. They do this by hitting them on a rock that they lay on their chest as they float on their backs. They carry their rock and sometimes their food back to the surface in the skin pockets that they have behind each foreleg.

Sea otters are famous for eating sea urchins. To eat them, they have to break off the prickly spines of the urchin with their paws, and then they bite open the urchin’s body and lick out its insides.

Sea Otter Mating Behavior And Life History

Sea otter males are polygynous, meaning that they mate with multiple females. Mating takes place in the water, and sometimes males drown female sea otters in the act of mating. Male sea otters also bite the female on the nose in mating. Most females of reproductive age have nose scars.

Sea otter births occur year-round but peak between January and March in southern populations and mid-May through mid-June in northern populations.

The birth of their offspring varies anywhere from 4 to 12 months from the time of mating. This is because sea otter females can delay the time that the embryo is implanted in their uterus. Their actual gestation period lasts for about four months.

Most of the time, they give birth in the water, and generally, they give birth to a single pup. When they are born, after their mother has thoroughly licked them off, a sea otter pup’s fur is so dense and buoyant that they are incapable of diving. Their baby fur will be completely replaced with adult fur when they’re about 13 weeks old. When their mother dives to look for food, she leaves her pup on the water’s surface. She’ll sometimes wrap it in a strand of kelp to keep it from floating away.

Sea otter pups begin to practice diving when they’re about two months old, but they won’t be able to fully reach the bottom for a while. With their mother’s training, they’ll be able to feed themselves by the time they’re 6 months to 8 months old.

32% of sea otter pups won’t live to a year of age. If they make it through the first year, they’ll be able to reproduce when they are 2 to 3 years old. In the wild, the life span of sea otters ranges from 10 to 15 years for males and 15 to 20 years for females.