The Mammal Society

For Evidence Based Conservation

Otter – Lutra lutra

 

Habitat: Rivers and wetland, coastal & marshland.
 
Description: Brown fur, often pale on underside; long slender body; small ears on a broad head; long thick tail; webbed feet; swims very low in the water, head and back barely showing.
 
Size: About 60-80cm; tail about 32-56cm
 
Weight: Average 8.2kg for males; 6.0kg for females.
 
Lifespan: Up to 10, though few survive more than five years.
 
Origin & Distribution: The otter is a secretive semi-aquatic species which was once widespread in Britain. By the 1970s, otters were restricted mainly to Scotland, especially the islands and the north-west coast, western Wales, parts of East Anglia and the West Country (though they remained common and widespread also in Ireland). This decline was caused by organo-chlorine pesticides. Since these were withdrawn from use, otters have been spreading back into many areas, especially in northern and western England.
 

Otter distribution (in green), taken from ‘Britain’s Mammals 2018: The Mammal Society’s Guide to their Population and Conservation Status.’

 
Diet: Fish, especially eels and salmonids are eaten by the otter, and crayfish at certain times of the year. Coastal otters in Shetland eat bottom-living species such as eelpout, rockling and butterfish. Otters occasionally take water birds such as coots, moorhens and ducks. In the spring, frogs are an important food item.
 
General Ecology: Otters can travel over large areas. Some are known to use 20 kilometres or more of river habitat. Otters deposit faeces (known as spraints, with a characteristic sweet musky odour) in prominent places around their ranges. These serve to mark an otter’s range, defending its territory but also helping neighbours keep in social contact with one another. Females with cubs reduce sprainting to avoid detection.
 
Breeding: In England and Wales, otter cubs, usually in litters of two or three, can be born at any time of the year. In Shetland and North-west Scotland most births occur in summer. Cubs are normally born in dens, called holts, which can be in a tree root system, a hole in a bank or under a pile of rocks. About 10 weeks elapse before cubs venture out of the holt with their mother, who raises the cubs without help from the male.
 
Conservation Status: Otters are strictly protected by the Wildlife and Countryside Act (1981) and cannot be killed, kept or sold (even stuffed specimens) except under licence. In the late 1950s and early 1960s otters underwent a sudden and catastrophic decline throughout much of Britain and Europe. The cause was probably the combined effects of pollution and habitat destruction, particularly the drainage of wet areas. Otters require clean rivers with an abundant, varied supply of food and plenty of bank-side vegetation offering secluded sites for their holts. Riversides often lack the appropriate cover for otters to lie up during the day. Such areas can be made more attractive to otters by establishing “otter havens,” where river banks are planted-up and kept free from human disturbance. Marshes may also be very important habitat for raising young and as a source of frogs.

While otters completely disappeared from the rivers of most of central and southern England in just 50 years, their future now looks much brighter. There is evidence that in certain parts of the UK the otter is extending its range and may be increasing locally. However, otter populations in England are very fragmented and the animals breed slowly. Attempts have been made to reintroduce otters to their former haunts by reintroducing captive bred and rehabilitated animals, with some attempts proving very successful.

Identification

Milk chocolate brown fur (darker when wet) with a slightly pale underside. Long slender body and long thick tapering tail. Small ears on a broad head.Adults often a metre or more in length. Swims low in water with top of head and back only just visible and a V-shaped bow wave. When walking/running on land has marked ‘hump-back’ appearance.

Field Signs
Download a printable field sign guide here!

Footprints: Tracks can be found in sand and mud (and snow) alongside rivers and streams. They are five-toed, but often only four toes appear in the print. The large, round prints (5-7cm in width, 6-9cm in length) are often pushed deep into the clay providing clear ID field signs.

Droppings: Otters leave spraints (droppings) on rocks or logs close to water. They contain mainly fish shells, bones, shells of crustaceans, feathers or fur. Highly variable in size. Colour: greenish, black-grey. Smell: Sweet smelling; jasmine tea or laurel flowers. Often found in small quantities.

Confusion species

American mink (Neovison vison)
Dark brown coat, compared to otter’s lighter mid-brown coat. Mink is same colour all over, except for a white chin, whilst otter has a paler underside. Cylindrical, fluffy, blunt tail, not muscular and tapering like the otter. Pointed muzzle and smaller than a domestic cat. Otter has a broader muzzle and is larger than a cat.

Eurasian beaver (Castor fiber)
Broad, flat tail, unlike the long, muscular, tapering tail of the otter. The beaver’s broader rodent muzzle is less pointed than the otter’s carnivore muzzle. Beaver has a stockier body, compared to the long body of the otter.

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