Otter Biology

Distribution

The only species of otter that inhabits the British Isles is the Eurasian Otter (Lutra lutra). This species occurs right across the Northern Hemisphere, from the UK to South east Asia and from North Africa up to the Arctic circle. It has declined over much of its range is now extinct or threatened in many areas of its former range. In the UK otter populations have declined least in Wales and South West England. Whilst it is largely absent from central England, other areas do have a low population.

Taxonomy

The Eurasian otter is a member of the family Mustelidae. This family is the largest of the Carnivore order and also contains badgers and stoats. There are 13 species of otter in a subfamily called Lutrinae.

Body

Long slender body with a thick, long, tapering, flattened tail.
Brown body with a light underside.
White throat patches are individual if present.
Total length: 1 - 1.3m.
Tail length: up to 45cm.
Weight male: 10.1kg average, 11kg max.
Weight female: 7.0kg average, 30% smaller than male.
Otters swim gracefully and low in the water with only their eyes, nose and small ears on their flat heads showing above the surface leaving a U-shaped wake.
The broad muzzle has long stiff viribrasse (whiskers).
Feet are comparatively large and more than half webbed.
Male width: 70mm.
Female width: 60mm
When wet the fur looks spiky due to the coarse waterproof guard hairs and shorter denser insulating fur.

Life Cycle

Seasonal peaks occur regionally, but otters can breed year round.
Male territories cover several females, but otters usually only come together to mate.
Gestation period is 63 days
1-5 (2/3 average) cubs are born in a holt.
Cubs are weaned by 12 weeks.
They start to catch food after 4 months but spend 7-12 months with their family group to learn to fish properly.
Sexual maturity is achieved after 2 years, and an age of 15 years may be reached.

Diet

Otters primarily eat fish, although other animals are taken depending on regional and seasonal availability. Eel, roach and perch are slower swimming species and therefore caught more frequently.
Adults require on average 1kg of food per day.

Behaviour.

Typically 10-40 second dives.
Otters can swim 8-16km per night.
Male range: 70km
Female range: 25-40km
Otters spend a lot of time resting. Each otter may have up to 30 rest sites in its territory and may spend only 30% of its time in an active phase and this includes further resting and grooming time.

Habitat and Ecology.

Otter population distribution is affected by the habitat. A key feature is the presence of secure breeding and rest sites. Otters occur on rivers, streams, lakes, marshes and on the coast. Whilst rivers can provide vital food supplies, streams are also used to access more sheltered habitat and to cross over into different river basins. Otters are capable of travelling considerable distances over land to cross over to other river catchments. It is important that good otter areas are linked by corridors of suitable habitat, this reduces population fragmentation and inbreeding. The coastal populations of Shetland and Scotland exhibit distinct behavioural differences to our southern populations.

Holts

Natural holts often consist of natural cavities, such as burrows or the root systems of bankside trees. Above ground resting places range fromvegetation lined depressions to piles of sticks lined with bedding material.