The Eurasian otter, also known as European otter, common otter and Old World otter is a species of otter of the genus Lutra. It is the most widely distributed of all otters and inhabits most of Eurasia and parts of Africa.
Eurasian otters grow between 1 and 1.3 meters long and can weigh up to 12 kilograms. It is brown in colour except for its neck and chest, which is cream-coloured. Female Eurasian otters are on average 20 centimeters shorter and 10 kilograms lighter. The Eurasian otter's fur is very thick, and the individual hairs fasten together when diving to form an airtight seal, keeping the otter warm.
The Eurasian otter has one of the widest distributions among mammals, ranging from Ireland to China and South-East Asia and including North Africa (Algeria, Tunisia and Morocco). Its status is declining or unknown in many parts of its range.
Twelve subspecies of Lutra lutra are known to exist across its vast range, the most widely distributed of which being Lutra lutra lutra, which is found across most of Europe, in Russia, and in central and eastern continental Asia. Other subspecies are:
- L. l. angustifrons, found in North Africa
- L. l. aurobrunnea, found in the Himalayas
- L. l. barang, found in Sumatra, Thailand, Vietnam and Laos,
- L. l. chinensis, found in southern China,
- L. l. hainana, found on the island of Hainan,
- L. l. kutab, found in Kashmir,
- L. l. meridionalis, found in Iran and in the Caucasus,
- L. l. monticolus, found in Punjab, Kumaon, Sikkim, and Assam, India,
- L. l. nair, found in southern India and Sri Lanka,
- L. l. seistanica, found in Central Asia,
- L. l. whiteleyi, found in Hokkaido, Japan.
The Eurasian otter is found in both inland water and coastal environments.
The diet of the Eurasian otter is versatile and depends on the local availability of prey. Precise data on the diet and food supply of Eurasian otters is difficult to obtain due to its secretive and nocturnal nature.
The Eurasian Otter, being a piscivore predator, preys underwater and along the water's edge. When the otter spots its prey, the pursuit may last for two or three minutes. Otters are often observed swimming beneath a shoal of fish, pursuing its slowest member. Fish that seek cover in the brambles or rocks near the water's edge easily fall prey to the otter.
In coastal Eurasian otters, preying typically occurs within 10-100 metres of the shore at depths between 2 and 5 metres, with most prey species being demersal fish (groundfish) and crabs. In marine environments, Eurasian otters dive down vertically and rarely have to pursue their prey. Foraging can also occur directly on the water's edge during low tide, with otters searching for food in the seaweed.
Eurasian Otters are solitary animals who live in intra-sexually exclusive territories. That means that both males and females will have their own home ranges which they defend from other specimen of their respective sex. These home ranges are several kilometers, and often in excess of 18 kilometers in size.
The status of the Eurasian otter throughout most of Asia has suffered from a lack of research. However, most areas that have been researched show a declining or disappearing population. Likewise, little is known about the status of Eurasian otters in North Africa. In Morocco, only minor changes in population occurred between 1983 and 2011. In Europe, the species' status is classified as "good" in the British Isles, Eastern Europe, Iberia, southern Italy, Greece, and the French shores of the Bay of Biscay, while receiving a "poor" classification in Germany, Slovakia and south-central France and a "bad" classification in Sweden and southern France. Otters are notably absent from the urbanised areas of the western European "Blue Banana", with the exception of England. 
Chemical pollutants, especially organochlorine compounds such as polychlorinated biphenyls (PCBs) are characterized as one of the factors, if not the definitive cause, of the decline of Eurasian otter populations in Europe. These compounds can lead to many health effects in otters, such as immune, reproductive and endocrine failures.  Other researchers have contested that the significance of PCBs is overstated, citing the fact that thriving otter populations with high PCB levels also exist.
- ↑ 1.0 1.1 1.2 Biologie des Otters. Aktion Fischotterschutz e. V. Otter Spotter. https://www.otterspotter.de/biologie-des-otters Retrieved: 25 Oct 2021.
- ↑ 2.0 2.1 International Otter Survival Fund: Otter Species: Lutra Lutra. https://otter.org/Public/AboutOtters_OtterSpecies.aspx?speciesID=1. Retrieved: 25 Oct 2021
- ↑ Eurasian otter (Lutra lutra). Carol Bennetto. https://ottered.com/13-otter-species/eurasian-otter/ Retrieved: 25 Oct 2021.
- ↑ Lutra lutra (Carnivora: Mustelidae). Nancy Hung, Chris J. Law. In: Mammalian Species, Volume 48, Issue 940, 30 December 2016, Pages 109–122, https://doi.org/10.1093/mspecies/sew011
- ↑ 5.0 5.1 5.2 C. F. Mason, S. M. Macdonald. Otters: Ecology and Conservation. Cambridge University Press, 1986.
- ↑ 6.0 6.1 Watson, Hugh Christopher (1986) The feeding ecology of the European otter (lutra lutra l.) in a marine environment, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/6777
- ↑ Ó Néill, L., Veldhuizen, T., Jongh, A. de and Rochford, J. (2009). Ranging behaviour and socio-biology of Eurasian otters (Lutra lutra) on lowland mesotrophic river systems. Eur J Wildl Res, 55: 363-370
- ↑ Citation: Conroy, J, Melisch, R and Chanin, P (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
- ↑ Delibes M., Calzada J., Clavero M., Fernández N., Gutiérrez-Expósito C., Revilla E. & Román J. (2012) The Near Threatened Eurasian otter Lutra lutra in Morocco: no sign of recovery. Oryx 46: 249–252
- ↑ European Environment Agency (EEA): Eurasian otter - Lutra lutra (Linnaeus, 1758) https://eunis.eea.europa.eu/species/Lutra%20lutra Retrieved: 21 Dec 2021.
- ↑ Gutleb, A.C., Kranz, A. (1998). Estimation of Polychlorinated Biphenyl (PCB) Levels in Livers of the Otter (Lutra lutra) from Concentrations in Scats and Fish. Water, Air, and Soil Pollution, 106:481 - 491
- ↑ Mason, C. (1997). The Significance of PCBs in Otters at National and Regional Scale. IUCN Otter Spec. Group Bull. 14 (1): 3 - 12
- ↑ Sauer, P. J. J., et al. “Effects of Polychlorinated Biphenyls (PCBs) and Dioxins on Growth and Development.” Human & Experimental Toxicology, Dec. 1994, pp. 900–906, doi:10.1177/096032719401301213.
- ↑ Kruuk, H. (1997). The Significance of PCBs in Otters: A Reply. IUCN Otter Spec. Group Bull. 14 (2): 54 - 55