The sea otter is an aquatic member of the mustelid family that lives along the Pacific coast of North America and Asia. Sea otters spend most of their time in the water, but occasionally come ashore to sleep or rest. Sea otters have webbed feet, water-repellent fur to keep them dry and warm, and nostrils and ears that close in water.
The word “kalan” appeared in Russian from the Koryak kalag (kolakh) and is translated as “beast”. Previously, the name “sea beaver”, sometimes “Kamchatka beaver” or “sea otter” was used. In English-speaking countries, the name “sea otter” is used.
Species origin and description
Sea otters are the largest members of the mustelidae family. The animal is unique in that it does not burrow, has no functional anal glands, and is able to live its entire life in water. The sea otter is so different from other mustelid species that, as early as 1982, some scientists believed that it was more closely related to earless seals.
Genetic analysis indicates that the closest extant relatives of the sea otter were: the African and Cape clawless otters and the eastern weakly clawed otter. Their common ancestor existed about 5 mil. years ago.
Fossils indicate that the Enhydra lineage became isolated in the North Pacific about 2 mil. years ago, which led to the disappearance of Enhydra macrodonta and the appearance of the modern sea otter, Enhydra lutris. The current sea otters originated first in the north of Hokkaido and in Russia, and then spread to the east.
Video: Sea otter
Compared to cetaceans and pinnipeds that have entered the water, approximately 50, 40, and 20 mil. years ago, sea otters were relative newcomers to marine life. However, they are more fully adapted to water than pinnipeds, which come out onto land or ice to give birth. The genome of the northern sea otter was sequenced in 2017, which will allow studying the evolutionary divergence of the animal.
Appearance and features
Sea otter — a small marine mammal, but one of the largest members of the Mustelidae family, a group that includes skunks and weasels. Adult males reach an average length of 1.4 m with a typical weight of 23–45 kg. The length of the female is 1.2 m, weight 20 kg. Sea otters have a very buoyant, elongated body, a blunt muzzle and a small, wide head. They have a keen sense of smell and can see well both above and below the surface of the water.
Sea otters have adaptations to help them survive in difficult marine environments:
- long whiskers help detect vibrations in muddy waters;
- sensitive front paws with retractable claws, help grooming, find and capture prey and use tools;
- The sea otter's hind feet are webbed and fin-like, which the animal uses along with its lower body to propel itself through the water;
- the long, flattened tail is used as a rudder for added traction;
- hearing & #8212; this is a sense that has not yet been fully explored, although studies show that they are particularly sensitive to high frequency sounds;
- teeth are unique in that they are blunt and designed to break;
- the body of the sea otter, with the exception of the nose and paw pads, is covered with thick fur, which consists of two layers. The short brown underfur is very dense (1 million hairs per square meter), making it the densest of all mammals.
A top layer of long, waterproof guard hairs helps keep the undercoat dry, keeping cold water out of the skin. It is usually dark brown in color with silvery gray highlights, and the head and neck coloration is lighter than the body. Unlike other marine mammals such as seals and sea lions, sea otters do not have any blubber, so they depend on this exceptionally thick, water-resistant fur to keep warm in the cold, coastal Pacific.
Where does the sea otter live?
Sea otters live in coastal waters with a depth of 15 to 23 m and are usually found within ⅔ kilometers from the coast. They are more likely to choose areas sheltered from strong ocean winds, such as rocky coastlines, dense algae, and barrier reefs. Although strongly associated with rocky substrates, sea otters can also inhabit areas where the seabed is composed of mud, sand, or silt. Their northern range is limited by ice, because. Sea otters can survive on drifting ice, but not on ice floes.
Today, three subspecies of E. lutris are recognized:
- the common sea otter or Asian (E. lutris lutris) habitat range extends from the Kuril Islands north to the Commander Islands in the western Pacific;
- the southern or California sea otter (E. lutris nereis) is off the coast of central California;
- The northern sea otter (E. lutris kenyoni) is distributed throughout the Aleutian Islands and southern Alaska and has been repopulated in various places.
Sea otters, Enhydra lutris, are found in two geographic regions on the Pacific coast: along the Kuril and Commander Islands off the coast of Russia, the Aleutian Islands below the Bering Sea, and coastal waters from the Alaska Peninsula to Vancouver Island in Canada. And also along the central coast of California from the island of Año Nuevo to Point Sur. Sea otters live in Canada, USA, Russia, Mexico and Japan.
Sea ice limits their northern range to below 57°N, and the placement of kelp (seaweed) forests limits their southern range to about 22°N. Hunting in the 18th and 19th centuries greatly reduced the distribution of sea otters.
Sea otters live in coastal forests of giant brown algae (M. pyrifera) and spend most of their active time looking for food. They eat, rest and groom themselves on the surface of the water. Although sea otters can dive to a depth of 45 m, they prefer coastal waters up to 30 m deep.
What does a sea otter eat?
Sea otters consume over 100 types of prey. They spend a lot of energy to maintain a body temperature of 38 ° C. Therefore, they need to eat food 22-25% of their body weight. The animal's metabolism is 8 times higher than that of land-dwelling counterparts of a similar size.
Their diet mainly consists of:
- sea urchins;
- tunicates, etc.
Otters also eat crabs, octopuses, squid and fish. As a rule, the menu depends on the habitat. They get most of their fluid from prey, but also drink seawater to quench their thirst. In studies in the 1960s, when sea otters were under threat, 50% of the food found in the stomachs of sea otters was fish. However, in places with a lot of other food, fish made up a small part of the diet.
Sea otters feed in small groups. Hunting takes place on the seabed. They use their sensitive whiskers to locate small creatures in dense kelp beds and crevices. Animals use movable forepaws to capture prey and place invertebrates in loose folds of their skin under the armpits, feeding on them on the surface. Sea otters usually eat 3-4 times a day.
California sea otters break prey with hard objects. Some otters hold a stone on their chest and knock their prey against the stone. Others hit prey with a stone. One stone is saved for many dives. Sea otters often wash their prey by pressing it against their body and turning it in the water. Males steal food from females if they have the chance. For this reason, females feed in separate places.
Peculiarities of character and lifestyle
Sea otters gather in groups during the rest. Females tend to avoid males except when mating. They spend most of their time in the ocean but rest on land. Sea otters communicate through body contact and vocal cues, though not overly loud. The cry of a cub is often compared to the cry of a seagull. Females grunt when they are clearly pleased, while males may grunt instead.
Unhappy or frightened adults may whistle, hiss, or, in extreme circumstances, scream. Although animals are quite sociable, they are not considered to be fully social. Sea otters spend a lot of time alone, and each adult can satisfy its own needs in terms of hunting, grooming and protection.
Sea otters use vertical undulating body movements to swim by pulling their forelimbs and using their hind limbs and a tail to control movement. They swim at a speed of 9 km. per hour underwater. Dives in search of food last from 50 to 90 seconds, but sea otters can stay underwater for almost 6 minutes.
The sea otter has a period of appetite and eating in the morning, starting about an hour before sunrise, after resting or sleeping in the middle of the day. Foraging continues for several hours after lunch until sunset, and a third foraging period may occur around midnight. Females with cubs are more likely to feed at night.
When resting or sleeping, sea otters swim on their backs and wrap themselves in seaweed to prevent drifting. Their hind limbs stick out of the water, while their front limbs either fold over their chest or close their eyes. They carefully groom and clean their fur to maintain its insulating properties.
Social Structure and Reproduction
Sea otters are polygamous animals. Males actively defend their territory and mate with the females that inhabit it. If there are no females on the territory of the male, he can go looking for a mate with estrus. Arguments between challengers are resolved with bursts and beeps, and fights are rare. When male sea otters find a receptive female, they are playful and sometimes aggressive.
Communication occurs in water and continues throughout the entire period of estrus, about 3 days. The male holds the head or nose of the female with his jaws during copulation. Visible scars often form on females caused by such activities.
Sea otters breed throughout the year. There are fertility peaks in May-June in the Aleutian Islands and in January-March in California. It is one of several mammalian species that have delayed implantation, meaning the embryo does not attach to the uterine wall during the immediate period after fertilization. He remains in a state of arrested growth, allowing him to be born under favorable conditions. Delayed implantation results in variable gestation periods ranging from 4 to 12 months.
Females give birth approximately once a year, with births occurring every 2 years. More often, one cub weighing from 1.4 to 2.3 kg is born. Twins occur in 2% of cases, but only one child can be successfully raised. The cub stays with the mother for 5-6 months after birth. Females mature sexually by the age of 4, males at the age of 5 to 6 years.
Mothers of sea otters give their babies constant attention, pressing him to her chest from cold water and carefully caring for his coat. When looking for food, the mother leaves her baby floating on the water, sometimes wrapped in seaweed to keep it from floating away. If the cub is awake, it cries loudly until the mother returns. There have been reports of mothers carrying their babies for several days after death.
Natural enemies of sea otters
The leading mammal predators of this species include killer whales and sea lions. In addition, bald eagles can capture cubs from the surface of the water when their mothers go for food. On land, sheltering on the sand during stormy weather, sea otters can face attack by bears and coyotes.
Also in California, great white sharks have become their main predators, but there is no evidence that sharks ride sea otters. Sea otters die from predator bites. Killer whales (Orcinus orca) were once thought to be responsible for the declining population of sea otters in Alaska, but the evidence is currently inconclusive.
The main natural enemies of sea otters are:
- coyotes ( Canis Lantrans);
- great white sharks (Carcharadon charcarias);
- bald eagles (Haliaeetus leucocephalus);
- killer whales (Orcinus orca);
- sea lions (Zalophus californianus);
- humans (Homo sapiens).
Despite the measures taken against hunting for sea otters, the growth in the number of sea otters stopped. Scientists believe that the reason lies in environmental problems. The number of people in the places of distribution of sea otters is constantly growing, and in addition, the possibility of technogenic risks is increasing.
City runoff carrying cat feces into the ocean brings Toxoplasma gondii, an obligate parasite that kills sea otters. Parasitic infections of Sarcocystis neurona are also associated with human activities.
Population and species status
The sea otter population is believed to have ranged from 155,000 to 300,000 individuals and arc across the North Pacific Ocean from northern Japan to the central Baja California peninsula in Mexico. The fur trade, which began in the 1740s, reduced the number of sea otters to about 1000-2000 in 13 small colonies.
Hunting records examined by historian Adele Ogden establish the westernmost limit of the hunting grounds off the northern Japanese island of Hokkaido and the easternmost limit about 21.5 miles south of California's westernmost cape in Mexico.
In about ⅔ of its former range, this species is at various levels of recovery, with high population densities in some areas and threatened populations in others. Currently, sea otters have stable populations in parts of the Russian east coast, Alaska, British Columbia, Washington, and California, with recolonization in Mexico and Japan. Estimates of the number of individuals made between 2004 and 2007 show a total of about 107,000 individuals.
Sea otters are important for the general health and diversity of the algae ecosystem. They are considered key species and play a critical role in the community by controlling herbivorous invertebrates. Sea otters prey on sea urchins, thereby preventing their overgrazing.
Sea otter protection
In 1911, when it became obvious to everyone that the situation of sea otters was deplorable, an international agreement was signed banning the hunting of sea otters. And already in 1913, enthusiasts created the first reserve in the Aleutian Islands in the United States. In the USSR, a hunting ban occurred in 1926. Japan joined the ban on hunting in 1946. And in 1972, they adopted an international law designed to protect marine mammals.
Thanks to the measures taken by the international community, by the middle During the 20th century, the number of sea otters increased by 15% each year and by 1990 it had reached a fifth of its original size.
According to the Otter Foundation, the population of California sea otters declined from July 2008 to July 2011. Other populations practically did not increase between 1990 and 2007. Enhydra lutris was placed under the Endangered Species Act (ESA) in 1973 and is currently listed under CITES Appendix I and II.
In Canada, sea otters are protected under the Endangered Species Act risk. As of 2008, the sea otter (E. lutris) is considered endangered by the IUCN. Sea otters (sea otters) are vulnerable to massive population declines, with oil spills posing the greatest anthropogenic threat.