Weddell Seals Research Articles

Temporal variation in isotopic composition and diet of Weddell seals in the western Ross Sea

Weddell seals (Leptonychotes weddellii) are important predators in the Antarctic marine ecosystem, yet little is known about their diet. Previous studies have used scat and stomach content analyses to examine Weddell seal diet, however, these methods are biased towards prey with indigestible hard parts. To provide a more complete picture of their diet, we analyzed the stable isotope composition (δ13C and δ15N values) of red blood cells (RBC, n=96, representing a time scale of weeks to months) and vibrissae (n=45, representing months to a year) collected over a three year period (2010–2012). Our objectives were to (1) examine isotopic variation in relation to Weddell seal mass, sex, season, location, percent lipid, and age, and (2) quantify the contribution of prey items to overall diet. Body mass was a significant predictor of δ13C and δ15N values for both tissues, though the strength and direction of the relationship varied by year. The prey group consisting of Pleurogramma antarcticum and Trematomus newnesi was found to be an important dietary component, but its proportional contribution to Weddell seal diet varied with the timeframe represented by each tissue type [median RBC (range): 59.2% (40.2–8 1.1%); median mean vibrissae (range): 69.3% (43.9–89.6%)]. Results from mixing models ran for each seal indicate individual variation in diet. Overall, this study presents novel information on the isotopic variation and diet of Weddell seals over two time scales and provides insight into the feeding ecology of an important Antarctic predator.

Bimodal Winter Haul-Out Patterns of Adult Weddell Seals (Leptonychotes weddellii) in the Southern Weddell Sea.

Hauling out is an essential component of pinniped life-history. Haul-out behaviour may be affected by biological (e.g. sex, age and condition) and physical factors (e.g. food availability and environmental conditions), and identifying these factors may help explain the spatio-temporal distribution and habitat use of pinnipeds. The aim of this study is to describe observed winter haul-out patterns of adult Weddell seals in the Weddell Sea and investigate the role of potential predictors to gain insight into the way these animals interact with the physical environment in this region. We examined the haul-out behaviour in relation to available biological (i.e., diving effort, sex) and physical information (i.e., sun angle). Thirty-three satellite telemetry tags were deployed on adult Weddell seals in the southern Weddell Sea during February 2007, 2009 and 2011, following their annual moult recording information on the behavioural mode of the animal: at surface, hauled out or diving. At the end of the austral summer Weddell seals spent, on average, more than 40% of their time hauled out on the ice. Under constant light conditions, it appears that physiological factors drive sex differences in the timing and duration of haul-out behaviour, with females spending on average more time hauled out than males during daylight hours. This time spent hauled-out declined to around 15% in both sexes by the beginning of autumn and remained at this level with a clear nocturnal haul-out pattern during the winter. The time spent diving increased during this period, indicating an increase in foraging effort during the winter months, and led to a common haul-out pattern in both sexes over winter. We found a positive relationship between haul-out duration and the percentage of time spent diving prior to a haul-out in both sexes, with the exception of female daytime haul-outs early in the year.

Escherichia coli out in the cold: Dissemination of human-derived bacteria into the Antarctic microbiome

Discharge of untreated sewage into Antarctic environments presents a risk of introducing non-native microorganisms, but until now, adverse consequences have not been conclusively identified. Here we show that sewage disposal introduces human derived Escherichia coli carrying mobile genetic elements and virulence traits with the potential to affect the diversity and evolution of native Antarctic microbial communities. We compared E. coli recovered from environmental and animal sources in Antarctica to a reference collection of E. coli from humans and non-Antarctic animals. The distribution of phylogenetic groups and frequency of 11 virulence factors amongst the Antarctic isolates were characteristic of E. coli strains more commonly associated with humans. The rapidly emerging E. coli ST131 and ST95 clones were found amongst the Antarctic isolates, and ST95 was the predominant E. coli recovered from Weddell seals. Class 1 integrons were found in 15% of the Antarctic E. coli with 4 of 5 identified gene cassette arrays containing antibiotic resistance genes matching those common in clinical contexts. Disposing untreated sewage into the Antarctic environment does disseminate non-native microorganisms, but the extent of this impact and implications for Antarctic ecosystem health are, as yet, poorly understood.

Circulating Concentrations of Progesterone and Estrogen in Weddell Seals During the Breeding Period and Early Pregnancy

Weddell seals (Leptonychotes weddellii) experience a synchronized annual reproductive cycle. Females give birth in the austral spring (October‐November) and are bred towards the end of lactation in November and December; following a brief period of embryonic diapause, active gestation begins. To examine endocrine dynamics during the breeding period and early gestation, we handled adult, post‐parturient Weddell seals with known pupping dates ~1 week prior to weaning (29–44 days post‐partum, n=32) in mid‐November to mid‐December (Nov/Dec) and approximately 60 days later, mid‐January to mid‐February (Jan/Feb). A second group of previously parous females that did not pup in the current season (non‐parturient) were also handled at equivalent dates (n=21). Seals were weighed, body composition (lipid as %body mass) was determined using isotopic dilution, and serum progesterone concentrations were measured using commercial radioimmunoassays validated for use in Weddell seals. Total estrogens were also measured by validated radioimmunoassay in a representative subset of animals. In Jan/Feb, transrectal ultrasonography was used to determine pregnancy status.Serum progesterone concentrations in Nov/Dec study animals fell into two distinct groups: a low‐concentration group, with values ranging from 0.80 to 2.50 ng•mL−1 (mean±SEM = 1.65±0.08 ng•mL−1, n=26), and a high‐concentration group, with values between 20.60 and 146.40 ng•mL−1 (59.76±6.40 ng•mL−1, n=27). Total estrogens were elevated in low progesterone seals (163.59±12.98 pg•mL−1, n=8) relative to those with high progesterone (95.71 ±12.09 pg•mL−1, n= 4) (t‐test, p value= 0.004). As elevated progesterone concentrations indicate that ovulation has occurred, we examined the likelihood that animals’ progesterone levels were in the high group using binomial logistic regressions to determine what factors may influence ovulation timing in Weddell seals. Females that did not give birth were more likely to exhibit high progesterone at later calendar dates, with no detectable effects of mass or condition. Relative to non‐parturient seals, post‐parturient seals exhibited low progesterone later in the season. The likelihood of high progesterone increased with calendar date as well as days since parturition in these females, suggesting seals that give birth later in the pupping period ovulate at fewer days post‐partum than those that give birth early. All Jan/Feb study animals had progesterone levels greater than 10 ng•mL−1, and there were no differences in progesterone (85.17±7.89ng•mL−1, n=48) or estrogen concentrations (57.70± 2.95 pg•mL−1, n=12) between females that were detectably pregnant and those that were not. This study shows that timing of ovulation in post‐parturient Weddell seals is not driven solely by parturition date, and that circulating progesterone and estrogen concentrations are not likely clear indicators of early pregnancy in this species.Support or Funding InformationThis research was funded by NSF award ANT‐1246463 to JMB and JWT and by an Institutional Development Award (IDeA) from the National Institute Of General Medical Sciences of the National Institutes of Health under Award Number P20GM103395. The content is solely the responsibility of the authors and does not necessarily reflect the official views of the NIH.

Contrasting responses to a climate regime change by sympatric, ice-dependent predators.

BackgroundModels that predict changes in the abundance and distribution of fauna under future climate change scenarios often assume that ecological niche and habitat availability are the major determinants of species’ responses to climate change. However, individual species may have very different capacities to adapt to environmental change, as determined by intrinsic factors such as their dispersal ability, genetic diversity, generation time and rate of evolution. These intrinsic factors are usually excluded from forecasts of species’ abundance and distribution changes. We aimed to determine the importance of these factors by comparing the impact of the most recent climate regime change, the late Pleistocene glacial-interglacial transition, on two sympatric, ice-dependent meso-predators, the emperor penguin (Aptenodytes forsteri) and Weddell seal (Leptonychotes weddellii).MethodsWe reconstructed the population trend of emperor penguins and Weddell seals in East Antarctica over the past 75,000 years using mitochondrial DNA sequences and an extended Bayesian skyline plot method. We also assessed patterns of contemporary population structure and genetic diversity.ResultsDespite their overlapping distributions and shared dependence on sea ice, our genetic data revealed very different responses to climate warming between these species. The emperor penguin population grew rapidly following the glacial-interglacial transition, but the size of the Weddell seal population did not change. The expansion of emperor penguin numbers during the warm Holocene may have been facilitated by their higher dispersal ability and gene flow among colonies, and fine-scale differences in preferred foraging locations.ConclusionsThe vastly different climate change responses of two sympatric ice-dependent predators suggests that differing adaptive capacities and/or fine-scale niche differences can play a major role in species’ climate change responses, and that adaptive capacity should be considered alongside niche and distribution in future species forecasts.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0630-3) contains supplementary material, which is available to authorized users.

Birth dates vary with fixed and dynamic maternal features, offspring sex, and extreme climatic events in a high-latitude marine mammal.

Reproductive synchrony tends to be widespread in diverse species of plants and animals, especially at higher latitudes. However, for long‐lived mammals, birth dates for different individuals can vary by weeks within a population. A mother's birth timing can reveal useful information about her reproductive abilities and have important implications for the characteristics and survival of her offspring. Despite this, our current knowledge of factors associated with variation in birth dates is modest. We used long‐term data for known‐age Weddell seals in Antarctica and a Bayesian hierarchical modeling approach to study how birth dates varied with fixed and temporally varying features of mothers, whether sex allocation varied with birth timing, and annual variation in birth dates. Based on birth dates for 4465 pups born to 1117 mothers aged 4–31, we found that diverse features of mothers were associated with variation in birth dates. Maternal identity was the most important among these. Unlike most studies, which have reported that birth dates occur earlier as mothers age, we found that birth dates progressively occurred earlier in the year in the early part of a mother's reproductive life, reached a minimum at age 16, and then occurred later at later ages. Birth dates were positively related to a mother's age at primiparity and recent reproductive effort. The earliest birth dates were for pups born to prime‐age mothers who did not reproduce in the previous year but began reproduction early in life, suggesting that females in the best condition gave birth earlier than others. If so, our finding that male pups tended to be born earlier than females provides support for the Trivers–Willard sex‐allocation model. Average birth dates were quite consistent across years, except for 2 years that had notable delays and occurred during the period when massive icebergs were present and disrupted the ecosystem.

Joint estimation over multiple individuals improves behavioural state inference from animal movement data.

State-space models provide a powerful way to scale up inference of movement behaviours from individuals to populations when the inference is made across multiple individuals. Here, I show how a joint estimation approach that assumes individuals share identical movement parameters can lead to improved inference of behavioural states associated with different movement processes. I use simulated movement paths with known behavioural states to compare estimation error between nonhierarchical and joint estimation formulations of an otherwise identical state-space model. Behavioural state estimation error was strongly affected by the degree of similarity between movement patterns characterising the behavioural states, with less error when movements were strongly dissimilar between states. The joint estimation model improved behavioural state estimation relative to the nonhierarchical model for simulated data with heavy-tailed Argos location errors. When applied to Argos telemetry datasets from 10 Weddell seals, the nonhierarchical model estimated highly uncertain behavioural state switching probabilities for most individuals whereas the joint estimation model yielded substantially less uncertainty. The joint estimation model better resolved the behavioural state sequences across all seals. Hierarchical or joint estimation models should be the preferred choice for estimating behavioural states from animal movement data, especially when location data are error-prone.

A draft fur seal genome provides insights into factors affecting SNP validation and how to mitigate them

Custom genotyping arrays provide a flexible and accurate means of genotyping single nucleotide polymorphisms (SNPs) in a large number of individuals of essentially any organism. However, validation rates, defined as the proportion of putative SNPs that are verified to be polymorphic in a population, are often very low. A number of potential causes of assay failure have been identified, but none have been explored systematically. In particular, as SNPs are often developed from transcriptomes, parameters relating to the genomic context are rarely taken into account. Here, we assembled a draft Antarctic fur seal (Arctocephalus gazella) genome (assembly size: 2.41Gb; scaffold/contig N50 : 3.1Mb/27.5kb). We then used this resource to map the probe sequences of 144 putative SNPs genotyped in 480 individuals. The number of probe-to-genome mappings and alignment length together explained almost a third of the variation in validation success, indicating that sequence uniqueness and proximity to intron-exon boundaries play an important role. The same pattern was found after mapping the probe sequences to the Walrus and Weddell seal genomes, suggesting that the genomes of species divergent by as much as 23 million years can hold information relevant to SNP validation outcomes. Additionally, reanalysis of genotyping data from seven previous studies found the same two variables to be significantly associated with SNP validation success across a variety of taxa. Finally, our study reveals considerable scope for validation rates to be improved, either by simply filtering for SNPs whose flanking sequences align uniquely and completely to a reference genome, or through predictive modelling.

A colostrum trypsin inhibitor gene expressed in the Cape fur seal mammary gland during lactation

The colostrum trypsin inhibitor (CTI) gene and transcript were cloned from the Cape fur seal mammary gland and CTI identified by in silico analysis of the Pacific walrus and polar bear genomes (Order Carnivora), and in marine and terrestrial mammals of the Orders Cetartiodactyla (yak, whales, camel) and Perissodactyla (white rhinoceros). Unexpectedly, Weddell seal CTI was predicted to be a pseudogene. Cape fur seal CTI was expressed in the mammary gland of a pregnant multiparous seal, but not in a seal in its first pregnancy. While bovine CTI is expressed for 24–48h postpartum (pp) and secreted in colostrum only, Cape fur seal CTI was detected for at least 2–3months pp while the mother was suckling its young on-shore. Furthermore, CTI was expressed in the mammary gland of only one of the lactating seals that was foraging at-sea. The expression of β-casein (CSN2) and β-lactoglobulin II (LGB2), but not CTI in the second lactating seal foraging at-sea suggested that CTI may be intermittently expressed during lactation. Cape fur seal and walrus CTI encode putative small, secreted, N-glycosylated proteins with a single Kunitz/bovine pancreatic trypsin inhibitor (BPTI) domain indicative of serine protease inhibition. Mature Cape fur seal CTI shares 92% sequence identity with Pacific walrus CTI, but only 35% identity with BPTI. Structural homology modelling of Cape fur seal CTI and Pacific walrus trypsin based on the model of the second Kunitz domain of human tissue factor pathway inhibitor (TFPI) and porcine trypsin (Protein Data Bank: 1TFX) confirmed that CTI inhibits trypsin in a canonical fashion. Therefore, pinniped CTI may be critical for preventing the proteolytic degradation of immunoglobulins that are passively transferred from mother to young via colostrum and milk.

Field Use of Ultrasonography to Characterize the Reproductive Tract and Early Pregnancy in a Phocid, the Weddell Seal (Leptonychotes weddellii)

The utility of transrectal ultrasonography was tested in a field setting to characterize the reproductive tract and detect early pregnancy (embryonic vesicles < 3 mm in diameter) in 17 multiparous female Weddell seals (Leptonychotes weddellii). Female Weddell seals give birth in October/November each year, followed by the breeding season (December) and embryonic diapause. Transrectal ultrasonography was attempted in January/February 2014 to examine the entire reproductive tract (uterine horns and body, ovaries with follicles and corpora lutea) using a 5-10 MHz linear-array probe with a 70 cm-long extension. A single pregnancy was detected in 14 of 17 seals (82.4%) as a circular or guitar-pick shaped nonechogenic (black) vesicle with a clearly visible echogenic border within the lumen of the uterus. The stage of embryonic development (ostensibly the gestational age) varied markedly among individuals, ranging from a vesicle with no embryo proper to a large fetus with an ocular orbit, nose/mouth, limb buds, spinal column, umbilical cord, and prominent vasculature. Two of the pregnant seals were re-examined 3-6 days after the initial examination to obtain longitudinal growth rates. Images of one or both ovaries were obtained in nine and seven of the 19 examinations, respectively. Numerous ovarian follicles (3 to 12 mm diameter) were detected and animals typically had a single well-perfused corpus luteum (determined by Doppler color-flow) ipsilateral to the uterine horn containing the pregnancy. We conclude that real-time transrectal ultrasonography is an effective tool for characterizing reproductive events in phocids including ovarian dynamics, and for elucidating the nature of embryonic diapause.

Estimating total body heat dissipation in air and water from skin surface heat flux telemetry in Weddell seals

Accurate estimates of thermoregulatory costs in air and water are necessary to predict the impacts of changing habitats to individuals and populations of ice-obligate seals. Investigations that would provide such estimates of thermoregulatory physiology over natural activities in free-ranging marine mammals have been limited. This study describes a biotelemetry method for measuring skin surface heat flux in free-ranging Weddell seals. These data are then applied to estimations of thermoregulatory heat dissipation from multiple point measurements. Data loggers collecting skin surface heat flux telemetry at four body locations (head, neck, axilla and flank) from 40 free-ranging Weddell seals were deployed and recovered over periods of 1–13 days in Erebus Bay, Antarctica. We derive equations for estimating total body heat dissipation from these point measurements and demonstrate the subsequent calculation of heat dissipated from obligate thermoregulatory costs. Heat lost to air or water was described by heat flux sensor data extrapolated across the whole-body surface, as informed by skin surface infrared thermal patterns. Heat lost directly to the ice surface during haul-out was best described by physical features of the seal, rather than environmental variables. Heat flux inputs from the four sensors could be reduced to two principal components, and corresponding regressions indicated that the axilla and flank sensors were most correlated with total body heat dissipation in air and water. Variability in head sensor heat flux was least described by the two principal components. This method can be used to estimate total body heat dissipation during daily activities in marine mammals, and under steady-state conditions, it can be used to identify obligate thermoregulatory heat costs. Ultimately this type of data will provide relevant empirical information for parameterizing models of thermoregulatory energetics in ice-obligate seals, which may improve our ability to predict outcomes of altered ice conditions at high latitudes.

Weddell seals do not lengthen calls in response to conspecific masking

Some mammalian and avian species alter their vocal communication signals to reduce masking by background noises (including conspecific calls). A preliminary study suggested that Weddell seals (Leptonychotes weddellii) increase the durations of some underwater call types when overlapped by another calling seal. The present study examined the durations and overlapping sequences of Weddell seal calls recorded in Eastern Antarctica. The calling rate, call type (13 major categories), total duration, numbers of elements per call and overlapping order of 100–200 consecutive calls per recording location were measured. In response to increased conspecific calling rates, the call durations and numbers of elements (within repeated-element call types) did not change or became shorter. Calls that were not overlapped were 3.8 ± 6.1 s long, the first call in a series of overlapped calls was 14.4 ± 15.7 s and subsequent calls in an overlapping series were 6.5 ± 10.3 s. The mean durations of non-overlapped and overlapped calls matched random distributions. Weddell seals do not appear to be adjusting the durations or timing of their calls to purposefully avoid masking each other’s calls. The longer a call is, the more likely it is to overlap another call by chance. An implication of this is that Weddell seals may not have the behavioural flexibility to reduce masking by altering the temporal aspects of their calls or calling behaviours as background noises (natural and from shipping) increase.

From high-resolution to low-resolution dive datasets: a new index to quantify the foraging effort of marine predators

In the last decade, thousands of satellite-relayed data loggers (SRDLs) have been deployed, providing large datasets on marine predator movement patterns at sea and their diving behaviour. However, the latter is in a highly summarised, low-resolution form, from which it is difficult to make the sorts of important behavioural inferences that are possible from higher-resolution datasets (such as detection of likely foraging events). The main objective of this study was to develop a simple, but accurate tool to detect and quantify within-dive foraging periods in low-resolution dives. Two southern elephant seals were fitted with a head-mounted time depth recorder (TDR) (recording depth at 1 Hz) and an accelerometer (recording 3 axes of acceleration at 16 Hz) from which prey capture attempts were estimated (PrCA), and a Weddell seal was also fitted with a TDR (1 Hz).The resulting high-resolution dive profiles were used to: (1) calculate an accurate index of foraging effort based on the detection of vertical sinuosity switches (i.e. huntinghighres time); (2) produce an SRDL-equivalent low-resolution dataset using a broken stick algorithm; and (3) from each low-resolution dive calculate a set of candidate foraging effort indices. Huntinglowres time, which is the total time spent in decreased vertical velocity segments of the dive, was the foraging effort index that best correlated with huntinghighres time. Huntinghighres mode of SES dives (highly sinuous parts of high-resolution dives) was associated with 77 % of total PrCA. In comparison, Huntinglowres segments of SES dives were associated with 68 % of PrCA as well as with four times more PrCA than transitlowres segments. We found a low-resolution index which indicates foraging activity within a highly summarised dive profile and which identified most PrCA, despite degraded information transmitted by SLDRs. Used in combination with other measurements of the in situ environment, the huntinglowres index could be used in numerous integrated marine ecology studies, such as habitat use studies that are crucial to facilitate more effective conservation.

The cephalopod prey of the Weddell seal, Leptonychotes weddellii, a biological sampler of the Antarctic marine ecosystem

Weddell seals, Leptonychotes weddellii, are important apex predators in the food web of the Antarctic marine ecosystem. However, detailed information on their trophic relationships with cephalopods is scarce. Moreover, cephalopods play a key role in the marine environment, but knowledge of their feeding habits is limited by lack of data. Here, we have combined the use of this seal as a biological sampler together with measurements of the stable isotopic signature of the beaks of their cephalopod prey. Thus, the aims of the present study were: (1) to examine in detail the cephalopod portion of the diet of Weddell seals by means of scat analysis and (2) to assess the habitat use and trophic level of the different cephalopod prey taxa identified. From January to February 2009, a total of 48 faecal droppings were collected at Hope Bay, Antarctic Peninsula. Cephalopods were mainly represented by beaks (n = 83) which were identified to the lowest possible taxonomic level. Furthermore, subsamples of beaks were separated for further isotopic analysis. Relative abundance of stable isotopes of carbon (δ13C) and nitrogen (δ15N) was determined by continuous-flow isotope-ratio mass spectrometry. Cephalopods were represented uniquely by octopods of the subfamily Eledoninae. Pareledone turqueti was the dominant prey species followed by the papillated Pareledone species group and Adelieledone polymorpha. We conclude that Weddell seals preyed primarily on benthic prey resources. Furthermore, the relatively similar δ13C and δ15N values in beaks of the three octopod prey taxa suggest that these share the same type of habitat and occupy similar trophic level positions.

Records of three vagrant Antarctic seal species (Family Phocidae) from New Zealand: crabeater seal (Lobodon carcinophaga), Weddell seal (Leptonychotes weddellii) and Ross seal (Ommatophoca rossii)

Records of three vagrant Antarctic seal species from New Zealand are summarised. Crabeater seals (Lobodon carcinophaga) occurred on eight occasions between 1885 and 2015, and Weddell seals (Leptonychotes weddellii) on five occasions between 1926 and 2007. There was a single record of a Ross seal (Ommatophoca rossii), from Paekakariki in 2002. The majority of occurrences for all three species were from the southern North Island, particularly Wellington, where five of the crabeater seals either swam up the Hutt River or were on the adjacent Petone Beach. There are no known verifiable records from any of New Zealand's subantarctic islands. Specimens of nine animals (six crabeater seals and three Weddell seals) are held by New Zealand museums.

Death age, seasonality, taphonomy and colonization of seal carcasses from Ulu Peninsula, James Ross Island, Antarctic Peninsula

AbstractThe origin and nature of seal carcasses scattered around the Ulu Peninsula, James Ross Island, is examined using robust and novel multidisciplinary analysis. Spatial distribution analysis indicates their predominance at low elevations and on surfaces with negligible slope. The seals died throughout the last century. Dental cement increments indicate that the seals died in late winter, and we interpret this to show an influence of the persistence and break-up of sea ice and the appearance of pools/cracks in the northern Prince Gustav Channel on death. Specifically, after being trapped by a late winter freeze-up the seals search for open water, become disoriented by snow-covered flat valleys and move inland. Carcasses from all age groups of crabeater seal are found on land, but inland movement is less notable for Weddell and leopard seals. Although most carcasses appear to have remained unchanged during the last 10 years due to the cold and dry conditions, a few carcasses that are located in sites of snow accumulation and subsequent melting have undergone enhanced decay. Decaying seal carcasses represent loci of nutrient release in a nutrient deficient environment and are colonized by algae, cyanobacteria, lichens and mosses. This research suggests further useful studies for the future.

Scaling matters: incorporating body composition into Weddell seal seasonal oxygen store comparisons reveals maintenance of aerobic capacities

Adult Weddell seals (Leptonychotes weddellii) haul-out on the ice in October/November (austral spring) for the breeding season and reduce foraging activities for ~4 months until their molt in the austral fall (January/February). After these periods, animals are at their leanest and resume actively foraging for the austral winter. In mammals, decreased exercise and hypoxia exposure typically lead to decreased production of O2-carrying proteins and muscle wasting, while endurance training increases aerobic potential. To test whether similar effects were present in marine mammals, this study compared the physiology of 53 post-molt female Weddell seals in the austral fall to 47 pre-breeding females during the spring in McMurdo Sound, Antarctica. Once body mass and condition (lipid) were controlled for, there were no seasonal changes in total body oxygen (TBO2) stores. Within each season, hematocrit and hemoglobin values were negatively correlated with animal size, and larger animals had lower mass-specific TBO2 stores. But because larger seals had lower mass-specific metabolic rates, their calculated aerobic dive limit was similar to smaller seals. Indicators of muscular efficiency, myosin heavy chain composition, myoglobin concentrations, and aerobic enzyme activities (citrate synthase and β-hydroxyacyl CoA dehydrogenase) were likewise maintained across the year. The preservation of aerobic capacity is likely critical to foraging capabilities, so that following the molt Weddell seals can rapidly regain body mass at the start of winter foraging. In contrast, muscle lactate dehydrogenase activity, a marker of anaerobic metabolism, exhibited seasonal plasticity in this diving top predator and was lowest after the summer period of reduced activity.

Cephalopod remains in scats of Weddell seals (Leptonychotes weddellii) at Cape Shirreff, South Shetland Islands, Antarctica

The diet of Weddell seals (Leptonychotes weddellii) varies regionally, and fish and cephalopods are thought to be the most important food source. However, there is limited information on the cephalopod component of the Weddell seal’s diet in the South Shetland Islands. We investigated cephalopod remains in the diet of Weddell seals by analysing 21 scats collected on three beaches at Cape Shirreff, Livingston Island, Antarctica, from 1 to 20 February 1999. Although the number of scats is small and collected from only 1 month a long time ago, fish and cephalopods were present in 21 and 16 of the scats, respectively. Only cephalopods of the order Octopoda were represented. Thaumeledone sp. was the most abundant prey species in terms of numbers, followed by Pareledone charcoti and P. turqueti. The latter two species showed the highest frequency of occurrence in scats (10 and 9, respectively). Graneledone macrotyla, Opistoteuthis sp., Argonauta sp., Haliphron sp. and Thaumeledone sp. are new species identified in the diet of Weddell seals in the present study, but all made a negligible contribution to their diet at Cape Shirreff. Our findings agree with previous dietary studies of Weddell seals at other localities in the South Shetland Islands and the Antarctic Peninsula, which showed a relatively greater contribution of octopods to the diet compared with squid in summer.

Tight coupling of primary production and marine mammal reproduction in the Southern Ocean.

Polynyas are areas of open water surrounded by sea ice and are important sources of primary production in high-latitude marine ecosystems. The magnitude of annual primary production in polynyas is controlled by the amount of exposure to solar radiation and sensitivity to changes in sea-ice extent. The degree of coupling between primary production and production by upper trophic-level consumers in these environments is not well understood, which prevents reliable predictions about population trajectories for species at higher trophic levels under potential future climate scenarios. In this study, we find a strong, positive relationship between annual primary production in an Antarctic polynya and pup production by ice-dependent Weddell seals. The timing of the relationship suggests reproductive effort increases to take advantage of high primary production occurring in the months after the birth pulse. Though the proximate causal mechanism is unknown, our results indicate tight coupling between organisms at disparate trophic levels on a short timescale, deepen our understanding of marine ecosystem processes, and raise interesting questions about why such coupling exists and what implications it has for understanding high-latitude ecosystems.

Locomotion and the Cost of Hunting in Large, Stealthy Marine Carnivores.

Foraging by large (>25 kg), mammalian carnivores often entails cryptic tactics to surreptitiously locate and overcome highly mobile prey. Many forms of intermittent locomotion from stroke-and-glide maneuvers by marine mammals to sneak-and-pounce behaviors by terrestrial canids, ursids, and felids are involved. While affording proximity to vigilant prey, these tactics are also associated with unique energetic costs and benefits to the predator. We examined the energetic consequences of intermittent locomotion in mammalian carnivores and assessed the role of these behaviors in overall foraging efficiency. Behaviorally-linked, three-axis accelerometers were calibrated to provide instantaneous locomotor behaviors and associated energetic costs for wild adult Weddell seals (Leptonychotes weddellii) diving beneath the Antarctic ice. The results were compared with previously published values for other marine and terrestrial carnivores. We found that intermittent locomotion in the form of extended glides, burst-and-glide swimming, and rollercoaster maneuvers while hunting silverfish (Pleuragramma antarcticum) resulted in a marked energetic savings for the diving seals relative to continuously stroking. The cost of a foraging dive by the seals decreased by 9.2-59.6%, depending on the proportion of time gliding. These energetic savings translated into exceptionally low transport costs during hunting (COTHUNT) for diving mammals. COTHUNT for Weddell seals was nearly six times lower than predicted for large terrestrial carnivores, and demonstrates the importance of turning off the propulsive machinery to facilitate cost-efficient foraging in highly active, air-breathing marine predators.