The otter (Lutra lutra) is a top predator in freshwater ecosystems, being at home both on land and in water, and is renowned for its agility and playful nature.
The European or Eurasian otter is the most widely-distributed of the world’s 12 otter species, and it occurs throughout Europe and much of Northern Asia, including Russia, China and the Korean peninsula. Its range also encompasses Morocco, Algeria and Tunisia in North Africa, Middle Eastern countries from Turkey to Iran and Afghanistan, the Himalayan river valleys of Pakistan, India, Nepal and Bhutan, and parts of Southeast Asia, including Thailand, Laos, Vietnam and the island of Sumatra in Indonesia.
Distribution in Scotland
The otter occurs throughout Scotland, both on the mainland, and on many of the islands, including Mull, Skye, the Western Isles, Orkney and Shetland. A detailed survey in 2003-04 of 1,376 sites all over the country found evidence of otters at 92% of them, including in large urban areas such as Glasgow, Edinburgh and Dundee. Unlike other parts of the UK, where they occur mainly in freshwater ecosystems (rivers and lakes), otters in Scotland live along coastlines, as well as in lochs and rivers. Shetland in particular has a dense population of otters, and is estimated to be home to 12% of the UK total for the species.
The European otter is classified as Near Threatened in the IUCN Red List of Threatened Species, meaning that it is likely to be considered threatened in the near future. In some parts of its range, including India, Pakistan, Burma and Thailand, it is already considered to be Endangered, and in Mongolia it is listed as Critically Endangered. Although it was previously widespread in Japan, it is now believed to be extinct there. In Europe the otter populations declined substantially in the 1960s and 1970s, due to mortalities caused by pesticide use. In recent years, though, the otter has recovered considerably in the UK and much of Europe due to conservation efforts and the banning of pesticides such as dieldrin.
The European otter is protected in various international conventions, including the European Union’s Habitats and Species Directive and the Convention on International Trade in Endangered Species (CITES), where it is listed in Appendix 1, which prohibits all trade in individuals from the wild.
In the UK, the otter is protected under the Wildlife and Countryside Act and is listed as a priority species for conservation under the Biodiversity Action Plan (BAP).
The European otter is a medium-sized carnivore in the Mustelidae, or weasel, family, which also includes the pine marten, badger and stoat. Individuals are up to 90 cm. in body length, with a tail that is up to 45 cm. long. Males, known as dogs, are longer than the females, which are called bitches. Their weight ranges from 7-12 kg. on average, although large males have been recorded reaching up to 17 kg.
The otter’s coat is brown on top, while the underside is a paler cream colour. The dense fur acts as insulation, helping to keep it warm in the water, and the guard hairs are covered in a water-repelling oil, which keeps the skin underneath dry. The otter also has some other adaptations that support its aquatic lifestyle, including its sleek, streamlined body shape, the ability to close its nose and ears with flaps of skin when underwater, and webbing between the toes of its feet. It has large lungs, and its heart rate slows down to conserve oxygen when underwater, enabling the otter to dive for several minutes.
The eyes are located on the top of the head, so that they are above the water when the animal is swimming. The otter has good senses of sight, hearing and smell, and the long whiskers on each side of its snout are highly sensitive to touch, helping it to find food in murky conditions underwater. To grasp its prey, the otter has sharp, non-retractable claws on its feet, which each have five toes. The hind feet are larger than the forefeet, to provide greater propulsion while swimming.
The otter is active mainly at dusk or after dark, and during the day rests in a burrow, known as a holt, that it makes in riverbanks or under the roots of a tree. It is territorial and solitary, and will mark its territory with spraints, or droppings that are left on distinctive points, such as rocks or fallen trees. The spraints usually contain fish bones and have a distinctive, pleasant smell, sometimes compared to that of jasmine tea. Territories range in size, depending on the availability of food, and may be up to 3 km. in length along the coast, or from 5-20 km. along a river, and are fiercely defended, sometimes resulting in death. Female territories are about half the size of those of the males. Otters that live in coastal waters need to visit fresh water regularly to clean their fur.
The otter can live for up to 10 years, but in the wild its average lifespan is often 3-4 years. A major cause of death is injuries sustained in territorial fighting, while others are killed whilst crossing roads or by drowning after getting caught in traps for fish and crustaceans.
The otter is carnivorous and eats almost exclusively live prey, such as trout (Salmo trutta), young salmon (Salmo salar) and other fish, crustaceans, eels, frogs, water birds and insects. It is an opportunistic feeder, taking whatever prey is available, and is also known to eat small mammals, including young European beavers (Castor fiber). Otters that live along coastlines feed mainly on crabs and dogfish (Scyliorhinus spp.). Captive otters have been recorded eating an average of 1.5 kg. of food per day.
A female otter reaches sexual maturity at between 18 months and 2 years of age, although most breeding begins at between 2 and 3 years. Mating takes place in the water, and can occur throughout the year; there is no fixed breeding season. After a gestation period of 60-64 days, 2-3 (or sometimes 4) pups are born. These are covered in fur, but have their eyes closed for the first 5 weeks. After 10 weeks they are able to swim, but will remain with their mother for up to a year. The male plays little, if any, role in rearing the young. Mortality can be high amongst young otters, often due to starvation when they disperse in areas where there are well-defended territories of adults.
The otter is at the top of the aquatic food chain in much of its range today, with no natural predators. However, in the past it is likely that wolves (Canis lupus) preyed on the otter, as wolves in North America today are known to catch the related North American river otter (Lontra canadensis). Like all predators, the otter fulfils a regulatory function on the numbers of the species that it preys upon.
In mainland Europe, otter territories often overlap with those of the European beaver, and the ponds created by beavers are important for otters in rivers where there is little deep water. The ponds also provide otters with a source of fish, and disused beaver lodges are used by otters for shelter.
Like most wild mammals, the otter is host to a range of parasites, and these include a common trematode (Pseudamphistomum truncatum) and a fluke (Metorchis albidus), which have been found in otter gall bladders. Two species of tapeworms (Diphyllobothrium latum and Diphyllobothrium medium) that are parasites of fish have been found in otters. The hedgehog tick (Ixodes hexagonus), which is a close relative of the deer tick (Ixodes ricinus), is also a common parasite on otters.
The main problem the otter has faced in the recent past has been habitat loss and hunting by humans, but with conservation efforts addressing those issues in the UK, its population has expanded again, and its future now looks assured here.
By Alan Watson Featherstone
- Jefferies, D. J.; Hanson, H. M.; Harris, E. A. (1990) The prevalence of Pseudoterranova decipiens (Nematoda) and Corynosoma strumosum (Acanthocephala) in otters Lutra lutra from coastal sites in Britain. Journal of Zoology Vol. 221 No. 2 pp. 316-321
- Strachan, R. (2007). National survey of otter Lutra lutra distribution in Scotland 2003-04. Scottish Natural Heritage Commissioned Report No. 211 (ROAME No. F03AC309).
- Eurasian Otter entry on IUCN Otter Specialist Group site
- European otter entry on Wikipedia
- Lutra lutra entry on IUCN Red List of Threatened Species
- Otter entry on Forestry Commission website
- Otter entry on Scottish Wildlife Trust website