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Otters

Diet

Play

Sea otter

River otters

Clawless otters

Giant otter

Human and otters

Resources

Otters are small to medium-sized mammals with a long body, flattened head, broad muzzle, and long stiff whiskers. Their tail is strong, long, flattened, and somewhat tapered. Otters have short legs and webbed toes; they are well adapted to a semi-aquatic existence and are skilled swimmers. The outer fur of otters is short, very dense, and highly water resistant. They also have a layer of soft underfur that traps an insulating layer of air and helps them stay warm when in the water. Otters are carnivores and have teeth adapted either to eating fish or to crushing the shells of crustaceans, depending on the diet of the species. The ears of otters are small and can close when swimming (with the help of special muscles), while their hearing is good. Their eyes are small but their sight is good due

to special lenses that help them see clearly underwater. Male otters are about 28% larger than females.

Otters are members of the weasel family, Mustelidae. There are five subfamilies within this family: weasels, minks, and polecats (Mustelinae); skunks (Mephitinae); badgers (Melinae); honey badgers (Mellivorinae); and otters (Lutrinae). The Lutrinae subfamily includes six genera: sea otters, river otters, clawless otters, giant otters, and two genera of small-clawed otters. There are 18 species, with about 63 subspecies (depending on the taxonomic treatment).

Diet

Otters can be separated into two groups on the basis of their diet. The first group, which includes river otters and giant otters, specializes in eating fish. These species have sharp teeth that are useful in catching and gripping their slippery prey. The second group, which includes the small clawed otters and sea otters, specializes in eating invertebrates such as shellfish. These otters have blunted teeth useful in breaking shells. However, otters are highly adaptive, and neither group solely eats just one type of prey.

Play

Otters are extremely playful. Anyone who visits a zoo can see otters sliding down embankments and flipping about in the water. Otters typically twist and turn as they swim, sometimes on their back and sometimes on their side. Having seemingly unlimited energy, otters often slide down muddy banks over and over again with no apparent motive other than sheer enjoyment.

There is some disagreement about how much time otters spend in play in the wild. Some think that play in the wild is limited to teaching the young the fighting and hunting skills they will need to survive, and that sliding activity is simply a way for otters to move quickly. Others think otters play extensively in the wild for pure enjoyment as well as for more practical reasons.

Sea otter

The sea otter (Enhydra lutris ) measures up to 4 ft (1.3 m) long with a 12 in (30.5 cm) tail. Sea otters are common on rocky coastlines and islands on both sides of the North Pacific Ocean, from Japan north to the Aleutian Islands and south to the coast of California. Sea otters spend almost all of their lives at sea and are the only mustelids able to do so. While they are in the water, they usually lie on their back, grooming themselves, feeding their young, resting, or eating. Sea otters come to land only to breed or when the weather is bad, for while they are skilled swimmers, they are slow and clumsy on land. When sea otters swim, they use their tail and hind feet, tucking their front feet under their chest. Their webbed hind feet, resembling those of sea lions, are much bigger than the hind feet of other otters. The tail is shorter than that of other otters, as are the fingers, which have small, rectractile claws.

The thick reddish to black fur, which is soft and silky in texture, serves to insulate sea otters from the cool water. Sea otters do not have an excess layer of fat for insulation, like many other aquatic mammals. They rely on a layer of air in their fur to protect them from the cold, and they keep their fur aerated by rubbing it with their feet to squeeze the water out. They contort themselves and wriggle around until the fur on even the most hard-to-reach parts of their body is aerated. Also, sea otters tend to blow on their coats to increase the amount of trapped air.

Sea otters feed on clams, mussels, and other crustaceans. To break open these hard shells, they use rocks, which they bring up from the sea bed, as tools. As a sea otter lies on its back, it places the stone on its chest and beats the prey against it, thereby cracking the shell and exposing the meat inside. At twilight, sea otters move into kelp beds to sleep, tangling themselves in the vegetation so that they do not drift out to sea.

Sea otters breed every two years. The female gives birth to one pup after a gestation period of eight to nine months. The newborn pup is well developed, having all of its teeth and open eyes. The mother carries and nurses her offspring on her stomach while swimming on her back.

Sea otters were once relentlessly hunted for their dense, lustrous pelage, and were taken to the brink of extinction. In fact, it was considered extinct until the 1930s, when remnant populations were discovered in the Aleutian Islands and off the coast of northern California. These animals were protected, and the sea otter has since increased greatly in abundance and has repopulated much of its original range. Their total population now exceeds 100,000 animals.

River otters

There are 11 species of river otter, including the Eurasian river otter (Lutra lutra ), the North American river otter (Lutra canadensis ), the southern river otter (Lutra provocax ), and the smooth otter (Lutra perspicillata ). Often confused with European mink, the river otter is heavier, with a broader face and a tail that is stout at the base, becoming flatter and more tapered toward the end. River otters are most prevalent in Eurasia and North America, although a few species are found in Central and South America, as well as in limited areas of Africa and Southeast Asia.

River otters usually live near rivers, although some species live near flooded areas, lakes, brackish water, and on coastal islands. When the food supply runs low, river otters will move away from their native waters to hunt. They prefer to move via water but will travel on land if they must. These otters usually hunt at night, staying underwater for up to eight minutes at a time. Normally, the adults hunt alone, but mothers will hunt with their young for a significant period of time after they are born. Traveling long distances during a single nights hunt, they conceal themselves in the day in reeds and other vegetation before hunting again the next night. In a few days, these otters return to their home waters. During the winter, river otters slip through cracks in ice to hunt, sometimes surfacing through the hole to breathe. River otters eat fish, muskrats, and aquatic birds.

The female river otters give birth to their young in burrows between April and June. Born with their eyes closed, the young nurse for about four months, opening their eyes about one month after birth. They grow to adult size in two years.

Grooming is very important to river otters. However, unlike many other mammals, river otters do not nibble their coats looking for insects. Instead, like sea otters, they tend to groom themselves with the goal of drying out their fur to keep it waterproof. They do this by rolling and squirming on dry land or rubbing against trees.

Clawless otters

There are three species of clawless otter in the genus Aonyx two are found in Africa and one in Asia. Otters in this genus differ from river otters and the giant otter in having much smaller claws and in having webbing on their feet that is either absent or does not extend to the ends of their toes. The Asian small-clawed otter (Aonyx cinereus ) is the worlds smallest otter, measuring just 26-36 in (65-90 cm) and weighing about 11 lb (5 kg). This species lives in small streams, rice paddies, and coastal mangrove swamps from the Philippines through Indonesia, Southeast Asia, and southern China westward to southern India. It is a social animal, and lives in groups of up to 15 individuals. Its diet consists primarily of fish, mollusks, and crabs.

Two other species of clawless otter are found in Africa. These are the Cape clawless otter (Aonyx capensis ) and the Congo clawless otter (A. congica ). The Cape clawless otter of sub-Saharan Africa lives in swamps, rivers, streams, estuaries, and lakes. This species has no webbing on its forefeet, enabling it to use its fingers freely to probe mud and gravel for prey. Its diet includes crabs, mollusks, frogs, and fish. The head and body of the Cape clawless otter measures 28-36 in (72-91 cm) and its tail is 16-28 in (40-71 cm) long. The male is larger than the female.

The Congo clawless otter, found in west and central equatorial Africa, is not as well known as the closely related Cape clawless otter. It is similar in size and color, but is distinguished by silver tips on the fur of the head and neck, and by dark patches of fur between the eyes and nostrils. Of all the otters, this species is least adapted to an aquatic environment. It prefers swampy habitats such as marshes and lake margins, where it preys upon frogs, crabs, earthworms, and fish. The Congo clawless otter has shorter, thinner (less insulating) fur than other otters. Its forefeet are unwebbed, hairless, and clawlessall adaptations for searching for its food in mud, gravel, or other debris.

Giant otter

The giant otter (Pteronura brasiliensis ) of Brazil is the largest otter species. It measures up to 7 ft (2.1 m) long, including its tail, and can weigh more than 50 lb (23 kg). Like other otters, it has webbed hind feet and a large flat tail suited for swimming. Giant otters hunt in groups of 20 or more during the morning and at twilight. Having a diet similar to the river otter, giant otters consume their prey by holding it in their forepaws and consuming it head first. These otters live in dens dug in riverbanks, and have one or two offspring each year.

Human and otters

Otters have been hunted by humans for centuries for their soft, thick fur and because they have been viewed as competitors for fish. Trade in otter fur was once very active, but the hunting of otters for their fur has declined in recent years, due both to the decline in otter populations (especially species of river otter) and the passage of laws protecting otters. The best otter pelts are reportedly from the North American river otter, specifically from otters living in Labrador.

Otters, being fairly intelligent animals, have occasionally been trained. Otters catch and retrieve fish in Sweden and China, and in India, tame, muzzled otters have been used to drive fish into nets.

Resources

BOOKS

Chanin, Paul. The Natural History of Otters. New York: Facts on File Publications, 1985.

The Illustrated Encyclopedia of Wildlife. London: Grey Castle Press, 1991.

Kruuk, Hans. Otters: Ecology, Behaviour and Conservation. New York: Oxford University Press, 2006.

Macmillan Illustrated Animal Encyclopedia. New York: Macmillan, 1992.

Mason, C.F., and S.M. Macdonald. Otters: Ecology and Conservation. London: Cambridge University Press, 1986.

Nowak, Ronald M. Walkers Mammals of the World. 6th ed. Baltimore: The Johns Hopkins University Press, 1999.

Kathryn Snavely

views updated

Otters

Otters are small to medium-sized mammals with a long body, flattened head, broad muzzle, and long stiff whiskers. Their tail is strong, long, flattened, and somewhat tapered. Otters have short legs and webbed toes; they are well adapted to a semi-aquatic existence and are skilled swimmers. The outer fur of otters is short, very dense, and highly water resistant. They also have a layer of soft underfur that traps an insulating layer of air and helps them stay warm when in the water. Otters are carnivores and have teeth adapted either to eating fish or to crushing the shells of crustaceans, depending on the diet of the species . The ears of otters are small and can close when swimming (with the help of special muscles), while their hearing is good. Their eyes are small but their sight is good due to special lenses that help them see clearly underwater. Male otters are about 28% larger than females.

Otters are members of the weasel family, Mustelidae. There are five subfamilies within this family: weasels , minks, and polecats (Mustelinae); skunks (Mephitinae); badgers (Melinae); honey badgers (Mellivorinae); and otters (Lutrinae). The Lutrinae subfamily includes six genera: sea otters, river otters, clawless otters, giant otters, and two genera of small-clawed otters. There are 18 species, with about 63 subspecies (depending on the taxonomic treatment).


Diet

Otters can be separated into two groups on the basis of their diet. The first group, which includes river otters and giant otters, specializes in eating fish. These species have sharp teeth that are useful in catching and gripping their slippery prey . The second group, which includes the small clawed otters and sea otters, specializes in eating invertebrates such as shellfish. These otters have blunted teeth useful in breaking shells. However, otters are highly adaptive, and neither group solely eats just one type of prey.


Play

Otters are extremely playful. Anyone who visits a zoo can see otters sliding down embankments and flipping about in the water. Otters typically twist and turn as they swim, sometimes on their back and sometimes on their side. Having seemingly unlimited energy, otters often slide down muddy banks over and over again with no apparent motive other than sheer enjoyment.

There is some disagreement about how much time otters spend in play in the wild. Some think that play in the wild is limited to teaching the young the fighting and hunting skills they will need to survive, and that sliding activity is simply a way for otters to move quickly. Others think otters play extensively in the wild for pure enjoyment as well as for more practical reasons.


Sea otter

The sea otter (Enhydra lutris) measures up to 4 ft (1.3 m) long with a 12 in (30.5 cm) tail. Sea otters are common on rocky coastlines and islands on both sides of the North Pacific Ocean, from Japan north to the Aleutian Islands and south to the coast of California.

Sea otters spend almost all of their lives at sea and are the only mustelids able to do so. While they are in the water, they usually lie on their back, grooming themselves, feeding their young, resting, or eating. Sea otters come to land only to breed or when the weather is bad, for while they are skilled swimmers, they are slow and clumsy on land. When sea otters swim, they use their tail and hind feet, tucking their front feet under their chest. Their webbed hind feet, resembling those of sea lions , are much bigger than the hind feet of other otters. The tail is shorter than that of other otters, as are the fingers, which have small, rectractile claws.

The thick reddish to black fur, which is soft and silky in texture, serves to insulate sea otters from the cool water. Sea otters do not have an excess layer of fat for insulation, like many other aquatic mammals. They rely on a layer of air in their fur to protect them from the cold, and they keep their fur aerated by rubbing it with their feet to squeeze the water out. They contort themselves and wriggle around until the fur on even the most hard-to-reach parts of their body is aerated. Also, sea otters tend to blow on their coats to increase the amount of trapped air.

Sea otters feed on clams, mussels, and other crustaceans. To break open these hard shells, they use rocks , which they bring up from the sea bed, as tools. As a sea otter lies on its back, it places the stone on its chest and beats the prey against it, thereby cracking the shell and exposing the meat inside. At twilight, sea otters move into kelp beds to sleep , tangling themselves in the vegetation so that they do not drift out to sea.

Sea otters breed every two years. The female bears one pup after a gestation period of eight to nine months. The newborn pup is well developed, having all of its teeth and open eyes. The mother carries and nurses her offspring on her stomach while swimming on her back.

Sea otters were once relentlessly hunted for their dense, lustrous pelage, and were taken to the brink of extinction . In fact, it was considered extinct until the 1930s, when remnant populations were discovered in the Aleutian Islands and off the coast of northern California. These animals were protected, and the sea otter has since increased greatly in abundance and has repopulated much of its original range. Their total population now exceeds 100,000 animals.


River otters

There are 11 species of river otter, including the Eurasian river otter (Lutra lutra), the North American
river otter (Lutra canadensis), the southern river otter (Lutra provocax), and the smooth otter (Lutra perspicillata). Often confused with European mink , the river otter is heavier, with a broader face and a tail that is stout at the base, becoming flatter and more tapered toward the end. River otters are most prevalent in Eurasia and North America , although a few species are found in Central and South America , as well as in limited areas of Africa and Southeast Asia .

River otters usually live near rivers , although some species live near flooded areas, lakes, brackish water, and on coastal islands. When the food supply runs low, river otters will move away from their native waters to hunt. They prefer to move via water but will travel on land if they must. These otters usually hunt at night, staying underwater for up to eight minutes at a time. Normally, the adults hunt alone, but mothers will hunt with their young for a significant period of time after they are born. Traveling long distances during a single night's hunt, they conceal themselves in the day in reeds and other vegetation before hunting again the next night. In a few days, these otters return to their home waters. During the winter, river otters slip through cracks in ice to hunt, sometimes surfacing through the hole to breathe. River otters eat fish, muskrats, and aquatic birds .

The female river otters bear its young in a burrow between April and June. Born with their eyes closed, the young nurse for about four months, opening their eyes about one month after birth . They grow to adult size in two years.

Grooming is very important to river otters. However, unlike many other mammals, river otters do not nibble their coats looking for insects . Instead, like sea otters, they tend to groom themselves with the goal of drying out their fur to keep it waterproof. They do this by rolling and squirming on dry land or rubbing against trees.


Clawless otters

There are three species of clawless otter in the genus Aonyx—two are found in Africa and one in Asia. Otters in this genus differ from river otters and the giant otter in having much smaller claws and in having webbing on their feet that is either absent or does not extend to the ends of their toes. The Asian small-clawed otter (Aonyx cinerea) is the world's smallest otter, measuring just 26-36 in (65-90 cm) and weighing about 11 lb (5 kg). This species lives in small streams, rice paddies, and coastal mangrove swamps from the Philippines through Indonesia, southeast Asia, and southern China westward to southern India. It is a social animal , and lives in groups of up to 15 individuals. Its diet consists primarily of fish, molluscs, and crabs .

Two other species of clawless otter are found in Africa. These are the Cape clawless otter (Aonyx capensis) and the Congo clawless otter (A. congica). The Cape clawless otter of sub-Saharan Africa lives in swamps, rivers, streams, estuaries, and lakes. This species has no webbing on its forefeet, enabling it to use its fingers freely to probe mud and gravel for prey. Its diet includes crabs, molluscs, frogs , and fish. The head and body of the Cape clawless otter measures 28-36 in (72-91 cm) and its tail is 16-28 in (40-71 cm) long. The male is larger than the female.

The Congo clawless otter, found in west and central equatorial Africa, is not as well known as the closely related Cape clawless otter. It is similar in size and color , but is distinguished by silver tips on the fur of the head and neck, and by dark patches of fur between the eyes and nostrils. Of all the otters, this species is least adapted to an aquatic environment. It prefers swampy habitats such as marshes and lake margins, where it preys upon frogs, crabs, earthworms, and fish. The Congo clawless otter has shorter, thinner (less insulating) fur than other otters. Its forefeet are unwebbed, hairless, and clawless—all adaptations for searching for its food in mud, gravel, or other debris.


Giant otter

The giant otter (Pteronura brasiliensis) of Brazil is the largest otter species. It measures up to 7 ft (2.1 m) long, including its tail, and can weigh more than 50 lb (23 kg). Like other otters, it has webbed hind feet and a large flat tail suited for swimming. Giant otters hunt in groups of 20 or more during the morning and at twilight. Having a diet similar to the river otter, giant otters consume their prey by holding it in their forepaws and consuming it head first. These otters live in dens dug in riverbanks, and have one or two offspring each year.


Human impact on otters

Otters have been hunted by humans for centuries for their soft, thick fur and because they have been viewed as competitors for fish. Trade in otter fur was once very active, but the hunting of otters for their fur has declined in recent years, due both to the decline in otter populations (especially species of river otter) and the passage of laws protecting otters. The best otter pelts are reportedly from the North American river otter, specifically from otters living in Labrador.

Otters, being fairly intelligent animals, have occasionally been trained. Otters catch and retrieve fish in Sweden and China, and in India, tame, muzzled otters have been used to drive fish into nets.


Resources

books

chanin, paul. the natural history of otters. new york: facts on file publications, 1985.

grzimek, h.c. bernard, dr., ed. grzimek's animal life encyclopedia. new york: van nostrand reinhold company, 1993.

the illustrated encyclopedia of wildlife. london: grey castle press, 1991.

macmillan illustrated animal encyclopedia. new york: macmillan, 1992.

mason, c.f., and s.m. macdonald. otters: ecology and conservation. london: cambridge university press, 1986.


Kathryn Snavely

views updated

otterall-nighter, biter, blighter, fighter, igniter, inciter, indicter, inviter, lighter, mitre (US miter), overnighter, reciter, righter, sighter, smiter, writer •shyster • rhymester • backbiter •expediter • prizefighter • dogfighter •bullfighter • gunfighter • lamplighter •highlighter • downlighter •moonlighter • uplighter • firelighter •screenwriter • scriptwriter •copywriter • signwriter • typewriter •songwriter • ghostwriter •underwriter •blotter, cotta, cottar, dotter, gotta, hotter, jotter, knotter, otter, pelota, plotter, potter, ricotta, rotter, spotter, squatter, terracotta, totter, trotter •crofter •concocter, doctor, proctor •Volta • prompter • wanter •adopter, dioptre •Costa, coster, defroster, foster, Gloucester, impostor, paternoster, roster •lobster, mobster •oxter • monster • songster •witchdoctor • helicopter •teleprompter • globetrotter

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ot·ter / ˈätər/ • n. a fish-eating mammal (Lutra and other genera) of the weasel family, typically semiaquatic, with an elongated body, dense fur, and webbed feet. Its several species include the river otter (L. canadensis). See also sea otter.

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otter Semi-aquatic carnivore of the weasel family found everywhere except Australia. They have narrow, pointed heads with bristly whiskers, sleek furry bodies and short legs with webbed hind feet. They feed mainly on fish. The river otter (genus Lutra) is small to medium-sized. Family Mustelidae.

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otter OE. otr, ot(t)or = MLG., Du. otter, OHG. ottar (G. otter), ON. otr :- Gmc. *otraz :- IE. *udros. repr. by Skr. udrá-, Gr. húdros water-snake; rel. to WATER.

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otter otters are the emblem of St Cuthbert.

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otters See MUSTELIDAE.