Lutra Lutra (Carnivora: Mustelidae)

Abstract

Lutra lutra (Linnaeus, 1758), commonly known as the Eurasian otter, is the most widely distributed of the lutrinids (otters). L. lutra is primarily a piscivorous predator but also preys on amphibians, crustaceans, small mammals, birds, and reptiles. Extant populations of this semiaquatic mustelid occur in a wide variety of aquatic freshwater and marine habitats throughout Asia, all of Europe, and parts of northern Africa. Despite the large distribution, habitat loss has led to dwindling L. lutra populations, particularly in Asia, and the species is currently listed as “Near Threatened” by the International Union for Conservation and Nature and Natural Resources.

Full text

109
Lutra lutra (Carnivora: Mustelidae)
NaNcy HuNg aNd cHris J. Law www.mammalogy.org
Presentation High School, San Jose, CA 95125, USA; nhung@presentationhs.org (NH)
Department of Ecology and Evolutionary Biology, Long Marine Laboratory University of California, Santa Cruz, 100 Shaffer Road,
Santa Cruz, CA 95060, USA; cjlaw@ucsc.edu (CJL)
Present address of NH: Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Abstract: Lutra lutra (Linnaeus, 1758), commonly known as the Eurasian otter, is the most widely distributed of the lutrinids
(otters). L. lutra is primarily a piscivorous predator but also preys on amphibians, crustaceans, small mammals, birds, and reptiles.
Extant populations of this semiaquatic mustelid occur in a wide variety of aquatic freshwater and marine habitats throughout Asia,
all of Europe, and parts of northern Africa. Despite the large distribution, habitat loss has led to dwindling L. lutra populations, par-
ticularly in Asia, and the species is currently listed as “Near Threatened” by the International Union for Conservation and Nature and
Natural Resources.
Key words: Asia, Eurasian otter, Europe, Lutrinae, mustelid, river otter
Synonymy completed 28 August 2014
DOI:10.1093/mspecies/sew011
Version of Record, first published online December 30, 2016, with fixed content and layout in compliance with Art. 8.1.3.2 ICZN.
Nomenclatural statement.—A life science identifier (LSID) number was obtained for this publication: urn:lsid:zoobank.
org:pub:E1B2A866-06A0-4687-A18D-482D27424816
Lutra lutra (Linnaeus, 1758)
Eurasian Otter
Mustela lutra Linnaeus, 1758:45. Type locality “Europae aquis
dulcibus, fluviis, flagnis, piscinis;” restricted to “Upsala”
[Sweden] by Thomas (1911:138).
Lutra vulgaris Erxleben, 1777:448. Type locality “Europae atque
Asiae Americaeque borealis aquis dulcibus, fluuiis, stagnis,
piscinis, non in mari. Est quoque in Persia [= In freshwaters
of North America, Europe and Asia, with the rivers, dams,
reservoirs, and not in the sea. It is also in Persia].”
M[ustela] lutra piscatoria Kerr, 1792:173. Type locality
“Europe, North America, Asia, as far south as Persia.”
Lutra fluviatilis Leach, 1816:6. Type locality unknown.
Lutra barang Cuvier, 1823:246. Type locality “Java…Sumatra.”
Lutra nair Cuvier, 1823:247. Type locality “qui les a rap-
portes de Pondichery, ou pespece est nommee nir-nayie. [=
Pondicherry, India].”
[Lutra vulgaris] marinus Billberg, 1827:28. Type locality
“Scandinaviae.”
Viverra lutra Pallas, 1831:76. Type locality “Per omnem
Rossiam et Sibiram ad usque Camtschatcam…In Americam
quoque transiit…in Caucaso ad Cyrum praesertim fluvium,
in Persia et per omnem tatariam magnam, forte ad Indos
usque.”
Lutra nudipes Melchior, 1834:50. Type locality “Meget almin-
delig paa Sokysterne i det nordlige Norge, for- nemmelig i
Nordlandene; sindes udentvivl ogsaa i Danmark lige- ledes
i Sverrig [= Sokysterne, Norway as well as Denmark and
Sweden].”
MaMMalian SpecieS 48(940):109–122
© 2016 by American Society of Mammalogists.
Fig. 1.—Adult Lutra lutra from Biotop Wildpark Anholter Schweiz,
Germany. Photograph by Arjan Haverkamp used with permission.

110 MAMMALIAN SPECIES 48(940)—Lutra lutra
Lutra roensis Ogilby, 1834:111. Type locality “Ireland.”
Lutra chinensis Gray, 1837:580. Type locality “China.”
Lutra indica Gray, 1837:580. Type locality “Bombay.”
[Lutra] monticolus nobis Hodgson, 1839:28. Type locality
“Nepal.”
[Lutra] auro-brunneus nobis Hodgson, 1839:29. Type locality
“Nepal.”
Lutra kutab Schinz, 1844:354. Type locality “Kashmir.”
Lutra simung Horsfield, 1851:116. Type locality “Sumatra and
Borneo.”
L[utra]. sinensis Hodgson, 1855:126. Type locality “lower
[region of the Himalayas].”
Barangia nepalensis Gray, 1865:124. Type locality “Nepaul.”
Lutonectes whiteleyi Gray, 1867:180. Type locality “Japan.”
Leutronectes whiteleyi Gray, 1869:107. Incorrect subsequent
spelling of Lutonectes whiteleyi Gray, 1867.
Lutra angustifrons Lataste, 1885:115. Type locality “Algeria.”
Lutra lutra: Lataste, 1885:116. First use of current name
combination.
[Lutra] japonica Nehring, 1887:22. Type locality “japanischen.”
Lutra hanensis Matschie, 1906:150. Type locality “Hing-an-fu
[China].”
Lutra lutra splendida Cabrera, 1906:360. Type locality “Mogador
[Essaouira, Morocco].”
Lutra seistanica Birula, 1912:274. Type locality “Gil’mend
River, Seistan, Iran.”
Lutra lutra oxiana Birula, 1915:21. Type locality “Pamir
[Mountains].”
Lutra intermedia Pohle, 1920:62. Type locality “Sumatra.”
Lutra l. ceylonica Pohle, 1920:72. Type locality “Ceylon.”
Lutra vulgaris var. amurensis Dybowski, 1922:349. Type locality
“Amur, Ussuri,” Russia.
Lutra vulgaris var. baicalensis Dybowski, 1922:349. Type locality
“Okolice Baikal,” Russia.
Lutra vulgaris var. kamtschatica Dybowski, 1922:349. Type
locality “Kamchatka,” Russian Far East.
Lutra meridionalis Ognev, 1931:374. Type locality “Teheran.”
Lutra stejnegeri Goldman, 1936:164. Type locality “from near
Petropavlovsk, Kamchatka,” Russian Far East.
Lutra lutra borealis Stroganov, 1960:156. Type locality “Tyumen
Province [Russia].”
Lutra hainana Xu et al., 1983:299. Type locality “Hainan Island.”
Lutra nippon Imaizumi and Yoshiyuki, 1989:178. Type locality
“Nenokubi Seaside, Shimoda, Nakamura City, Kôchi
Prefecture,” Japan.
Context and Content. Order Carnivora, family Mustelidae,
subfamily Lutrinae. Seven to 28 subspecies of Lutra lutra have
been recognized (Larivière and Jennings 2009). In addition, the
now extinct L. l. nippon has been considered a distinct species
based on previous phylogenetic analyses (Suzuki et al. 1996);
however, these analyses were not well supported and additional
information is required to determine its taxonomic status. We
recognized the following 12 extant subspecies, as well as the
extinct L. l. nippon (Wozencraft 2005).
L. l. angustifrons Lataste, 1885. See above; splendida Cabrera,
1906 is a synonym.
L. l. aurobrunnea Hodgson, 1839. See above; auro-brunneus
Hodgson, 1839 and nepalensis Gray, 1865 are synonyms.
L. l. barang Cuvier, 1823. See above; simung Horsfield, 1851
and intermedia Pohle, 1920 are synonyms.
L. l. chinensis Gray, 1837. See above; hanensis Matschie, 1906
and sinensis Hodgson, 1855 are synonyms.
L. l. hainana Xu et al., 1983. See above.
L. l. kutab Schinz, 1844. See above.
L. l. lutra (Linnaeus, 1758). See above; fluviatilis Leach, 1816,
marinus Billberg, 1827, nudipes Melchior, 1834, roen-
sis Ogilby, 1834, stejnegeri Goldman, 1936, and vulgaris
Erxleben, 1777 are synonyms.
L. l. meridionalis Ognev, 1931. See above.
L. l. monticolus Hodgson, 1839. See above.
L. l. nair Cuvier, 1823. See above; ceylonica Pohle, 1920 and
indica Gray, 1837 are synonyms.
L. l. seistanica Birula, 1912. See above; oxiana Birula, 1915 is
a synonym.
L. l. whiteleyi Gray, 1867. See above; japonica Nehring,
1887 and nippon Imaizumi and Yoshiyuki, 1989 are
synonyms.
NoMenclatural NoteS. Other vernacular names for Lutra
lutra are European otter, European river otter, common otter, old
world otter, loutre commune, loutre de rivere, loutre d’Europe,
nutria, and nutria común. The synonyms for Lutra include
Mustela, Viverra, Barangia, and Lutonectes.
DIAGNOSIS
Lutra lutra does not occur sympatrically with other lutrinid
species in Europe and the majority of Asia and can be differ-
entiated from other mustelids by its fully webbed feet, long
tapered tail, and larger size (head-body length and body mass
up to 90 cm and 12 kg, respectively; all other mustelids are
< 82 cm in head-body length and < 6 kg in body mass). In
Southeast Asia, L. lutra occurs sympatrically with the hairy-
nosed otter Lutra sumatrana, the smooth-coated otter Lutrogale
perspicillata, and the Asian small-clawed otter Aonyx cinerea.
Body sizes and pelage coloration are similar between L. lutra
and L. sumatrana; the key difference between these 2 sister
species is the presence of a hair-covered rhinarium as well as
the whitish coloration of the lips, chin, and upper throat found
in L. sumatrana. In contrast, several characteristics distinguish
the smooth-coated otter from L. lutra, including the more
massive head, short smooth fur, naked rhinarium, dark brown
pelage with a clearly demarcated light underbelly, and dorso-
ventrally flattened tail of L. perspicillata (Hwang and Larivière
2005). Lastly, the Asian small-clawed otter can be easily dif-
ferentiated from L. lutra due to the former’s much smaller size
(body mass < 3.8 kg; head-body length < 45 cm) and reduction
of claw size on all feet (Larivière 2003).

48(940)—Lutra lutra MAMMALIAN SPECIES 111
GENERAL CHARACTERS
Physically, Lutra lutra is similar to other otters in having
a broad, round head with whiskers and semiwebbed feet such
that toes are visible (Fig. 1). Its body is elongate and ends with
a cone-shaped tail (Kruuk 2006). The pelage is dense and dark
brown throughout, though lighter on the underside (Larivière and
Jennings 2009). Due to the wide extent of geographical distribu-
tion of L. lutra, intraspecific variation is substantial. L. lutra that
resides in Asia has shorter hair and lighter-colored fur (Sivasothi
and Nor 1994) with a few light patches near the throat (Kruuk
2006) than individuals found in other parts of the distribution
area.
Lutra lutra is sexually dimorphic in that males are 50% larger
than females (Larivière and Jennings 2009). Body mass is 5.45–
11.4 kg for males and 3.36–7.6 kg for females (Conroy et al.
2000). Head-body length is 60–90 cm for males and 59–70 cm
for females, and tail length is 36–47 cm for males and 35–42 cm
for females (Macdonald 1993). Hind foot length is 11–13.5 cm
(Macdonald 1993).
Mean skull measurements (mm; with range and n) for
adult males and females, respectively, from East Germany
were: condylobasal length, 117.41 (106.1–124.3, 102), 109.57
(104.1–121.0, 64); zygomatic breadth, 73.87 (65.9–81.5, 96),
67.33 (61.8–74.8, 58); braincase breadth, 51.09 (45.8–56.1,
101), 48.61 (45.5–52.9, 64); skull height without sagittal crest,
35.43 (32.5–38.2, 101), 33.36 (29.8–38.0, 62); length of upper
toothrow (C–M1), 35.68 (32.4–39.5, 121), 33.41 (30.4–36.9,
80); angular length, 75.19 (66.9–82.0, 132), 68.88 (63.5–76.9,
91); length of lower toothrow (C–M2), 43.42 (38.4–47.9, 138),
40.28 (37.5–44.2, 95); M1 length, 13.55 (11.3–15.4, 145), 12.71
(10.5–14.4, 98); and M1 breadth, 6.82 (5.9–7.7, 147), 6.36 (5.8–
7.1, 97—Ansorge and Stubbe 1995; Fig. 2).
DISTRIBUTION
Lutra lutra is the most widely distributed otter species in the
world, with extant populations occurring throughout Asia, all of
Europe, and parts of northern Africa (Fig. 3). Historical popula-
tions originally extended from Japan in the east to Portugal in the
west, and from the Arctic regions of Asia and Europe to as far
south as Indonesia (Foster-Turley et al. 1990). Although extant
populations remain widespread, L. lutra numbers, particularly in
Europe, are in great decline due to the presence of environmen-
tal pollution, habitat fragmentation, direct persecution, and acci-
dental trappings of otters in fishing nets (Koelewijn et al. 2010).
In Southeast Asia, L. l. chinensis resides in China, Indochina,
Thailand, Malaysia, Vietnam, Ryukyu, and the Tawushan Nature
Reserve in southeast Taiwan (Harris 1968; Lai and Nepal
2006). Two additional subspecies are found in Southeast Asia:
L. l. barang in Thailand, Vietnam, and Sumatra (Koepfli et al. 2008)
and L. l. hainana in Hainan, China. Four subspecies are endemic to
the Indian subcontinent: L. l. aurobrunneus in the lower and cen-
tral hilly region of Nepal; L. l. kutab in Kashmir; L. l. monticolus
in Punjab, Kumaon, Sikkim, and Assam, India; and L. l. nair
in Pondicherry, Sri Lanka, and southern India (Harris 1968;
Romanowski et al. 2010). In the Middle East, L. l. meridiona-
lis occurs in the vicinity of Tehran, northern Iran; from Georgia
through Armenia; Iran to the Persian Gulf; and in Azerbaijan
(Harris 1968; Kasumova and Askerov 2009). L. l. seistanica
occurs in the Helmand River (in Afghanistan), Sistan, Eastern
Iran, Kazakhstan, Uzbekistan, and Turkmenistan (Harris 1968;
Conroy et al. 1998). One subspecies, L. l. angustifrons, is endemic
to Africa and occurs in Morocco and Algeria (Broyer et al. 1988).
Of the 12 extant subspecies, L. l. lutra is the most widely
distributed in Europe and Asia, with populations spanning from
Portugal to South Korea (Kruuk 2006). Countries with recovering
or stable populations of L. l. lutra include Britain (Crawford 2010),
Denmark (Elmeros et al. 2006), France (Janssens et al. 2006),
Germany (Honnen et al. 2011), northwestern Greece and Corfu
Island (Ruiz-Olmo 2006; Karamanlidis et al. 2014), Italy (Marcelli
and Fusillo 2009), Portugal (Trindade 1994), Spain (García Diaz
2008), Slovakia (Urban et al. 2011), and Sweden (Roos et al. 2012).
In addition, L. l. lutra has expanded in northern Upper and Lower
Austria and in the south, across the Danube River; the northern pop-
ulation is comparatively larger in size, differing from the southern
Fig. 2.—Dorsal, ventral, and lateral views of skull and lateral view of
mandible of an adult female Lutra lutra. Photograph taken by Chris
Conroy at the Museum of Vertebrate Zoology, University of California,
Berkeley (Museum of Vertebrate Zoology [MV] Mamm:34264) used
with permission. Total skull length is 10.9 cm.

112 MAMMALIAN SPECIES 48(940)—Lutra lutra
Austrian population, though there is evidence that both populations
meet in the Northern Limestone Alps (Conroy and Chanin 2000).
In Britain, L. l. lutra populations have greatly recovered over the
last 35 years and are now present in every county (Crawford 2010).
Though more abundant in lower altitudinal areas, L. l. lutra may
also be found in the midst of mountainous habitats in European
countries as well as in Tibet at 4,120 m (Ruiz-Olmo 2007).
Recently, L. l. lutra has been reintroduced to areas where
its population remains low, such as the Netherlands (Koelewijn
et al. 2010), Spain (Saavedra and Sargatal 1998), Sweden
(Sjöåsen 1996), Switzerland (Conroy and Chanin 2000), and in
specific areas in Britain (Mason and Macdonald 2004). Breeding
and immigration in these areas in Britain led to a population
annual growth rate of 1–7% with rapid growth following natural
colonization and slower growth as the population reached carry-
ing capacity (Mason and Macdonald 2004). Though L. lutra has
re-expanded in Italy, suitable habitat in the northern area of Italy
remains uninhabited, suggesting a need to expand conservation
efforts to those areas (Marcelli and Fusillo 2009). Populations
remain in decline in several countries such as Israel (Cohen et al.
2013) and Georgia (Gorgadze 2013), and there are several areas
that lack demographic information (Conroy and Chanin 2000).
FOSSIL RECORD
The genus Lutra is known from the late Miocene (Greece
and Spain) and early Pliocene (France), with Lutra affinis
appearing in the fossil record approximately 5.8 million years
ago (Koufos 2011; Montoya et al. 2011). Lutra palaeindica,
from the Pleistocene sediments of the Upper Siwalik Group,
Pakistan, is believed to be ancestral to extant Lutra lutra and
Lutra sumatrana due to the close resemblance and locality
(Willemsen 2006). L. lutra is hypothesized to have originated in
Asia and dispersed into Europe during the latest Pleistocene and
early Holocene (Willemsen 1992). The oldest L. lutra fossils are
known from several Holocene localities in Europe, but no fossil
specimens are known in Asia (Willemsen 1992). It has also been
suggested this species has an earlier origin; however, the major-
ity of L. lutra specimens of Pleistocene age have been assigned
to the extinct species Lutra simplicidens, based on differences in
the dentition and postcranial skeleton (Willemsen 1992).
FORM AND FUNCTION
The dental formula of Lutra lutra is i 3/3, c 1/1, p 4/3, m
1/2, total 36 (Larivière and Jennings 2009). Mean measure-
ments (mm) of P4 (upper carnassial blade) from 7 adult speci-
mens were: greatest length, 10.93; greatest width, 8.01; length
of carnassial shearing blade, 5.79; and greatest length of lingual
sulcus, 6.31. Mean measurements (mm) of M1 from 7 speci-
mens were: length of buccal surface, 6.97; and greatest width,
10.62. Mean measurements of m1 (lower carnassial blade) from
7 specimens were: greatest length, 12.47; greatest width, 5.66;
and length of carnassial shearing blade, 5.34 (Sealfon 2007).
Bite forces calculated using the dry skull method are estimated
to be 147.8 and 216.0 N at the canine and carnassial, respectively
(Christiansen and Wroe 2007).
Ovarian follicle size for immature females, nonbreeding
mature females, and breeding mature females were 1.0–1.6 mm
(mean ± SD 1.30 ± 0.24), 1.2–2.6 mm (mean 1.72 ± 0.32), and
1.0–2.4 mm (mean 1.66 ± 0.36), respectively (Hauer et al. 2002).
The largest follicular diameter in ovaries of estrous females
measured 2.0 mm (Heggberget and Christensen 1994). The pri-
mary corpus luteum is derived from an ovulated follicle, and
the corpus luteum verum is derived from the primary corpus
luteum, which is functionally related to an implanted embryo
(Heggberget and Christensen 1994). Corpus lutea can also be
differentiated into thriving corpus lutea, which is affiliated with
Fig. 3.—Geographic distribution of Lutra lutra. Map redrawn from (Romanowski et al. 2010). Subspecies are: 1, L. l. angustifrons; 2, L. l. auro-
brunnea; 3, L. l. barang; 4, L. l. chinensis; 5, L. l. hainana; 6, L. l. kutab; 7, L. l. lutra; 8, L. l. meridionalis; 9, L. l. monticolus; 10, L. l. nair; 11,
L. l. seistanica; and 12, L. l. whiteleyi.

48(940)—Lutra lutra MAMMALIAN SPECIES 113
embryo implantation (filling 75% of the ovary), and regressing
corpus lutea, which is characterized by placental scars (filling at
least 10% of the ovary—Hauer et al. 2002). Uterine horn lengths
are 17–54 mm in immature females and 26–81 mm in mature
females (Heggberget 1988). The left ovary (168 ± 22 mg)
weighs more than the right (140 ± 16 mg—Heggberget 1988).
Uterus lengths range from (mean ± SD) 45.1 ± 9.2 for immature
females, 62.1 ± 18.1 for nonreproductive, and 65.1 ± 15.3 for
reproductive females (Hauer et al. 2002).
Lutra lutra exhibits several adaptations to survive in cold
environments, such as those in northern Europe and Asia, where
water temperatures are usually below 20°C during the summer
and close to 0°C during the winter (Kruuk et al. 1997). Fur serves
as the primary thermo-insulating mechanism for L. lutra (Kruuk
2006). L. lutra exhibits hair density of about 70,000 hairs/cm2
throughout the body that insulates and regulates internal body
temperature by absorbing air (Kuhn et al. 2010). The majority
of the coat is comprised of secondary hairs, whereas primary
hairs make up only 1.26% of the coat; the coat composition is
not influenced by sex or seasonal variation (Kuhn et al. 2010).
Lutra lutra displays continuous molting (Kruuk 2006; Kuhn
et al. 2010). Grooming and drying occurs in undisturbed places
which are associated with a trail, well-worn from rolling, leading
from the water (Erlinge 1967). L. lutra regularly grooms after
exiting the water to eliminate parasites by rubbing on the ground
or shaking its fur (Kruuk 2006; Kuhn et al. 2010). Grooming
time doubles in a sea water environment compared to when in
a freshwater environment due to the interference of sea water
with the ability to retain air in the fur underwater (Kruuk and
Balharry 1990). In seawater, fur soaks up water rather than air,
which is counterproductive for insulation, as the crystals stiffen
guard hairs and result in the hair forming small bundles, which
could interfere with the spread of lipid secretions from the skin
glands (Kruuk and Balharry 1990).
Lutra lutra has a mean internal body temperature of 38.1°C,
ranging from 35.9°C to 40.4°C (Kruuk et al. 1997). Upon enter-
ing cold water, individuals exhibited a body cooling rate of 2.3°C
per hour (Kruuk et al. 1997). Infrared thermography revealed
that L. lutra primarily dissipates heat through its feet rather than
its trunk, with temperatures at the surface of the feet rising up to
20°C above the temperature at the surface of the trunk (Kuhn and
Meyer 2009). Infrared thermography also revealed that the ears,
peripalpebral region, and vibrissal pads remained consistently
warm and never dropped below 15°C despite being in water
temperatures as low as 4°C (Kuhn and Meyer 2009). Kuhn and
Meyer (2009) suggest that high temperatures are maintained to
ensure functioning of the sensory organs.
Lutra lutra exhibits a high basal metabolism compared to
other mammals of similar sizes. On land, resting metabolic rate
in L. lutra is 4.1 W/kg (38–48% higher than similar-sized terres-
trial mammals), and in water, resting metabolic rate is 6.4 W/kg
(Pfeiffer and Culik 1998; Kruuk 2006). Mean (± SE) energy
expenditure during swimming ranged from 10.3 ± 3.3 W/kg
at speeds of 0.5 m/s to 14.8 ± 4.5 W/kg at speeds of 1.5 m/s
(Pfeiffer and Culik 1998).
Lutra lutra most often dives in shallow areas 0–3 m deep with
a mean (± SE) descending velocity of 0.62 ± 0.02 m/s at an angle of
70° with respect to the surface (Nolet et al. 1993). An adult female
L. lutra is estimated to swim at maximum speeds of 1.3–1.5 m/s
when underwater and swim at about 0.26 m/s when searching for
food (Nolet et al. 1993; Pfeiffer and Culik 1998). However, L. lutra
prefers to swim at speeds of 0.89 m/s (Pfeiffer and Culik 1998).
ONTOGENY AND REPRODUCTION
Young are mostly born during the summer and early autumn
in northern Europe and during the winter and spring in southern
Europe (Ruiz-Olmo et al. 2002). Young are born blind and cov-
ered in short gray fur and each weigh 100–120 g, measure 12 cm
(Wayre 1979; Heggberget and Christensen 1994; Mason and
Macdonald 2009). At 30–35 days old, young weigh 700–800 g
and their eyes have opened (Mason and Macdonald 2009). By
2 months, young weigh 1,075–1,250 g and begin hunting and
eating solid food (Ruiz-Olmo et al. 2002). Lutra lutra young stay
in the den until 2–3 months of age, when they accompany their
mother on their 1st fishing trips (Ruiz-Olmo et al. 2002). Young
also begin to interact with other dyads, such as the occasion of
feeding or playing together (Kruuk 1995). Rearing of young lasts
until at least the age of 5–6 months, and the litter reaches inde-
pendence by 9–12 months (Heggberget and Christensen 1994).
Adult body size is reached by their 1st spring (Ruiz-Olmo et al.
2002), and sexual maturity is attained after 2–3 years (Mason
and Macdonald 2009). Mortality of young is high, with 42% sur-
vival within the 1st year and 33% survival within the 2nd year;
only 25% live longer than 2 years (Stubbe 1969; Jenkins 1980).
Lutra lutra is continuously polyestrous, with mating occur-
ring throughout the year in England and Wales (Mason and
Macdonald 2009). However, some populations—including
Norway (Heggberget and Christensen 1994), Denmark (Elmeros
and Madsen 1999), Shetland (Kruuk 1995), and Sweden (Erlinge
1968a)—exhibit breeding seasons coinciding with favorable
climate conditions that generate greater prey availability (Liles
2000). Individuals of 6–9 years of age form the bulk of reproduc-
tively active females, followed by 10- to 15-year-olds and then
3- to 5-year-olds (Hauer et al. 2002). The frequency of ovulation
and the frequency of pregnancy per mature female per year is 2.0
and 1.1, respectively (Heggberget and Christensen 1994).
Females are receptive 14 days during the 40- to 45-day estrous
cycle (Wayre 1979). Gestation lasts 61–74 days, and peak birth
occurs from late summer to late autumn during the months of
August through November (Heggberget and Christensen 1994;
Hauer et al. 2002). Two to 3 (mean ± SD = 2.5 ± 0.3) young are
born per litter, with mean litter size slightly increasing with the
mother’s age (Hauer et al. 2002).
ECOLOGY
Population characteristics.—Distribution of Lutra lutra is
widespread across Europe and Asia, though population density

114 MAMMALIAN SPECIES 48(940)—Lutra lutra
is uneven in these areas. In southern Sweden, population den-
sity is about 1 individual per 0.7–1.1 km2 of water, 2–3 km of
lake shore, and 5 km of stream (Erlinge 1968a). In Shetland,
based on a stratified random sample survey, densities reach an
estimated 1 adult per 1.2 km and a total of 718 adults with 392
resident females (Kruuk 2006). A survey conducted in the mid-
1980s estimated 6,600 L. lutra in Scotland and 750 in England
and Wales (Kruuk 2006). Using 8 radiotracked individuals
along the Norwegian coastline, Heggberget (1995) estimated
0.4–0.6 individuals per km on islands and 0.1–0.2 individuals
per km on the mainland for a total of 10,000–15,000 individu-
als in the area (Heggberget 1995).
In Germany, Norway, and mainland Shetland, subadults
and adults comprise 8.5–33% and 14.0–43%, respectively, of
the population, whereas juveniles represent 31.7–42.0% of the
population (Ruiz-Olmo et al. 1998). Total mortality rates, which
are correlated with body condition, culminate in November–
December at 43.2% and decline to a minimum of 3.4%, in May–
June (Ruiz-Olmo et al. 1998). Juveniles are the most susceptible
age class to death, as 18.6% die before the age of 1 year (Kruuk
2006). The average life span is generally 12 years; however, a
maximum of 16 years has been recorded in a single individual
from the British Isles (Gorman et al. 1998). In Britain, a study
on road mortality estimated a male:female sex ratio of 1.28:1
(n = 673—Philcox et al. 1999).
Space use.—Lutra lutra primarily lives in coastal or ripar-
ian habitats throughout Europe and Asia and parts of northern
Africa. The home ranges of groups of female L. lutra extend
1–14 km linearly along the coast (Kruuk and Moorhouse
1991). Although individual L. lutra within the group shares
home ranges, each individual spends the majority of its time
within a 0.5–1.6 km core area. Home ranges of up to 19.3
km have been reported for males and oftentimes these over-
lap with female home ranges (Kruuk and Moorhouse 1991).
In southern Italy, genotyped spraint analyses with a sample
of 214 otter spraints identified at least 15 individuals within
Pollino National Park (1,930 km2 in area—Prigioni et al.
2006). Prigioni et al. (2006) estimated maximum watercourse
usage ranged from 0.02 to 34.8 km between individuals.
Genotyped spraint analyses suggest home ranges between up
to 4–6 individuals partially overlap 0.02–14.1 km (Prigioni
et al. 2006). In the Mediterranean climate of southern
Portugal, L. lutra may use reservoirs for food and a constant
water source, especially during the intense droughts of the
dry season (Basto et al. 2011).
In Pertshire Scotland, 2 radiotracked adult females exhib-
ited home ranges of 16 and 22.4 km of waterway, respectively,
a single radiotracked adult male exhibited home ranges of 39.1
km of waterway, and 2 radiotracked subadult males exhibited
home ranges of 20 and 31.6 km of waterway, respectively (Green
et al. 1984). Individuals did not use all locations evenly (Green
et al. 1984). In addition, individuals used a number of resting sites
within their home ranges within a single 24-h period (Green et al.
1984). Traveling between resting sites usually occurred at night;
the 2 radiotracked adult females’ longest distance traveled between
resting sites were 3.8 and 8.9 km (mean distance traveled per night
was 1 and 2.5 km), respectively, and the radiotracked adult male’s
longest distance traveled per night was 16.2 km (mean distance
traveled per night was 3.8 km—Green et al. 1984).
Lutra lutra primarily utilizes a narrow strip of water along
the shore for food and rarely ventures > 2 km away from the
shoreline (Kruuk 2006). An observational survey of 500 dives off
the coast of Shetland revealed that coastal L. lutra dives for food
within 20 m of the shore 62% of the time, within 50 m 84% of the
time, and within 80 m 98% of the time (Kruuk and Moorhouse
1991). L. lutra prefers to dive in shallow waters (0–3 m) and rocky
intertidal areas where benthic prey are more abundant (Kruuk and
Moorhouse 1990). A study of 2 captive L. lutra in Italy indicated
a preference for water close to river banks covered by trees for
hunting, swimming, or playing (Fumagalli 1995).
Lutra lutra may travel long distances, up to 20 km dur-
ing the winter, to find shelter (Erlinge 1967). Throughout the
year, L. lutra uses eutrophic coves for feeding sites, and fish-
ing holes in frozen-over lakes during the winter (Erlinge 1967).
Once the lakes are frozen, streams become its primary feeding
area (Erlinge 1967). L. lutra tends to be more transient during
autumn and spring and more residential during summer and win-
ter (Erlinge 1968a).
Although most individuals spend their time foraging for
prey in the water, they emerge on land to raise their young
in holts, or dens. Depending on the location, different types
of vegetation are more important in constructing holts
(Macdonald and Mason 1983). Bedding includes heather
(Calluna vulgaris), sea weed (Ascophyllum nodosum),
and occasionally, plastic bags (Kruuk 2006). In Shetland,
L. lutra prefers to make holts most commonly within peats
that contain freshwater pools rather than areas with cliffs
and agricultural plots (Kruuk 2006). Mature ash and syca-
more trees are important for L. lutra in Wales and the West
Midlands of England; bankside bramble (Rubus) and reef
swamps are significant components in its habitat in Greece
(Macdonald and Mason 1983). In southern Sweden, L. lutra
uses burrows made by rabbits that are located close to water
(Erlinge 1967). Natal holts are frequently further from
the sea in unobtrusive entrances and are rarely marked by
spraints (Kruuk 2006). L. lutra may dig a system of tunnels
that reach up to 50 m in length and 0.5 m below the surface;
it also uses tunnels created by erosion of soil, rock, or rab-
bit warrens (Kruuk 2006). Females with large young prior
to dispersal tend to inhabit wider streams with rough waters
and rich feeding areas, whereas females with small young
select calm waters and the narrowest stretches of the stream
(Ruiz-Olmo et al. 2005).
Some factors that limit the geographic distribution of L. lutra
include prey abundance, available shelter, and human-induced
influences. Natural factors that limit the spatial distribution of
L. lutra include reproduction, birth, mortality, migration, and
disease.

48(940)—Lutra lutra MAMMALIAN SPECIES 115
Diet.—The diet of Lutra lutra encompasses fish, amphibi-
ans, birds, small mammals, and aquatic invertebrates; however,
diet composition is highly dependent on local prey abundance
and availability (Kruuk 2006). In Europe, a clear latitudinal
gradient in diet composition occurs, where the diet of north-
ern European L. lutra is primarily piscivorous and that of
Mediterranean L. lutra relies less on fish and more on aquatic
invertebrates and reptiles (Clavero et al. 2003). Although the
majority of northern L. lutra populations specialize on fish prey,
some populations exhibit seasonal dietary variation. Along the
Norwegian coast, L. lutra primarily eats fish (92.3% frequency
of occurrence); spraint and stomach content analyses indicate
that Gadidae (17.5%), Cottidae (12.8%), and Pholis gunnellus
(12.4%) are the 3 top fish prey (Heggberget and Moseid 1994).
In the Dee and Don rivers of Scotland, 95% of L. lutra spraint
contained salmonids (Salmo trutta and Salmo salar), followed
by the European eel (Anguilla anguilla—12%), and mammals
(12%—Kruuk et al. 1993). Observations in Shetland found eel-
pout (Zoarces viviparous—34%), rocklings (Ciliata—17%),
and sea scorpion (Taurulus bubalis—14%) are the most impor-
tant prey species (Kruuk and Moorhouse 1990). In Portugal,
L. lutra feeds mostly on small blennies (Blennidae), eels
(A. anguilla), gobies (Gobius), rocklings (Ciliata mustela and
Guidropsarus), wrasses (Labridae—Beja 1991). In Bialowieza
National Park, Eastern Poland, carp species (Cyprinidae) com-
prise 49.7% of prey biomass during the spring and summer
and the common frog (Rana temporaria) make up 65.8% of
prey biomass in the autumn and winter (Brzezinski et al. 1993).
In small watercourses in southwestern Hungary, L. lutra pri-
marily eats fish (33.3–89.9% of total prey biomass), followed
by amphibians (3.4–48.5—Lanszki et al. 2009); fish are eaten
more in winter than in spring, whereas amphibian consumption
is highest in winter and lowest in spring (Lanszki et al. 2009).
In the Ebro Basin rivers of Spain, salmonids (S. trutta) and
cyprinids (mainly Barbus graellsi, B. haasi, and Chondrostoma
toxostoma) represent 85–100% of recorded prey items (Ruiz-
Olmo 2007). However, the relative frequency of fish prey var-
ies with elevation where S. trutta was the dominant prey at
elevations > 500 m and cyprinids were the dominant prey at
elevations < 500 m (Ruiz-Olmo 2007).
Dietary diversification of Mediterranean L. lutra may
be correlated to the unpredictable prey availability in the
Mediterranean, a region that is characterized by hot and humid
summers with little surface water and irregular interannual pre-
cipitation and temperatures (Clavero et al. 2003). The irregular
climate contributes to the fluctuations of droughts and floods that
ultimately lead to unstable fish availability (Clavero et al. 2003).
In Serra de Monfurado of southern Portugal, L. lutra diet varies
seasonally, where American crayfish (Procambarus clarkia) and
fruit are consumed in the dry season and fish (Lepomis gibbosus,
Gambuzia holbrooki, and Micropterus salmoides) and amphib-
ians are consumed during the wet season (Basto et al. 2011). In
Doñana National Park, Spain, fish (A. anguilla, Gambusia affi-
nis, and Cobitis paludicola) occur in 94.3% of spraint, followed
by red-swamp crayfish Procambarus (80.3%), insects (32.3%),
amphibians (28.1%), and reptiles (7.2%—Adrian and Delibes
1987). In Morocco, L. lutra mainly eats fish (76% of frequency
of occurrence), amphibians (22%), and insects (8%—Broyer
et al. 1988). Spraint analysis of L. lutra associated with the
Jajrood River in Iran revealed that L. lutra mainly feeds on fish,
preferring Leuciscus cephalus, Alburnoides bipunctatus, and
Capoeta (Mirzaei et al. 2014). Seasonal variation in prey avail-
ability induces more feeding on birds during the cold season and
more insects during the warm season, although the proportion of
crab consumed remained constant throughout the year (Mirzaei
et al. 2014).
Diet of Asian L. lutra populations is not as well known.
In Sri Lanka, spraint analyses show L. lutra feeds on freshwa-
ter crabs Potamon (81.2% of occurrence), fish (37.5%), and
frogs (8.7%—Silva 1996). Diet of L. lutra from the Huay Kha
Khaeng River, Uthai Thani Province, Thailand, is composed of
fish (76% of spraint), amphibians (64%), and small mammals
(11%—Kruuk et al. 1994). Medium (10–15 cm in length) fish
are preferred—accounting for 51% of total consumed fish—fol-
lowed by small (< 10 cm) fish (34%) and large (> 15 cm) fish
(14%—Kruuk et al. 1994). Females taking care of young bring
back larger prey to their young but consume smaller prey them-
selves (Kruuk 2006).
Lutra lutra dive with a tail-flip in areas usually less than
50 m from the shore and less than 8 m deep and bring their prey
one at a time back to the surface of the water to finish eating,
with dives lasting up to 96 s (Nolet et al. 1993). Hunting usually
occurred in periods of about 13.7 min interspersed with groom-
ing and resting (Nolet and Kruuk 1989). L. lutra brings prey to
land if difficult to manage, such as when eating sea scorpions or
crabs. Though young oftentimes dive with their mother, L. lutra
seldom exhibits cooperative fishing (Kruuk 2006).
Diseases and parasites.—Diseases of wild Lutra lutra
populations are poorly understood due to limited examination
by veterinary pathologists. In South West England, adiaspiro-
myocis, which is caused by inhaling the fungus Emmonsia,
was the most common infectious disease that L. lutra exhibits
(Simpson 2000). Adrenocortical nodular hyperplasia is also
commonly found in L. lutra and is attributed to stress (Simpson
2000). Other recorded conditions include Aleutian disease,
arteriosclerosis, arteritis, distemper virus, hepatic adenocar-
cinoma, leiomyoma, renal calculi, Salmonella infection, and
tuberculosis (Keymer et al. 1988; Wells et al. 1989; Madsen
et al. 2000; Simpson 2000).
Lutra lutra is susceptible to endoparasites such as nema-
todes (Angiostrongylus vasorum, Anisakis, Aonchotheca
putorii, Cryptosporidium, Eucoleus schvalovoj, Dirofilaria
immitis, and Strongyloides lutrae), protozoans (Giardia and
Gigantorhynchus), and trematodes (Phagicola—Madsen et al.
2000; Torres et al. 2004; Méndez-Hermida et al. 2007).
Interspecific interactions.—The distribution range of Lutra
lutra overlaps with the invasive American mink (Neovison
vison) in several regions across Europe and Asia (McDonald
2007). In contrast to what is normally associated with inva-
sions, native L. lutra appears to regulate invading American

116 MAMMALIAN SPECIES 48(940)—Lutra lutra
mink populations (Bonesi and Macdonald 2004a, 2004b).
Increased populations of L. lutra lead to decreased population
size and distribution range of American mink through food
theft (Bonesi et al. 2000), direct aggression (Simpson 2006),
and dietary competition (Clode and Macdonald 1995; Bueno
1996; Bonesi and Macdonald 2004a). In locations where the
2 species are sympatric, American mink altered its diet from
predominately aquatic prey (e.g., Anguillidae and Gadidae) to
more terrestrial prey (birds and mammals), whereas L. lutra
maintained its primarily piscivorous diet (Clode and Macdonald
1995; Bueno 1996; Melero et al. 2008). There are no known
natural predators to adult L. lutra.
In Southeast Asia, L. lutra occurs sympatrically with the
smooth-coated otter, and the Asian small-clawed otter. Direct
competition may be minimized due subtle differences in resource
use and prey specialization. Although L. lutra and the smooth-
coated otter both feed on fish, L. lutra exhibits a relatively more
generalist diet and consumes amphibians and small mammals,
whereas the smooth-coated otter exhibits a more piscivorous
specialized diet and typically feeds on larger fish than L. lutra
(Kruuk et al. 1994). In addition, L. lutra dominates more rapid-
flowing rivers, whereas the smooth-coated otter occurs more
frequently in slow meandering rivers (Kruuk et al. 1994). The
Asian small-clawed otter, on the other hand, is predominantly
a crab specialist and inhabits shallower bodies of water such as
rice fields (Larivière 2003). Lastly, very little is known about
the smooth-coated otter because of low population numbers and
its rather elusive nature; thus, interspecific interactions between
L. lutra and the smooth-coated otter are virtually unknown
(Wright et al. 2008).
HUSBANDRY
Zoos worldwide hold Lutra lutra in captivity for the purpose
of public education and breeding. Captive breeding success of
L. lutra was initially very low until the Otter Trust successfully
raised a litter of L. lutra young in 1972 (Sivasothi and Nor 1994).
Beginning in 1985, the European breeding program for self-
sustaining captive populations (Europaisches Erhaltungszucht
Programm) has successfully bred many L. lutra individuals and
reintroduced them back to the species’ once degraded habitats
(Vogt 1995). Full husbandry and management guidelines can
be found in the Europaisches Erhaltungszucht Programm’s
Eurasian Otter Lutra lutra, Husbandry Guidelines, EEP/
Studbook for Lutra lutra (Melissen 2000) as well as International
Union for Conservation of Nature and Natural Resources Otter
Specialist Group’s Summary of Husbandry Guidelines for the
Eurasian Otter in Captivity (Heap et al. 2010).
BEHAVIOR
Grouping behavior.—Lutra lutra is generally described as
territorial and solitary (Erlinge 1968a), and its shyness and sen-
sitivity to human disturbances make behavioral studies difficult
(Kruuk 1995; Garcia de Leaniz et al. 2006). L. lutra primar-
ily exhibits intrasexual territorial behaviors (Erlinge 1968a; Ó
Néill et al. 2009), and individual territories of the same sex
rarely overlap (Erlinge 1968a; Quaglietta et al. 2014). In a
study of 84 L. lutra interactions, 11% of these interactions were
between males, 27% between females, 40% between male and
female, and 21% between individuals of unknown sex (Kruuk
and Moorhouse 1991).
Male territories are much larger than female territories (Ó
Néill et al. 2009). In Ireland, mean (± SD) male territories was
13.2 ± 5.3 km with aquatic ranges of 30.2 ± 9.5 ha, whereas
mean (± SD) female territories was 7.5 ± 1.5 km with aquatic
ranges of 16.8 ± 7.0 ha (Ó Néill et al. 2009). A hierarchy exists
among L. lutra, where dominate males obtain the best home
ranges in the area and possibly encroach on the territories of
other individuals while the subdominant males occupy less pref-
erable areas (Erlinge 1968a). On rare occasions, interactions that
occur between 2 male individuals result in aggressive behaviors
with physical contact (Kruuk and Moorhouse 1991). Aggression
between males involved fast-speed chases and high-pitched
“wickering” and often resulted in the fleeing of the losing indi-
vidual (Kruuk and Moorhouse 1991; Kruuk 1995). The results of
aggressive encounters are dependent on body size, where smaller
individuals usually portrayed a defensive posture or avoided
larger conspecifics (Kruuk and Moorhouse 1991). Although
scent and sound play a prominent role in communication, visual
displays of males patrolling their territory and sprainting at cer-
tain sites, and swimming in a conspicuous manner parallel to
the shore, 5–10 m out in the water (Kruuk 1995). Males expand
their home range upon the death of neighboring male individuals
(Ó Néill et al. 2009).
In contrast, interactions between female L. lutra are met with
avoidance and “chittering” vocalization; aggression with physi-
cal contact was rare (Kruuk and Moorhouse 1991). Females
within the same home range also exhibit playful behavior, such
as making slides in the snow during winter (Wayre 1979).
Interactions between males and females vary from avoidance
and defensive postures to friendly play (Kruuk and Moorhouse
1991). Females with young are territorial and aggressive toward
adult males because of infanticide risk (Kruuk 1995; Simpson
and Coxon 2000). However, males occasionally force a family
group consisting of mother and young to relocate to another area
(Erlinge 1968a). Recent investigation of sociospatial organiza-
tion suggests that L. lutra may be more social than once believed
(Quaglietta et al. 2014). Individuals of opposite sexes spent
much time together resting, rearing young, and playing rather
than merely converging to forage in high-density prey patches
(Quaglietta et al. 2014).
Reproductive behavior.—Home ranges of adult males and
females with young may overlap, suggesting a polygynous and
polyandrous mating system and intrasexual territoriality (Mason
and Macdonald 2009; Quaglietta et al. 2014). Male-biased dis-
persal also supports the possibility of polygynous mating sys-
tems (Quaglietta et al. 2013). Courtship involves play and mock
fights both in the water and on land (Wayre 1979). In Shetland,

48(940)—Lutra lutra MAMMALIAN SPECIES 117
Lutra lutra mating occurs in the water and during the months
of February until the end of May (Kruuk 2006). Although
L. lutra is able to breed throughout the entire year, mating
typically occurs when food is maximally available (Ruiz-Olmo
et al. 2002). L. lutra in Britain are thought to breed once a year
(Mason and Macdonald 2009), whereas it has been suggested
the females can breed only every 2 year in Sweden (Erlinge
1968a). Estrus and subsequent mating can occur when young
become grown and fully independent (Simpson and Coxon
2000). Females reach sexual maturity at 2 years of age and stay
in breeding condition until 15 years of age (Hauer et al. 2002).
Litter size can range from 1 to 5, but females generally pro-
duce small litters of 1–2 young (Hauer et al. 2002; Ruiz-Olmo
et al. 2011). Higher litter sizes are associated with thriving cor-
pora lutea while lower litter sizes correlated with less implanted
embryos and less appearances of placental scars, an indicator of
giving birth to young (Hauer et al. 2002).
Females with young prefer their personal space and tend to
stay outside of other females’ home ranges, defending their own
core areas (Kruuk and Moorhouse 1991; Kruuk 1995). Although
mating pairs spent a few days together before and then after mating,
the male plays little part in raising young, and females often turn
aggressive toward males (Mason and Macdonald 2009). Males are
kept away from the young by females because males may exhibit
cannibalistic behavior toward unrelated young (Simpson and
Coxon 2000). The suspected reason for this behavior is that males
are interested in increasing their own reproductive fitness; killing
young sired by another male would force the female into estrus,
giving the male a chance to mate (Simpson and Coxon 2000).
Communication.—Lutra lutra, like most other lutrinids,
uses spraints, small amounts of feces deposited at conspicu-
ous vantage point, to claim an area along a strip of land for
the purposes of foraging for food as well as to mark and signal
entrances to holts or dens (Erlinge 1968a). A high amount of
marking occurs when there is a high population density within
an area (Erlinge 1968a). Some postulate that L. lutra spraints
are used for signaling breeding status or maintaining territory
boundaries (Kruuk 2006). However, an observational study in
Shetland found no significant differences in sprainting rates
between otters of different sex or status (Kruuk 1992). In addi-
tion, sprainting rates were not significantly different between ter-
ritory boundaries and within the territory (Kruuk 1992). Instead,
Kruuk (1992) suggests that sprainting is used to communicate
food resources on a seasonal basis. Positive correlations between
the percentage of spraints next to pools of water with high vol-
ume of prey items suggest that territory owners concentrate scent
marks on key resources to drive potential competing conspecif-
ics away (Kruuk 1995; Remonti et al. 2011). More than 30% of
spraints occurred in the intertidal area, and thus the incoming
tides limited the function of its communication for only a short
time (Kruuk 1992). Furthermore, sprainting was seasonal, with
high rates (10 times greater) coinciding with low prey availabil-
ity during the winter compared to the summer (Kruuk 1992).
Vocally, the mother communicates with her young
through whistling (Gnoli and Prigioni 1995; Kruuk 2006).
This melodious whistle is a common call that can carry over hun-
dreds of meters (Kruuk 1995). Whereas a loud whistle is used at
a distance to express uneasiness between a mother and its young,
a feeble whistle, defined as a contact call at close range between
2 individuals, is used between 2 pups (Gnoli and Prigioni 1995).
Similarly, a low cooing sound, described as a murmur, is emit-
ted at close contact interpreted as a greeting exhibited between
mother and young after a short period of separation (Gnoli and
Prigioni 1995). When alarmed by humans or perhaps a predator,
L. lutra exerts a “huff” sound with a quick exhalation of air or
a noisy “blow” sound, with a frequency of 0–10 kHz (Kruuk
1995). Other, vocal calls include “wickering”, which may occur
when alarmed by an intruder on its territory, and the cat-like
“caterwailing” when cornered during a fight (Kruuk 1995).
Aggressive cries, which are characterized with frequencies
higher than 16 kHz, may also occur when quarreling for food
or territory, oftentimes uttered at close range of less than 1 m or
during physical contact (Gnoli and Prigioni 1995).
Miscellaneous behavior.—Lutra lutra swims with only its
eyes and some of its back showing above the surface of the
water (Kruuk 2006). While swimming at the surface, L. lutra
paddles with all 4 feet to keep afloat and uses the tail as a rud-
der (Wayre 1979). To dive, L. lutra flexes its body and propels
down using 2–3 kicks with its hind feet (Wayre 1979).
Hunting bouts occupied a mean time of 13.7 min, with rest-
ing bouts averaging 17.0 min, grooming time 9.1 min, and sleep
6.6 min (Nolet and Kruuk 1989). Although diving behavior does
not differ with depth, metabolic costs are greater at low tempera-
tures, because L. lutra tends to dive for longer periods of time at
shallow depths and shorter times at deeper depths (Nolet et al.
1993). During a dive, L. lutra swims toward the bottom of the
river and then moves upward to attack its prey from below with
an element of surprise (Wayre 1979).
Lutra lutra eats the head of fish first to quickly kill and
consume the prey in a seemingly fixed action pattern (Erlinge
1968b). Young L. lutra spend much time playing with their prey
before eating it, following fish at a distance of 0.2–0.3 m (Erlinge
1968b). L. lutra prefers live to dead prey and slower moving prey
to fast-moving; however, hungry individuals will eat anything
available, including dead fish (Erlinge 1968b).
Lutra lutra living in freshwater habitats tends to be more
nocturnal than coastal individuals (Beja 1996; Karamanlidis
et al. 2014). Depending on its prey’s lifestyle, L. lutra is active
during the opposite time of day so they can more easily prey on
the animals in torpor (Kruuk and Moorhouse 1990). For exam-
ple, important prey for L. lutra that are active during the night,
but hide under rocks during the daytime, are vulnerable to hunt-
ing during the day (Kruuk and Moorhouse 1990).
GENETICS
Despite being widely distributed in Europe, Lutra lutra pop-
ulations exhibit low genetic variability. Network analyses using
mitochondrial DNA (mtDNA) found no signal of phylogenetic

118 MAMMALIAN SPECIES 48(940)—Lutra lutra
structuring despite high haplotype diversity (0.79 ± 0.037 SD—
Mucci et al. 2010). Low nucleotide diversity (0.0014 ± 0.00012
SD) and average number of pairwise differences (2.25) suggest
that extant L. lutra mtDNA lineages originated recently (Mucci
et al. 2010). Autosomal microsatellites reveal moderate genetic
diversity across European populations (Randi et al. 2003;
Mucci et al. 2010). The average observed heterozygosity was
(Ho = 0.50) with the lowest observed heterozygosity in Denmark
(Ho = 0.35) and highest observed heterozygosity in Belarus,
Finland, Latvia, and Sweden (Ho > 0.65) (Mucci et al. 2010).
Furthermore, there was no evidence for geographical distribu-
tion within these European populations (Mucci et al. 2010).
Lutra lutra populations in Israel are genetically unique
from European populations, indicating limited or absent gene
flow between the 2 localities (Cohen et al. 2013). Similarly to
European L. lutra populations, observed heterozygosity in Israeli
L. lutra was moderate (Ho = 0.482—Cohen et al. 2013). Genetic
diversity in other Asian L. lutra populations is poorly studied.
Because L. lutra is an elusive species that is hard to cap-
ture, noninvasive genetic monitoring from hair and feces can use
DNA as a molecular “tag” to track the efforts of reintroduced
populations (Mucci and Randi 2007; Seignobosc et al. 2011).
Accounting for time, estimations of survival and reproduction
rates may be able to predict how much mortality a population
tolerates (Seignobosc et al. 2011).
Phylogenetic analyses using mitochondrial and nuclear
DNA demonstrated that the genus Lutra consists of only L. lutra
and Lutra sumatrana (Koepfli et al. 2008). Lutra, in turn, is sister
to a clade containing Aonyx and Lutrogale (Koepfli et al. 2008).
CONSERVATION
Lutra lutra is listed as “Near Threatened” by the International
Union for Conservation of Nature and Natural Resources since
2004 (Roos et al. 2015) and under Appendix I by the Convention
on International Trade in Endangered Species of Wild Fauna and
Flora (CITES 2016). Additionally, L. lutra is protected by sev-
eral European and Asian governments such as Appendix II of
the Convention on the Conservation of European Wildlife and
Natural Habitats (Bern Convention 2016) and Wild Animals
Protection Ordinance Cap 170 in Hong Kong (Wild Animals
Protection Ordinance 2016).
During the 2nd half of the 20th century, many L. lutra popu-
lations in several European and Asian countries sharply declined
due to hunting and pollution (Mucci et al. 2010). L. lutra was
hunted for its prized pelt or for sport (Conroy et al. 2000). In
addition, L. lutra was persecuted for being a nuisance to fish-
erman, eating fish and playing in rice fields, which resulted in
profit loses for farmers (Rasooli et al. 2007). In Europe, contami-
nants such as polychlorinated biphenyl (PCB) severely dimin-
ished the population of L. lutra (Mason and Macdonald 1993).
Major threats to current populations of L. lutra are pollution
and habitat alterations (Mucci et al. 2010). Originally, misled
theories hypothesized that the steep L. lutra population decline
in the 2nd half of the 20th century was caused by competition
with the America mink. However, it is now well established that
organochlorine pollution that peaked before the mink’s arrival
brought about L. lutra population decline (McDonald 2007).
Organochlorines dieldrin (HEOD) and DDT/DDE, PCBs, and
mercury are the main pollutants that pose a danger to L. lutra
in western and central Europe (Roos et al. 2015). An average
of 80 mg/kg of DDT, a substance that causes neuronal damage,
was found in the bodies of L. lutra in Spain (Ruiz-Olmo et al.
2002). Bioaccumulation of organochlorines and heavy metals
has also indirectly damaged L. lutra by harming its prey (Mucci
et al. 2010). L. lutra is sensitive to pH changes in the water,
with acidification affecting the carrying capacity in the area,
and requiring large numbers of lakes and fjords for breeding
uses (Madsen and Prang 2001). Anthropogenic habitat altera-
tions—including mining, construction of river canals, dams, and
aquacultures, and habitat degradation through drainage of wet-
lands and removal of—are all detrimental to L. lutra populations
(Mucci et al. 2010). Lastly, L. lutra is occasionally accidentally
caught in traps and cages meant for other species such as musk-
rats (Ondatra zibethicus) as well as hit by vehicles on the road
(Madsen and Prang 2001).
Population surveys and monitoring through analyses of scat,
spraint, and genetics have been conducted over most of Western
Europe and in parts of Asia (Roos et al. 2015). These sampling
efforts play a huge role in determining the status of L. lutra pop-
ulations. Since the establishment of environmental protection
efforts in 1974, the population in Europe has rebounded in many
European countries including Britain (Crawford 2010), Denmark
(Elmeros et al. 2006), France (Janssens et al. 2006), Germany
(Honnen et al. 2011), northwestern Greece and Corfu Island
(Ruiz-Olmo 2006; Karamanlidis et al. 2014), Italy (Marcelli
and Fusillo 2009), Portugal (Trindade 1994), Spain (García Diaz
2008), Slovakia (Urban et al. 2011), and Sweden (Roos et al.
2012). However, although L. lutra are protected several govern-
ments and organizations, the improvements are at best minimal
because of their unprotected habitat areas in remaining coun-
tries (Mucci et al. 2010). Pollution and exploitation of land areas
diminish the ability of L. lutra to rebound in numbers (Sivasothi
and Nor 1994). L. lutra continues to face the same problems in
multiple countries and it is highly endangered or nearly extinct in
countries such as Morocco, Austria, Slovenia, Poland, Tajikstan,
and Uzbekistan; it is considered extinct in Albania, Slovakia,
Hungary, Belarus, Romania, Bulgaria, Kazakhstan, Andorra,
Luxeumbourg, and Switzerland (Conroy et al. 2000).
ACKNOWLEDGMENTS
We are grateful to A. Haverkamp for providing the photo-
graph of Lutra lutra as well as to C. Conroy for taking pho-
tographs of the skull arrangement at the Museum of Vertebrate
Zoology, University of California, Berkeley. Lastly, we thank
an anonymous reviewer for helpful feedback on this species
account and the Science Internship Program (University of
California, Santa Cruz) for giving NH the opportunity to con-
duct research as a high school student. Financial support was

48(940)—Lutra lutra MAMMALIAN SPECIES 119
provided by the Department of Ecology and Evolutionary
Biology at the University of California, Santa Cruz and National
Science Foundation Graduate Research Fellowship to CJL.
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Associate Editor of this account was jaMie M. HarriS. Editor was
Meredith J. HaMilton.