Sea otters
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Sea otter ( Enhydra lutris ) |
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| Enhydra lutris | ||||||||||||
| ( Linnaeus , 1758) |
The sea otter , kalan or sea otter ( Enhydra lutris ) is a species of predator from the subfamily of otters (Lutrinae). Besides the coastal otter of the South Pacific, it is the only species of otter that only lives in the sea . Sea otters are considered intelligent and capable of learning, and they are best known for their regular use of tools. The species was almost extinct because of its fur by the beginning of the 20th century; after the hunting ban in 1911, the population recovered. Sea otters are now considered a key species .
Appearance
anatomy
The sea otter, along with the longer but lighter giant otter and the much longer- legged wolverine, is one of the largest representatives of the marten family. Sea otters reach a length of up to 150 cm, of which about 30 cm are on the tail. The weight of a male animal can be up to about 40 kg, the females weigh less and stay smaller. The fur is dark brown, the head a little lighter.
The adaptation to aquatic life is even stronger in this species than in other otters. The hind legs are set back and the toes are connected by large webbed feet. The front paws are much smaller. In its movement sequences, both on water and on land, the sea otter therefore resembles the ear seals, which put their hind fins under their bodies and can therefore walk on four legs (in contrast to the seals). The tail is not round, as with other otters, but flattened and does not taper towards the tip. The similarities to seals are evolutionary adaptations to the same living conditions ( convergent evolution ).
Sea otters have 32 teeth, which is very unusual for the otter subfamily. Almost all other otters have 36 teeth , only the Asian dwarf otter 34. The sea otter is the only predator to have only two pairs of incisors in its lower jaw. He also has strong, massive molars that adapt to biting mussels and snails .
hide
The sea otter is the only mammal living in the sea that does not have an insulating layer of fat. Instead, an extremely thick fur protects it from the cold of the North Pacific . Around 100,000 hairs grow on a square centimeter; about as many as an average person has on their entire head. The fur, which is considered the finest in the animal kingdom, consists of coarser, darker outer hair and a very fine, light brown-gray undercoat. There are about 70 hairs of the undercoat for one hair of the cover coat. Between the silky hair, there are usually tiny air bubbles that the otter regularly blows into its fur, providing good insulation. These vesicles ensure that the otter does not get wet to the skin while swimming. The skin of the fur, which the otter regularly grooms, lies loosely against the body and forms folds and pockets in which food can be transported. Due to the numerous folds, the fur is significantly larger than that of animals of comparable size. The picture under " Use as a fur animal " gives an approximate impression of the size of the fur.
Grooming takes a lot of time with this species. The animals can often be seen "scratching" themselves. However, this behavior is used for grooming. Front and rear paws are also licked for cleaning. Older animals have a paler coat on the head, neck and shoulders than on the rest of the body.
distribution
Sea otters live on the coasts of the Bering Sea in Alaska , the Aleutian Islands and the Commander Islands ; smaller stocks also on the Canadian and Californian Pacific coasts. Originally the sea otter was distributed from northern Japan over the entire north Pacific coast to Mexico (Baja California). Heavy hunting has reduced the range, but the populations are now recovering thanks to protective measures. The southern limit of the original distribution area coincided approximately with the southern limit of the upflow of cold deep water on the American west coast. Only here do the large kelp forests occur, in which the otter particularly likes to stay.
Today the sea otter has completely disappeared from the Baja California peninsula and thus from the Mexican coasts. It is still present in California, but is absent from Oregon and Washington , where resettlements have not been successful either. From the Canadian Pacific coast the distribution area extends over Alaska, the Aleutian Islands to Siberia. Originally it was also located on the north coast of Hokkaidō ( Japan ). Since the species has been protected, it has been spreading again and again.
To the north, the range is apparently limited by the boundary of the drift ice. The northernmost secured occurrence of obviously drifted sea otters was found in the East Siberian Sea at 70 degrees north.
habitat
Sea otters spend most of their lives in the water. They do not leave the coastal waters and are almost always close to land. They prefer rocky stretches of coast.
Sea otters are a typical species of the great kelp forests of the American Pacific coast, where they often go for food. Swimming animals can be seen particularly frequently in large stocks of seaweed.
nutrition
General
The metabolism of the sea otter is about three times higher than that of land mammals. This adaptation allows him to maintain his internal body temperature of 38 ° C, but on the other hand is forced to consume very large amounts of high-calorie food. The main part of its diet consists of sea urchins , and starfish are not spurned, as well as mussels , various types of sea snails, for example limpets , beetle snails and abalones , and more rarely slow-swimming fish . Well over 70 percent of the diet consists of sea urchins as long as a population is small. But if the population on a stretch of coast approaches a maximum, the food is much more diverse. However, individual otters develop individual preferences and specialize in up to three different prey animals.
Some males also appear to have focused on hunting waterfowl (e.g. red divers or spectacled ducks ), which attack them from below while the birds are resting on the surface.
Tool use
The hard shells of the preferred prey are opened with stones that are used as tools . To do this, the otter swims on its back, lays a stone as an anvil on its chest and hits the prey on it; conversely, he sometimes lays the prey on his chest and smashes it with the stone. The fur that is not tightly attached to the chest and forms folds and pockets prevents self-harm. The otter also uses stones, for example, to break loose clams on the ocean floor. The use of tools in animals is otherwise known only by very few species (e.g. chimpanzees and corvids ). Besides stones, other objects are also used by sea otters. Animals have already been observed breaking shellfish on glass bottles.
To prevent captured crabs from running away while other prey is being eaten, sea otters can tie up these animals: They wrap crabs with strands of seaweed .
Ecological role
On the American west coast it has been observed that the otters do a lot to protect the kelp forests , as they feed on herbivorous sea urchins to a large extent . The influence of the otters varies greatly from region to region, but is comparatively easy to determine because the animals are now repopulating several areas where they were exterminated during the fur hunt (see below).
Special
The ability of the sea otter to drink seawater unharmed is interesting. Its special, relatively large kidneys can excrete the excess salt again.
Way of life
Reproduction
Mating also takes place in the water, in the belly-to-belly position, which is very rare for mammals, in which the animals literally hug each other. Mating can take up to 35 minutes. Marten style is pretty rough: mated females often have wounds on their noses. This behavior helps the male to hold onto the slippery, damp peritoneum of the female better. The severity of the injuries varies greatly from male to male.
Mating can take place all year round, but a large number of mating occur in summer and fall. It has been observed that females become ready to mate when they have just left or lost a young.
Sea otters do not make permanent pairs. Males and females stay together for a maximum of a few days. During this time, however, they maintain very close contact by eating, playing, grooming and mating together. Such pairs break up when the female becomes pregnant. Through this pair bond with very intensive contact, the male ensures that his genes are passed on.
Males become sexually mature at five and females at three to five years. Older, stronger males claim territories within the quiet zones of the females, which they guard and in which they only tolerate other sexually mature males “in transit”. If there are temporarily only a few females ready to mate in a territory, they will leave the territory, but the males prove to be true to their location and return here.
After a gestation period of around six to nine months, the females only give birth to one young per litter that weighs around 1.8 kilograms. The gestation period is variable, as they, typical for marten-like, have a dormancy of different lengths. The birth usually takes place in the water, but it is also possible on land. Twin births have been observed in the sea otter, but it is extremely unlikely that both cubs will survive.
Regional differences can be observed in the number of cubs per year and female - as well as in the time that the cubs stay with their mother. The latter is usually longer in Alaska than in California. In Alaska, a female often gives birth to a cub only every two years. The reasons for this are still unclear.
The young is suckled by the mother swimming on her back in the water while the mother tends the fur. Older young animals, on the other hand, also lie in the water and drink while they drift at right angles to the mother. Similar to whales and seals, the milk of the sea otter is very high in fat. From around the second month of life, the boy, who does not swim actively at birth, but can drift in his downy natal fur, begins to dive and learn from the mother to look for food. Nevertheless, it only becomes independent from its mother after six to eight months.
Special
Sea otters sleep in the water and wrap themselves with seaweed beforehand to prevent them from being driven off. In this way, dams also protect their young if they have to leave them on the surface of the water during a dive.
Unlike most other species of marten, sea otters are not strictly solitary animals. Large groups often gather both in the kelp forests off the coast and on the rocks to rest. A group of sea otters is called raft , which means something like raft . As already mentioned under "Reproduction", the resting areas of the sea otters are often separated into males and females, whereby the resting areas of the males are often smaller and accordingly more densely populated. In the rest areas of the females, the males claim territories in which they mate with the corresponding females.
At least 19 cases have been documented in which male sea otters forced juvenile female seals to copulate, some with fatal results.
Sea otters and humans
Use as a fur animal
The sea otter fur is the thickest and finest fur of all fur types. In addition to the fine, soft hair, the durability of the fur is remarkable, which was very popular as a coat trim , especially among Chinese and Russian dignitaries . In 1741 the otters were discovered during the Kamchatka expedition Vitus Berings , who also brought the first pelts with him. This new source of income was very welcome to the Russian state, especially since the sable had already been decimated by the strong stalking. As a result, fur hunters settled in eastern Siberia. Until the population collapsed, the sea otter played a role that should not be underestimated as an economic factor in the North Pacific region; some areas were first settled because of the sea otter hunt.
Although Russia took first steps to protect otters as early as 1799, the populations continued to decline. Not least because of this, Alaska, for which sea otter skins were an important economic factor, was sold to the USA with the Alaska Purchase in 1867. This made the protective measures of 1799 ineffective. It is estimated that over 800,000 sea otters had been killed in Alaska by the end of the hunt. A good coat sold for $ 1,100 in London in 1903.
By 1910 the sea otter was almost extinct; only small remnants remained. With a few exceptions, trade in sea otter skins has been banned since 1911.
Protection of the sea otter
1911 included Japan, Russia , the United States and Great Britain (at that time as a colonial power in Canada) called the Fur Seal Treaty , which is also the high risk equally by the fur hunt beside the sea otter fur seals should be protected. Since then the stocks have increased again. From around 1,000 sea otters in 1910, the population has grown again to around 107,000 animals today. At the end of the 1960s, a few thousand more animals were killed in Alaska - mainly at the instigation of fishermen, who still see the otters as competitors. In Alaska, the populations are still increasing today.
The California sea otter has long been considered extinct. Although 32 otters were observed again near Point Sur in 1915, the discovery was kept secret. It was not until 1938, when the Pacific Coast Highway between Monterey and San Simeon was opened , that a small population of the famous Bixby Creek Bridge became known to the public. Today around 3000 animals live in California again.
Today's perception
Today the sea otter is considered cute and lovable. He is the model for plush toys, T-shirts, postcards and photos. Drawings of sea otters floating on their backs in the water decorate illustrated books, greeting and greeting cards. The fact that sea otters lying on their backs often lift their front paws in such a way that the impression is created that they are “waving” plays a not insignificant role here. The California sea otters are now a tourist attraction on Monterey Bay and are mentioned in numerous brochures and travel reports. Representations of sea otters of all kinds are common souvenirs on the California Pacific coast.
Sea otters are extremely trusting towards humans, which was often their undoing during the "great hunt" before 1911. In Monterey, the otters swim far into the harbor and even search for food between the sailboats.
Today's threat
The recurring oil spill is a major threat to sea otters. By the Exxon Valdez triggered oil spill 1989 killed about 5,000 sea otters. The oil sticks the fur and makes it permeable to water. When trying to cleanse, the body also absorbs the poisonous oil. The otters also damage environmental toxins such as PCBs , which are highly enriched in the high-fat animals that make up their diet. This leads to a degeneration of the brain, especially in adult animals, so that the animals unlearn how to hunt and use their tools and starve to death. If the animals concerned raise young, they suffer the same fate. To alleviate the consequences of this mortality, orphaned otter pups were raised in a specialty section of the Monterey Bay Aquarium. These activities have since been discontinued because the "whole species" and not individual animals would be the focus of efforts to preserve the species.
Now that sea otters are fairly effectively protected, the killer whale is the enemy to which most otters fall prey. Usually he hunts seals ; However, since their stocks have also decreased due to the lack of fish, it now also feeds on smaller martens. Great white sharks also occasionally prey on sea otters. Occasionally there is also the illegal killing of individual sea otters.
Algal blooms are also a major threat . Toxins from certain diatoms accumulate in the shellfish that the otter eats. While they themselves do not mind its prey, the sea otter falls ill or dies from poisons. Another danger is Toxoplasma gondii , a unicellular parasite that causes severe brain damage in marine mammals, while it is mostly harmless to terrestrial mammals. The corresponding germs get into the sea through faeces in particular. For this reason, in California, for example, there is a very intensive call to not dispose of cat feces in the toilet.
In the winter of 2006/2007, many sea otters starved to death in western Alaska because large areas of their feeding grounds, the sea coasts, were frozen over. The weak, starved animals migrated for miles into the tundra in search of food , where they were easy prey for wolves. In addition, many of them were slaughtered by the native Aleutians for their fur . The natives of North America are still allowed to subsistence hunting for sea otters.
Keeping in captivity
Outside of their home, sea otters are rarely found in zoos. A group of sea otters is one of the great attractions of the Monterey Bay Aquarium in California. The Aquarium of the Pacific in Long Beach and the zoo in Vancouver , Canada also show sea otters, as do other zoos and aquariums in the United States. In Europe they were shown at Antwerp Zoo and Rotterdam Zoo, and they can currently be found in the Ozeaneum in Lisbon . Young animals have already been born and raised in Lisbon. The sea otters "Mojoe" and "Agnes" live in the Danish National Aquarium Den Blå Planet in Copenhagen .
According to the Antwerp Zoo, zoo animals are fed fish fillets , shellfish, crabs and squid. Feeding closed clams creates problems as the otters quickly learn to hit them against panes of glass to open them. The closed mussels are therefore fed in the stables of the animals. However, it has already been observed that the otters hid clams in their fur pockets and took them into the viewing tank.
Systematics
External system
The sea otter is so different from other otters that it has long been accorded an exclusive special position. This went so far that a closer relationship to the dog seals was assumed. It has often been customary to separate it from the other otters in its own tribe Enhydrini. According to the morphological analyzes by Berta and Morgan, the sea otter, together with the fossil genera Enhydritherium and Enhydriodon, form a clade that is a sister group to all other otters . Koepfli and Wayne came to a different conclusion after molecular genetic analyzes of the mitochondrial cytochrome b gene of nine species of otter. According to their results, the sea otter split off only after the giant otter and the new world otter branched off . Thus the sea otter is more closely related to the ancient otters. The age of the branch leading to the sea otter is estimated to be 13 million years. Its position in the cladogram is therefore as follows:
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Subspecies
Nothing is known about the original subspecies before the “great hunt”. Three subspecies can be distinguished within the remaining and now regained stocks:
- The Asian sea otter ( Enhydra lutris gracilis) lives on the Kuriles , on the coast of Kamchatka and on the commanders' islands . It is considered the smallest subspecies.
- The Alaska sea otter ( E. l. Lutris ) lives on the coasts of Alaska and the Aleutian Islands. It is the most numerous subspecies today, some of which have also been reintroduced on the coast of British Columbia and southern Alaska. Alaskan sea otters feed comparatively often on bottom-dwelling fish and come to rest on land more often than the other subspecies. The naming of the Asian and the Alaskan subspecies is controversial among zoologists.
- The Californian sea otter ( E. l. Nereis ) has long been native to the entire US west coast as far as Baja California . Already believed to be extinct, fewer than 100 animals were rediscovered near Carmel in 1938 (see above). Even when the populations recover, this subspecies is still considered the rarest. Although the otters continue to spread along the California coast, the number of animals is hardly increasing. In addition to environmental pollution, increasing hunting pressure from killer whales is discussed as a reason. The Californian otters eat fish much less frequently than their Alaska relatives and are more inclined to use tools. They also come ashore less often.
literature
- Ronald M. Nowak: Walker's Mammals of the World . 6th edition. Johns Hopkins University Press, Baltimore 1999, ISBN 0-8018-5789-9 (English).
- Marianne Riedman: Sea Otters . Monterey Bay Aquarium Natural History Series, 1990
- JA Estes: Enhydra lutris . In: Mammalian Species . No. 133, 1980, pp. 1-8.
- B. Konar: Limited effects of a keystone species on community structure: long term trends at the Semichi Islands, Alaska. In: Marine Ecology Progress Series. No. 199, 2000, pp. 271-280.
Individual evidence
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↑ Unlike Dolphins, Sea Otters That Use Tools Are Not Closely Related. On: smithsonianmag.com of March 30, 2017
Why otters are the smartest craftsmen in the animal kingdom. On: stern.de from March 30, 2017 - ↑ Heather S. Harris et al. Lesions and Behavior Associated with Forced Copulation of Juvenile Pacific Harbor Seals (Phoca vitulina richardsi) by Southern Sea Otters (Enhydra lutris nereis) In: Aquatic Mammals 2010, 36 (4), 331-341, doi : 10.1578 / AM.36.4.2010.331
- ↑ Description of the sea otters on the website of the National Danish Aquarium Den Blå Planet [1]
- ↑ C. de Muizon: Les relations phylogenetiques des Lutrinae (Mustelidae, Mammalia) . In: Geobios 1982, No. 6, pp. 259-277
- ^ A. Berta, GS Morgan: A new sea otter (Carnivora: Mustelidae) from the late Miocene and early Pliocene (Hemphillian) of North America. In: Journal of Paleontology. No. 59, 1985, pp. 809-819
- ↑ KP Koepfli, RK Wayne: Phylogenetic relationships of otters (Carnivora: Mustelidae) based on mitochondrial cytochrome b sequences. In: Journal of Zoology. No. 246, 1998, pp. 401-416
Web links
- Photos and videos (French)
- Sea Otter Research Project (English)
- Enhydra lutris in the endangered Red List species the IUCN 2008. Posted by: A. Doroff, A. Burdin, 2008. Accessed January 6 of 2009.