|Otters (Lutrinae) are amphibious (or in one case aquatic) carnivorous mammals. The otter subfamily forms part of the family Mustelidae, which also includes weasels, polecats, badgers, as well as others. With 13 species in 7 genera, otters have an almost worldwide distribution.
An otter's den is called a holt. Male otters are dog-otters, females are bitches and babies are cubs. The collective noun romp is sometimes used for a group of otters, being descriptive of their often playful nature. Otter dung is called spraint (or sometimes scat as for other carnivores) - in the European otter at least this has a not unpleasant, perfume-like smell.
Otters have a very soft under fur which is protected by their outer layer of long guard hair. This keeps them dry under water and traps a layer of air to keep them warm.
All otters have long, slim bodies and short limbs. They have webbed paws. Most have sharp claws, and all but the sea otter have long muscular tails.
Diet and behavior
Otters do not depend on their specialized fur alone for survival in the cold waters where many live: they also have very high metabolic rates. For example Eurasian otters must eat 15% of their body weight a day, and sea otters, 20 to 25%, depending on the temperature. In water as warm as 10c. an otter needs to catch 100 g of fish per hour to survive. Most species hunt for 3 to 5 hours a day, and nursing mothers up to 8 hours a day.
Most otters have fish as the primary item in their diet, supplemented by frogs, crayfish and crabs. Some are expert at opening shellfish, and others will take any available small mammals or birds. This prey-dependence leaves otters very vulnerable to prey depletion.
Otters are very active, chasing prey in the water or searching the beds of rivers, lakes or the sea. Most species live beside water, entering it mainly to hunt or travel, otherwise spending much of their time on land to avoid their fur becoming waterlogged. The sea otter lives actually in the sea.
Otters are playful animals, for example sliding repeatedly down snowy slopes, apparently from sheer enjoyment. Different species vary in their social structure, with some being largely solitary, while others live in groups - in a few species these groups may be fairly large.
Origin of name
The word otter derives from the Old English word otr, otor or oter. This and cognate words in other Indo-European languages ultimately stem from a root which also gave rise to the English words "water", "wet" and "winter".
Northern River Otter
The Northern River Otter, Lontra canadensis, is a North American member of the Mustelidae or weasel family. It is also known as the North American River Otter. It is a common animal in North American waterways. However, its numbers have significantly dropped since Europeans came to the Americas.
The Northern River Otter is a species of otter, or the family lutrinae. It is a member of the genus lontra, which is comprised of North American otters. It was previously included, with the other members of lontra, included in the genus lutra, but was placed in a newly-created genus when it was determined that the North American otters are more closely related to the genera Lutrogale and Pteronura than to the other species in Lutra.
The Northern River Otter has a streamlined, muscular body with short legs, webbed toes and a long muscular tail. The North American river otter’s body measure is somewhere between 25.98" to 42.13", and its tail measure is between 12.40" to 18.11";a river otter’s tail makes up 30 to 40% of the total length of its body. It can weigh between 6 and 31 pounds. The river otter has a round, small head, short yet powerful legs, and large whiskers. Otters display sexual dimorphism, as the male otter is often larger than the female. Its fur is glossy and dark brown fur, and the throat is often silver grey. The otter is a powerful swimmer, but can also travel quickly on land and often propel itself into a rapid slide on its belly on snow or ice; it also likes to slide down river banks into the water. The North American River Otters has nostrils which close underwater and its fur is soft and dense; both of these adaptations help it to have extended excursions underwater.
On land, a Northern River Otter can run up to 18 miles per hour. Its life span is 10-15 years in the wild, but it may live up to 25 years in captivity.
The Sea otter or Kalan (Enhydra lutris) is a large otter native to the North Pacific, from northern Japan and Kamchatka east across the Aleutian Islands south to California. The heaviest of the otters, sea otters are the only species within the genus Enhydra.
Sea otters have been hunted extensively for their luxurious fur - the densest of all mammals with up to 394,000 hairs per square centimeter or up to 1,000,000 hairs per inch. From 1741 onwards, over-hunting reduced sea otter populations to the point of extermination in many parts of their historic range. The population is thought to have been 150,000 to 300,000 historically before the years of the great hunt. It is estimated that a half million to a million otters were killed over time. By 1911, the world population was estimated to be just 1,000-2,000 individuals in 13 colonies. Although several subspecies are still endangered, the otters have since been legally protected. Reintroduction efforts have shown positive results in some areas.
With long, streamlined bodies, sea otters are built for life at sea. They have exceptionally thick brown fur with densities of 26,000 to 165,000 hairs/cm2 to assist in retaining heat. Sea otters have sebaceous gland secretions of squalene, which are normally found only in minor concentrations in other mammals. This creates an effective barrier between the water and the skin and acts as a substitute for subcutaneous insulating fat, as the otters have only 1cm of it. Underneath each powerful front paw is a pouch of skin used to temporarily store food collected during extended dives to the bottom. The front paws also have retractable claws, while the hind flippers are long & broadly flattened and webbed. The fifth digit on the hind flipper is the longest, unlike that of any other mammal and this makes walking on land difficult. Sea otters have a fairly short, thick, muscular tail. They have no scent glands.
They have specially adapted spinal columns and bone structures to allow great flexibility. Sometimes the bones will be dyed pale violet from eating purple sea urchins and absorbing polyhydroxynaphthoquinone. They have 38 chromosomes. Sea otters have large lung capacity compared to pinnipeds: 2 to 4 times greater in size. Sea otters store 66% of their oxygen in their lungs, so the large lungs are well suited for their brief shallow dives. This also helps with buoyancy.
Sea otters have a highly unique eye development for mammals, leading to an accommodation at least 3 times greater than any other mammal. This enables them to see clearly and focus on objects above and below water. They are roughly emmetropic in both conditions.
Sea otters have compact molars with smooth cusps; they are the only carnivore with no more than four lower incisors. Male sea otters may reach a maximum weight of 45 kilograms (nearly 100 pounds) and a length of up to 1.5 meters (nearly 5 feet). Females are smaller. Males are generally 35% heavier and 8% longer and have heavier heads and necks.
In the wild the sea otters live about 15-20 years, and can live longer than 20 years in captivity.
This sub-species (Lutrogale perspicillata maxwelli) of the Smooth-coated Otter was the subject of the book Ring of Bright Water by the British naturalist Gavin Maxwell, and is named after him. It is native to the Tigris-Euphrates alluvial salt marsh of Iraq, but it has been suggested that it may have become extinct as a result of the large-scale drainage that has taken place in the region since the 1960s.
The European Otter, Lutra lutra, also known as the Eurasian River Otter, Common Otter, and Old World Otter, is a European member of the Mustelidae or weasel family, and is typical of freshwater otters. For the rest of this article 'otter' will refer specifically to the European otter, although the information may be applicable to other otter species.
The European otter is the most widely distributed otter species, the name being something of a misnomer, as its range includes parts of Asia and Africa as well as being spread across Europe. The otter is believed to be extinct in Liechtenstein, the Netherlands, and Switzerland. Otters are now very common along the coast of Norway and in Northern Britain, especially Shetland where 12% of the UK breeding population exist. In Italy, they can be found in the Calore river area.
An otter's diet mainly consists of fish but can also include birds, insects, frogs, crustaceans and sometimes small mammals. In general this opportunism means they may inhabit any unpolluted body of freshwater, including lakes, streams, rivers, and ponds, as long as there is good supply of food. Otters may also live along the coast, in salt water, but require regular access to freshwater to clean their fur.
The Giant Otter, Pteronura brasiliensis, (also known as the river wolf) is the longest of the world's otters, as well as the largest mustelid. It is native to South America but is endangered and is also very rare in captivity. A group of giant otters is called a romp, a bevy, a family, or a raft.
The Giant Otter can reach up to 6 ft (1.8 m) in length, and weigh up to 76 lb (34 kg) The females are smaller and weigh only 57-60 lb (26-27 kg). It has a lifespan of 12 years in their natural habitat, and 21 years in captivity. Its fur is dense, thick and velvety, and is highly sought after by fur traders. The guard hairs are short, 5/16 in (8 mm) long, twice as long as the under-fur. The fur is water repellent and is a deep chocolate brown in color. A unique white mark is located on the throat that can be used to distinguish between individuals. The head is round and the ears are small. The nose is completely covered in fur, with only the two slit-like nostrils visible. The eyes are large and they have acute vision, an adaptation for hunting underwater. The legs are short and stubby and end in large webbed feet tipped with sharp claws. The Giant Otter is well suited for an aquatic life, and can close its ears while underwater. Giant Otters can also close their nostrils when they swim under water.
African Clawless Otter
The African Clawless Otter, Aonyx capensis, also known as the Cape Clawless Otter or Groot otter, is the second largest freshwater species of otter. African Clawless Otters are found near permanent bodies of water in savannah and lowland forest areas. They are characterized by partly webbed and clawless feet, from which their name is derived.
Aonyx capensis is a member of the weasel family (Mustelidae) and of the Order Carnivora. The earliest known species of otter, Potamotherium valetoni, occurred in the upper Oligocene of Europe, but A. capensis is first recorded in the Pleistocene.
African Clawless Otters have thick, smooth fur with an almost silky underbelly. Chestnut in color, they are characterized by white facial markings that extend downward towards their throat and chest area. Paws are partially webbed with five fingers, and no opposable thumbs. All lack claws except for digits 2, 3, and 4 of the hind feet. Their large skull is broad and flat, with relatively small orbits and a short rostrum. Molars are large and flat, used for crushing of prey.
African clawless otters can be found anywhere from open coastal plains, to semiarid regions, to densely forested areas. Surviving mostly in southern Africa, the otters live in areas surrounding permanent bodies of water, usually surrounded by some form of foliage. Logs, branches, and loose foliage greatly appeal to the otter as this provides shelter, shade and great rolling opportunities. Slow and rather clumsy on land, they build burrows in banks near water, allowing for easier food access and a quick escape from predators.
The Speckle-throated Otter (Hydrictis maculicollis syn. Lutra maculicollis) is an otter native to sub-Saharan Africa. It is also called the Spotted-necked Otter. It is about a meter long and weighs about six kilograms. Like other otters it is sleek and has webbed paws for swimming. Its fur is deep brown and marked with light spots around its throat.
The Speckle-throated Otter hunts for fish and crustaceans in rivers and lakes. A visual hunter, it stays in clear water with good visibility. It is very vocal, uttering high, thin whistles. The female bears a litter of about three young in an underground burrow, and cares for them for almost a year. The otters are sometimes found in family groups. It is a clever animal, quite capable of using rocks to smash open shells. This rudimentary use of tools speaks volumes about the intelligence of the otter.
The Speckle-throated Otter is in decline, mostly due to habitat destruction and pollution of their clear-water habitats. They are hunted as bush meat.
- Genus Lutra
- European Otter (Lutra lutra)
- Hairy-nosed Otter (Lutra sumatrana)
- Spotted necked Otter (Lutra maculicollis)
- Lutra bravardi
- Lutra libyca
- Lutra palaeindica
- Lutra simplicidens
- Genus Hydrictis
- Speckle-throated Otter (Hydrictis maculicollis)
- Genus Lutrogale
- Smooth-coated Otter (Lutrogale perspicillata)
- Genus Lontra
- Northern River Otter (Lontra canadensis)
- Southern River Otter (Lontra provocax)
- Long-tailed Otter (Lontra longicaudis)
- Marine Otter (Lontra felina)
- Genus Pteronura
- Giant Otter (Pteronura brasiliensis)
- Genus Aonyx
- African Clawless Otter (Aonyx capensis)
- Congo Clawless Otter (Aonyx congicus)
- Oriental Small-clawed Otter (Aonyx cinereus)
- Genus Enhydra
- Sea Otter (Enhydra lutris)
- Kingdom: Animalia
- Phylum: Chordata
- Class: Mammalia
- Order: Carnivora
- Family: Mustelidae
- Subfamily: Lutrinae