Serum chemistry and antibodies against pathogens in antarctic fur seals, Weddell seals, crabeater seals, and Ross seals

Information on health parameters, such as antibody prevalences and serum chemistry that can reveal exposure to pathogens, disease, and abnormal physiologic conditions, is scarce for Antarctic seal species. Serum samples from Antarctic fur seals (Arctocephalus gazella, n=88) from Bouvet?ya (2000-2001 and 2001-2002), and from Weddell seals (Leptonychotes weddellii, n=20), Ross seals (Ommatophoca rossii, n=20), and crabeater seals (Lobodon carcinophagus, n=9) from the pack-ice off Queen Maud Land, Antarctica (2001) were analyzed for enzyme activity, and concentrations of protein, metabolites, minerals, and cortisol. Adult Antarctic fur seal males had elevated levels of total protein (range 64-99 g/l) compared to adult females and pups (range 52-79 g/l). Antarctic fur seals had higher enzyme activities of creatine kinase, lactate dehydrogenase, and amylase, compared to Weddell, Ross, and crabeater seals. Antibodies against Brucella spp. were detected in Weddell seals (37%), Ross seals (5%), and crabeater seals (11%), but not in Antarctic fur seals. Antibodies against phocine herpesvirus 1 were detected in all species examined (Antarctic fur seals, 58%; Weddell seals, 100%; Ross seals, 15%; and crabeater seals, 44%). No antibodies against Trichinella spp., Toxoplasma, or phocine distemper virus (PDV) were detected (Antarctic fur seals were not tested for PDV antibodies). Antarctic seals are challenged by reduced sea ice and increasing temperatures due to climate change, and increased anthropogenic activity can introduce new pathogens to these vulnerable ecosystems and represent a threat for these animals. Our data provide a baseline for future monitoring of health parameters of these Antarctic seal species, for tracking the impact of environmental, climatic, and anthropogenic changes in Antarctica over time.     

Dinucleotide microsatellite markers from the Antarctic seals and their use in other Pinnipeds

Twenty‐four microsatellite loci were isolated from three species of Antarctic seals (Subfamily Monachinae, Tribe Lobodontini). Eleven loci were cloned from Weddell seal, Leptonychotes weddellii, seven from leopard seal, Hydrurga leptonyx, and six from crabeater seal, Lobodon carcinophagus. Variability was assessed in Weddell seals collected in McMurdo Sound, leopard seals from Bird Island, South Georgia, and crabeater seals sampled in the eastern Ross Sea. All loci were variable in the three species used for cloning and 22 of these loci amplified variable products in the Ross seal, Ommatophoca rossii. Cross‐species amplification was largely successful, with an average of 19 loci amplifying products in other phocids.     

Genetically effective population sizes of Antarctic seals estimated from nuclear genes

We analyzed eight nuclear microsatellite loci in three species of Antarctic seals; Weddell seal (Leptonychotes weddellii; mean N = 163), crabeater seal (Lobodon carcinophaga; 138) and Ross seal (Ommatophoca rossii; 35). We estimated genetic diversity (Θ) and effective population size (N _E) for each species. Autosomal microsatellite based N _E estimates were 151,200 for Weddell seals, 880,200 for crabeater seals, and 254,500 for Ross seals. We screened one X-linked microsatellite (Lw18), which yielded similar N _E estimates to the autosomal loci for all species except the Ross seals, where it was considerably larger (~103 times). Microsatellite N _E estimates were comparable with previously published N _E estimates from mitochondrial DNA, but both are substantially lower than direct estimates of population size in all species except the Ross seals. The ratio of maternally versus biparentally derived estimates of N _E for Ross seals was not consistent with the hypothesis that they are a polygynous species. We found no sign of a recent, sustained genetic bottleneck in any of the species.     

Population structure of ice-breeding seals

The development of population genetic structure in ice-breeding seal species is likely to be shaped by a combination of breeding habitat and life-history characteristics. Species that return to breed on predictable fast-ice locations are more likely to exhibit natal fidelity than pack-ice-breeding species, which in turn facilitates the development of genetic differentiation between subpopulations. Other aspects of life history such as geographically distinct vocalizations, female gregariousness, and the potential for polygynous breeding may also facilitate population structure. Based on these factors, we predicted that fast-ice-breeding seal species (the Weddell and ringed seal) would show elevated genetic differentiation compared to pack-ice-breeding species (the leopard, Ross, crabeater and bearded seals). We tested this prediction using microsatellite analysis to examine population structure of these six ice-breeding species. Our results did not support this prediction. While none of the Antarctic pack-ice species showed statistically significant population structure, the bearded seal of the Arctic pack ice showed strong differentiation between subpopulations. Again in contrast, the fast-ice-breeding Weddell seal of the Antarctic showed clear evidence for genetic differentiation while the ringed seal, breeding in similar habitat in the Arctic, did not. These results suggest that the development of population structure in ice-breeding phocid seals is a more complex outcome of the interplay of phylogenetic and ecological factors than can be predicted on the basis of breeding substrate and life-history characteristics.     

An apparent population decrease,or change in distribution,of Weddell seals along the Victoria Land coast

Ground counts during 1959–1968 compared with counts using high resolution (0.6 m²) satellite imagery during 2008–2012 indicated many fewer Weddell seals (Leptonychotes weddellii) at two major molting areas in the western Ross Sea: Edisto Inlet‐Moubray Bay, northern Victoria Land, and McMurdo Sound, southern Victoria Land. Breeding seals have largely disappeared from Edisto‐Moubray, though the breeding population in McMurdo Sound appears to have recovered from harvest in the 1960s. The timing of decline, or perhaps spreading (lower numbers of seals in more places), is unknown but appears unrelated to changes in sea ice conditions. We analyzed both historic and satellite‐derived ice data confirming a large expansion of pack ice mostly offshore of the Ross Sea, and not over the continental shelf (main Weddell seal habitat), and a thinning of fast ice along Victoria Land (conceivably beneficial to seals). Timing of fast ice presence and extent in coves and bays along Victoria Land, remains the same. The reduction in numbers is consistent with an altered food web, the reasons for which are complex. In the context of a recent industrial fishery targeting a seal prey species, a large‐scale seal monitoring program is required to increase understanding of seal population changes.     

Histological,histochemical, and ultrastructural investigations on the gastrointestinal system of antarctic seals: Weddell seal (Leptonychotes weddellii) and crabeater seal (Lobodon carcinophagus)

The morphology of the principal sections of the gastrointestinal system of two Antarctic seals with different dietary habits, namely, the Weddell seal (Leptonychotes weddellii) and the crabeater seal (Lobodon carcinophagus), has been investigated. Histologically examined by light microscopy, the tissue layers of the gastrointestinal tract of both seals are almost identical to those observed in most other mammals and no major differences in principle organization could be found between the two seal species. The ultrastructure of the gastric and intestinal epithelial cells has been examined and is also closely comparable to that of these cells in other mammals; however, Paneth cells have not been found in our material. In general, therefore, adaptations of the gastrointestinal tract to the aquatic environment or the diet are not obvious at the morphological levels of organization studied. Histochemical differences are found between the two closely related species; mucins of the surface epithelium in the stomach of Weddell seals are highly sulfated, while those in the crabeater seal are not. Mucous neck cells in Weddell seals contain acid mucosubstances, while those of crabeater seals contain neutral ones. Goblet cells in the small and large intestine in Weddell seals contain both neutral and acid mucosubstances. Both mucin types are detected in the crabeater seal; however, the mucins of the colon in the crabeater seal are more highly sulfated than those in the Weddell seal. The ratio of globet cells to enterocytes in the large intestine of crabeater seals is higher than that in Weddell seals. © 1995 Wiley-Liss, Inc.     

Cooperative hunting behavior,prey selectivity and prey handling by pack ice killer whales (Orcinus orca), type B,in Antarctic Peninsula waters

Currently, there are three recognized ecotypes (or species) of killer whales (Orcinus orca) in Antarctic waters, including type B, a putative prey specialist on seals, which we refer to as “pack ice killer whale” (PI killer whale). During January 2009, we spent a total of 75.4 h observing three different groups of PI killer whales hunting off the western Antarctic Peninsula. Observed prey taken included 16 seals and 1 Antarctic minke whale (Balaenoptera bonaerensis). Weddell seals (Leptonychotes weddellii) were taken almost exclusively (14/15 identified seal kills), despite the fact that they represented only 15% of 365 seals identified on ice floes; the whales entirely avoided taking crabeater seals (Lobodon carcinophaga; 82% relative abundance) and leopard seals (Hydrurga leptonyx; 3%). Of the seals killed, the whales took 12/14 (86%) off ice floes using a cooperative wave‐washing behavior; they produced 120 waves during 22 separate attacks and successfully took 12/16 (75%) of the Weddell seals attacked. The mean number of waves produced per successful attack was 4.1 (range 1–10) and the mean attack duration was 30.4 min (range 15–62). Seal remains that we examined from one of the kills provided evidence of meticulous postmortem prey processing perhaps best termed “butchering.”     

Identification of hairs found in leopard seal (<Emphasis Type="Italic">Hydrurga leptonyx</Emphasis>) scats

The leopard seal is a top-order predator in the Southern Ocean ecosystem and preys on a wide variety of vertebrate species including seals and penguins. We assessed the use of hairs found in leopard seal scats to identify the species of pinniped consumed. A reference collection of hairs was obtained from four potential leopard seal prey species including crabeater, Weddell, Ross, and Southern elephant seals. Discrimination techniques applied to terrestrial mammals did not allow for identification of the seal hairs. Instead, a 2-dimensional (2-D) and 6-dimensional (6-D) analysis technique utilising Mahalanobis distances (D ²) was used. The smallest Mahalanobis distance together with the largest value of p(F) positively identified hairs from each species. The 6-D analysis was more accurate and applied to hairs found in the leopard seal scats. The majority of prey species were identified as crabeater seals, which are a known prey item of the leopard seal.     

Trophic interactions of Antarctic seals as determined by stable isotope signatures

The diets and trophic interactions among Weddell, crabeater, Ross, and leopard seals in the eastern Ross Sea, Antarctica, were investigated by the use of stable isotope techniques during the 1999–2000 summer seasons. The ¹³C and ¹⁵N values in seal serum clearly distinguished the three Antarctic pack-ice seal species at different trophic positions (Weddell>Ross>crabeater). These patterns appeared to reflect a close linkage to their known foraging ecology and diving behaviors, and agreed well with their presumed dietary diversity. The more enriched ¹³C and ¹⁵N values in male Weddell seals than those in females suggested differences in foraging preferences between them. Significant differences in ¹⁵N were also found among different age groups of Weddell seals. A strong correlation between the C:N ratios and serum cholesterol was probably due to extremely high cholesterol levels in phocids. Comparisons of isotope data with harbor seals revealed distinct differences between Antarctic phocids and the northern seal species.     

Movements and diving behavior of weaned Weddell seal (Leptonychotes weddellii ) pups

Between 1993 and 1995, the diving behavior and movement patterns of 23 weaned Weddell seal pups (Leptonychotes weddellii) were tracked in the Ross Sea. Antarctica, using satellite-linked time-depth recorders. Regression analyses revealed that for seals of between 8 and 27 weeks old, age was poorly correlated with the dive depth, duration, or frequency. However, changes in dive parameters suggested that Weddell seal pups were attempting to maximize dive time, but the manner in which this was done depended on age and time of day. Movement patterns indicated that most Weddell seal pups left their natal area by the end of February, and traveled north along the Antarctic continent coastline. Several individuals returned to McMurdo Sound, but others were last located more than 400 km from McMurdo. Routes followed suggest that pups can use the pack ice habitat, but prefer to remain closer to the coastline than do adults. Accepted: 21 July 1998     

Temporal variation in distribution and density of ice-obligated seals in western Hudson Bay, Canada

Recent unidirectional climatic trends and changes in top predator population ecology suggest that long-term modifications may be happening in Hudson Bay, Canada. Effects of such changes on ice-obligated seal populations are expected but long-term studies are required to differentiate climate-induced changes from natural variation. We conducted strip-transect surveys in late spring in 1995–1997, 1999–2000 and 2007–2008 to estimate distribution, density and abundance of ice-obligated ringed (Phoca hispida) and bearded (Erignathus barbatus) seals in western Hudson Bay. When hauled out, ringed seals preferred land-fast and consolidated pack ice, whereas bearded seals preferred unconsolidated pack ice. Bearded and ringed seal density estimates varied from 0.0036 to 0.0229 seals/km² of ice and from 0.46 to 1.60 seals/km² of ice, respectively. Strong inter-annual variations were recorded in the abundance estimates of both species, with the largest abundance estimates in 1995 (104,162 and 1,494 ringed and bearded seals, respectively) and the lowest in 2008 for ringed seals (33,701) and 1997 for bearded seals (278). A sine function best described seal density estimates in western Hudson Bay and suggested a decadal cycle. Previous studies that reported low ringed seal demographic parameters in the 1990s and a recovery in the 2000s supported our interpretation of the survey results. We discuss our results in the context of climate warming and suggest that a long-term decline in ice-obligated seal density estimates may overlay a possible natural decadal cycle.     

Antibodies against european phocine herpesvirus isolates detected in sera of Antarctic seals

Summary Neutralizing antibodies against European phocine herpesvirus were detected in sera of to two Antarctic seal species, Weddell seals (Leptonychotes weddellii) and crabeater seals (Lobodon carcinophagus), collected in the eastern Weddell Sea. A large number of positive sera crossneutralized canine herpesvirus, but only few sera also contained antibodies to feline herpesvirus. The Weddell seals suffered from a respiratory disease when the sera were collected (January–February, 1990). The significance and possible origin of herpesvirus infections in Antarctic seals documented for the first time in this communication is discussed. All sera were negative for antibodies against phocine and canine distemper viruses.     

Habitat Use by Weddell Seals and Emperor Penguins Foraging in the Ross Sea, Antarctica

The only apex predators that live year-round at high latitudesof the Ross Sea are the Weddell seal and emperor penguin. Theseasonal distribution, foraging depths, and diet of these twospecies appear to overlap. What makes it possible for emperorpenguins and Weddell seals to co-exist at high latitude throughoutthe winter when other marine tetrapods apparently cannot? Bothspecies have similar adaptations for exploitation of the deep-waterhabitat, forage on the same species, and routinely make longand deep dives. Yet, despite these similarities, there is probablylittle trophic overlap between the adults of both species dueto geographical and seasonal differences in habitat use. Forexample, during the winter months while female emperor penguinsare ranging widely in the pack ice, adult seals are foragingand fattening for the upcoming summer fast, literally beneaththe feet of the male penguins. However, there is more extensiveoverlap between juvenile seals and adult penguins, and shiftsin prey abundance and/or distribution would likely affect thesetwo groups similarly. In contrast, juvenile penguins appearto avoid inter- and intra- specific competition by leaving theRoss Sea once they molt.     

Long-term monitoring of Antarctic pinnipeds in Admiralty Bay (South Shetlands, Antarctica)

Year-round monitoring of five Antarctic pinnipeds was conducted in Admiralty Bay from 1988 up to 2000. Two breeding species: southern elephant sealsMirounga leonina (Linnaeus, 1758) and Weddell sealsLeptonychotes weddellii (Lesson, 1826), were present throughout the year. Three other species: crabeater seals Lobodon carcinophagus (Hobron and Jacquinot, 1842), leopard sealsHydrurga leptonyx (Blainville, 1820), and Antarctic fur sealsArctocephalus gazella (Peters, 1875) visited the area only for short periods. During this study, the abundance of elephant seals was stable, whereas those of Weddell and crabeater seals declined. Leopard seals numbers fluctuated irregularly. We detected a possible immigration from South Georgia: of a stable magnitude for elephant seals, and of variable magnitude, depending on food accessibility, for Antarctic fur seals. We found a strong recurrence of the spatial distributions of elephant, Weddell, and Antarctic fur seals in the 13 oases on the shore of Admiralty Bay. Annual distribution patterns were characteristic for each species. The innermost beaches were used predominantly by the animals during their annual fasts: the breeding and the moulting seasons.     

Contrasting behavior between two populations of an ice‐obligate predator in East Antarctica

The Austral autumn–winter is a critical period for capital breeders such as Weddell seals that must optimize resource acquisition and storage to provision breeding in the subsequent spring. However, how Weddell seals find food in the winter months remains poorly documented. We equipped adult Weddell seals after their annual molt with satellite‐relayed data loggers at two sites in East Antarctica: Dumont D'Urville (n = 12, DDU) and Davis (n = 20). We used binomial generalized mixed‐effect models to investigate Weddell seals’ behavioral response (i.e., “hunting” vs. “transit”) to physical aspects of their environment (e.g., ice concentration). Weddell seal foraging was concentrated to within 5 km of a breathing hole, and they appear to move between holes as local food is depleted. There were regional differences in behavior so that seals at Davis traveled greater distances (three times more) and spent less time in hunting mode (half the time) than seals at DDU. Despite these differences, hunting dives at both locations were pelagic, concentrated in areas of high ice concentration, and over areas of complex bathymetry. There was also a seasonal change in diving behavior from transiting early in the season to more hunting during winter. Our observations suggest that Weddell seal foraging behavior is plastic and that they respond behaviorally to changes in their environment to maximize food acquisition and storage. Such plasticity is a hallmark of animals that live in very dynamic environments such as the high Antarctic where resources are unpredictable.     

Investigation of mercury concentrations in fur of phocid seals using stable isotopes as tracers of trophic levels and geographical regions

Recent studies have shown that the complementary analysis of mercury (Hg) concentrations and stable isotopic ratios of nitrogen (δ¹⁵N) and carbon (δ¹³C) can be useful for investigating the trophic influence on the Hg exposure and accumulation in marine top predators. In this study, we propose to evaluate the interspecies variability of Hg concentrations in phocids from polar areas and to compare Hg bioaccumulation between both hemispheres. Mercury concentrations, δ¹⁵N and δ¹³C were measured in fur from 85 individuals representing 7 phocidae species, a Ross seal (Ommatophoca rossii), Weddell seals (Leptonychotes weddellii), crabeater seals (Lobodon carcinophagus), harbour seals (Phoca vitulina), grey seals (Halichoerus grypus), ringed seals (Pusa hispida) and a bearded seal (Erignathus barbatus), from Greenland, Denmark and Antarctica. Our results showed a positive correlation between Hg concentrations and δ¹⁵N values among all individuals. Seals from the Northern ecosystems displayed greater Hg concentrations, δ¹⁵N and δ¹³C values than those from the Southern waters. Those geographical differences in Hg and stable isotopes values were likely due to higher environmental Hg concentrations and somewhat greater number of steps in Arctic food webs. Moreover, dissimilarities in feeding habits among species were shown through δ¹⁵N and δ¹³C analysis, resulting in an important interspecific variation in fur Hg concentrations. A trophic segregation was observed between crabeater seals and the other species, resulting from the very specific diet of krill of this species and leading to the lowest observed Hg concentrations.     

Distribution and diving behaviour of crabeater seals (Lobodon carcinophagus) off Queen Maud Land

Eight crabeater seals (Lobodon carcinophagus) (three females, five males), ranging in body mass between 125 and 220 kg, were captured off Queen Maud Land (70–72°S, 7–16°W) during the last week of February, just after moulting, and tagged with Argos satellite-linked dive recorders to provide data on location and diving depth and duration. During the first few weeks of March the seals were moving in the pack ice along the continental shelf edge, close to the coast of Queen Maud Land. In April and May, when the pack ice extended northwards, most of the seals moved north, one reaching 63°S in late May. In the first half of June the two remaining seals turned south and moved back deep into the pack ice. The seals made about 150 dives per day each throughout the study period. Ninety percent of these were made to depths of less than 52 m. Individual maximum diving depths varied between 288 and 528 m. In March the seals were most active at night, when the dive depth was shallower than during the day. In April and May the seals were more active during day-time, with an absence of any diurnal change in divng depth. These results support the notion that crabeater seals predominantly feed on krill in Antarctic pack ice, even when winter returns to the waters off Queen Maud Land.Publication no. 134 of the Norwegian Antarctic Research Expedtion 1992/1993     

A preliminary investigation of the effect of repeated pedestrian approaches to Weddell seals (Leptonychotes weddellii)

Repeated exposure to human activity can change the behavioural response of wildlife, having implications for management. Weddell seals (Leptonychotes weddellii) breeding close to Antarctic research stations are easily accessible and regularly visited by people. To investigate the responses of Weddell seals to repeated pedestrian approaches, we tested the effect of regular visitation over a short-time period (<2 h) on the behaviour of lactating seals. Seals showed evidence of rapid habituation, as assessed by the higher proportion of seals that responded, with 67% looking up during the first approach compared to 18% during the 10th approach (R² = 0.398, P = 0.050), and by a decrease in the time spent looking at the approacher with repeated exposure (, P < 0.001). The effect of irregular pedestrian activity over a long-time period (approximately 3 weeks) was also examined, with results suggesting that such activity did not result in habituation, rather, adult female seals appeared to become sensitised to people (the majority of seals in both colonies looked up G₁ = 0.027, P = 0.870). Weddell seal pups observed during the same experiment also failed to display signs of habituation to irregular pedestrian activity, with 47% of pups looking up in the colony subjected to pedestrian activity compared to 10% in the control colony (G₁ = 5.811, P = 0.016). The implications of these results for managing human activity around breeding Weddell seals are discussed.     

Movements and dive behaviour of two leopard seals (<Emphasis Type="Italic">Hydrurga leptonyx</Emphasis>) off Queen Maud Land,Antarctica

Two adult female leopard seals (Hydrurga leptonyx) were tagged with satellite-linked dive recorders off Queen Maud Land, Antarctica, just after moulting in mid-February. The transmitters transmitted for 80 and 220 days, respectively. Both seals remained within the pack ice relatively close to the Antarctic Continent until early May, when contact was lost with one seal. The one remaining seal then migrated north, to the east side of the South Sandwich Islands in 3 weeks, whereafter it headed east, until contact was lost at 55°S in early September. From mid-May to late September this animal always stayed close to the edge of the pack ice. Both seals made mostly short (<5 min) dives to depths of 10–50 m and only occasionally dove deeper than 200 m, the deepest dive recorded being 304 m. A nocturnal diving pattern was evident in autumn and early winter, while day-time diving prevailed in mid-winter. Haul out probability was highest at mid-day (about 40% in late February and more than 80% in March and April). From May till September the remaining animal mainly stayed at sea, in the vicinity of the pack ice, with only occasional haul outs. These data suggest that a portion of the adult leopard seals may spend the winter mainly in open water, off the edge of the pack ice, where they primarily hunt near the surface. In that case, it is likely that krill (Euphausia superba), as well as penguins, young crabeater seals (Lobodon carcinophaga) and a variety of fish are important prey items.     

Brain size in neonatal and adult Weddell seals: Costs and consequences of having a large brain

Little is known about the ontogeny of brain size in pinnipeds despite potential functional implications of brain substrate (glucose, oxygen) requirements for diving, fasting, growth, and lactation strategies. We measured brain mass (brM) and cranial capacity (CC) in newborn and adult Weddell seals. Neonatal Weddell seals had brM that represented ~70% of adult brM. Weddell seals have the largest neonatal brain, proportional to adult brain, reported for any mammal to date, which is remarkable considering the relatively small size of Weddell seal pups at birth (6%–7% of maternal body mass) compared to neonates of other highly precocial mammals. Provision of sufficient glucose to maintain the large, well‐developed brain of the neonatal Weddell seal has a nontrivial metabolic cost to both pup and mother. We therefore hypothesize that this phenomenon must have functional significance, such as allowing pups to acquire complex under‐ice navigation skills during the period of maternal attendance.