ABOUT OTTERS

Otters (the Eurasian otter, Lutra lutra) are one of the U.K.'s most charismatic animals but, being largely nocturnal and solitary, are rarely seen. They are members of the Mustelid family which includes badgers, stoats and mink.

DISTRIBUTION

The Eurasian otter (Lutra lutra) is the most widely distributed of the thirteen otter species worldwide. Their range extends through much of Europe and on to North Africa and across to China. Found throughout the United Kingdom it is the only otter species native to the area. Whilst it is often found in marine environments, especially in Scotland, unlike the sea otters off the east coast of North America, the Eurasian otter cannot remain at sea but requires fresh water to drink and bathe in and land on which to rest up.
SEA otter

LIFESPAN

In the wild Eurasian otters are unlikely to live much more than 5 years but in captivity 10-15 years is possible. One exceptional wild female otter was killed on a road in Shetland aged 16 years. It is likely that about one third of otters die in their first year of life and, of the those still alive at one year, only one half may survive the challenging transition to full independence.

SIZE AND WEIGHT

Body length: 60-80cm
Tail length: 32-56cm.
Weight: 5-12kg but weights are very variable; adult females (bitches) tend to be 5-7kg and males (dogs) 7-10kg. Both sexes can be significantly heavier, some males of 16kg having been recorded.  IMAGE HSC WHITE SPOT

TERRITORIES (HOME RANGES)

Otters can occupy as much as 20km of river but only 4km is possible, especially in the case of females. A single dog otter is likely to have multiple female otters within his range. Territories are well defended and have no overlap with adjacent territories whereas home ranges are less well defined and can have some overlap. Male otters are more likely to hold and defend a territories but females can (and do) live in home ranges, sometimes overlap with neighbouring females.

SENSES

An otter’s sense of smell is likely to be  similar to that of a pet dog. Of limited use underwater, above water otters use their sense of smell to detect danger, to find food and, most importantly, to learn about the presence and breeding status of other otters in the area. Otters regularly mark their environment with both faeces (in a behaviour known as sprainting) and urine.
Both the eyesight and the hearing of an otter, whilst not exceptional, are likely to be similar to that of pet dogs.
It is their long whiskers around the muzzle (vibrissae) that give otters their most impressive of senses. Remarkably, in the dark and in turbulent water, otters are able to locate and chase down fish using their whiskers alone to detect the turbulence (vortices) left behind by prey moving through water.

COAT

With 50,000 hair per sq cm (humans only have 100,000 on their whole head), otters are well insulated from the cold environment in which they spend much of their time. It is the insulating properties of an otter's coast that has lead to widespread hunting of the species in the past.

SWIMMING ABILITY

Otters are powerful and agile swimmers, their muscular and stream-lined bodies, long tail and webbed feet powering them through the water.   VIDEO

DIET

Living and feeding in aquatic environments the bulk, but not all, of an otter's diet is fish based. Which species of fish varies tremendously depending on the habitat. Amphibians, small mammals, birds, crustaceans and carrion are also taken.

BREEDING

Breeding can take place at anytime of year, the peaks likely to match the annual cycle of food availability in the area in which they live. Litters of one to three young (cubs) are normal but four and five are possible. 
Female otters are in oestrous (in "season") for 2-3 weeks. This is a time when otter activity can increase dramatically as various dog otters strive to be the one to mate with the in oestrous female. After 9 weeks gestation the cubs are born, remaining in their natal holt before venturing out in to the water for the first time at 8-10 weeks of age. Having left the breeding holt, up until about 16 weeks of age, their mother will often leave her cubs in one of a number of resting places (holts) but from about 16 weeks they tend to remain with her. Then, from 8-10 months of age the cubs spend increasing amounts of time alone before dispersing to find a home of their own at about 12 months of age.

CONSERVATION STATUS AND PROTECTION IN THE U.K.

The U.K. otter population crashed through the late 50's and 60's (see below) but has subsequently recovered to made a good recovery. Internationally the Eurasian otter is classified by the I.U.C.N. as near threatened. A recent survey in Wales has suggested that, after many years of recovery, there has now been the possibility of a decline.
Otters are strictly protected by the Wildlife and Countryside Act (1981) and cannot be killed, kept or sold except under licence. Otter sheltering, resting and breeding sites are protected from disturbance.

OTTER SPRAINT

Otters regularly mark their environment with droppings known as spraint. Spraints vary enormously depending on the food remains that they contain and how old they are. They tend to be deposited on raised sites such as the ledges under bridges, large rocks beside or in the middle of watercourses, tree roots and where otters leave a watercourse on a "short cut". Junctions of two watercourses are often used. 

Otter spraint usually has a not unpleasant fishy smell (likened to jasmine). However, if the otter has eaten a bird or mammal, the spraint will contain feathers or hair and my well smell very unpleasant.

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"SAND CASTLES"

In the absence and obvious features on which to spraint, on banks of soft mud and soil otters create small "sand castles" on which to deposit their spraint.

FOOTPRINTS

Adult foot prints are 5-7cm wide with four toes (sometimes a fifth toe is visible in soft mud).

DID I SEE AN OTTER OR A MINK?

TELLING THE DIFFERENCE

If one only had a fleeting glimpse of a dark coated small mammal in or near water (or if one rarely sees mink and/or otters), it can be difficult to be sure if one has seen a mink or an otter. Mink are significantly lighter in weight and about half the length of an otter. The way they move may well help to differentiate the two.

THE DECLINE

In the late 50's the U.K. otter population started a dramatic decline which continued through to the 1970s. In a time when there were relatively few people studying them, one of the first groups to be aware were the otter hunts who were finding it increasingly difficult to find otters.

Very quickly the link was made with recent introduction and widespread use in agriculture of organochlorine pesticides (such as DDT and Dieldrin). The journalist Rachel Carson, in her book "The Silent Spring" published in 1962, was one of the first to bring to the world's attention the devastating effect of these chemicals on ecosystems. Their persistence was deal for the purpose for which they were developed but it was this that persistence allowed them to accumulate in the environment. In a process known as bio-accumulation, their were concentrated in top predators such as otters and birds of prey. They disrupted the endocrine systems of otters causing a fall off in reproductive ability and in birds they caused the birds to lay soft shelled eggs that fractured before hatching. 

Other factors such as the falling water quality of aquatic environments may well have played their part too. 

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THE RECOVERY

With the realisation that organochlorine pesticides were probably to blame for dramatics affects on ecosystems, including the decline in otters and birds of prey, these chemicals were increasingly banned through the 60s, 70s and early 80s. As these chemicals started to work there way out of aquatic ecosystems, otter populations started to recover. The ban of otter hunting in 1978 and a start in the improvement in the quality of aquatic ecosystems in general may too have contributed to the improved fortune of otters.

WHAT NEXT?

Whilst the increase in the otter population (now closely monitored) over the last 40 years is to be celebrated, it has come on the back of a devastating decline. Further concerns have been raised by a recent Welsh National Otter Survey (2015-2018) that revealed a substantive decline since 2010. The sixth National Otter Survey is underway in England at present (2022). The Cardiff Otter Project monitors road kill otters for novel and potentially harmful new chemicals entering aquatic ecosystems.

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