Arctic Seals Research Articles

An Arctic seal in temperate waters: History of the ringed seal (Pusa hispida) in the Baltic Sea and its adaptation to the changing environment

The ringed seal ( Pusa hispida) is an early immigrant in the Baltic Basin and has since its arrival experienced substantial changes in the climate, salinity and productivity of the Basin. In this paper, we discuss the dispersal and distribution of the ringed seal during different stages of the Baltic Sea in relation to past and ongoing environmental changes. Subfossil ringed seal remains around the Baltic Sea and the Danish Straits were radiocarbon dated in order to map the distribution of the species in different time periods. The δ13C data were used in evaluating the changes in the marine character of the Baltic Basin. The sequence of the dates indicates a continuous presence of the species in the Baltic Basin. The earliest ringed seal finds come from the Skagerrak/Kattegat area (Denmark, Swedish west coast) and date to the full glacial period and Baltic Ice Lake. In the Baltic Basin, the species appears in the subfossil record during the Ancylus period, but the main part of the remains date to the Littorina stage. During the Littorina stage, the distribution of the species was at least periodically wider than today, covering also southern parts of the Baltic. The presence of breeding populations in southern parts of the Baltic during the Holocene Thermal Maximum (HTM) indicates that the winters were at least periodically cold enough for winter ice. The changes in the marine influence in the Baltic Basin can be seen in the seal collagen δ13C values, which serve as a proxy for qualitative changes in water mass salinity.

The use of DNA barcoding to monitor the marine mammal biodiversity along the French Atlantic coast

In the last ten years, 14 species of cetaceans and five species of pinnipeds stranded along the Atlantic coast of Brittany in the North West of France. All species included, an average of 150 animals strand each year in this area. Based on reports from the stranding network operating along this coast, the most common stranding events comprise six cetacean species (Delphinus delphis, Tursiops truncatus, Stenella coeruleoalba, Globicephala melas, Grampus griseus, Phocoena phocoena)and one pinniped species (Halichoerus grypus). Rare stranding events include deep-diving or exotic species, such as arctic seals. In this study, our aim was to determine the potential contribution of DNA barcoding to the monitoring of marine mammal biodiversity as performed by the stranding network.We sequenced more than 500 bp of the 5’ end of the mitochondrial COI gene of 89 animals of 15 different species (12 cetaceans, and three pinnipeds). Except for members of the Delphininae, all species were unambiguously discriminated on the basis of their COI sequences. We then applied DNA barcoding to identify some “undetermined” samples. With again the exception of the Delphininae, this was successful using the BOLD identification engine. For samples of the Delphininae, we sequenced a portion of the mitochondrial control region (MCR), and using a non-metric multidimentional scaling plot and posterior probability calculations we were able to determine putatively each species. We then showed, in the case of the harbour porpoise, that COI polymorphisms, although being lower than MCR ones, could also be used to assess intraspecific variability. All these results show that the use of DNA barcoding in conjunction with a stranding network could clearly increase the accuracy of the monitoring of marine mammal biodiversity.

The Gut Bacterial Community of Mammals from Marine and Terrestrial Habitats

After birth, mammals acquire a community of bacteria in their gastro-intestinal tract, which harvests energy and provides nutrients for the host. Comparative studies of numerous terrestrial mammal hosts have identified host phylogeny, diet and gut morphology as primary drivers of the gut bacterial community composition. To date, marine mammals have been excluded from these comparative studies, yet they represent distinct examples of evolutionary history, diet and lifestyle traits. To provide an updated understanding of the gut bacterial community of mammals, we compared bacterial 16S rRNA gene sequence data generated from faecal material of 151 marine and terrestrial mammal hosts. This included 42 hosts from a marine habitat. When compared to terrestrial mammals, marine mammals clustered separately and displayed a significantly greater average relative abundance of the phylum Fusobacteria. The marine carnivores (Antarctic and Arctic seals) and the marine herbivore (dugong) possessed significantly richer gut bacterial community than terrestrial carnivores and terrestrial herbivores, respectively. This suggests that evolutionary history and dietary items specific to the marine environment may have resulted in a gut bacterial community distinct to that identified in terrestrial mammals. Finally we hypothesize that reduced marine trophic webs, whereby marine carnivores (and herbivores) feed directly on lower trophic levels, may expose this group to high levels of secondary metabolites and influence gut microbial community richness.

Complex masking scenarios in Arctic environments

Critical ratios obtained using octave-band noise and narrowband signals provide a useful first approximation for understanding the effects of noise on hearing. When considering realistic listening scenarios, it may be necessary to examine the effects of spectrally complex, time-varying noise sources on an animal’s ability to detect relevant signals. In the case of Arctic seals, the increasing prevalence of seismic exploration makes an examination of masking by impulsive sounds particularly relevant. However, the characteristics of received sounds from airgun operations vary dramatically depending on the seismic source, environmental parameters, and distance. In order to determine the potential for auditory masking by airguns, we developed a paradigm to quantify the influence of spectral and temporal variations in typical seismic noise on signal detectability. This method calls for calculation of detection probabilities for seals listening for the same signal embedded at different time windows within a background of distant airgun noise. We believe this approach will enable an experimental assessment of masking potential by impulsive noise as distance between the receiver and source is increased. Such an assessment will aid in determining the extent to which standard critical ratio data can be reasonably applied in complex masking scenarios. [Work supported by OGP-JIP.]

Global change effects on the long‐term feeding ecology and contaminant exposures of East Greenland polar bears

Rapid climate changes are occurring in the Arctic, with substantial repercussions for arctic ecosystems. It is challenging to assess ecosystem changes in remote polar environments, but one successful approach has entailed monitoring the diets of upper trophic level consumers. Quantitative fatty acid signature analysis (QFASA) and fatty acid carbon isotope (δ(13) C-FA) patterns were used to assess diets of East Greenland (EG) polar bears (Ursus maritimus) (n=310) over the past three decades. QFASA-generated diet estimates indicated that, on average, EG bears mainly consumed arctic ringed seals (47.5±2.1%), migratory subarctic harp (30.6±1.5%) and hooded (16.7±1.3%) seals and rarely, if ever, consumed bearded seals, narwhals or walruses. Ringed seal consumption declined by 14%/decade over 28years (90.1±2.5% in 1984 to 33.9±11.1% in 2011). Hooded seal consumption increased by 9.5%/decade (0.0±0.0% in 1984 to 25.9±9.1% in 2011). This increase may include harp seal, since hooded and harp seal FA signatures were not as well differentiated relative to other prey species. Declining δ(13) C-FA ratios supported shifts from more nearshore/benthic/ice-associated prey to more offshore/pelagic/open-water-associated prey, consistent with diet estimates. Increased hooded seal and decreased ringed seal consumption occurred during years when the North Atlantic Oscillation (NAO) was lower. Thus, periods with warmer temperatures and less sea ice were associated with more subarctic and less arctic seal species consumption. These changes in the relative abundance, accessibility, or distribution of arctic and subarctic marine mammals may have health consequences for EG polar bears. For example, the diet change resulted in consistently slower temporal declines in adipose levels of legacy persistent organic pollutants, as the subarctic seals have higher contaminant burdens than arctic seals. Overall, considerable changes are occurring in the EG marine ecosystem, with consequences for contaminant dynamics.

Seals and sound in a changing Arctic: Ongoing psychoacoustic studies of spotted and ringed seals

Arctic environments are changing rapidly as a result of climate warming and industrialization, and as sea ice recedes, activity associated with transportation and oil and gas production increases. Among the many concerns for ice-living seals in the region is the potential for behavioral or auditory effects resulting from noise exposure. Currently there are limited data available concerning the hearing sensitivity of arctic seals - some data exist for harp and ringed seals, while the most comprehensive data are for harbor seals. As the phylogenetic relationships among northern seals are not well resolved, extrapolation across species for management purposes is difficult. To this end, we are working to describe the species-typical hearing of spotted (Phoca largha) and ringed seals (Pusa hispida). Thus far, measurements of the underwater hearing sensitivity of spotted seals show best sensitivity between 3.2–25.6 kHz and peak sensitivity of 51 dB re 1 μPa at 25.6 kHz. Absolute thresholds for airborne tonal signals indicate acute sensitivity of <10 dB re 20 μPa from 0.80–12.8 kHz. Audiometric testing for ringed seals is ongoing, as are critical ratio measurements for both species. These studies will provide valuable insight into how arctic seals perceive acoustic signals, as well as inform management practices for these vulnerable species.

The slowest fish: Swim speed and tail-beat frequency of Greenland sharks

Locomotory muscle function of ectothermic fishes is generally depressed in cold waters, making them vulnerable to avian and mammalian predators whose body temperature remains high. Paradoxically, Greenland sharks Somniosus microcephalus exhibit the reverse of this usual predator–prey thermal pattern by apparently hunting seals in Arctic waters. To examine whether this species possesses cold-adaptations that enhance its swimming performance, we used data-logging tags to measure swim speed and tail-beat frequency (which reflects muscle-shortening speed) of six free-swimming sharks (204–343kg). For comparison, we compiled these parameters for wild fishes from the literature over a wide body mass range (0.2–3900kg) and examined the scaling relationships using phylogenetically informed statistics. The sharks cruised at 0.34m·s−1 with a tail-beat frequency of 0.15Hz, both of which were the lowest values for their size across fish species. The mean and maximum speed (0.74m·s−1) and acceleration during burst swimming (0.008m·s−2) were much lower than those of seals. Our results indicate that the swimming performance of Greenland sharks is limited by cold waters (~2°C) and insufficient to catch swimming seals. However, Arctic seals sleep in water to avoid predation by polar bears Ursus maritimus, which may leave them vulnerable to this cryptic slow-swimming predator.

Seasonal presence of ringed, ribbon, and bearded seal vocalizations in the Chukchi Sea north of Barrow, Alaska

Long-term autonomous acoustic recordings were collected between September and June from 2006 through 2009 in the Northeastern Chukchi Sea along the continental slope 120 km north of Barrow, Alaska. These recordings were analyzed for the presence of vocalizations of ringed seals (Phoca hispida), ribbon seals (Histrophoca fasciata), and bearded seals (Erignathus barbatus). We present detailed descriptions of the acoustic repertoire of each species in addition to three-year time series of seal vocalizations and mean daily sea ice concentration. Ringed seal vocalizations are present throughout each winter and spring, indicating that they both overwinter and breed in offshore pack ice. Ribbon seal calls occur only during the open water period in 2008, but their acoustic behavior is more varied than previously described. Bearded seal vocalizations closely match well-documented calls recorded offshore near Point Barrow but have shorter duration and smaller frequency range, suggesting that demographic or behavioral differences related to breeding habitat selection may exist within the population. Bearded seal calls peak during the breeding season from March through June, but also occur in December and January annually. These long-term autonomous recordings provide details of seasonal distribution and behavior of Arctic seals that previously have not been possible to observe with other methods.

FATAL MASS INGESTION OF GASTRIC FOREIGN BODIES IN JUVENILE HOODED SEALS (CYSTOPHORA CRISTATA) STRANDED IN NORTH-WESTERN IBERIAN PENINSULA

The hooded seal (Cystophora cristata) is a subarctic and arctic pinniped species with its limit of distribution in southern Europe established west of the British Isles. Nevertheless, since 1970, strandings of juvenile individuals have been reported much further south than this limit. The special clinical and management considerations to take into account with these arctic seals have become a new challenge to veterinary clinicians of southern North-Atlantic stranding networks. We present here three clinical cases involving mass ingestion of foreign bodies, which seems to be a generalized finding in this species. Although the presence of gastroliths are considered to be normal in pinnipeds, the fast and ultimately lethal cases presented here highlights how an excessive presence of gastric foreign bodies could result in a gastrointestinal stasis syndrome, which has to be quickly resolved, medically or surgically. Portable ultrasound and X-ray equipments have demonstrated their value as gastric foreign bodies diagnostic procedures with nervous wildlife patients, such as the juvenile hooded seals. Finally, we conclude that it is extremely important to avoid the use of loose stones or sand over resting areas and to take extreme precautions with small items near the rehabilitation pools when dealing with this seal species.

Spatio-temporal variations and age effect on Toxoplasma gondii seroprevalence in seals from the Canadian Arctic

Toxoplasmosis is a significant public health threat for Inuit in the Canadian Arctic. This study aimed to investigate arctic seals as a possible food-borne source of infection. Blood samples collected from 828 seals in 7 Canadian Arctic communities from 1999 to 2006 were tested for Toxoplasma gondii antibodies using a direct agglutination test. Polymerase chain reaction (PCR) was used to detect T. gondii DNA in tissues of a subsample of seals. Associations between seal age, sex, species, diet, community and year of capture, and serological test results were investigated by logistic regression. Overall seroprevalence was 10·4% (86/828). All tissues tested were negative by PCR. In ringed seals, seroprevalence was significantly higher in juveniles than in adults (odds ratio=2·44). Overall, seroprevalence varied amongst communities (P=0·0119) and by capture year (P=0·0001). Our study supports the hypothesis that consumption of raw seal meat is a significant source of infection for Inuit. This work raises many questions about the mechanism of transfer of this terrestrial parasite to the marine environment, the preponderance of infection in younger animals and the natural course of infection in seals. Further studies to address these questions are essential to fully understand the health risks for Inuit communities.

Predicting recurrent PDV epizootics in European harbour seals (Phoca vitulina)

Phocine Distemper Virus (PDV) caused mass mortality in European harbour seals (Phoca vitulina) in 1988 and in 2002. Both epizootics likely originated from refugia in Arctic seals, where data indicate PDV hops among populations and species. The metapopulation structure of host populations is suggested to be the reason why PDV is preserved among Arctic seals, since the high rate of spread of PDV would require much larger panmictic populations to maintain an infection. The pattern of sudden outbreaks of PDVis also seen in grey seals (Halichoerus grypus), the only to date identified species that could act as a vector between Arctic and North Sea seal populations. Harbour seal populations along mainland Europe were below critical herd immunity levels by 3-5 years after the events, and thus vulnerable for new outbreaks, but historical data and the 14 years between the 2 epizootics suggest that harbour seals in the North Sea area are only rarely exposed to the infective agent. The risk for new outbreaks of the seal plague in North Sea harbour seals is likely linked to the dynamics of the disease in Arctic seal species as well asvector species.

Multiple fossil calibrations, nuclear loci and mitochondrial genomes provide new insight into biogeography and divergence timing for true seals (Phocidae, Pinnipedia)

AbstractAim To better understand the historical biogeography of the true seals, Phocidae, by combining nuclear DNA (nDNA) and mitochondrial DNA (mtDNA) in a divergence time analysis using multiple fossil calibrations.Location Arctic, Antarctic, Pacific and Atlantic Oceans, Lake Baikal, Caspian Sea.Methods Fifteen nuclear genes totalling 8935 bp plus near‐complete mitochondrial genome sequences were used in a Bayesian divergence time analysis, incorporating eight soft‐bound fossil calibrations across the phylogeny. All species of true seals were included, plus the walrus, three otariids and seven carnivore outgroups. The majority of the nuclear sequences and four phocid mitochondrial genomes (plus three non‐phocid mitochondrial genomes) were newly generated for this study using DNA extracted from tissue samples; other sequences were obtained from GenBank.Results Using multiple nuclear genes and multiple fossil calibrations resulted in most divergence time estimations within Phocidae being much more recent than predicted by other molecular studies incorporating only mtDNA and using a single calibration point. A new phylogenetic hypothesis was recovered for the Antarctic seals.Main conclusions Incorporating multiple nuclear genes and fossil calibrations had a profound effect on the estimated divergence times. Most estimated divergences within Phocinae (Arctic seals) correspond to Arctic oceanic events and all occur within the last 12 Myr, a time when the Arctic and Atlantic oceans were freely exchanging and perennial Arctic sea ice existed, indicating that the Arctic seals may have had a longer association with ice than previously thought. The Monachinae (‘southern’ seals) split from the Phocinae c. 15 Ma on the eastern US coast. Several early trans‐Atlantic dispersals possibly occurred, leaving no living descendants, as divergence estimates suggest that the Monachus (monk seal) species divergences occurred in the western Atlantic c. 6 Ma, with the Mediterranean monk seal ancestor dispersing afterwards. The tribes Lobodontini (Antarctic seals) and Miroungini (elephant seals) are also estimated to have diverged in the eastern Atlantic c. 7 Ma and a single Lobodontini dispersal to Antarctica occurred shortly afterwards. Many of the newly estimated dates are used to infer how extinct lineages/taxa are allied with their living relatives.

First record of the harp seal ( Pagophilus groenlandicus) extralimital presence in the Mediterranean Sea

The stranding of a harp seal on the beach in the municipality of Motril (southern Spain) represents the first record of this species in the Mediterranean Sea and the southernmost known report. It was a male which reached the beach very tired and sick, dying after two hours on the sand. The specimen presented three species of epibionts. This is the second species of Arctic seal recorded in the Mediterranean Sea.

Research Advances: Scientists Discover Historic Sample of Bomb-Grade Plutonium; Mercury Levels in Arctic Seals May Be Linked to Global Warming; Oh Rats! New Wireless Sensor for Instant Brain [O2]; New Material with Record High Surface Area

Identifying the source of radioactive samples. Hg levels in seals. New device nets [O2]. MCP maximizes H2 uptake.

A study of metal concentrations and metallothionein binding capacity in liver, kidney and brain tissues of three Arctic seal species

Arctic seals are known to accumulate relatively high concentrations of potential toxic heavy metals in their vital organs, such as livers and kidneys, as well as in their central nervous system. We therefore decided to determine whether mercury, copper, cadmium and zinc levels in liver, kidney and brain tissues of three Arctic seal species were associated with the intracellular metal-binding protein metallothionein (MT) as a sign of toxic exposure. Samples from four ringed ( Phoca hispida), five harp ( P . groenlandica) and five hooded ( Cystophora cristata) seals taken during field trips to Central West Greenland (Godhavn) and the Barents Sea in the spring of 1999 were used for the present study. In all three seal species concentrations of mercury, zinc and copper were highest in the liver, except for cadmium which was highest in the kidneys. Metal concentrations increased significantly in the order: ringed seal < harp seal < hooded seal for both kidney and liver tissues. MT concentrations were highest in the kidneys and the concentrations increased in the order: ringed seal < hooded seal < harp seal. MT metal-binding capacity was highest in the kidneys for all three species and increased in the same order: ringed seals (2–10%) < hooded seals (8–15%) < harp seals (27–63%). We therefore suggest that there are species-specific differences in the sub-cellular handling of heavy metals which indicate differences in sensitivity and health implications. However, a larger sample size is needed in order to test the relationship between metal concentrations and MT up-regulation in order to decide which metals are the most important and to elucidate whether the MT binding capacity is sufficient to protect tissues (i.e. kidney) from metal toxicosis. MT with its binding capacity could be a useful marker for environmental exposure to metals and their potential toxicity in the Arctic.

Diet differences among age classes of Arctic seals: evidence from stable isotope and mercury biomarkers

A basic understanding of current food web dynamics and baseline data from which to measure future change is necessary to understand species re-distribution and altered competition for food with climate change. We use mercury (Hg) and carbon (δ13C) and nitrogen (δ15N) stable isotope ratios as biomarkers to understand species diet differences and age class differences among ringed (Phoca hispida), bearded (Erignathus barbatus), and harbour (P. vitulina) seals in a subarctic marine ecosystem. Adult bearded seals had significantly lower δ15N and muscle Hg than bearded seal pups, whereas the opposite was observed in ringed seals where pups had lower δ15N than adults, suggesting age specific foraging differences in trophic food level for both species. For harbour seals, δ15N did not differ significantly among ages while Hg and δ13C did. The δ13C in muscle supports that bearded seals in this study are benthic feeders and are part of a separate food web from ringed seals and harbour seals. Harbour seals had the highest levels of mercury and δ15N, indicating they feed at a higher trophic level relative to the other two seal species. Carbon and nitrogen isotopic ratios and Hg levels illustrate how resources are partitioned among three seal species and offer evidence for separation based on life stages within species.

Transfer of lipids from plankton to blubber of harp and hooded seals off East Greenland

Sub-Arctic marine ecosystems are some of the most productive ecosystems in the world's oceans. The capacity of herbivorous zooplankton, such as Calanus, to biosynthesize and store large amounts of lipids during the short and intense spring bloom is a fundamental adaptation which facilitates the large production in these ecosystems. These energy-rich lipids are rapidly transferred through the food chain to Arctic seals. The fatty acids and stable isotopes from harp seal (Phoca groenlandica) and hooded seal (Cystophora cristata) off East Greenland as well as their potential prey, were analysed. The results were used to describe the lipid dynamics and energy transfer in parts of the East Greenland ecosystem. Even if the two seal species showed considerable overlap in diet and occurred at relatively similar trophic levels, the fatty acid profiles indicated that the bases of the food chains of harp and hooded seals were different. The fatty acids of harp seals originate from diatom-based food chain, whereas the fatty acids of hooded seals originate from dinoflagellate and the prymnesiophyte Phaeocystis pouchetii-based food chain. Stable isotope analyses showed that both species are true carnivores on the top of their food chains, with hooded seal being slightly higher on the food chain than harp seal.

Probabilistic biokinetic modelling of radiocaesium uptake in Arctic seal species: verification of modelled data with empirical observations

The necessity to provide information about radionuclide concentrations in Arctic marine species has been heightened in recent years due to a number of accidents in Arctic regions involving nuclear vessels and the presence of a large number of potential radioactive contamination sources. The provision for such information is largely dependant on the use of radionuclide uptake and transfer models. The uptake of radionuclides in Arctic seal species in this study has been modelled using a probabilistic biokinetic approach. In this paper, model results are compared with empirical data from relevant samples taken within the Arctic region. Results indicate that the model performs well when estimating concentrations of 137Cs in two seal species for both median values and reproduction of the distribution of data values, but not as well for a third seal species. Likely factors affecting the results are the probability density functions used for the input parameters.

Digestion of capelin, Mallotus villosus (Müller), herring, Clupea harengus L., and polar cod, Boreogadus saida (Lepechin), otoliths in a simulated seal stomach

Abstract The ability of otoliths to withstand digestion in a seal stomach appears to differ between fish taxa with the otoliths of gadoids being particularly resistant to gastric erosion. Few studies have examined the effect of otolith size on the rate of otolith dissolution. We exposed 50 otoliths (total sagittal length: 1.4–7.0 mm) from capelin (Mallotus villosus, n = 20), herring (Clupea harengus, n = 10), and polar cod (Boreogadus saida, n = 20) as well as nine whole capelin (total body length = 100–120 mm) to digestive solutions assumed to mimic the gastric environment of Arctic seals in vitro (pH: ∼2, temperature: ∼37°C, pepsin concentrations: 0–750-μg ml−1 solution). Pepsin did not affect the dissolution rates of sagittae but resulted in a complete digestion of whole capelin within 10 h. Irrespective of species examined, sagittae fitted the same pattern of dissolution rate with the smaller sagittae being dissolved faster than did the larger ones. We suggest that scaling controls sagittal dissolution rates (DR, μm min−1), and that the sagittae from the three forage fish combined dissolve according to sagittal length (SL, mm) as shown by the equation: DRCommon = 27.348e−0.120 SL (n = 46, r2 = 0.688, p &lt; 0.001). Given this relationship, the numerical importance of prey taxa with the smaller otoliths – i.e. also the small-sized gadoids (polar cod) – is likely to be underestimated in feeding studies with Arctic seals.

Bioaccumulation of radiocaesium in Arctic seals

Seals are high trophic level feeders that bioaccumulate many contaminants to a greater degree than most lower trophic level organisms. Their trophic status in the marine food web and wide-spread distribution make seals useful sentinels of arctic environmental change. The purpose of this investigation is to document the levels and bioaccumulation potential of radiocaesium in high latitude seal species for which data have not previously been available. The study was carried out on harp, ringed, and bearded seals caught north of the island archipelago of Svalbard (82°N) in 1999. The results are then compared with previous studies in order to elucidate factors responsible for bioaccumulation in Arctic seals. Concentrations of 137Cs were determined in muscle, liver and kidney samples from a total of 10 juvenile and one adult seal. The mean concentration in muscle samples for all animals was 0.23±0.045 Bq/kg f.w. 137Cs concentrations in both liver and kidney samples were near detection limits (≈0.2 Bq/kg f.w.). The results are consistent with previous studies indicating low levels of radiocaesium in Arctic seals in response to a long term trend of decreasing levels of 137Cs in the Barents Sea region. Bioconcentration factors (BCFs) estimated for seals from NE Svalbard are low, ranging from 34 to 130. Comparing these values with reported BCFs for Greenland seals from other sectors of the European Arctic, we suggest that the combination of physiological and ecological factors on radiocaesium bioaccumulation is comparable among different Arctic seal populations. The application of this work to Arctic monitoring and assessment programs is discussed.