The status of Asian populations of the Eurasian otter Lutra lutra is largely unknown. Since its designation as a Natural Monument (in 1983) and as Endangered (in 1997) in South Korea the authorities there have been trying to conserve and recover the species. We conducted a national otter survey by standard methods in 2017 and compared the current otter distribution to those recorded in a previous survey (2010). We found otter signs in 84.5% of 1,105 10 × 10 km grid cells, with the highest sprainting intensity in the south-west in the Yeongsan River Basin and on the south coast, where we recorded 7.05 and 6.26 spraints/site, respectively. Despite relatively low spraint densities, the otter has expanded its range since 2010 by colonizing urban areas. This trend suggests that South Korea could be a source area for the recovery of the Eurasian otter in East Asia.

Toxoplasma gondii, a zoonotic parasite of global importance, infects all endothermic vertebrates, with extensive health implications. The prevalence of this parasite is seldom monitored in wildlife. Here, a semi-aquatic species, the Eurasian otter (Lutra lutra) was used as a model to assess the potential effect of climate, land cover and biotic factors on T. gondii seroprevalence in British wildlife. The Sabin–Feldman cytoplasm-modifying dye test identified T. gondii antibodies in 25·5% of blood samples from otters found dead, mainly as road kill, in England and Wales, between 2004 and 2010. Otters in the east of England were more likely to be infected with T. gondii than those in western regions. Land cover and temperature are key determinants of T. gondii infection risk, with more infection in arable areas and lower infection where temperatures are higher. The probability of T. gondii infection increased with host age, reflecting cumulative exposure with time, but there was no association between T. gondii seroprevalence and cause of host death.

In this study the diet of otters Lutra lutra was examined following the establishment of a population of non-native ruffe Gymnocephalus cernuus in Loch Lomond, Scotland. Otter spraints (n=453) were collected at monthly intervals from four sites during 2002. Overall, 98% of spraints contained at least one species of fish, invertebrates were found in 49%, 17% contained amphibians, while mammals and birds were found in 9%. The most frequent prey from all sites were ruffe, which were found in 69% of spraints. Eel Anguilla anguilla, cyprinids (roach Rutilus rutilus, dace Leuciscus leuciscus and minnow Phoxinus phoxinus) and Salmo spp. were also relatively common and were recovered in 60%, 35% and 33% of spraints, respectively. Northern pike Esox lucius (14%), perch Perca fluviatilis (12%), stickleback Gasterosteus aculeatus (9%), powan Coregonus lavaretus (14%) and lampreys Lampetra spp. (2%) were less common. The fact that ruffe were the most frequent prey in otter spraints in all regions and in all seasons of the year indicated that they are one of the most important prey for otters in Loch Lomond at the present time.

Direct observation of Eurasian otters was used to demonstrate the characteristics and interannual use of small patches of habitats by females and litters in stretches of two rivers in north-east Spain. During censuses and other vigils, 215 otter sightings (involving 265 otters) were obtained, 14–18% of which were observations on females and litters. Thirty-five additional sightings were obtained in stretches used by litters of large cubs (47 individuals). Six small cub (2- to 6-month-old) and 15 large cub (>7-month-old) different family units (litters) were detected in both rivers as a whole. Average sizes of litters of small and large cubs were significantly similar, being respectively 1.17 (SD=0.41, range 1–2, n=6) and 1.27 (SD=0.46, range 1–2, n=15), so mortality of cubs was low at the period before dispersal. Litters were detected in significantly different patches from other otters, and litters of small and large cubs were also found in significantly different river sections. Litters of large cubs used small home ranges and core areas, and selected sections at reservoir tails, reservoirs, wider stretches, rough waters and refuges. Small cubs were found in narrow river stretches with calm waters. Selected patches had sheltered zones with abundant fish. This reduced use of space may result in the low rate of mortality.

Data obtained from the dissection of 1067 otters Lutra lutra were used to compare the causes of mortality in relation to age composition, time trends, and regions. Age determination was based on the analysis of incremental cementum lines in teeth. Major causes of mortality of otters were traffic accidents (69.9%), followed by natural deaths (6.6%), deaths in fish-traps (6%), hunting (4.1%), and other violent events (4.4%). No significant differences in mortality structure between the sexes were found. Resulting from a log-linear and a contrast analysis, significant differences in frequencies of mortality causes in relation to different time periods, regions and age classes of otters were observed. The frequency of otters dying from hunting or diseases was highest in youngest (AC I) and oldest (AC V) otters. Generally, the greatest differences between age classes resulted from comparison of frequencies of traffic-mortality, hunting, and fish-traps. Concerning time trends, the greatest differences were found in the periods before and after 1990. In addition to the increase of traffic-mortality, hunting and deaths in fish-traps influenced the distribution of mortality in different time periods. In eastern Germany, there is a clear difference in mortality between northern and southern regions. This results mainly from commercial fish-trapping being more common at the northern coast and lakes. However, in all different subsamples of time, region or age-class, traffic-killed otters amounted to >50% of all otters found dead.

Recent studies show that the availability of prey influences the ecology of otters by regulating breeding, carrying capacity and mortality. Mediterranean habitats experience extreme seasonal variation in water flow – a stress period can occur in summer when water flows and levels are low with long periods of drought, while torrential floods usually occur in autumn and spring. Reservoirs can affect this situation by further influencing water flow regimes and acting as a barrier. Our data show the close relationship between the amount of food (fish) available to otters and their use of a stretch of water and the otter density there. The adjustment of the number of individuals (and carrying capacity) in an area can be seen from their mortality, a decrease in their reproductive success, or migration. Our results are consistent with the hypothesis that otters are food-limited. Torrential rains, summer droughts and dams for water management have repercussions for otter populations in as much as they affect their prey-species. Barbels Barbus spp. and, secondarily, nases Chondrostoma spp. are shown to be important to otter ecology and breeding in Mediterranean Iberian rivers. The conservation and management of the otter in these habitats must not ignore the management of food sources. In order not to affect otter populations, the effect of the reservoirs and their dams also must be considered. The release and cessation of floodwater from reservoirs must be progressive and mimic more closely the flow regime of natural rivers.

Cysts of a Sarcocystis species were found in large numbers in skeletal muscle of an otter (Lutra lutra) which was raised in Norway and died in captivity in Sweden. This is the first report of Sarcocystis infection in the otter. The sarcocysts were 0·3–2·3 mm long and 0·06–0·25 mm wide. As judged by light microscopy the sarcocyst walls were thin (<3 μm) with a serrated surface but without visible projections. By transmission electron microscopy, the sarcocyst wall measured 0·6–1·8 μm and had minute undulations covering the entire sarcocyst surface giving the wall a wavy appearance. Septa were indistinct. The sarcocysts contained few metrocytes and numerous bradyzoites. Sarcocysts were not found in 69 other otters subjected to necropsy in Sweden.

Otters are classified in the Lutrinae and are united by a suite of semi-aquatic adaptations that distinguish them from the rest of the Mustelidae. Past systematic studies have been based primarily on overall similarity of morphological characters but have not been concordant, with regard either to relationships within the subfamily or to the relationships of the Lutrinae to other taxa in the Mustelidae. We evaluate the relationships among nine of the 13 species of otters and their position in the Mustelidae through phylogenetic analysis of the complete nucleotide sequence of the mitochondrial cytochrome b gene. Based on the sequence data presented here, our results suggest that otters are divided into three primary clades that include: (1) the North American river, neotropical and marine otters; (2) the sea, Eurasian, spotted-necked, cape clawless and small-clawed otters; and (3) the giant otter. Furthermore, our results indicate that among sampled mustelid taxa, members of the genus Mustela are most closely related to otters. The hierarchical relationships among clades are not well resolved, particularly the monophyly of otters, largely because a pattern of short internal branches combined with long terminal branches suggests a rapid evolutionary radiation. Estimates of divergence time calibrated by the fossil record suggest that the lineages leading to the North American river, neotropical and marine otters, and the giant otter diverged before the end of the Miocene, much earlier than predicted from the fossil record.

Les niveaux de contamination en pesticides organochlorés mesurés dans les poissons des rivières luxembourgeoises sont peu élevés, à l'exception des concentrations en lindane, pp'DDE et pp'DDT dans la basse-Sûre et ses affluents. Toutefois, ces concentrations ne sont pas particulièrement inquiétantes pour la santé humaine ou pour la survie des loutres. Les concentrations de PCBs mesurées dans les poissons des rivières sont comprises entre 50 et 3500 ng/g P.F., et sont extrêmement variables selonles cours d'eau et les espèces considérés. Dans le lac d'Esch-sur-Sûre, les concentrations sont plus faibles (10 à 200 ng/g P.F.), probablement parce qu'il s'agit d'individus qui ont fait l'objet de rempoissonnements. Dans les populations de poissons des rivières luxembourgeoises, les PCBs sont donc non seulement présents à des concentrations considérées comme problématiques ou dangereuses pour la survie des loutres, mais les standards de consommation pour la santé humaine sont aussi régulièrement dépassés dans les anguilles et chevesnes.

This study is an investigation into the influence of activity on otter (Lutra lutra) spraint production and composition, based on feeding trials involving captive, tame otters. Trials were of two types: ‘active’ where animals were encouraged to run, swim and dive for at least 33% of the time during the first six hours after each meal, and ‘inactive’ where activity varied between zero and 18% of this period. Trial types were balanced for number of fish, meal volume and fish size. Activity was found to have a large effect on spraint production and composition. For active trials, median minimum gut transit time was 67 minutes and median number of spraints per trial was 23. Corresponding figures for inactive trials were 170 minutes and 14, respectively. Of ingested salmonid (Salmo spp.) atlas vertebrae, 60% were recovered in spraints after active trials, while only 32% were recovered after inactive ones. Analyses of these effects showed that our previous models for estimating prey size distribution from bones recovered in spraints gave a better fit for inactive than for active trials. As otters in the wild are likely to spraint mostly during periods of activity, especially foraging, further feeding trials were undertaken to refine an earlier model better to mimic the field situation. Trials, involving active otters, were undertaken to: (i) produce in vivo bone to fish length equations for salmonid atlases and eel (Anguilla anguilla) thoracic vertebrae; and (ii) model the size-related differential recovery of these bones. These refined equations are more soundly based to provide estimates of prey size distribution than the earlier ones and their use in future studies of size-selection is recommended. The present study also highlights the potential limitations of extrapolating from the captive situation to the wild.