OTTERS
ABOUT OTTERS
The Eurasian otter is one of the United Kingdom's most charismatic animals but, being largely nocturnal and solitary, is rarely seen. However, daylight sightings are relatively common in some coastal areas and are becoming more frequent inland. The thirteen species of otter across the globe are all members of the Mustelid family which includes badgers, stoats and mink.
FACT FILE
DISTRIBUTION
The Eurasian otter (Lutra lutra) is the most widely distributed of the thirteen otter species worldwide. Its 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. In the UK most otters live on inland waterways but they can also be 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 and requires fresh water to drink and bathe in and land on which to rest up.
Sea otter off California
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 female otter in the wild 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.
Female otter (named Hammer Scar) and male otter (named White Spot). Image complied of two superimposed "selfies" taken at the same site and to the same scale.
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 territory but females can (and do) live in home ranges, sometimes overlapping 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 faeces (in a behaviour known as sprainting) and urine.
Both the eyesight and the hearing of an otter, whilst not exceptional, are also likely to be similar to that of pet dogs.
It is their long whiskers around the muzzle that give otters their most impressive of senses. In turbulent and murky water otters are able to locate and chase down fish using their whiskers to detect the turbulence left behind by prey items moving through the water.
Probable dog otter clearly showing the large whiskers
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 coat 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.
Chasing down a trout
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 (often known as 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 a mother will often leave her cubs in one of a number of resting places (called 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.
14 week old cub
CONSERVATION STATUS AND PROTECTION IN THE UK
The UK otter population crashed through the late 50s and 60s (see below) but has subsequently 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, on some catchments numbers may be once again be declining (ref: Sixth Otter Survey of Wales).
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.
SIGNS OF OTTERS
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, on tree roots and where otters leave a watercourse on a "short cut". Junctions of two watercourses are often used.
As with pet dogs, otters will sniff the spraint of other otters to obtain information such as which otters are using the water course and t0 assess their reproductive status.
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 (not dissimilar to a fox scat).
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A typical spraint
Ledge under a bridge used as a spraint site.
Multiple spraints of differing ages.
Base of a riverside tree used as a spraint site.
"SAND CASTLES"
In the absence of obvious features on which to spraint, otters create small 'sand castles' on banks of soft mud and soil.
Trail in soft mud with two "sand castles"
"Sand castling"
FOOTPRINTS
Adult foot prints are 5-7cm wide with four toes (sometimes a fifth toe is visible in soft mud). The toe and nails combined are said to look like a pear drop.
DID I SEE AN OTTER OR WAS IT A MINK?
TELLING THE DIFFERENCE
If one only has a fleeting glimpse of a dark coated mammal in or near water or if one rarely sees mink and/or otters, it can be difficult to be sure which of the two one has seen. Mink are significantly lighter in weight and about half the length of an otter. The way they move and the shape of the tail may well help to differentiate the two.
Both camera trap images taken from the same position
Otter then mink (plus a kingfisher!)
DECLINE AND RECOVERY
THE DECLINE
In the late 50's the UK otter population started a dramatic decline which continued through to the 70's. At a time when there were relatively few people studying otters, one of the first groups to be aware of a decline were the otter hunts who were finding it increasingly difficult to find otters to hunt.
Very quickly the link was made with the 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 people to bring to the world's attention the devastating effect of these chemicals on ecosystems. Their persistence was ideal for the purpose for which they were developed but it was this persistence that allowed them to accumulate in the environment. In a process known as bio-accumulation, the pollutants moved up the food chain and were concentrated in top predators such as otters and birds of prey. The toxic effects of the pollutants disrupted the endocrine systems of otters causing a fall off in reproductive ability and in birds they caused them to lay soft shelled eggs that fractured before hatching.
Other factors such as the declining water quality of aquatic environments may well have contributed to the crash in the populations of top predators.
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The otter population decline: Hunting records 1950 - 1976
(taken from Otter Survey of England 1991 - 1994 and redrawn from Chanin and Jefferies, 1978)
THE RECOVERY
With the realisation that organochlorine pesticides were probably to blame for some of the dramatic changes in our ecosystems, including the decline in otters and birds of prey, these chemicals were increasingly banned through the 60's, 70's and early 80's. As these chemicals started to work their way out of aquatic environments, otter populations started to recover. The ban on 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 came on the back of a devastating decline. New concerns have been raised by the recent Welsh National Otter Survey (2015-2018) which suggests a substantive decline in otter numbers on some catchments since 2010. The sixth National Otter Survey of England is under way at present (2022). Monitoring of novel and potentially harmful new chemicals entering aquatic ecosystems is carried out by the Cardiff Otter Project which conducts postmortems on dead otters and the chemicals contained within them.
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THREATS
CHEMICAL CONTAMINATION OF THE ENVIRONMENT
See above (The Decline)
ROADS
It is difficult to estimate the total number of otter road casualties. An indication comes from the records of the Somerset Otter Group who record, on average, 30 dead otters annually from the county. Virtually all are road kill.
Otter road deaths tend to be at their highest at times of heavy rain when peak flows make it difficult for otters to travel under bridges and through culverts. Otters are also at risk when the move overland from one catchment to another.
RTA otter (named William)
OTHER OTTERS
As is the case with lions, a new dog otters moving into an area can, and do, kill the cubs belonging to the resident female. By doing so, the female will come back into season far sooner than would otherwise be the case, allowing the female to raise the offspring of the new dog otter at the earliest opportunity.
Otters have large canine teeth and often inflict deep bite marks and injuries on each other.
HUMAN-RELATED CONFLICT
As otters recolonise areas from which they have been absent for many years, it brings them into conflict with the owners of both commercial fisheries and the owners of pet fish. The killing of otters continues despite their legal protection.
Pet dogs can both disturb and injure/kill otters, especially if they find them out of the water or in shallow streams and ditches.
Golden orfe half eaten by an otter
Otter raiding a pond sunken into decking.
Given the nature of the conflict between fish owners and their local otters, there is now an increasing knowledge base and sound advice as to how fish owners can try to mitigate the "problem" by legal means (see here for advice from the UK Wild Otter Trust).
IF YOU FIND A DEAD OTTER
If you find a dead otter, by the road or elsewhere, follow this link to find out how report it: REPORT A DEAD OTTER
CALLS
Most of the time otters don't call (vocalise) but there are times when they do, such as when a female is accompanied by cubs or when an in oestrous/in season female is accompanied by a male otter.
FEMALE CALLING HER CUBS:
CUB CALLING:
MATING:
HAMMER SCAR
A Remarkable Relationship between one man and a wild otter.
Over five magical years I was able to get a rare and privileged insight into the lives of the otters below my house and one otter in particular. I named her Hammer Scar.
