Otter

Eurasian otters are the only species of otter in the British Isles, though they range across many different habitats – including rivers, lakes, and even along the coast and sea. 

Taxonomy chart

Animalia - Chordata - Mammalia - Carnivora - Mustelidae - Lutra - L. lutra

Conservation status: UK Red List

GB: Least Concern

England: Least Concern

Scotland: Vulnerable

Wales: Vulnerable

Global: Near Threatened 

Summary

Diet: Fish, crustaceans, amphibians, birds, eggs, small mammals, insects. 

Habitat: Rivers, canals, lakes, wetlands, coastlines. 

Size: Weight: 6 - 8 kg. Length: 60 - 80 cm, Tail: 32 - 56 cm. 

Lifecycle: Average lifespan: 5 - 10 years. Otters can mate year-round, but this usually occurs in spring. The gestation period lasts 9 weeks, and litter sizes typically consist of 2 – 3 cubs. Cubs (named pups in otters) are born between May and August. They stay with and remain dependent on their parents for over a year and start to leave the nest between 14 – 15 months old. Sexual maturity is reached when they are 2 years old.  

Conservation concerns: Otters are fully protected in the UK under the Wildlife and Countryside Act (1981) and are a priority Species under the UK Post-2010 Biodiversity Framework. They are also designated and protected as European protected species and protected under the Conservation of Habitats and Species Regulations 2017. Otters face threats from road traffic accidents, habitat destruction, wildlife crimes, drowning in fishing nets, and the increasing use of pesticides.

Terminology

Holt: an otter’s den – a hole in the ground used for sleeping or resting. Sometimes also called a couch.  

Spraints: otter droppings, which are used to mark territories. 

Pups: juvenile otters. 

Geography

Otters  can be found in most parts of the British Isles but are absent from parts of central and southern England, the Isle of Man, the Isles of Scilly, and the Channel Islands. 

Otters live where they can find clean fresh water with enough food and secluded areas of vegetation where they can rest and raise their pups. They tend to live in and near rivers, canals, lakes, and coastlines if there's a freshwater source nearby.

Biology

Otters have a body length of 60 – 80 cm, a tail length of 32 – 56 cm, and weigh 6 – 8 kg. On average, males are bigger than females.  They have thick grey-brown fur but a pale chest, belly, and throat. Their body is slender, they have a broad nose and small ears, and their eyes are set high on their face, so they have better vision when submerged in the water. Otters have strong and muscular tails and webbed feet making them strong swimmers. They have an average age span between 5 -10 years old. In the wild, however, otters typically do not live beyond 4 years old.  

Otters are mainly solitary animals but will come together to mate. They can mate year-round; however, most cubs are born between May and August. Females have a gestation period of 9 weeks and will usually give birth to 2 -3 blind cubs. These cubs are born blind, are about 12cm long and weigh about 100 grams. The cubs are raised solely by their mother and leave the holt for the first time after about 10 weeks. A few weeks later, they will take their first swim. The mother protects her cubs until they are about a year old, after which they will leave and start breeding around 2 years old.

Ecology

Otters are carnivorous and mainly feed on fish such as trout, carp, and eel. They will also eat amphibians, crustaceans, and waterbirds such as moorhens and coots. Occasionally, otters will get food from the land. This includes birds, eggs, insects, and small mammals. They can eat more than 2 pounds of food per day. Otters are formidable predators who can catch prey equal to their body weight! 

Otters live in dens called holts. These are usually made in natural cavities found in riverbanks, tree roots, shrubby thickets, or rocky crevices. Inside, the holt is lined with grasses, ferns, reeds and leaves. There can be one or several chambers, which in the case of the latter are connected by a tunnel system. Some holts will also include a chamber used as a latrine. There are multiple entrances to the holt, which are both on land and underwater. In addition to their holt, otters will use resting places in areas of overgrown vegetation if they live in a large territory.  

Otters living in freshwater habitats are largely nocturnal, although occasionally they come out during the daytime. Otters living near the coast will hunt in the sea by day when the conditions are favourable – when the tide is coming in and bringing prey closer to shore. 

Otters maintain the ecological balance of their habitats by controlling fish populations. They are also an important indicator species for the health of freshwater ecosystems. 

Conservation 

Otters are protected under several legislations including the Wildlife and Countryside Act (1981) and the Conservation of Habitats and Species Regulations (2017) since they are a European protected species. They are also a priority species under the UK Post-2010 Biodiversity Framework. Besides this, it is illegal to damage, destroy or stop otters from accessing their breeding sites or shelters. 

Otters nearly became extinct in some areas in the UK between the 1950s and 1970s. One of the main reasons for this was the increasing use of organochlorine pesticides in farming. The chemicals from these pesticides seeped into rivers and lakes, which depleted the fish stocks that otters relied on for survival. Thanks to legislation which banned or restricted the use of these chemicals, as well as increased protection of otters and improved water quality, the otter managed to make a comeback. Apart from legislation, reintroductions of otters happened in some areas in the 1980s and 1990s to help recovery efforts. The last captive-bred otter was released in 1999.  However, otters still face threats. Mortality on roads, entanglement in illegally set crayfish traps and fyke nets, and habitat degradation continue to harm otter populations. 

History

Otters re-colonised the British Isles after the last Ice Age and were hunted for their furs. During historic times, otter hunting used to be a popular sport. One of the earliest records of otter skinning comes from a Late Neolithic cairn at Pierowall Quarry in Orkney.  

The otter features in the folklore of the British Isles. In Scottish traditions, “Otter Kings” are mentioned. These kings were accompanied by seven black otters, who when captured, would grant any wish to their captor in exchange for their freedom. The skins of these otters would make warriors invincible and would protect the wearer against drowning. Otters also appear in many folktales. For example, there is the Welsh tale of the sorceress Ceridwen who turned into an otter, and in Celtic folklore, the otter is seen as a friendly and helpful creature. In the Irish folktale of “the Voyage of Maelduin”, otters bring the sailors salmon. In Christianity, there is even a patron saint of otters, St. Cuthbert! 

In more recent times, otters swimming together as a family in a single file have been suggested to cause the (in)famous sightings of Loch Ness. They also feature in literature such as Kenneth Graham’s “Wind in the Willows”, Henry Williamson’s “Tarka the Otter” and Gavin Maxwell’s “Ring of Bright Water”. 

How to identify 

Footprints: otter tracks can be found in mud and sand close to water. They are 40-80 mm across and show four or five toes. The claw marks are usually not present, but sometimes the webbing can be seen between the toes.   

Feeding signs: Otters drag fish up the bank to feed and leave the head behind. You can also find mussels and crabs with otter bite marks, or leftover crayfish claws.  

Holts: On riverbanks, holts are found amongst tree roots, underbrush, bushes, piles of boulders, or small holes in the bank. A good indicator is the presence of spraints, tracks and the characteristic smooth wear at entrances and smell.  

Spraints: Spraints are the droppings of otters, which they use to mark their territories. They have minimal ‘goo’ and are typically packed with fish scales, fish bones, hollow frog bones, and similar remains. This makes the droppings very crumbly. They smell like fish with a hint of jasmine tea. The colour is black but can be pink if they consume a lot of crayfish.  

Surveying period: Surveys can be undertaken year-round, but spring is the best time since this is when water levels recede.