The otter is a sleek animal with a long, tapering tail. Males (dogs) are up to 1.2 m in length and weigh about 10 kg. Females (bitches) are generally smaller at up to 1.1 m and 6 kg. The size of large
terrier, the otter appears much smaller in the water. The brown coat looks black or brown and spiky when wet, the chest is cream.
Young cubs are grey. The head is flat with a long neck, body and tail. They have short legs and webbed feet. Otters walk with a distinctive hump-back gait on land and may stand on their back legs to get a better view of their surroundings. In the water they
swim with only the top of the head in view, appearing quite small, but with a prominent bow wave. The otter is most frequently confused with the much smaller (650mm, 1.5 kg) American mink. The mink is usually chocolate-brown to black, often with a white patch on the chin or chest. Its tail is shorter, bushier and less tapered. Mink swim with more of their body out of the water. Mink droppings (scats) often contain fur and feathers and have a rancid smell which fades after a few days.
© David Groves
Tracks seen in soft mud or gravel show 4-5 toes arching around a large pad. The adult track is 5-7 cm wide. In soft mud webbing between toes or claw marks may be visible. Otters mark their territories with droppings (1-10cm long), called spraints, using prominent rocks, trees or banks in the river. In sand or gravel they may scrape a
heap and spraint on top of this. Fresh spraints are dark and slimy with a distinctive musky smell (like a fishy jasmine tea). Older spraints fade to grey and crumble like ash but retain their smell. Spraints often contain bones and scales.
Otters use freshwater and coastal habitats, although they need access to fresh
water for grooming. They are also recorded from open moorland and urban waterways, often in transit between feeding areas. They visit lakes, marshes, and even garden ponds. Otters are mainly active between dusk and dawn, although in
Scotland, where there is less disturbance they are often seen during the day as
their feeding behaviour is driven by tidal cycles. Male otters occupy ranges of up
to 40 km of river, overlapping several female ranges. With good coastal habitat and rich feeding grounds ranges can be much smaller.
Dens (holts) are made in holes created by bank-side tree root systems or in rocks or stick piles and flood debris; each holt has several entrances, including an underwater one. Above ground resting places, on flattened vegetation such as reeds, are called ‘couches’. Otters use up to 30 holts within their territory.
In Cornwall otters feed mainly on eels, but they also take fish, including game species and carp from ornamental ponds or lakes. Frogs and crustaceans are important seasonal food sources, while birds and small mammals are rarely taken.
Otters breed at any time of the year and research in Cornwall has shown no evidence of seasonal bias. A female will breed in her second year and the litter of one or two (occasionally up to 5) cubs stay with the bitch for up to a year. Males do not assist with rearing cubs. Normally silent, occasionally a contact ‘whistle’ call between mother and cub is heard. There is also a harsher ‘hah’ alarm call. Very young cubs make a chirruping noise.
Despite the lack of natural predators, few wild otters survive 5 years, and many die in the first year of independence. Forty years ago pollution was responsible for dramatic declines in the otter population, now the biggest threat to otters is road traffic, and this is the main cause of otter deaths in Cornwall. Drowning in fishing gear has also been recorded and domestic dogs occasionally kill otters. Otters also fight each other in competition for resources, and there is evidence of this happening in Cornwall which reflects a strong population in the County.
The Life Story of An Otter written by J. C. Tregarthen in 1909 in Cornwall is said to have inspired Henry Williamson to write Tarka the Otter in 1927.