The European otter, a semi-aquatic species, lives along coasts and in a wide variety of freshwater habitats. It is a European branch of the weasel or Mustelidae family. It is the otter species with the widest distribution, being spread widely across Europe. It is an elusive animal which has sleek brown fur, often paler on its underside, covering its long lithe body, thick tail and little legs. Adaptations to an aquatic lifestyle are its webbed feet, its ability to close its small ears and its nose when it is under water, and its very dense, short fur that traps a layer of air for the purpose of insulating the animal. It has many sensitive whiskers around its snout; these help to locate prey.
European otters live throughout Europe, North Africa and Asia, inhabiting streams, rivers, lakes, freshwater and peat swamp forests, ocean shores, rice fields, fjords, caves, and other terrestrial habitats close by waterways. Dry resting sites and covered dens are found in tree roots, earth tunnels, boulder piles, banks and shrubs.
European otters have their most active time at dusk and at night. During the day they are in their dens on the land, staying cool, coming out at night to eat. They will spend several hours nightly foraging in water. They nest on land, tending to build underground tunnels to move between the two. They are solitary animals unless in a mating pair or a mothers with her young. However, sometimes they form loosely knit groups numbering as many as six animals. They are the most territorial of otter species. Their territory can be as big as 25 miles wide but is usually about 11 miles. They are able to cross territorial boundaries without incident, but aggressive behavior will occur if the same gender tries to enter a territory.
European otters are carnivores, they eat mainly fish, but they also hunt amphibians and other aquatic prey, as well as birds, eggs, insects, worms, and a small amount of vegetation
Although the mating system in European otters has not been well studied, they are thought to be either polygynous (one male mates with multiple females) or polygynandrous (promiscuous) (both males and females have multiple mates), as both males and females associate with each other only during mating. They will breed any time during the year, most likely determined by the individual’s physiological state and reproductive maturity. Gestation is for 60 to 70 days, each female bearing 2 or 3 pups. The pups are 99 to 122gm when born, their eyes open at one month and after two months they start to leave the nest. Weaning takes place when they are 3 months old. They remain with their mothers up to the age of 14 months, reaching reproductive maturity at the age of 2 or 3 years.
The aquatic habitat of otters is very vulnerable in the face of change. Removal of vegetation from stream or river banks, the draining of wetlands, the construction of dams and other man-made interventions impact greatly on otter populations. Those living on the coast are susceptible to oil spills. The pollution of lakes and rivers affects the fish that are their main food source. Other threats are being caught in nets and fishing traps set for other species, as well as being hunted for their coat.
The European otter has a wide distribution but no overall population estimate is available. According to the scientific resources, the total population size of European otters in Belarus is around 12, 000 individuals and in Sweden - 500-1000 individuals. According to the IUCN Red List, the overall estimate of the population in the United Kingdom was around 10,395 individuals in 2004. Currently this species is classified as Near Threatened (NT) and its numbers today are decreasing.