Zoology

European otter

Content Cover Image

European otter, Devonshire, England. @ Ivan Teage

The European otter (Lutra lutra) is a broadly distributed marine mammal found in both marine and freshwater systems over considerable portions of Europe, Asia and North Africa; in fact, this species has one of the broadest distributions of all mammals in the Palaearctic ecozone (Eurasia and North Africa).

caption Lutra Lutra. Source: Biopix

Conservation Status:

Scientific Classification

Kingdom: Animalia
Phylum:--- Chordata
Class:------ Mammalia
Order:-------- Carnivora
Family:-------- Mustelidae
Genus:--------- Lutrinae
Species:-------- Lutra lutra (Linnaeus, 1758)

This carnivore was once abundant from the Eemian to early Holocene in locales when glaciation was not present. However, as a result of persecution by humans, habitat destruction and water pollution from agricultural runoff, L. lutra is currently at risk of extirpation in some parts of its historic range, and is clearly a rare species in much of its primordial habitat. It is officially globally classified as Near Threatened by the IUCN.

Lutra lutra chiefly consumes a wide gamut of fish species, which are mostly of non-commercial value; moreover, much of the diet comes from an assortment of arthropods and mollusks. To the extent that the Earth's climate may be becoming warmer, the threatened species European otter may be a beneficiary, since its northern range limit is confined by the tundra biome, and could be enlarged by a warmer Northern Hemisphere.

Subspecies

The following taxa are recognised as subspecies:

  • L. l. aurobrunnea i: This subspecies occurs in the Garhwal Himalayas of northern India and at higher altitudes in Nepal
  • L. l. barang: This taxon is found only in Southeast Asia (Thailand, Indonesia and Peninsular Malaysia)
  • L. l. chiensis: This subspecies occurs in southern China and in Taiwan.
  • L. l. kutab: This subspecies is found only in northern India and Kashmir
  • L. l. lutra: This northern subspecies is known from the far north of Eurasian Russia, where it inhabits only taiga to North Africa. In the far north, this taxon is found in the myriad of small pools and rivulets, but depends on an ice-free environment to feed and navigate. The fact that it is able to colonise any areas where tundra has thawed implies that the subspecies may benefit from a range expansion, if there is a warming trend in the Northern Hemisphere. For example, L.l.lutra is a permanent resident on some of the very cold islands off the Kolsky Peninsula.  
  • L. l. monticola: iThis taxon occurs only in northern India (Himachal Pradesh, Sikkim and Assam regions) Nepal, Bhutan and Burma
  • L. l. nair: This taxon is found in southern India and Sri Lanka

Morphology

This mammal exhibits a pelage that is brown and sleek, but commonly paler on the ventral side. Lutra lutra adults generally range from 55 to 100 centimeters (cm) in body length, plus a tail extending about another 40 cm. Adult body mass is characteristically in the range of seven to twelve kilograms.

Like most otters it manifests an elongated supple body, thick tail and abbreviated leg structure. A key adaptations for natation involves its webbed feet. The extremely dense, short fur traps an air layer to insulate this otter, assisting in its adaptation to cold waters. Numerous highly sensitive specialised hairs, known as vibrissae, frame the snout and assist in prey location.

Habitat and Ecology

caption Habitat of the subspecies L.l.batang at Mai Po Marsh
Hong Kong Territory. @ C.Michael Hogan

European otters are found along fractal protected coastlines and near coastal rivers, estuaries and lakes; however, they may also occur in more interior freshwater systems, so long as the water quality is relatively high. When occurring in marine waters, they require a nearby freshwater source to periodically scour their fur in order to retain its insulation character. They are most often seen in relatively shallow waters, frequently along rocky shorelines and where there is a significant amount of aquatic vegetation, the buoyant fronds of which they can use for cover and assistance in flotation, in much the same fashion as their distant cousins the Southern sea otter of California utilises kelp.

Lutra lutra also prefers natural environments where access to coastal, riparian or lacustrine terrestrial vegetation provides good quality natural cover and additional foraging potential. Notable riverine characteristics promoting high Lutra lutra densities also feature: presence of a high density hydrographic net; presence of sandy river banks versus clay plains; abundance of small tributaries that are rich in small frogs and fish; and presence of high numbers of European beaver (Castor fiber). In the latter regard, L lutra are known to utilize beaver burrows as cover.

Distribution

caption Prime coastal habitat for the European otter,
Mull, Scotland. @ C.Michael Hogan

Coastal habitat is suitable over large portions of the European continent, including perimeters of the Celtic Sea, English Channel, Bay of Biscay, Irish Sea, Sea of the Hebrides, North Sea, Norwegian Sea, Baltic Sea, Gulf of Riga and Mediterranean Sea. Furthermore, some European countries offer suitable otter habitat hundreds of kilometres inland from the nearest sea. For example, in Romania, not only are European otter found within the Danube Delta, but far inland within the Carpathian Mountains. In Poland and Bulgaria, otters are found far inland in the rivers that have sufficiently high water quality and have a minimum of hydroelectric installations. The European otter, in fact, can be found in mountain valleys as high as 1400 metres in places such as Bulgaria, including numerous small watersheds in West Rhodopy Mountain, Bulgaria. In Turkey, however, overgrazing of riparian terrestrial cover, human hunting and water pollution have almost extirpated L. lutra from inland areas, except for parts of the Coruh River. In Soain L .lutra is found along parts of the coastline but also in interior riparian zones in such ecosystems as the Iberian sclerophyllus forests, where populations may be considered relicts of broader prehistoric distributions.

The southern limit of the European otter range in the Middle East is comprised by Israel, Jordan, Iraq and Iran. Lutra lutra is also found in northern parts of Morocco, Algeria and Tunisia in North Africa, particularly along the coastal zone of the Mediterranean Sea and its western arm the Alboran Sea.In Eurasia, the northern limits of the European otter range are defined by the presence of tundra.

This otter is found broadly and patchily across Russia; moreover south of the Tundra, in Mongolia, L. lutra is found along the Halh River in Ikh Hyangan Mountain Range. It has also been reported from downstream of the Tengis River in northern parts of Hövsgöl Mountain Range and around the Eröö River Basin in western Khentii Mountain Range.

The Southeast Asian distribution includes Sumatra, South Korea, southern and eastern China, northern Vietnam and Cambodia, Laos, Burma,  and Bangladesh. In India L.lutra is found in the very north and in the southeast, as well as in Sri Lanka. The species is thought to be extirpated in Japan. The Eurasian otter can also be found occasionally along the Tes River in northern Khangai.

Population Density

Some of the most detailed population density data of Lutra lutra has been accumulated in the British Isles and in the Baltic states. Correspondingly these areas reveal some of the loci of highest otter concentrations. Along the coastlines of the Shetland Islands, Island of Jura, Isle of Mull, Island of Islay as well as the nations of Latvia, Lithuania and Estonia, marine densities of one individual per 1.0 to 3.7 linear kilometer of coastline are characteristic.

In riverine systems the densities are not dissimilar as measured per kilometer of bank-line. For example surveys along the Altai River between Siberia and Mongolia, the L. lutra counts vary from one individual per 2.5-5.0 lineal river kilometers. In Lithuania riverine densities are even better ranging from one individual per 1.8-5.0 kilometers, with the greatest numbers found in the Jura, Gruda and Anyksta Rivers.

While general population trends of the European otter have trended downward in accordance with the human population explosion of the twentieth century, there are some notable regional trends. In Russia, for example, populations were in general decline during the 1900s, but most of the losses were in Asian Russia as opposed to European Russia. Latvia offers some of the best census data, showing the L.lutra systematic decline of the late 1960s to late 1980s, corresponding to what Bleiere et al refer to as the intense collectivisation period, where enterpreneurial family farms were replaced by state run communal farms. Habitat loss and adverse farming practises resulted from poor conservation practises of the central planned economy rather than human population intensity. Correspondingly the L. lutra population rebounded sharply with the end of Soviet control and the return to capitalistic local run farming at the end of the Cold War.

Feeding Habits

The European otter is a carnivorous mammal that feeds primarily on fish; however, the great majority of fish consumption is of species and fish sizes that are of little commercial importance. If driven by need or opportunity, Lutra lutra can take and devour a fish of several kilograms in body mass. A Romanian stomach contents study found the diet of L .lutra to consist of 78 percent fish; eight percent frogs: six percent other small mammals; and eight percent invertebrates (crustaceans, mollusks, insects) . (Council of Europe. 1996) Furthermore, the European otter is known to be sufficiently opportunistic to consume carrion or even human garbage.

Behaviour

The European otter is rather mobile and has been tracked to cover a typical distance of about 12 kilometers per day, with less need for travel in the summer feeding season when food is most plentiful; however, if necessary, Lutra lutra can cover a distance of 20 to 30 kilometers in a day.  Typical ranges for the species are on the order of ten to twenty square kilometers; home ranges of males do not overlap. Lutra lutra engages in scent marking of territories.

Lutra lutra can close its diminutive ears and its nose when submerged. Mother otters are known to engage in elaborate teaching techniques to instruct cubs in fishing. After a mother has caught a live fish, she will often release it to allow the cubs a close range prey pursuit, sometimes with the fish slightly disabled.

Vocalisations of the European otter may involve a high frequency whistle between a female and her cubs, and also twittering noises emanating during play-fighting; furthermore, cat-like sounds are sometimes produced when members of the same species fight.

Reproduction and Survival

The Lutra lutra species is considered of low fecundity; moreover, female European otters attain sexual maturity at age approximately two years. Only in the far north of the species range is birthing seasonal, with these extreme northern latitude populations giving birth preferentially in late spring to early autumn, coincident with maximum availablity of many prey species. Litter sizes typically range from one to four cubs, with a mean of about 2.4 to 2.6 offspring, depending on regional variance. The young are dependent on maternal care and instruction until age 1.0 to 1.5 years.

Survival of cubs is best illustrated by the age structure of a total L.lutra population. Within sample sizes in the hundreds of total individuals, the first year animals (cubs) represent about 26 to 30 percent of all individuals. Second year animals (advanced cubs and young adults) represent 14 to 16 percent of the total population. The balance of the population are sexually mature adults. The sex composition of the species is extremely stable, with virtually equal numbers of animals of both sexes present in all age cohort groups, from birth to adults.

Conservation

Lutra lutra is classified by the IUCN as Near Threatened. Up until the 1990s there was a generally held opinion that the species was in widespread world decline. More detailed research released at the Netherlands conference in 1994 suggested that L. lutra populations were chiefly suffering in areas subject to relatively high industrialisation, and that the source of mortality was chemical contamination by organochlorine pesticides and herbicides, PCBs and mercury; specifically, the population declines were triggered by bioaccumulation in the food chain of these lipid seeking chemicals. In addition to habitat threat and aquatic related mortality, there are a significant number of deaths from motor vehicles in developed countries, where automobile usage is high.

The European otter has some level of protection in most European countries and parts of Russia. Chief mechanisms of conservation include preservation of coastal habitat; afforestation of inland riparian areas; reduction in use of herbicides and pesticides that can result in aggravation of deleterious runoff to rivers; bans on human killing of otters; and use of gully plugs for overgrazed watersheds experiencing excess erosion.

Specific areas of regional extinction include the Kuril Islands of Russia, as well as numerous rivers and lakes of the Russian regions of Krasnodar and Kursk.

References

  • Daina Bleiere, Butulis Ilgvar, Antonijs Zunda, Aivars Stranga & Inesis Feldmanis. 2006. History of Latvia: the 20th century. Riga: Jumava. ISBN 9984380386
  • J.Conroy, R.Melisch & P.Chanin. 1998 The Distribution And Status Of The Eurasian Otter (Lutra Lutra) In Asia - A Preliminary Review. IUCN Otter Spec.Group Bull. 15(1): 15-30
  • Council of Europe. 1996. Seminar on the conservation of the European otter (Lutra lutra): Leeuwarder, the Netherlands, 7-11 June 1994. 239 pages
  • Encyclopedia of Life. 2011. Lutra lutra
  • S.Hauer et al. 2002. Reproductive performance of otters Lutra lutra (Linnaeus, 1758) in Eastern Germany: Low reproduction in a long-term strategy. Biological Journal of the Linnean Society. 77.3: 329-340.
  • D.Macdonald. 2001. The New Encyclopedia of Mammals. Oxford University Press, Oxford.
  • J.Ruiz-Olmo, A.Loy, C.Cianfrani, P.Yoxon, G.Yoxon, P.K.de Silva, A.Roos, M.Bisther, P.Hajkova & B.Zemanova. 2008. Lutra lutra. In: IUCN 2008. IUCN Red List of Threatened Species. [Database entry explains NearThreatened status of this taxon]
Glossary

Citation

Hogan, C. (2012). European otter. Retrieved from http://www.eoearth.org/view/article/51cbf1f47896bb431f6a74fa

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