IUCN Red List Status: Near threatened.
Size: male (dog): head and body up to 90cm (36 in); tail 40 cm (16in). Female (bitch) is smaller.
Life-span: uncertain - perhaps 9-10 years in the wild, but many die before they are 4 years old; have lived to be 20 in captivity.
Food: mainly fish - eels are a favourite; also frogs, birds, small mammals, crustaceans, aquatic insects.
Habitat: mainly the area around freshwater lakes, rivers, some coasts - as long as they are undisturbed and there is plenty of cover.
Distribution: the Eurasian otter exists in scattered populations in the British Isles, Europe, Scandinavia, most of Russia and North Africa. In the British Isles, they are found mainly on the coast of Scotland and Ireland, along the Welsh borders, the South-west and East Anglia.
Description: streamline, tapering body and tail, ideal for fast swimming. Brown with paler underparts. Short, strong legs and webbed feet. Small ears and broad flat head. Ears, eyes and nostrils are set on top of head to help surface swimming.
The otter is an appealing, playful animal but they can be very sensitive - it is an offense under the Wildlife & Countryside Act to disturb them or their habitat.
The Wildlife Trust has published a useful guide for spotting otters in the UK - but remember to tread quietly! Other places to see otters on the coast include Shetland, Skye and the Western Isles.
Territory: the otter is a shy, solitary animal and needs a large territory. One male has a territory of up to 40km of clean, undisturbed riverbank. It regularly patrols the territory, marking it here and there with droppings called 'spraints'. These have a scent which tells other otters that the territory is already occupied. Female otters also spraint to mark territory. Female otters with cubs live in holt which is often away from the riverbank and well hidden in a smaller territory within the male's territory, who is usually the cubs' father.
Daily Life: otters are mainly nocturnal and hunt in open, marshy places, rivers, lakes, seashores and estuaries. They will often travel a long way overland, from one river system to another, in search of food. However, the majority of the UK's otters are now found on our wilder coasts. They are strong, agile swimmers and catch fish by chasing them underwater. They grip the prey with sharp teeth and powerful jaws, carrying the catch ashore to eat it. An adult otter needs to eat 20 per cent of its body weight in food every day - about 2.5kg.
In undisturbed areas an otter often spends part of the day playing away from water, near to a 'lying up' den, which is usually under riverside tree roots.
An otter grooms itself frequently and this keeps its coat sleek and waterproof. The coat's long, stiff guard hairs are covered with oil to repel water. The thick underfur traps an insulating layer of air and the skin never gets wet.
Breeding: otters breed throughout the year. The dog and bitch live separate lives, meeting only for mating. Usually there are two or more females living in a male's territory and when they are receptive, he will mate with all of them. They find each other by scent and by whistling. The two often playfully chase each other and pretend to fight.
The gestation period is about 62 days and during this time the bitch builds a holt, an underground burrow, often under the roots of a waterside tree. In Scotland, where otters frequent seashores and lochs, the holt may be in a more open space such as a rocky cairn. The holt is lined with grass or moss and this is where a litter of two or three cubs is born. At birth they are about 12cm in length and are covered in very fine grey fur; their eyes open when they are four or five weeks old. The cubs are helpless for the first 6 weeks of their lives, relying entirely on their mother's milk. The mother drives the father away as soon as the cubs are born and he plays no part in their upbringing. Coastal otters need access to freshwater pools to wash the salt off their fur - otherwise this affects the insulation that the fur provides.
The cubs develop an adult waterproof coat at two or three months and this is when their mother teaches them to swim. To begin with they are often reluctant to go into the water and may have to be pushed in! An otter family is very playful and enjoys sliding games, using a steep snowy or muddy river bank to toboggan down on their chests, forepaws tucked in! The young soon become proficient underwater hunters and the family splits up when the cubs are about a year old. They may stay on in the mother's territory for a few more months and then leave to look for territories of their own.
Otters and Humans
Otters were once hunted for their fur and were thought of as a pest, competing with fishermen for fish. In spite of these pressures, otters were widespread throughout Britain and the population remained steady until the 1950s when it declined rapidly. Otter-hunting was banned in England and Wales in 1979 and in Scotland in 1982. They are now rare or absent from lowland areas of England such as the midlands and the south.
The main reasons for the dramatic reduction in the number of otters has been disturbance and pollution. Since the 1950s riverside habitats have been drastically changed by farming and building techniques in addition to clearing for drainage. In other words, riverbanks have become far too tidy for the secretive otter. Watersports have also added to the disturbance of waterways.
Pollution of freshwater habitats has probably had the greatest impact on otters. The use of pesticides was greatly increased during the 1950s, particularly aldrin and dieldrin. These were washed off the land into rivers etc. and contaminated fish with tiny amounts of poison. Even though the fish may not be affected, the poison gradually accumalates in an otter eating a lot of fish, resulting in its death. Though most of these pesticides have been restricted since 1962, but residues still remain in the environment today. New chemical threats come from the build-up of substances like polybrominated dipehnyl ethers (PBDEs), which were commonly used as flame retardants in a wide range of household items including furnishings. PBDEs don't break down in the environment easily and have been shown to reduce fertility in humans. Though production of PBDEs is now controlled, they have been found at increased levels in a range of marine mammals.
In 2011 it was declared that the otter was again present in all of England's counties - a massive success as they had become very rare indeed. This success is due to better pollution control in our waterways and increased protection for this beautiful animal.
However, otters still face many threats to their survival, including chemical pollution (see above) roads, disturbance to their habitat and the fact that eels (one of their main foods) have declined by around 90%.
Image: Otter (Eurasian) by Helen Haden
Further information: International Otter Survival Fund