Mustela lutra Linnaeus, 1758
The Eurasian otter (Lutra lutra), also known as the European otter, Eurasian river otter, common otter, and Old World otter, is a semiaquatic mammal native to Eurasia. The most widely distributed member of the otter subfamily (Lutrinae) of the weasel family (Mustelidae), it is found in the waterways and coasts of Europe, many parts of Asia, and parts of northern Africa. The Eurasian otter has a diet mainly of fish, and is strongly territorial. It is endangered in some parts of its range, but is recovering in others.
The Eurasian otter is a typical species of the otter subfamily. Brown above and cream below, these long, slender creatures are well-equipped for their aquatic habits. Their bones show osteosclerosis, increasing their density to reduce buoyancy. This otter differs from the North American river otter by its shorter neck, broader visage, the greater space between the ears and its longer tail. However, the Eurasian otter is the only otter in much of its range, so it is rarely confused for any other animal. Normally, this species is 57 to 95 cm (22.5 to 37.5 in) long, not counting a tail of 35–45 cm (14–17.5 in). The female is shorter than the male. The otter's average body weight is 7 to 12 kg (15 to 26 lb), although occasionally a large old male may reach up to 17 kg (37 lb). The record-sized specimen, reported by a reliable source but not verified, weighed over 24 kg (53 lb).
Distribution and habitat
The Eurasian otter is the most widely distributed otter species, its range including parts of Asia and Africa, as well as being spread across Europe, south to Israel. Though currently believed to be extinct in Liechtenstein and Switzerland, they are now very common in Latvia, along the coast of Norway, in the western regions of Spain and Portugal and across Great Britain, especially Shetland, where 12% of the UK breeding population exists. Ireland's otters are geographically widespread and believed to be the most stable population in Europe. In Italy, they can be found in southern parts of the peninsula. The South Korean population is endangered. In India, the species is distributed in the Himalayan foothills, southern Western Ghats and the central Indian landscape.
In general, their varied and adaptable diets mean they may inhabit any unpolluted body of fresh water, including lakes, streams, rivers, canals and ponds, as long as the food supply is adequate. In Andalusia the golf courses became part of their habitat. Eurasian otters may also live along the coast, in salt water, but require regular access to fresh water to clean their fur. When living in the sea, individuals of this species are sometimes referred to as "sea otters", but they should not be confused with the true sea otter, a North Pacific species much more strongly adapted to a marine existence.
The extinct Japanese river otter is usually considered a subspecies.
The Eurasian otter's diet mainly consists of fish. Fish is their most preferred choice of food in Mediterranean and temperate freshwater habitats. During the winter and in colder environments, though, fish consumption is significantly lower, and the otters use other sources of food, including amphibians, crustaceans, insects, birds and sometimes small mammals, including young beavers.
Eurasian otters are strongly territorial, living alone for the most part. An individual's territory may vary between about 1 and 40 km (1–25 mi) long, with about 18 km (11 mi) being usual. The length of the territory depends on the density of food available and the width of the water suitable for hunting (it is shorter on coasts, where the available width is much wider, and longer on narrower rivers).The Eurasian otter uses its feces, spraints, to mark its territory and prioritize the use of resources to other group members. The territories are only held against members of the same sex, so those of males and females may overlap. Mating takes place in water. Eurasian otters are nonseasonal breeders (males and females will breed at any time of the year) and it has been found that their mating season is most likely determined simply by the otters' reproductive maturity and physiological state. Female otters become sexually mature between 18 and 24 months old and the average age of first breeding is found to be 2 1⁄2 years. Gestation for the Eurasian otter is 60–64 days, the litter weighing about 10% of the female body mass. After the gestation period, one to four pups are born, which remain dependent on the mother for about 13 months. The male plays no direct role in parental care, although the territory of a female with her pups is usually entirely within that of the male. Hunting mainly takes place at night, while the day is usually spent in the Eurasian otter's holt (den) – usually a burrow or hollow tree on the riverbank which can sometimes only be entered from underwater. Though long thought to hunt using sight and touch only, evidence is emerging that they may also be able to smell underwater – possibly in a similar manner to the star-nosed mole.
The Eurasian otter declined across its range in the second half of the 20th century primarily due to pollution from pesticides such as organochlorine and polychlorinated biphenyls. Other threats included habitat loss and hunting, both legal and illegal. Eurasian otter populations are now recovering in many parts of Europe. In the United Kingdom, the number of sites with an otter presence increased by 55% between 1994 and 2002. In August, 2011, the Environment Agency announced that otters had returned to every county in England since vanishing from every county except the West Country and parts of Northern England. Recovery is partly due to a ban on the most harmful pesticides that has been in place across Europe since 1979, partly to improvements in water quality leading to increases in prey populations, and partly to direct legal protection under the European Union Habitats Directive and national legislation in several European countries. In Hong Kong, it is a protected species under Wild Animals Protection Ordinance Cap 170. It is listed as Near Threatened by the IUCN Red List.
Most species that are victims of population decline or a loss of habitat tend to eventually lose their genetic difference due to inbreeding from small populations. A study conducted in 2001, examined whether or not the populations of Eurasian otters suffered from a lack of genetic variability. In the study, they examined teeth of otter skulls at the Zoological Museum, Copenhagen and the Natural History Museum, Aarhus. The samples were collected between 1883 and 1963 in Denmark (Funen, Zealand, and Jutland). The study examined the tissue on the teeth of the skulls and determined the genetic variability based on DNA analysis. In conclusion, the study discovered that despite the population declines, the Eurasian otter was not a victim of declining genetic variability.
The decline in population of native freshwater fishes, which is the preferred food of Eurasian otters, in the rivers of Iberia, along with the expansion of exotic fish species like centrarchids could potentially put Eurasian otters at risk for extinction. 
- Roos, A.; Loy, A.; de Silva, P.; Hajkova, P.; Zemanová, B. (2015). "Lutra lutra". The IUCN Red List of Threatened Species. IUCN. 2015: e.T12419A21935287. doi:10.2305/IUCN.UK.2015-2.RLTS.T12419A21935287.en.
- Hayashi, S.; Houssaye, A.; Nakajima, Y.; Chiba, K.; Ando, T.; Sawamura, H.; Inuzuka, N.; Kaneko, N.; Osaki, T. (2013). "Bone Inner Structure Suggests Increasing Aquatic Adaptations in Desmostylia (Mammalia, Afrotheria)". PLoS ONE. 8 (4): e59146. Bibcode:2013PLoSO...859146H. doi:10.1371/journal.pone.0059146. PMC 3615000. PMID 23565143.
- Godman, John Davidson (1836) American Natural History, Hogan & Thompson.
- Hans, Kruuk (2007). Otters ecology, behavior and conservation. Oxford University Press. ISBN 978-0-19-856587-1.
- European Otter. theanimalfiles.com
- European otter Archived 2011-12-23 at the Wayback Machine. purpleopurple.com
- Wood, Gerald L. (1983) The Guinness Book of Animal Facts and Feats. Sterling Pub Co Inc., ISBN 978-0-85112-235-9
- "Shetland Otters". Shetland Otters. Retrieved 2010-03-15.
- "Vincent Wildlife Trust, Ireland: Otter". Retrieved 28 October 2018.
- "Joshi, AS, Tumsare, VM, Nagar, AK, Mishra, AK and Pariwakam, MP (2016). Photographic Records of Eurasian Otter Lutra lutra from the Central Indian Landscape. IUCN Otter Spec. Group Bull. 33 (1): 73 – 78". www.otterspecialistgroup.org. IUCN. 2017. Retrieved 2017-01-27.
- "The Use of Artificial Lakes on Golf Courses as Feeding Areas by the Otter (Lutra lutra) in Southern Spain".
- Jędrzejewska, B.; Sidorovich, V. E.; Pikulik, M. M.; Jędrzejewski, W. (2001). "Feeding habits of the otter and the American mink in Białowieża Primeval Forest (Poland) compared to other Eurasian populations". Ecography. 24 (2): 165–180. doi:10.1034/j.1600-0587.2001.240207.x.
- Clavero, Miguel; Prenda, José; Delibes, Miguel (2003-05-01). "Trophic diversity of the otter (Lutra lutra L.) in temperate and Mediterranean freshwater habitats". Journal of Biogeography. 30 (5): 761–769. doi:10.1046/j.1365-2699.2003.00865.x. hdl:10272/2962. ISSN 1365-2699.
- Pagacz, Stanisław; Witczuk, Julia (2010). "Intensive exploitation of amphibians by Eurasian otter (Lutra lutra) in the Wolosaty stream, southeastern Poland" (PDF). Annales Zoologici Fennici. 47 (6): 403–410. doi:10.5735/086.047.0604.
- Weber, J.-M. (1990). "Seasonal exploitation of amphibians by otters (Lutra lutra) in north-east Scotland". Journal of Zoology. 220 (4): 641–651. doi:10.1111/j.1469-7998.1990.tb04740.x.
- Kitchener, Andrew (2001). Beavers. Whittet Books. p. 144. ISBN 978-1-873580-55-4.
- Kruuk, H. (1992-06-20). "Scent marking by otters (Lutra lutra): signaling the use of resources". Behavioral Ecology. 3 (2): 133–140. doi:10.1093/beheco/3.2.133. ISSN 1045-2249.
- Erlinge, S. (1968). "Territoriality of the otter Lutra lutra L.". Oikos. 19 (1): 81–98. doi:10.2307/3564733. JSTOR 3564733.
- Hauer, Silek; Ansorge, Hermann; Zinke, Olaf (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. doi:10.1046/j.1095-8312.2002.00097.x.
- Alleyne, Richard (2010-06-05). "Can otters smell underwater?". Daily Telegraph. London. Archived from the original on 2010-06-06. Retrieved 2010-06-06.
Hamilton James said: “I always had an inkling that otters could smell under water and I wanted to prove it. As it was dark and the fish was fully submerged, it proved that the otters had to be using a sense other than sight or touch to locate it. After reviewing the footage I noticed a tiny bubble which hit the fish and was sniffed back in by the otter.”CS1 maint: ref=harv (link)
- Director: Richard Taylor Jones; Camera Operators: Richard Taylor Jones, Charlie Hamilton James; Producer: Philippa Forrester (2010-06-06). "Late Summer". Halcyon River Diaries. Episode 4. London. BBC. BBC One.
- "The Eurasian Otter (Lutra lutra)". English Nature. Retrieved 2010-03-15.
- "Otter: Background to selection". Jncc.gov.uk. Retrieved 2010-03-15.
- Michael McCarthy (2011-08-18). "Otters return to every county in England". The Independent. Retrieved 2011-08-19.
- "Council Directive 79/117/EEC of 21 December 1978". Eur-lex.europa.eu. Retrieved 2010-03-15.
- "Council Directive 92/43/EEC of 21 May 1992". Eur-lex.europa.eu. Retrieved 2010-03-15.
- "Species other than birds specially protected under The Wildlife and Countryside Act, 1981: Schedule 5 (Animals)". Jncc.gov.uk. 2005-08-30. Archived from the original on 2009-01-22. Retrieved 2010-03-15.
- "Wildlife Act 1976 (Ireland)". Internationalwildlifelaw.org. 1976-12-22. Archived from the original on December 8, 2006. Retrieved 2010-03-15.
- Otters of the world. otter.org
- Pertoldi, Cino; Hansen, Michael Møller; Loeschcke, Volker; Madsen, Aksel Bo; Jacobsen, Lene; Baagoe, Hans (2001-09-07). "Genetic consequences of population decline in the European otter (Lutra lutra): an assessment of microsatellite DNA variation in Danish otters from 1883 to 1993". Proceedings of the Royal Society of London B: Biological Sciences. 268 (1478): 1775–1781. doi:10.1098/rspb.2001.1762. ISSN 0962-8452. PMC 1088808. PMID 11522195.
- Blanco-Garrido, F., Prenda, J., Narvaez, M. “Eurasian otter (Lutra lutra) diet and prey selection in Mediterranean streams invaded by centrarchid fishes.” Springer Science+Business Media B.V., 2007.
|Wikimedia Commons has media related to Lutra lutra.|
|Wikispecies has information related to Lutra lutra|