Wild Otters Research Articles

Present in the Aquatic Environment, Unclear Evidence in Top Predators-The Unknown Effects of Anti-Seizure Medication on Eurasian Otters (Lutra lutra) from Northern Germany.

Emerging contaminants are produced globally at high rates and often ultimately find their way into the aquatic environment. These include substances contained in anti-seizure medication (ASM), which are currently appearing in surface waters at increasing concentrations in Germany. Unintentional and sublethal, chronic exposure to pharmaceuticals such as ASMs has unknown consequences for aquatic wildlife. Adverse effects of ASMs on the brain development are documented in mammals. Top predators such as Eurasian otters (Lutra lutra) are susceptible to the bioaccumulation of environmental pollutants. Still little is known about the health status of the otter population in Germany, while the detection of various pollutants in otter tissue samples has highlighted their role as an indicator species. To investigate potential contamination with pharmaceuticals, Eurasian otter brain samples were screened for selected ASMs via high-performance liquid chromatography and mass spectrometry. Via histology, brain sections were analyzed for the presence of potential associated neuropathological changes. In addition to 20 wild otters that were found dead, a control group of 5 deceased otters in human care was studied. Even though none of the targeted ASMs were detected in the otters, unidentified substances in many otter brains were measured. No obvious pathology was observed histologically, although the sample quality limited the investigations.

Identification of three Asian otter species (Aonyx cinereus, Lutra sumatrana, and Lutrogale perspicillata) using a novel noninvasive PCR-RFLP analysis.

Four species of otters occur in tropical Asia, and all face multiple threats to their survival. Studies of distribution and population trends of these otter species in Asia, where they occur sympatrically, are complicated by their elusive nature and difficulties with reliable identification of species in field surveys. In Malaysia, only three species, the smooth-coated otter, Asian small-clawed otter, and hairy-nosed otter have been reliably reported as residents. We designed a replicable and cost-efficient PCR-RFLP protocol to identify these three species. Using published reference sequences of mitochondrial regions, we designed and tested three PCR-RFLP protocols on DNA extracted from reference samples and 33 spraints of wild otters collected along the North Central Selangor Coast of Malaysia. We amplified and sequenced two fragments (450 and 200 bp) of the mt D-loop region and a 300-bp fragment of the mt ND4 gene using primer sets TanaD, TanaD-Mod, and OTR-ND4, respectively. Amplification products were digested with restriction enzymes to generate species-specific RFLP profiles. We analyzed the costs of all three protocols and compared these with the costs of sequencing for species identification. Amplification success was highest for the smallest PCR product, with the TanaD-Mod primer amplifying DNA from all 33 spraints. TanaD and OTR-ND4 primers amplified DNA from 60.6% and 63.6% spraints, respectively. PCR products of TanaD-Mod provided the expected species-specific RFLP profile for 32 (97%) of the spraints. PCR products of OTR-ND4 provided the expected RFLP profile for all 21 samples that amplified, but TanaD produced spurious bands and inconsistent RFLP profiles. The OTR-ND4 primer-enzyme protocol was the least expensive (437 USD) for processing 100 samples, followed by TanaD-Mod (455 USD). We suggest the use of both OTR-ND4 and TanaD-Mod protocols that show potential for highly efficient and reliable species identification from noninvasive genetic sampling of three Asian otter species. We expect our novel noninvasive PCR-RFLP analysis methods to facilitate population monitoring, ecological and behavioral studies on otters in tropical and subtropical Asia.

Shiga toxin-producing E. coli (STEC) isolated from wild mammals in Portugal

Background Zoonoses are diseases common to humans and animals (livestock, wildlife, and pets). In 2018 about 360 000 zoonoses were reported in European Union. Shiga toxin-producing Escherichia coli (STEC) infections were among the most reported causes of these zoonotic diseases. Methods Faecal samples of mammal species (n=286) with distinct phenology (wild boar, red deer, otter, and red fox) were collected in Portugal. After the initial processing, the presence of STEC was screened by PCR, and suspicious samples were platted on CHROMagar STEC. STEC positive isolates were tested for antibiotic susceptibility. Thephylogenetic relationship of STEC strains was evaluated by PFGE. Of these, 20 representative strains were selected for whole genome sequencing with the Illumina NovaSeq 6000 system. For the assembly, annotation and genome characterization, multiple web-based bioinformatic tools were employed. Results Cultivable STEC (n=52) were recovered from 17% (n=49) of the samples collected from the four mammals. All the isolates were non-O157:H7 STEC encoding stx1 (n=2; 4%) and/or stx2 genes (n=51; 98%). Only one strain (2%) of red fox was resistant to ceftazidime, aztreonam and nalidixic acid. The 20 strains that were sequenced belong mainly to serotype O27:H30 (n=15), followed by O146:H28 (n=2), O146:H21 (n=1), O178:H19 (n=1) and O103:H2 (n=1). In addition to stx, all strains encode several virulence factors, mainly toxins, adhesins, fimbrae, secretion systems, among others. Additionally, several pathogenicity islands have been predicted for these strains. Conclusions Our results show that wild animals are reservoirs of STEC, potentially pathogenic to humans.

Stop the decline of China's wild otters

Stop the decline of China's wild otters

A Wild Animal Inside My House: An Analysis of the Children’s Picturebook Svenn the Otter and the Magic Rock by Espen Villseth and Anita Sletten

Svenn, a wild otter, has become an Instagram celebrity with over 140,000 followers around the world. Svenn has his own YouTube channel and Facebook page. Moreover, in December 2020, NRK, an influential Norwegian TV channel, released a series entitled “Oteren Svenn” (Svenn, the Otter), consisting of ten episodes. In addition to all of this, Svenn has his own picturebook for children, which is entitled Svenn the Otter and the Magic Rock (Villseth & Sletten, 2020). This article presents the picturebook and analyzes three of its significant spreads. The aim is to uncover aspects of the sociocultural context in which Svenn – along with other characters – is portrayed by images and verbal language in the book, and to provide a short discussion of how the book may be used in English Language Teaching (ELT). Our analysis builds on tools from multimodal text analysis (Kress & van Leeuwen, 2005; van Leeuwen, 2005) and Narrative Intelligence (Mateas & Senger, 2003). The analysis focuses on the significance of the picturebook to represent participants in actions, the relationship between the book’s participants and the reader, and the value of presenting images and verbal text together. Our analysis also touches on some implications for ELT, on the potential that visual literacy can have in language teaching.

Pulmonary hair embolism in a rescued free-ranging Eurasian otter Lutra lutra in Kinmen, Taiwan.

Eurasian otters Lutra lutra are listed as Near Threatened on the IUCN Red List and are imperiled by habitat loss, water pollution, and poaching. Harassment and attacks by stray animals are also recognized threats to the health of wild Eurasian otters. Pulmonary hair embolism is a possible complication in animals with deep traumatic injury, but to date no cases have been reported in wildlife. A free-ranging, adult male Eurasian otter was rescued due to severe emaciation and multiple bite wounds. The otter died 3 d after rescue and was necropsied. Grossly, a 1.5 × 1.5 × 1.5 cm firm nodule was observed in the left cranial lung lobe. Histologically, a fragment of hair shaft surrounded by multinucleated foreign body giant cells was observed in a medium-sized vein, and extensive eosinophilic infiltration was noted in the adjacent vascular wall and lung parenchyma. Based on the gross and histological findings, the pulmonary lesion was consistent with eosinophilic pneumonia and vasculitis induced by hair embolism. The presence of well-formed multinucleated foreign body giant cells and eosinophils may imply a late stage of foreign body reaction, and thus the presumptive source of hair embolism is an animal bite. This is the first report of pulmonary hair embolism associated with animal bite in a rescued free-ranging Eurasian otter.

Quantification of immunoreactive testosterone and estradiol-17ß metabolites to identify the sex of Neotropical otters (Lontra longicaudis annectens) in the field

Before there was use of ultrasonographic imaging, determination of the ratio of estrogens to androgens in the same individual was a technique used for differentiating the sex of monomorphic animals in captivity, with larger estrogen concentrations in the females. Due to species-specific differences in both concentration and changes throughout the year of these hormones, corroboration of the method is needed in each case. In this study, there was use of a chemo-immuno assay to quantify sex steroids in fecal samples collected from seven (five females and two males) Neotropical otters, Lontra longicaudis. The reproductive season for this species was determined to be between October and March, with increased estradiol in the females and relatively greater concentrations of testosterone in the males as compared with other seasons of the year. Results from utilization of a k-means analysis procedure indicated that the use of steroid ratios in fecal samples to differentiate otter sex is an effective technique when there are evaluations during the breeding season. The estrogen to androgen ratios during this period, however, are the inverse of what was expected, with there being larger testosterone concentrations in the female otters. The ratio of estrogens to androgens in feces of captive otters can be effectively used to determine the sex of otters in the field. We propose this method is reliable for sex determination in wild otter populations during the reproductive season.

Wild otter observation on Gurney Drive coast in Penang Island, Malaysia

Otter was irregularly observed on Gurney Drive coast in the northern part of Georgetown, Penang Island from June 2015 to March 2016. Authors examined relationship between the otters sighting date and time and the tide pattern. Otter was observed a total of five times on 27 th June, 17 th August, 6 th December 2015, 14 th March, and 16th March 2016. These otters were identified same species which was the smooth-coated otter, Lutrogale perspicillata , from the morphological characteristics. Swimming direction of the otters were characterized two patterns that the first was the otters swam from inner part to east coast in a cove of Gurney Drive coast and the second was the otters swam from the east coast to inner part of the cove. From this result, it was suggested that the otters swam to drive fish toward tide flow and the otters catch the fish efficiently.

Wildlife detection dog training: A case study on achieving generalization between target odor variations while retaining specificity

Wildlife detection dogs are required to correctly discriminate target wildlife species odor from nontarget species odors (specificity), while enabling some degree of target odor variation (generality). Because there is no standardized training protocol, and little knowledge on training efficiency, we conducted a case study to test a dog’s training efficiency in detecting 2-week-old wild otter (Lutra lutra) feces (spraint) odor among feces odors from 6 other large mammal species that often share the otter’s natural habitat, including fox (Vulpes vulpes), hare (Lepus europaeus), roe deer (Capreolus capreolus), and cattle (Bos taurus). The dog was trained using a standard multiple-choice carrousel in a stepwise protocol. We started with odor samples from fresh captive otter spraints and progressed toward 2-week-old spraints from wild otters among other mammalian dung odors and tested for specificity and generality after each training step. We show that training on only 2 variations of spraints from captive otters enabled the dog to detect all desired spraint odor variations in our protocol, indicating a rapid generalization to variations of spraint odor the dog was not trained on, while retaining specificity. Testing such concept formation of target odors should be included in detection dog training and certification and could serve as a quality control measure of detection dog performance.

Skinning toads is innate behaviour in otter (Lutra lutra) cubs

An experiment was performed with two subadult otters (Lutra lutra) born in captivity that had never seen or eaten amphibians, in which they were fed a new prey with toxic substances in its skin, the Iberian common toad (Bufo spinosus). It was observed that the otters recognised a poisonous amphibian that they had never come into contact with before as a potential prey in the absence of fish, which had previously been their only diet. As from the first test, and as described for wild otters in the literature, they consumed the toads following a learning process that consisted of ventral slicing and skinning in order to avoid contact with the dermal secretions, especially on the head and back, that toads use as a defensive mechanism. We observed the skill of the otters when handling the prey with regards to both killing them and eating them; the otters also immersed their prey in the water of their pond to remove the toxic substances emanating from the toads’ skins. The amount of remains left after the attack was gradually reduced over a period of 16 test experiments. No differences between the skins rejected in the experimental conditions and those found in nature were detected, the otter mainly eating the back legs and taking special care to reject the head, the back and viscera (especially the ovaries in the case of pregnant females). When they had brown trout together with toads in the same biomass, they neither attacked nor consumed the latter.

Non-Invasive Genetic Mark-Recapture as a Means to Study Population Sizes and Marking Behaviour of the Elusive Eurasian Otter (Lutra lutra).

Quantifying population status is a key objective in many ecological studies, but is often difficult to achieve for cryptic or elusive species. Here, non-invasive genetic capture-mark-recapture (CMR) methods have become a very important tool to estimate population parameters, such as population size and sex ratio. The Eurasian otter (Lutra lutra) is such an elusive species of management concern and is increasingly studied using faecal-based genetic sampling. For unbiased sex ratios or population size estimates, the marking behaviour of otters has to be taken into account. Using 2132 otter faeces of a wild otter population in Upper Lusatia (Saxony, Germany) collected over six years (2006–2012), we studied the marking behaviour and applied closed population CMR models accounting for genetic misidentification to estimate population sizes and sex ratios. We detected a sex difference in the marking behaviour of otters with jelly samples being more often defecated by males and placed actively exposed on frequently used marking sites. Since jelly samples are of higher DNA quality, it is important to not only concentrate on this kind of samples or marking sites and to invest in sufficiently high numbers of repetitions of non-jelly samples to ensure an unbiased sex ratio. Furthermore, otters seemed to increase marking intensity due to the handling of their spraints, hence accounting for this behavioural response could be important. We provided the first precise population size estimate with confidence intervals for Upper Lusatia (for 2012: = 20 ± 2.1, 95% CI = 16–25) and showed that spraint densities are not a reliable index for abundances. We further demonstrated that when minks live in sympatry with otters and have comparably high densities, a non-negligible number of supposed otter samples are actually of mink origin. This could severely bias results of otter monitoring if samples are not genetically identified.

A low-cost GPS GSM/GPRS telemetry system: performance in stationary field tests and preliminary data on wild otters (Lutra lutra).

BackgroundDespite the increasing worldwide use of global positioning system (GPS) telemetry in wildlife research, it has never been tested on any freshwater diving animal or in the peculiar conditions of the riparian habitat, despite this latter being one of the most important habitat types for many animal taxa. Moreover, in most cases, the GPS devices used have been commercial and expensive, limiting their use in low-budget projects.Methodology/Principal FindingsWe have developed a low-cost, easily constructed GPS GSM/GPRS (Global System for Mobile Communications/General Packet Radio Service) and examined its performance in stationary tests, by assessing the influence of different habitat types, including the riparian, as well as water submersion and certain climatic and environmental variables on GPS fix-success rate and accuracy. We then tested the GPS on wild diving animals, applying it, for the first time, to an otter species (Lutra lutra). The rate of locations acquired during the stationary tests reached 63.2%, with an average location error of 8.94 m (SD = 8.55). GPS performance in riparian habitats was principally affected by water submersion and secondarily by GPS inclination and position within the riverbed. Temporal and spatial correlations of location estimates accounted for some variation in the data sets. GPS-tagged otters also provided accurate locations and an even higher GPS fix-success rate (68.2%).Conclusions/SignificanceOur results suggest that GPS telemetry is reliably applicable to riparian and even diving freshwater animals. They also highlight the need, in GPS wildlife studies, for performing site-specific pilot studies on GPS functioning as well as for taking into account eventual spatial and temporal correlation of location estimates. The limited price, small dimensions, and high performance of the device presented here make it a useful and cost-effective tool for studies on otters and other aquatic or terrestrial medium-to-large-sized animals.

Evidence for a Novel Marine Harmful Algal Bloom: Cyanotoxin (Microcystin) Transfer from Land to Sea Otters

“Super-blooms” of cyanobacteria that produce potent and environmentally persistent biotoxins (microcystins) are an emerging global health issue in freshwater habitats. Monitoring of the marine environment for secondary impacts has been minimal, although microcystin-contaminated freshwater is known to be entering marine ecosystems. Here we confirm deaths of marine mammals from microcystin intoxication and provide evidence implicating land-sea flow with trophic transfer through marine invertebrates as the most likely route of exposure. This hypothesis was evaluated through environmental detection of potential freshwater and marine microcystin sources, sea otter necropsy with biochemical analysis of tissues and evaluation of bioaccumulation of freshwater microcystins by marine invertebrates. Ocean discharge of freshwater microcystins was confirmed for three nutrient-impaired rivers flowing into the Monterey Bay National Marine Sanctuary, and microcystin concentrations up to 2,900 ppm (2.9 million ppb) were detected in a freshwater lake and downstream tributaries to within 1 km of the ocean. Deaths of 21 southern sea otters, a federally listed threatened species, were linked to microcystin intoxication. Finally, farmed and free-living marine clams, mussels and oysters of species that are often consumed by sea otters and humans exhibited significant biomagnification (to 107 times ambient water levels) and slow depuration of freshwater cyanotoxins, suggesting a potentially serious environmental and public health threat that extends from the lowest trophic levels of nutrient-impaired freshwater habitat to apex marine predators. Microcystin-poisoned sea otters were commonly recovered near river mouths and harbors and contaminated marine bivalves were implicated as the most likely source of this potent hepatotoxin for wild otters. This is the first report of deaths of marine mammals due to cyanotoxins and confirms the existence of a novel class of marine “harmful algal bloom” in the Pacific coastal environment; that of hepatotoxic shellfish poisoning (HSP), suggesting that animals and humans are at risk from microcystin poisoning when consuming shellfish harvested at the land-sea interface.

Fecal genotyping and contaminant analyses reveal variation in individual river otter exposure to localized persistent contaminants

The present study investigated polyhalogenated aromatic hydrocarbon (PHAH) concentrations in feces of known river otters (Lontra canadensis) along the coast of southern Vancouver Island, British Columbia, Canada. Specifically, we combined microsatellite genotyping of DNA from feces for individual identification with fecal contaminant analyses to evaluate exposure of 23 wild otters to organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenylethers (PBDEs). Overall, feces collected from otters in urban/industrial Victoria Harbor had the greatest concentrations of nearly all compounds assessed. Fecal concentrations of OCPs and PBDEs were generally low throughout the region, whereas PCBs dominated in all locations. Re-sampling of known otters over space and time revealed that PCB exposure varied with movement and landscape use. Otters with the highest fecal PCB concentrations were those inhabiting the inner reaches of Victoria Harbor and adjacent Esquimalt Harbor, and those venturing into the harbor systems. Over 50% of samples collected from eight known otters in Victoria Harbor had total-PCB concentrations above the maximum allowable concentration as established for Eurasian otter (Lutra lutra) feces, with a geometric mean value (10.6 mg/kg lipid wt) that exceeded the reproductive toxicity threshold (9 mg/kg lipid wt). Those results are consistent with our findings from 1998 and 2004, and indicate that the harbors of southern Vancouver Island, particularly Victoria Harbor, are a chronic source of PCB exposure for otters. The present study further demonstrates the suitability of using otter feces as a noninvasive/destructive biomonitoring tool in contaminant studies, particularly when sampling of the same individuals at the local population-level is desired.

Detailed Devotion

Detailed Devotion

Cryptosporidium and Giardia in wild otters ( Lutra lutra)

A total of 437 faecal samples from wild otter ( Lutra lutra) were collected from 161 sites in Galicia (northwest Spain) and were analysed by a direct immunofluorescence antibody test (IFAT). Cryptosporidium sp. oocysts and Giardia sp. cysts were detected in 17 (3.9%) and 30 (6.8%) samples, respectively. The results demonstrate that otters may contribute to the contamination of watercourses, although further studies are required to establish which species or genotypes of Cryptosporidium and Giardia infect these animals and also the significance in terms of public health.

Non-invasive genetic sampling of the Eurasian otter (Lutra lutra) using hairs

The material for the genetic characterisation of wild Eurasian otters (Lutra lutra) has previously been derived from carcasses and spraints. Hair samples however have proved to be a much more reliable source of DNA than spraints, and offer the opportunity of sampling the living population non-invasively. Until now there has been no research into methods of sampling hairs from wild otters or on the DNA extraction efficiency from these hairs. A hair trap was therefore developed and tested on otters in captivity. The success rate of the trap was 0.71 samples collected per trap night. The suitability of genetic analysis from otter hairs was examined using paired samples of hair and tissue taken from 15 individual otters recovered from road mortalities. DNA was extracted from the tissue samples using a Proteinase K digestion in a PCR compatible buffer. This process had a 100% success rate. Individual root hair segments were treated by Chelex Ionic bead resin treatment and Proteinase K digestion in a PCR compatible buffer. The Chelex method gave a 55% ampli- fication success rate while the Proteinase K method gave a much higher amplification suc- cess rate of 87%. The DNA extracts were typed for 9 microsatellites using the latest versions of the primers. Proportions of allelic dropout and false allele detection associated with hair DNA extracts were estimated by comparing the genotypes of hair extracts with the geno- types from tissue. Preliminary attempts to develop a ZFX/Y assay to sex otters identified polymorphisms between ZFX and ZFY sequences, but typing based on restriction digests requires further optimisation. The use of recovered DNA from hair offers a step forward in the study of Eurasian otter populations as its continuing endangered status in many coun- tries creates legal and ethical constraints on capturing animals for marking or radio track- ing.

Genetic variability in the complete mitochondrial control region of the Eurasian otter (Lutra lutra) in the Iberian Peninsula

Sequencing of the complete mitochondrial DNA control region from 31 samples of the Eurasian otter, Lutra lutra, enabled us to establish the length and structure of this fragment, as well as to describe, for the first time, the RS3 repetitive region located at the 3′ end. In addition, genetic variability of the 5′ end was examined in 63 individuals, 57 of which were wild otters from the Iberian Peninsula and six captive reared otters. This analysis resulted in extremely low variability. All the samples from the Iberian Peninsula share a single haplotype, Lut 1, the most common haplotype in Europe. Captive otters showed two haplotypes: Lut 3, which has been described in wild otters from eastern Germany, and Lut 6, an haplotype not described to date. Higher variability was observed in the repetitive RS3 region. The tandem repeat was composed of an array of ten repeat units of 22 bp with differences in the repetitive motifs that differed in the arrays of different specimens. In total, 20 different haplotypes from 31 individuals were found. However, the geographical distribution of these haplotypes did not generate a phylogeographical signal. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 86, 397–403.

Induction of cytochrome P450 1A1 expression in captive river otters fed Prudhoe Bay crude oil: evaluation by immunohistochemistry and quantitative RT-PCR

Numerous studies have explored the relationships between exposure to a variety of environmental contaminants, such as polycyclic aromatic hydrocarbons, and induction of cytochrome P450 1A (CYP1A) in different vertebrates. Few controlled studies, however, simulated chronic long-term exposure with repeated non-lethal sampling of the same individuals, which should better represent repeated exposure incidents in animals inhabiting polluted areas. In this study, we investigated the effects of chronic exposure to crude oil on levels of CYP1A1 in endothelial cells of skin biopsies and peripheral mononuclear blood cells in captive river otters (Lontracanadensis) using repeated sampling of the same individuals. We hypothesized that ingestion of oil would result in an increase in levels of CYP1A1 in both targets, and predicted that the relationship between prolonged exposure and expression of CYP1A1 would reach a plateau indicative of continuous detoxification of hydrocarbons. Fifteen wild-caught male otters were acclimated to captivity, and then fed diets containing no oil (control) or diets containing weathered crude oil at 5 mg day-1 kg-1 body weight (low-dose) and 50 mg day-1 kg-1 body weight (high-dose), at the Alaska Sealife Center in Seward, Alaska, USA. Expression of CYP1A1 was assessed with immunohistochemical analysis of CYP1A1 protein in skin biopsies and by quantitative RT-PCR analysis of CYP1A1 mRNA in mononuclear blood cells. Both assays revealed a decrease between capture and the transfer to captivity, indicating that the enclosure at the Alaska Sealife Center, and the food we offered to the otters were free of potential inducers of CYP1A1. During the exposure period, increases in CYP1A1 expression were registered by both techniques, followed by a decline in CYP1A1 after oil administration ended. Levels of endothelial CYP1A1 in the high-dose group were comparable to those recorded for wild river otters in PWS in 1996 and 1997. Levels of CPY1A1 mRNA in mononuclear blood cells, however, were well below levels recorded for river otters in Prince William Sound, and no correlation was detected between values obtained from the two methods. Thus, our results from this longitudinal study with repeated sampling of the same individuals provide support for the use of cytochrome P450 1A1 as a biomarker for hydrocarbon exposure. Nonetheless, our results also suggest that the induction process of CYP1A1 may be complicated and interacting with other processes in vivo. Such interactions may obscure our ability to describe specific, quantitative, predictable, dose-response relationships between exposure to hydrocarbons and induction of CYP1A1, which are required of reliable biomarkers. Evaluations of such interactions based on theoretical physiological models in live-animals merit further investigation.

A long-term study of vitamin A and polychlorinated hydrocarbon levels in otters ( Lutra lutra) in south west England

Seventy-seven wild otters ( Lutra lutra) found dead in south west England between 1988 and 1996 were examined post mortem. Liver samples were analysed from 56 otters for polychlorinated hydrocarbons and from 40 for vitamin A (retinol). There was a significant decline in the levels of pollutants over the study period and this coincided with a marked increase in vitamin A levels. However, a causal relationship was not established. Low vitamin A levels were prevalent in the early years of the study but no conclusive pathological lesions due to deficiency were seen. It is suggested that vitamin A deficiency may have been widespread in Britain's otter population until recently and may have been implicated in the earlier decline.