A risk assessment of the effects of mercury on Baltic Sea, Greater North Sea and North Atlantic wildlife, fish and bivalves.

A wide range of species, including marine mammals, seabirds, birds of prey, fish and bivalves, were investigated for potential population health risks resulting from contemporary (post 2000) mercury (Hg) exposure, using novel risk thresholds based on literature and de novo contamination data. The main geographic focus is on the Baltic Sea, while data from the same species in adjacent waters, such as the Greater North Sea and North Atlantic, were included for comparative purposes. For marine mammals, 23% of the groups, each composing individuals of a specific sex and maturity from the same species in a specific study region, showed Hg-concentrations within the High Risk Category (HRC) and Severe Risk Category (SRC). The corresponding percentages for seabirds, fish and bivalves were 2.7%, 25% and 8.0%, respectively, although fish and bivalves were not represented in the SRC. Juveniles from all species showed to be at no or low risk. In comparison to the same species in the adjacent waters, i.e. the Greater North Sea and the North Atlantic, the estimated risk for Baltic populations is not considerably higher. These findings suggest that over the past few decades the Baltic Sea has improved considerably with respect to presenting Hg exposure to its local species, while it does still carry a legacy of elevated Hg levels resulting from high neighbouring industrial and agricultural activity and slow water turnover regime.

Life cycle bioenergetics of the gray seal (Halichoerus grypus) in the Baltic Sea: Population response to environmental stress.

Wildlife population dynamics are shaped by multiple natural and anthropogenic factors, including predation, competition, stressful life history events, and external environmental stressors such as diseases and pollution. Marine mammals such as gray seals rely on extensive blubber layers for insulation and energy storage, making this tissue critical for survival and reproduction. This lipid rich blubber layer also accumulates hazardous fat soluble pollutants, such as polychlorinated biphenyls (PCBs), that can directly impact adipose function or be mobilized during periods of negative energy balance or transferred to offspring to exert further impacts on target tissues or vulnerable life stages. To predict how marine mammals will respond to ecological and anthropogenic stressors, it is necessary to use process-based modelling approaches that integrate environmental inputs, full species life history, and stressor impacts with individual dynamics of energy intake, storage, and utilization. The purpose of this study was to develop a full lifecycle dynamic energy budget and individual based model (DEB-IBM) that captured Baltic gray seal physiology and life history, and showcase potential applications of the model to predict population responses to select stressors known to threaten gray seals and other marine mammals around the world. We explore variations of three ecologically important stressors using phenomenological simulations: food limitation, endocrine disrupting chemicals that reduce fertility, and infectious disease. Using our calibrated DEB-IBM for Baltic gray seals, we found that continuous incremental food limitation can be more detrimental to population size than short random events of starvation, and further, that the effect of endocrine disruptors on population growth and structure is delayed due to bioaccumulation, and that communicable diseases significantly decrease population growth even when spillover events are relatively less frequent. One important finding is the delayed effect on population growth rate from some stressors, several years after the exposure period, resulting from a decline in somatic growth, increased age at maturation and decreased fecundity. Such delayed responses are ignored in current models of population viability and can be important in the correct assessment of population extinction risks. The model presented here provides a test bed on which effects of new hazardous substances and different scenarios of future environmental change affecting food availability and/or seal energetic demands can be investigated. Thus, the framework provides a tool for better understanding how diverse environmental stressors affect marine mammal populations and can be used to guide scientifically based management.

Health effects from contaminant exposure in Baltic Sea birds and marine mammals: A review.

Here we review contaminant exposure and related health effects in six selected Baltic key species. Sentinel species included are common eider, white-tailed eagle, harbour porpoise, harbour seal, ringed seal and grey seal. The review represents the first attempt of summarizing available information and baseline data for these biomonitoring key species exposed to industrial hazardous substances focusing on anthropogenic persistent organic pollutants (POPs). There was only limited information available for white-tailed eagles and common eider while extensive information exist on POP exposure and health effects in the four marine mammal species. Here we report organ-tissue endpoints (pathologies) and multiple biomarkers used to evaluate health and exposure of key species to POPs, respectively, over the past several decades during which episodes of significant population declines have been reported. Our review shows that POP exposure affects the reproductive system and survival through immune suppression and endocrine disruption, which have led to population-level effects on seals and white-tailed eagles in the Baltic. It is notable that many legacy contaminants, which have been banned for decades, still appear to affect Baltic wildlife. With respect to common eiders, changes in food composition, quality and contaminant exposure seem to have population effects which need to be investigated further, especially during the incubation period where the birds fast. Since new industrial contaminants continuously leak into the environment, we recommend continued monitoring of them in sentinel species in the Baltic, identifying possible effects linked to climate change, and modelling of population level effects of contaminants and climate change.

Complementary methods assessing short and long-term prey of a marine top predator ‒ Application to the grey seal-fishery conflict in the Baltic Sea.

The growing grey seal (Halichoerus grypus) population in the Baltic Sea has created conflicts with local fisheries, comparable to similar emerging problems worldwide. Adequate information on the foraging habits is a requirement for responsible management of the seal population. We investigated the applicability of available dietary assessment methods by comparing morphological analysis and DNA metabarcoding of gut contents (short-term diet; n = 129/125 seals, respectively), and tissue chemical markers i.e. fatty acid (FA) profiles of blubber and stable isotopes (SIs) of liver and muscle (mid- or long-term diet; n = 108 seals for the FA and SI markers). The methods provided complementary information. Short-term methods indicated prey species and revealed dietary differences between age groups and areas but for limited time period. In the central Baltic, herring was the main prey, while in the Gulf of Finland percid and cyprinid species together comprised the largest part of the diet. Perch was also an important prey in the western Baltic Proper. The DNA analysis provided firm identification of many prey species, which were neglected or identified only at species group level by morphological analysis. Liver SIs distinguished spatial foraging patterns and identified potentially migrated individuals, whereas blubber FAs distinguished individuals frequently utilizing certain types of prey. Tissue chemical markers of adult males suggested specialized feeding to certain areas and prey, which suggest that these individuals are especially prone to cause economic losses for fisheries. We recommend combined analyses of gut contents and tissue chemical markers as dietary monitoring methodology of aquatic top predators to support an optimal ecosystem-based management.

Genetic Diversity and Population Structure of East Asian Raccoon Dog (Nyctereutes procyonoides): Genetic Features in Central and Marginal Populations.

The raccoon dog (Nyctereutes procyonoides) is endemic to East Asia but has been introduced in Europe. Its high adaptability enabled its rapid colonization of European countries, where population growth has been raising concerns regarding ecosystem disturbance and the spread of zoonotic diseases. The genetic diversity and structure of endemic, source, and introduced populations from seven locations across South Korea, China, Russian Far East, Finland (spread to Finland after introduction to European part of Russia from Russian Far East), Vietnam, and Japan (Honshu and Hokkaido) were examined based on 16 microsatellite loci. Two major and significantly different (FST = 0.236) genetic clusters were found: continental (South Korean, Chinese, Russian, Finnish, and Vietnamese) and island (Japanese) populations. The continental raccoon dog population comprises three subpopulations (Chinese_Russian_Finnish, South Korean, and Vietnamese) and the Japanese population consists of Honshu and Hokkaido subpopulations. The genetic diversity and geographic structure of raccoon dogs in East Asia has been influenced by natural barriers to gene flow and reveals a typical central-marginal trend in genetic diversity (continental vs. island, and central vs. marginal or source vs. introduced within continental populations). The detected differences between continental and island populations agree with those reported in previous studies that considered these populations as different species.

Isolation of Brucella pinnipedialis from Grey Seals (Halichoerus grypus) in the Baltic Sea.

Brucella infection in seals was reported for the first time in 1994 around the coast of Scotland. Since then, marine mammal Brucella infections were found to be widely distributed in the northern hemisphere. Two Brucella species affect marine mammals: Brucella pinnipedialis in pinnipeds and Brucella ceti in cetaceans. We examined the livers of Baltic grey seals (Halichoerus grypus) from the Finnish coast (n=122) hunted, found dead, or killed as by-catch in fishing gear in 2013-15 as part of population health monitoring. We detected B. pinnipedialis in the livers of three grey seals. The bacterium was isolated from livers displaying parasitic cholangitis. We also detected Brucella DNA in liver flukes (Pseudamphistomum truncatum) obtained from a Brucella-infected grey seal, suggesting that flukes might be possible vectors of this pathogen in the marine environment.

Invasion of the raccoon dog Nyctereutes procyonoides in Europe: History of colonization, features behind its success, and threats to native fauna.

We aimed to review the history of the introduction and colonization of the raccoon dog Nyctereutes procyonoides in Europe, the features behind its successful expansion and its impact on native fauna. The raccoon dog quickly colonized new areas after being introduced to the European part of the former Soviet Union. Today it is widespread in Northern and Eastern Europe and is still spreading in Central Europe. Features behind its success include its adaptability, high reproductive potential, omnivory, hibernation in northern areas, multiple introductions with > 9000 individuals from different localities, and tendency to wander enabling gene flow between populations. Firm evidence of the raccoon dog's negative impact on native fauna, such as a reduction in bird populations, is still scarce. Raccoon dogs may destroy waterfowl nests, although a nest predation study in Latvia did not confirm this. Predator removal studies in Finland suggested that the raccoon dog's impact on game birds is smaller than expected. However, raccoon dogs may have caused local extinction of frog populations, especially on islands. Raccoon dogs may compete with other carnivores for food, for example for carrion in winter, or for the best habitat patches. In northern Europe potential competitors include the red fox Vulpes vulpes and the badger Meles meles, but studies of their diets or habitat preferences do not indicate severe competition. The raccoon dog is an important vector of diseases and parasites, such as rabies, Echinococcus multilocularis and Trichinella spp. and this is no doubt the most severe consequence arising from the spread of this alien species in Europe.

Rabies in northeastern Europe--the threat from invasive raccoon dogs.

The red fox (Vulpes vulpes) is the main terrestrial wildlife rabies vector in Europe. However, recently the raccoon dog (Nyctereutes procyonoides)--an invasive species originating from East Asia--has become increasingly important as secondary host, especially in the Baltic States. This imposes problems on neighboring rabies-free countries (such as Finland), where the density of each of the two vector species on its own might be too low to sustain a long-term rabies epizootic, but the community of vectors could be large enough to support a rabies epizootic. In this modeling study, we analyzed rabies epizootics in a community of foxes and raccoon dogs. We focused on the impact of density and behavioral differences (hibernation) between the two vector species. We found that rabies could persist in the community, even if the disease would not spread in the single vector species because its density was too low. Epizootics in the community were stronger than expected for single species, and raccoon dogs were usually the major rabies host. If raccoon dog territory density was high, invasive raccoon dogs could even outcompete native foxes because of apparent competition via the rabies virus. The enhancement in disease risk and disease intensity caused by raccoon dogs suggests that current strategies to control wildlife rabies in Europe should be reviewed, and that oral rabies vaccination also should target raccoon dogs after they emerge from hibernation.

Seasonal rhythms of body temperature in the free-ranging raccoon dog (Nyctereutes procyonoides) with special emphasis on winter sleep.

The raccoon dog (Nyctereutes procyonoides) is the only canid with passive overwintering in areas with cold winters, but the depth and rhythmicity of wintertime hypothermia in the wild raccoon dog are unknown. To study the seasonal rhythms of body temperature (T(b)), seven free-ranging animals were captured and implanted with intra-abdominal T(b) loggers and radio-tracked during years 2004-2006. The average size of the home ranges was 306+/-26 ha, and the average 24 h T(b) was 38.0+/-<0.01 degrees C during the snow-free period (May-November). The highest and lowest T(b) were usually recorded around midnight (21:00-02:00 h) and between 05:00-11:00 h, respectively, and the range of the 24 h oscillations was 1.2+/-0.01 degrees C. The animals lost approximately 43+/-6% of body mass in winter (December-April), when the average size of the home ranges was 372+/-108 ha. During the 2-9-wk periods of passivity in January-March, the average 24 h T(b) decreased by 1.4-2.1 degrees C compared to the snow-free period. The raccoon dogs were hypothermic for 5 h in the morning (06:00-11:00 h), whereas the highest T(b) values were recorded between 16:00-23:00 h. The range of the 24 h oscillations increased by approximately 0.6 degrees C, and the rhythmicity was more pronounced than in the snow-free period. The ambient temperature and depth of snow cover were important determinants of the seasonal T(b) rhythms. The overwintering strategy of the raccoon dog resembled the patterns of winter sleep in bears and badgers, but the wintertime passivity of the species was more intermittent and the decrease in the T(b) less pronounced.

Effects of Protostrongylus sp. and Pneumocystis sp. on the pulmonary tissue and the condition of mountain and brown hares from Finland.

Mountain hares (Lepus timidus) and brown hares (Lepus europaeus) shot by hunters in several game management districts in southern and central Finland during the hunting season from September to the end of February 1998-2001 were examined for Protostrongylus sp. and Pneumocystis sp. Of the mountain hares, 96.5% (194/201) were infected with the lungworm Protostrongylus sp. and 16.9% (32/189) had cyst forms of the fungus Pneumocystis sp. in the lungs. The prevalence of the lungworm and fungus in brown hares was 60% (18/30) and 20.0% (6/30), respectively. The tissue changes associated with the lungworms were macroscopically and microscopically well demarcated. The majority and most severe histopathologic changes were seen at the distal part of the caudal lobes. Inflammatory cells, mainly eosinophils and macrophages, and in lesser degree neutrophils, lymphocytes, and plasma cells were typical findings in the worm-infected tissue. The condition and weight of the hare did not show any significant association with the intensity of the lungworm infection. All Pneumocystis-infected mountain hares were young, and their condition and weight correlated negatively with the intensity of the infection. The intensity of the Pneumocystis infection did not correlate with that of the lungworm infection. Within a tissue section, a slight but significant positive correlation was observed between presence of cysts and inflammatory cells.