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What the sources say

Eurasian OtterLutra lutra

Every figure, record and mechanism on the Eurasian Otter profile was written from a source, and this is the working table behind it: 44 claims checked word for word against these sources. The left column is what the page says. The right column is the source's own words, copied, not paraphrased; a ... marks a cut and[brackets] an insertion. Open any source and check it yourself.

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Source
01

Animal Diversity Web, University of Michigan

Lutra lutra (European otter). Animal Diversity Web, University of Michigan.

The page saysWhiskers that sense a fish moving through the water
The source saysThey use their vibrissae (whiskers) as sensing organs underwater to monitor the movements of fishes and other prey.Note: tagline
The page saysRivers, lakes, coastal fjords, peat swamps and rice paddies across Europe, North Africa and Asia, as far as Japan and Indonesia
The source saysThey inhabit rivers, lakes, streams, freshwater and peat swamp forests, ricefields, ocean shores, fjords, caves, and terrestrial habitats adjacent to waterways.Note: stats.habitat; ricefields -> rice paddies. Range portion (Europe, North Africa, Asia to Japan and Indonesia) is sdz-otter, same quote as the heading claim above
The page saysFish, crustaceans, amphibians, small mammals, birds, eggs, insects and worms
The source saysLutra lutra individuals eat fish, crustaceans, clams, small mammals and amphibians, birds, eggs, insects, worms, and a small amount of vegetation.Note: stats.diet; clams and the small amount of vegetation dropped for brevity, not misrepresented
The page saystrack the movements of fish and other prey underwater
The source saysThey use their vibrissae (whiskers) as sensing organs underwater to monitor the movements of fishes and other prey.Note: stats.superpower
The page saysRivers, lakes, coastal fjords, peat swamps and rice paddies count as home
The source saysThey inhabit rivers, lakes, streams, freshwater and peat swamp forests, ricefields, ocean shores, fjords, caves, and terrestrial habitats adjacent to waterways.Note: ricefields -> rice paddies
The page saysIn a territory of 1 to 4 miles, each otter keeps fixed places for getting in and out of the water, rolling, sunbathing and sliding down "otter stairways"
The source saysIn its territory of 1 to 4 miles, each river otter has fixed locations for getting into and out of the water, rolling, sunbathing, and sliding on "otter stairways".
The page saysand track the movements of fish underwater
The source saysThey use their vibrissae (whiskers) as sensing organs underwater to monitor the movements of fishes and other prey.
The page saysIt can dive for up to two minutes and is most active at dusk and during the night
The source saysRiver otters can dive for up to two minutes underwater and are most active at dusk and during the night.
The page saysIts catch list is long: fish, crustaceans, amphibians, small mammals, birds, eggs, insects and worms, about a kilogram of food a day
The source saysLutra lutra individuals eat fish, crustaceans, clams, small mammals and amphibians, birds, eggs, insects, worms, and a small amount of vegetation ... River otters hunt and feed several times a day, consuming about 1kg of food daily.
The page saysEurasian otters are basically solitary. Mates pair only briefly and mothers keep their young with them for a time, though loose groups of up to six sometimes turn up
The source saysLutra lutra are basically solitary animals with only temporary pairing of mates or mothers with their young, although they are sometimes found in loosely knit groups of up to six animals.Note: temporary -> briefly / for a time
The page saysThey are vocal too, with basic calls for alarm, greeting and mating plus up to 12 others, from shrill whistles and yelps to high-pitched screams of distress
The source saysLutra lutra are vocal, with basic calls of alarm, greeting, and mating as well as up to 12 other calls. The voice of L.lutra consists of short, shrill whistling, yelps, whimpers, and high pitched screams of distress.
The page saysPaired scent glands at the base of the tail give off a heavy, musky smell, and scent marks carry news of territory boundaries, identity and sexual state
The source saysRiver otters have paired scent glands at the base of their tail which give off a heavy, musky smell. Scent marking is a form of communication between otters about the territorial boundaries, identity, and sexual state of each otter.
The page saysWith its whiskers. The vibrissae work as sensing organs underwater, picking up the movements of fish and other prey
The source saysThey use their vibrissae (whiskers) as sensing organs underwater to monitor the movements of fishes and other prey.Note: faq 1
The page saysAn otter hunts and feeds several times a day and gets through about a kilogram of food daily
The source saysRiver otters hunt and feed several times a day, consuming about 1kg of food daily.Note: faq 1
The page saysfor an otter whose voice is short, shrill whistles and yelps
The source saysThe voice of L.lutra consists of short, shrill whistling, yelps, whimpers, and high pitched screams of distress.Note: vibe.reason
The page saysalarm, greeting and mating calls plus up to 12 others
The source saysLutra lutra are vocal, with basic calls of alarm, greeting, and mating as well as up to 12 other calls.Note: vibe.reason

Source
02

San Diego Zoo Wildlife Alliance

Otter. San Diego Zoo Wildlife Alliance.

The page saysThe World's Most Widespread Otter
The source saysThe most widely distributed otter is the Eurasian otter, found throughout Europe, North Africa, and Asia to Japan and Indonesia.Note: heading
The page saysa river range that stretches from Britain to Japan
The source saysThe most widely distributed otter is the Eurasian otter, found throughout Europe, North Africa, and Asia to Japan and Indonesia.Note: tagline; Britain is inside the stated European range
The page saysVibrissae, whiskers above its lips, that detect changes in the water current and track the movements of fish and other prey underwater.
The source saysAn otter's rounded nose has whiskers above the lips that detect water current changes as well as the presence of prey ... lurking in the water.Note: stats.superpower; general otter anatomy on the SDZ multi-species page; the fish-tracking half is ADW's Lutra lutra vibrissae line (next claim)
The page saysThe Eurasian otter (*Lutra lutra*) is the most widely distributed otter species, found across Europe, North Africa and Asia as far as Japan and Indonesia
The source saysThe most widely distributed otter is the Eurasian otter, found throughout Europe, North Africa, and Asia to Japan and Indonesia.
The page saysIts vibrissae, whiskers above its lips, detect changes in the water current and the presence of prey
The source saysAn otter's rounded nose has whiskers above the lips that detect water current changes as well as the presence of prey ... lurking in the water.
The page saysEurasian otter males form a dominance hierarchy, and the highest-ranking ones hold, and mark, the best ranges
The source saysEurasian otter males form a dominance hierarchy, with the highest-ranking individuals occupying the most favorable ranges and marking them accordingly.Note: names the Eurasian otter on the multi-species SDZ page

Source
03

AnAge: The Animal Ageing and Longevity Database, Human Ageing Genomic Resources

AnAge entry for Lutra lutra. AnAge: The Animal Ageing and Longevity Database, Human Ageing Genomic Resources.

The page saysThe longevity record in captivity belongs to a female who lived to 18.2 years old
The source saysThe longevity record in captivity belongs to a female that was 18.2 years of age when she died.Note: AnAge calls the older 22-year captivity figure (which ADW carries) unverified

Source
04

Woodland Trust

Otter (Lutra lutra). Woodland Trust.

The page saysIn the UK, otters weigh 7 to 11 kilograms and measure 94 to 155 centimetres from nose to tail, and males are larger on average
The source saysOne of our largest mustelids, they weigh in at 7-11kg and measure 94cm-155cm from nose to tail. On average, males are larger than females.Note: UK scope kept (Woodland Trust is a UK page: 'our largest mustelids'). AnAge's single 6,750 g adult weight dropped so the two don't read as contradicting.
The page saysSpraint is the name for otter droppings, left on rocks and logs close to the water as a way of communicating with other otters
The source saysotter droppings, known as spraints ... Left on rocks and logs close to the water, they are a method of communication with other otters.
The page saysThe Woodland Trust calls the otter's return across the UK a conservation success story: by the 1950s, hunting, habitat destruction and chemicals in rivers had left it on the brink of extinction there
The source saysThe return of the otter across the UK is a conservation success story. By the 1950s, the species was on the brink of extinction due to hunting, habitat destruction and chemicals leaching into watercourses.Note: current institution page (blog dates 2026) for the present-tense UK state

Source
05

Loy 2025

Loy (2025). Lutra lutra. The IUCN Red List of Threatened Species 2025: e.T12419A227078232.

The page saysNear Threatened
The source saysIUCN Red List category: Near Threatened (NT). Lutra lutra (Linnaeus, 1758), IUCN taxon 12419.Note: stats.conservationStatus, read through GBIF's copy of the Red List per docs/fact-check.md
The page saysThe IUCN Red List classes the Eurasian otter as Near Threatened
The source saysIUCN Red List category: Near Threatened (NT). Lutra lutra (Linnaeus, 1758), IUCN taxon 12419.Note: assessment year dropped: no cached text states it

Source
06

Jędrzejewska et al. 2001

Jędrzejewska et al. (2001). Feeding habits of the otter and the American mink in Białowieża Primeval Forest (Poland) compared to other Eurasian populations. Ecography.

The page saysOn five woodland rivers in eastern Poland, fish made up 51% of what otters ate by weight in spring and summer but 40% in autumn and winter, when amphibians rose to 58%
The source sayswere studied by scat analysis on five woodland rivers and streams in eastern Poland. Fish constituted 51% of food biomass consumed by otters in spring‐summer and 40% in autumn‐winter ... made up 34% of otters’ food biomass in spring‐summer and 58% in autumn‐winterNote: biomass -> by weight; the 34%/58% sentence's subject is 'Amphibians (mainly Rana temporaria ...)', split across lines in the cache

Source
07

Weber 1990

Weber (1990). Seasonal exploitation of amphibians by otters (Lutra lutra) in north-east Scotland. Journal of Zoology.

The page saysThe mix shifts with season and place
The source saysThe proportion of amphibians identified in otter droppings varies seasonally and according to the habitat.
The page saysIn north-east Scotland in 1987, the share of amphibians in otter droppings varied with the season and the habitat, rising in late winter and spring while the amphibians were hibernating or spawning, and it tracked how many amphibians were available
The source saysThe dietary importance of amphibians to otters was studied in north‐east Scotland in 1987. The proportion of amphibians identified in otter droppings varies seasonally and according to the habitat. The consumption of amphibians increases in late winter and spring while they are either hibernating or spawning ... There is a significant correlation between the availability of amphibians and their consumption by otters.Note: faq 3
The page saysCommon frogs made up 60.8% of the amphibian prey, common toads only 1.7%
The source saysThe main amphibian species involved in the diet is the common frog, Rana temporaria (60.8%), while the common toad, Bufo bufo, represents only 1.7% of the amphibian prey.Note: faq 3

Source
08

Clavero, Prenda & Delibes 2003

Clavero, Prenda & Delibes (2003). Trophic diversity of the otter (Lutra lutra L.) in temperate and Mediterranean freshwater habitats. Journal of Biogeography.

The page saysA review of 37 European diet studies found that otters in Mediterranean areas relied less on fish, and more on aquatic invertebrates and reptiles, than otters in temperate areas
The source saysThirty‐seven otter diet studies were reviewed, twenty‐one from temperate and sixteen from Mediterranean areas ... Mediterranean otters behaved as more generalist predators than temperate ones, relying less on fish, and more on aquatic invertebrates and reptiles.Note: 37 = 'Thirty-seven' in the quote

Source
09

Brzeziński & Romanowski 2006

Brzeziński & Romanowski (2006). Experiments on sprainting activity of otters (Lutra lutra) in the Bieszczady Mountains, southeastern Poland. Mammalia.

The page saysAlong 28 kilometres of the River San in south-eastern Poland, a three-week survey of both banks counted an average of 4.18 new spraints per kilometre per day, and the more of a stretch's banks were steep and rocky, the more spraints it collected
The source saysConsecutive surveys of otter spraints of both banks along a 28-km stretch of the River San showed an average of 4.18 deposited spraints/km per day during a 3-week pre-experimental period ... Spraint deposition was positively correlated with the proportion of steep and rocky riverbanksNote: south-eastern Poland is the paper's title (Bieszczady Mountains, southeastern Poland)
The page saysOn 28 km of the River San in south-eastern Poland, researchers cleared old spraints from 14 stretches of river
The source saysConsecutive surveys of otter spraints of both banks along a 28-km stretch of the River San ... in sections where otter spraints were removed (n=14)Note: faq 2; 28-km stretch is in the same abstract
The page saysIn the first week, sprainting on those stretches rose 1.6-fold, while on 14 untouched stretches it fell 1.5-fold
The source saysin sections where otter spraints were removed (n=14), sprainting intensity increased 1.6-fold, while in the control sections (n=14) the defecation ratio decreased 1.5-fold during the first week after removal.Note: faq 2
The page saysAdding spraints from unfamiliar otters made no further difference
The source saysPlacement of additional spraints of unfamiliar individuals on half the experimental sections did not stimulate otters to increase defecation on these sections compared to those where only old spraints were removed.Note: faq 2
The page saysThe otters make up for it
The source saysin sections where otter spraints were removed (n=14), sprainting intensity increased 1.6-foldNote: faq 2 lead

Source
10

Murk et al. 1998

Murk et al. (1998). Application of biomarkers for exposure and effect of polyhalogenated aromatic hydrocarbons in naturally exposed European otters (Lutra lutra). Environmental Toxicology and Pharmacology.

The page saysA 1998 study named PCBs, industrial chemicals, as one of the major factors in the otter's serious decline over the previous decades
The source saysIn the serious decline of European otters (Lutra lutra) over the last decades, polychlorinated biphenyls (PCBs) are considered to be one of the major factors.Note: 1998 is the reference's publication year; 'European otters' is the species name, not a region: 'across Europe' was cut
The page saysA 1998 study counted PCBs among the major factors in the otter's serious decline
The source saysIn the serious decline of European otters (Lutra lutra) over the last decades, polychlorinated biphenyls (PCBs) are considered to be one of the major factors.Note: 1998 is the reference's publication year; faq 4
The page saysIn wild otters, the more PCB a liver held, the less vitamin A it stored, and that went with more infectious disease
The source saysA strong negative correlation was found between hepatic vitamin A and polychlorinated biphenyl (PCB) concentrations expressed as TCDD-equivalents (TEQs), coinciding with a higher incidence of infectious diseases.Note: faq 4; 'naturally exposed' / 'feral otters' -> wild

Source
11

Fournier-Chambrillon et al. 2004

Fournier-Chambrillon et al. (2004). Evidence of secondary poisoning of free-ranging riparian mustelids by anticoagulant rodenticides in France: implications for conservation of European mink (Mustela lutreola). Journal of Wildlife Diseases.

The page saysin mustelids collected in south-western France from 1990 to 2002, the rodenticide bromadiolone was found in the livers of two of eleven otters
The source saysconcentrations of eight anticoagulant rodenticides were examined in livers from 122 carcasses of four species of free-ranging mustelids collected between 1990 and 2002 in southwestern France. Bromadiolone residue was found in all species and 9% of the sample (one of 31 European mink, three of 47 American mink [Mustela vison], five of 33 polecats [Mustela putorius], and two of 11 European otters [Lutra lutra]).Note: chlorophacinone was also found in one otter; the abstract doesn't say whether it was one of the two, so the count is bromadiolone only

Source
12

Harrington et al. 2009

Harrington et al. (2009). The impact of native competitors on an alien invasive: temporal niche shifts to avoid interspecific aggression. Ecology.

The page saysIn one area of southern England, otters and polecats were absent in the 1990s but back by the 2000s
The source saysWe compared the relative abundance and the behavior of mink in the 1990s and in the 2000s in an area of southern England where both otters and polecats were absent in the 1990s but reappeared in the intervening years.
The page saysa 2009 study found the invasive American mink there had switched from mostly nocturnal to mostly daytime activity, which the researchers suggest may help it avoid them
The source saysWe also found that mink were predominantly nocturnal in the 1990s (in the absence of competitors) but were predominantly diurnal in the 2000s (in the presence of competitors). We hypothesize that this temporal shift may be an avoidance mechanismNote: 2009 is the reference's publication year

How the table was made: a writer drafted the profile from these sources and logged each claim with its quote, a reviewer with nothing but this table checked every sentence said no more than its quote, and a script confirmed each quote appears word for word in the source. The method is in the site'sAbout page.