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Leopard seals (Hydrurga leptonyx) are top predators that can exert substantial top-down control of their Antarctic prey species. However, population trends and genetic diversity of leopard seals remain understudied, limiting our understanding of their ecological role. We investigated the genetic diversity, effective population size and demographic history of leopard seals to provide fundamental data that contextualizes their predatory influence on Antarctic ecosystems. Ninety leopard seals were sampled in the northern Antarctic Peninsula, during the austral summers of 2008–2019 and a 405bp region of the mitochondrial control region was sequenced for each individual. We uncovered moderate levels of nucleotide (π = 0.013) and haplotype (Hd = 0.96) diversity, and the effective population size was estimated at around 24,000 individuals (NE= 24,376; range 16,876 – 33,126). Consistent with findings from other ice-breeding pinnipeds, Bayesian skyline analysis also revealed evidence for population expansion during the last glacial maximum, suggesting that historical population growth may have been boosted by an increase in the abundance of sea ice. Although leopard seals can be found in warmer, sub-Antarctic locations, the species’ core habitat is centered around the Antarctic, making it inherently vulnerable to the loss of sea ice habitat due to climate change. Therefore, detailed assessments of past and present leopard seal population trends are needed to inform policies for Antarctic ecosystems.

With the advent of chromatin-interaction maps, chromosome-level genome assemblies have become a reality for a wide range of organisms. Scaffolding quality is, however, difficult to judge. To explore this gap, we generated multiple chromosome-scale genome assemblies of an emerging wild animal model for carcinogenesis, the California sea lion (Zalophus californianus). Short-read assemblies were scaffolded with two independent chromatin interaction mapping data sets (Hi-C and Chicago), and long-read assemblies with three data types (Hi-C, optical maps and 10X linked reads) following the "Vertebrate Genomes Project (VGP)" pipeline. In both approaches, 18 major scaffolds recovered the karyotype (2n = 36), with scaffold N50s of 138 and 147 Mb, respectively. Synteny relationships at the chromosome level with other pinniped genomes (2n = 32-36), ferret (2n = 34), red panda (2n = 36) and domestic dog (2n = 78) were consistent across approaches and recovered known fissions and fusions. Comparative chromosome painting and multicolour chromosome tiling with a panel of 264 genome-integrated single-locus canine bacterial artificial chromosome probes provided independent evaluation of genome organization. Broad-scale discrepancies between the approaches were observed within chromosomes, most commonly in translocations centred around centromeres and telomeres, which were better resolved in the VGP assembly. Genomic and cytological approaches agreed on near-perfect synteny of the X chromosome, and in combination allowed detailed investigation of autosomal rearrangements between dog and sea lion. This study presents high-quality genomes of an emerging cancer model and highlights that even highly fragmented short-read assemblies scaffolded with Hi-C can yield reliable chromosome-level scaffolds suitable for comparative genomic analyses.

In an era of rapid environmental change and increasing human presence, researchers need efficient tools for tracking contaminants to monitor the health of Antarctic flora and fauna. Here, we examined the utility of leopard seal whiskers as a biomonitoring tool that reconstructs time-series of significant ecological and physiological biomarkers. Leopard seals (Hydrurga leptonyx) are a sentinel species in the Western Antarctic Peninsula due to their apex predator status and top-down effects on several Antarctic species. However, there are few data on their contaminant loads. We analyzed leopard seal whiskers (n = 18 individuals, n = 981 segments) collected during 2018-2019 field seasons to acquire longitudinal profiles of non-essential (Hg, Pb, and Cd) and essential (Se, Cu, and Zn) trace elements, stable isotope (ẟ

Ross seals Ommatophoca rossii are one of the least studied marine mammals, with little known about their foraging ecology. Research to date using bulk stable isotope analysis suggests that Ross seals have a trophic position intermediate between that of Weddell Leptonychotes weddellii and crabeater Lobodon carcinophaga seals. However, consumer bulk stable isotope values not only reflect trophic dynamics, but also variations in baseline isotope values, which can be substantial. We used compound-specific isotope analysis of amino acids (CSI-AA) to separate isotopic effects of a shifting baseline versus trophic structure on the foraging ecology of these ecologically important Antarctic pinnipeds. We found that Ross seals forage in an open ocean food web, while crabeater and Weddell seals forage within similar food webs closer to shore. However, isotopic evidence suggests that crabeater seals are likely following sea ice, while Weddell seals target productive areas of the continental shelf of West Antarctica. Our CSI-AA data indicate that Ross seals have a high trophic position equivalent to that of Weddell seals, contrary to prior conclusions from nitrogen isotope results on bulk tissues. CSI-AA indicates that crabeater seals are at a trophic position lower than that of Ross and Weddell seals, consistent with a krill-dominated diet. Our results redefine the view of the trophic dynamics and foraging ecology of the Ross seal, and also highlight the importance of quantifying baseline isotope variations in foraging studies.

Intraspecific variation in animal mating systems can have important implications for ecological, evolutionary and demographic processes in wild populations. For example, patterns of mating can impact social structure, dispersal, effective population size and inbreeding. However, few species have been studied in sufficient detail to elucidate mating system plasticity and its dependence on ecological and demographic factors. Southern elephant seals (Mirounga leonina) have long been regarded as a textbook example of a polygynous mating system, with dominant ‘beachmaster’ males controlling harems of up to several hundred females. However, behavioural and genetic studies have uncovered appreciable geographic variation in the strength of polygyny among elephant seal populations. We therefore used molecular parentage analysis to investigate patterns of parentage in a small satellite colony of elephant seals at the South Shetland Islands. We hypothesised that dominant males would be able to successfully monopolise the relatively small numbers of females present in the colony, leading to relatively high levels of polygyny. A total of 424 individuals (comprising 33 adult males, 101 adult females and 290 pups) sampled over eight years were genotyped at 20 microsatellites and reproductive success was analysed by genetically assigning parents. Paternity could only be assigned to 31 out of 290 pups (10.7%), despite our panel of genetic markers being highly informative and the genotyping error rate being very low. The strength of inferred polygyny was weak in comparison to previous genetic studies of the same species, with the most successful male fathering only seven pups over the entire course of the study. Our results show that, even in a species long regarded as a model for extreme polygyny, male reproductive skew can vary substantially among populations.

Unoccupied aerial systems (UAS) have become common tools for ecological monitoring and management. However, UAS use has the potential to negatively affect wildlife. Both policy makers and practitioners require data about the potential impacts of UAS on natural biota, but few studies exist and some of the published results conflict. We conducted two experiments to assess the responses of chinstrap penguins (Pygoscelis antarcticus), Antarctic fur seals (Arctocephalus gazella), and leopard seals (Hydrurga leptonyx) to UAS overflights. First, to provide a baseline for assessing disturbance from UAS operations, we compare behavioral responses from UAS flights to those from traditional, ground surveys. Second, to inform users and policy makers about preferred flight methods, we assess behavioral and physiological responses to UAS flown at specific altitudes, during different stages of breeding chronology, and with other site factors. Between January 2017 and March 2018 we conducted 268 UAS flight approaches and 36 ground-based surveys at Cape Shirreff, Antarctic Peninsula. We applied generalized linear mixed effects models and Kruskal-Wallis tests to 10,164 behavioral scores obtained from three independent observers. When directly compared, behavioral responses by all species to UAS overflights at 30 m were not different from control periods, while responses to ground surveys were significantly more intense. Behavioral responses generally increased as UAS flew lower, and for penguins those increases intensified as the breeding season progressed (i.e., guard and molt stages). We argue that results from UAS wildlife response studies need to be assessed relative to the impacts of alternative methods, and within the ecological context of the target species. Finally, we suggest data-driven best practices for both UAS use and for the design of future UAS-wildlife response studies.

International audience; Southern Ocean ecosystems are under pressure from resource exploitation and climate change1,2. Mitigation requires the identification and protection of Areas of Ecological Significance (AESs), which have so far not been determined at the ocean-basin scale. Here, using assemblage-level tracking of marine predators, we identify AESs for this globally important region and assess current threats and protection levels. Integration of more than 4,000 tracks from 17 bird and mammal species reveals AESs around sub-Antarctic islands in the Atlantic and Indian Oceans and over the Antarctic continental shelf. Fishing pressure is disproportionately concentrated inside AESs, and climate change over the next century is predicted to impose pressure on these areas, particularly around the Antarctic continent. At present, 7.1% of the ocean south of 40°S is under formal protection, including 29% of the total AESs. The establishment and regular revision of networks of protection that encompass AESs are needed to provide long-term mitigation of growing pressures on Southern Ocean ecosystems.

To understand and predict current and future distributions of animals under a changing climate it is essential to establish historical ranges as baselines against which distribution shifts can be assessed. Management approaches also require comprehension of temporal variability in spatial distributions that can occur over shorter time scales, such as inter-annually or seasonally. Focussing on the Southern Ocean, one of the most rapidly changing environments on Earth, we used Species Distribution Models (SDMs) and satellite ocean data to reconstruct the likely historical foraging habitats of Antarctic fur seals (Arctocephalus gazella) from three populations during the non-breeding winter (Marion Island, Bird Island and Cape Shirreff), to assess whether habitat quality has changed in recent decades. We then quantified temporal variability in distributions to assess overlap with management areas (CCAMLR – Commission for the Conservation of Antarctic Marine Living Resources) and the potential for competition with fisheries. Despite notable physical ocean changes, the quality of foraging habitat during the non-breeding season has remained relatively consistent over 20 years at Marion and Bird Islands, but less so at Cape Shirreff, where reduced sea ice cover has improved habitat accessibility. Spatio-temporally explicit SDMs identified variability in habitats across the winter. Some areas overlapped significantly with fisheries activities, suggesting a potential for competition for prey resources at several key periods. A significant component of core habitat at all populations was not within the CCAMLR Convention Area. Although organisations such as CCAMLR adopt a precautionary, ecosystem-based approach to fisheries management, changes to the physical environment and developments in the fishing industry can affect how dependant species are impacted. The hindcasting of historical spatial distributions shown here are baselines against which future changes can be assessed. Given recent proposals for a system of marine protected areas (MPAs) in the Southern Ocean, our results can be used in the design and evaluation of MPAs, be they static or dynamic. Our study also demonstrates that the core habitat of species may fall outside of areas of active management, providing an important context for the interpretation of monitoring programs and management efforts.

Viral diversity associated with Antarctic wildlife remains poorly studied. Nonetheless, over the past 5 years, there has been a concerted effort using viral metagenomics approaches to identify and characterize viruses associated with Antarctic pinniped and avian species. Here we used a viral metagenomics approach to identify circular DNA viruses in buccal swab samples from Antarctic fur seals (Arctocephalus gazella) breeding on Livingston Island, Antarctica during the 2016/2017 field season. We identified two new lineages of anelloviruses, torque teno Arctocephalus gazella virus (TTAgV)-1 (2083 nts) and -2 (2127-2143 nts), which are most closely related to and cluster with a previously identified anellovirus associated with California sea lions (Zalophus californianus) sharing ~ 60% genome-wide pairwise identity. The ORF1 of TTAgVs share 26-41% amino acid similarity to the ORF1 of other previously identified pinniped-associated anelloviruses.

Quantification of the physical and biological environmental factors that influence the spatial distribution of higher trophic species is central to inform management and develop ecosystem models, particularly in light of ocean changes. We used tracking data from 184 female Antarctic fur seals (Arctocephalus gazella) to develop habitat models for three breeding colonies for the poorly studied Southern Ocean winter period. Models were used to identify and predict the broadly important winter foraging habitat and to elucidate the environmental factors influencing these areas. Model predictions closely matched observations and several core areas of foraging habitat were identified for each colony, with notable areas of inter-colony overlap suggesting shared productive foraging grounds. Seals displayed clear choice of foraging habitat, travelling through areas of presumably poorer quality to access habitats that likely offer an energetic advantage in terms of prey intake. The relationships between environmental predictors and foraging habitat varied between colonies, with the principal predictors being wind speed, sea surface temperature, chlorophyll a concentration, bathymetry and distance to the colony. The availability of core foraging areas was not consistent throughout the winter period. The habitat models developed in this study not only reveal the core foraging habitats of Antarctic fur seals from multiple colonies, but can facilitate the hindcasting of historical foraging habitats as well as novel predictions of important habitat for other major colonies currently lacking information of the at-sea distribution of this major Southern Ocean consumer.

Quantifying metabolic rates and the factors that influence them is key to wildlife conservation efforts because anthropogenic activities and habitat alteration can disrupt energy balance, which is critical for reproduction and survival. We investigated the effect of diving behaviour, diet and season on field metabolic rates (FMR) and foraging success of lactating northern fur seals (Callorhinus ursinus) from the Pribilof Islands during a period of population decline. Variation in at-sea FMR was in part explained by season and trip duration, with values that ranged from 5.18 to 9.68 W kg−1 (n = 48). Fur seals experienced a 7.2% increase in at-sea FMR from summer to fall and a 1.9% decrease in at-sea FMR for each additional day spent at sea. There was no effect of foraging effort, dive depth or diet on at-sea FMR. Mass gains increased with trip duration and were greater in the fall compared with summer, but were unrelated to at-sea FMR, diving behaviour and diet. Seasonal increases in at-sea FMR may have been due to costs associated with the annual molt but did not appear to adversely impact the ability of females to gain mass on foraging trips. The overall high metabolic rates in conjunction with the lack of any diet-related effects on at-sea FMR suggests that northern fur seals may have reached a metabolic ceiling early in the population decline. This provides indirect evidence that food limitation may be contributing to the low pup growth rates observed in the Pribilof Islands, as a high metabolic overhead likely results in less available energy for lactation. The limited ability of female fur seals to cope with changes in prey availability through physiological mechanisms is particularly concerning given the recent and unprecedented environmental changes in the Bering Sea that are predicted to have ecosystem-level impacts., Lay summary: We measured metabolic rates of northern fur seals from a declining population and examined the influence of season and foraging behavior on energy expenditure. Our results are relevant for bioenergetic modelling efforts and provide insight into the potential role of prey availability in the population decline.

Antarctic fur seals ( Arctocephalus gazella ) are polygynous and both sexes are typically faithful to a breeding site. These characteristics could promote remating among individuals over time, leading to increased relatedness levels and negatively affecting genetic diversity. To examine this issue, the reproductive output of 55 females was monitored annually for 12 years and their pups were sampled (n = 280) and genotyped using 17 microsatellite markers. A full likelihood pedigree inference method was used to confirm maternities inferred in the field and estimate the number of full sibling pups born across years. Relatedness coefficients were estimated for pairs of individuals in the pedigree and compared to simulated values for each relationship category. There were nine cases where a female mated with the same male twice and one case where a female mated with the same male three times over the study period. The observed relatedness coefficients estimated among the sampled pups matched the simulated distribution for half-siblings. In addition, no first order relatives were found among the fur seal mothers studied, nor did observed relatedness coefficient distributions differ significantly from simulated values. Together, these results suggest a low remating rate and a negligible effect of remating on pair-wise relatedness. Territorial male replacement over time as well as female small-scale movements, driven by suitable pupping habitat, likely contribute to the low remating frequency observed in Antarctic fur seals.

Leopard seals are conspicuous apex predators in Antarctic coastal ecosystems, yet their foraging ecology is poorly understood. Historically, the ecology of diving vertebrates has been studied using high-resolution time-depth records; however, to date such data have not been available for leopard seals. Twenty-one time-depth recorders were deployed on seasonally resident adult females in January and February between 2008 and 2014. The average deployment length was 13.65 ± 11.45 d and 40,308 postfilter dives were recorded on 229 foraging trips. Dive durations averaged 2.20 ± 1.23 min. Dives were shallow with 90.1% measuring 30 m or less, and a mean maximum dive depth of 16.60 ± 10.99 m. Four dive types were classified using a k-means cluster analysis and compared with corresponding animal-borne video data. Dive activity (number of dives/hour) was concentrated at night, including crepuscular periods. Haul-out probabilities were highest near midday and were positively correlated with available daylight. Visual observations and comparisons of diving activity between and within years suggest individual-based differences of foraging effort by time of day. Finally, dive and video data indicate that in addition to at-surface hunting, benthic searching and facultative scavenging are important foraging strategies for leopard seals near coastal mesopredator breeding colonies.

The large-scale spatial patterns and primary drivers of food web dynamics across seascapes can be investigated using isotope ratios in marine consumers. However, interpreting complex signatures from mobile animals can require good knowledge of spatial isotopic variations in the environment. This is particularly true in the Southern Ocean where regional differences in the physical environment affect habitat predictability and predator foraging. We applied a retrospective-isotope approach integrated with tracking locations for a model species, the Antarctic fur seal (Arctocephalus gazella), to generate large-scale spatially-explicit predictions of isotopic gradients (“isoscapes”) across the Southern Ocean. Vibrissae and blood samples were collected during post- and pre-breeding periods from both Antarctic and sub-Antarctic breeding environments. Stable isotope values from vibrissae growth and serially sampled blood enabled the reconstruction of an isotopic time-series that could be directly related to feeding locations at sea. Tracked seals were widely distributed in the southern Atlantic and Indian Oceans, with important foraging activity centred on productive upwelling areas, oceanic frontal zones and shelf environments. Corresponding seal δ13C and δ15N values were positively correlated to the Southern Ocean latitudes at which the tracked individuals foraged. Breeding site, bi-monthly foraging period and foraging location all explained significant variation in isotopic values during migration. Isotopic variation was largely driven by the latitudinal and inshore/offshore gradient in δ13C and δ15N at the base of the food web in neritic and oceanic waters. These delineate the spatio-temporal isotopic variability of important foraging habitats, providing a valuable perspective on the spatial and seasonal distribution of predators and forage availability. Differences in inferred predator distribution within and between breeding locations have implications for relative exposure to anthropogenic threats from fisheries interactions and climate change. This study demonstrates that isotope tracers in archival tissues are useful indicators of resource partitioning by marine consumers to directly inform spatial conservation planning and ecosystem management strategies at the cross-basin scale.

Understanding the effects of human exploitation on the genetic composition of wild populations is important for predicting species persistence and adaptive potential. We therefore investigated the genetic legacy of large-scale commercial harvesting by reconstructing, on a global scale, the recent demographic history of the Antarctic fur seal (Arctocephalus gazella), a species that was hunted to the brink of extinction by 18

Polybrominated diphenyl ethers (PBDEs) are “emerged” contaminants that were produced and used as flame retardants in numerous consumer and industrial applications for decades until banned. They remain ubiquitously present in the environment today. Here, a unique set of >200 biotic samples from the Antarctic was analyzed for PBDEs, including phytoplankton, krill, fish, and fur seal milk, spanning several sampling seasons over 14 years. PBDE-47 and -99 were the dominant congeners determined in all samples, constituting >60% of total PBDEs. A temporal trend was observed for ∑7PBDE concentrations in fur seal milk, where concentrations significantly increased (R2 = 0.57, p < 0.05) over time (2000–2014). Results for krill and phytoplankton also suggested increasing PBDE concentrations over time. Trends of PBDEs in fur seal milk of individual seals sampled 1 or more years apart showed no clear temporal trends. Overall, there was no indication of PBDEs decreasing in Antarctic biota yet, whereas numerous studies have reported decreasing trends in the northern hemisphere. Similar PBDE concentrations in perinatal versus nonperinatal milk implied the importance of local PBDE sources for bioaccumulation. These results indicate the need for continued assessment of contaminant trends, such as PBDEs, and their replacements, in Antarctica.

Recent advances in high throughput sequencing have transformed the study of wild organisms by facilitating the generation of high quality genome assemblies and dense genetic marker datasets. These resources have the potential to significantly advance our understanding of diverse phenomena at the level of species, populations and individuals, ranging from patterns of synteny through rates of linkage disequilibrium (LD) decay and population structure to individual inbreeding. Consequently, we used PacBio sequencing to refine an existing Antarctic fur seal (Arctocephalus gazella) genome assembly and genotyped 83 individuals from six populations using restriction site associated DNA (RAD) sequencing. The resulting hybrid genome comprised 6,169 scaffolds with an N50 of 6.21 Mb and provided clear evidence for the conservation of large chromosomal segments between the fur seal and dog (Canis lupus familiaris). Focusing on the most extensively sampled population of South Georgia, we found that LD decayed rapidly, reaching the background level ofr2= 0.09 by around 26 kb, consistent with other vertebrates but at odds with the notion that fur seals experienced a strong historical bottleneck. We also found evidence for population structuring, with four main Antarctic island groups being resolved. Finally, appreciable variance in individual inbreeding could be detected, reflecting the strong polygyny and site fidelity of the species. Overall, our study contributes important resources for future genomic studies of fur seals and other pinnipeds while also providing a clear example of how high throughput sequencing can generate diverse biological insights at multiple levels of organisation.

We examined the feeding ecology and lipid composition of Antarctic krill Euphausia superba around the northern Antarctic Peninsula from 2001 to 2012. We used lipid biomarkers to quantify feeding patterns and relate the variability in biomarkers to environmental conditions that structure the phytoplankton community. Fatty acid profiles varied among years, with some years dominated by lipids indicative of herbivory, while other years were indicative of greater omnivory. Principal component analysis of 60 fatty acids showed that 3 principal components (PCs) explained approximately 50% of the variability in fatty acid profiles. The first PC separated the fatty acid indi- cators along a herbivoryomnivorycarnivory gradient. Correlations between the gradient of her- bivory and carnivory, as summarized by the first PC, were found with both winter sea ice extent (r = 0.55, p < 0.01) and with ENSO conditions the previous winter (r = 0.88, p < 0.001). These findings suggest that climatic conditions during the late winter precondition the pelagic ecosystem around the Antarctic Peninsula, impacting the trophic ecology of Antarctic krill the following summer.

Measurements of body size and mass are fundamental to pinniped population management and research. Manual measurements tend to be accurate but are invasive and logistically challenging to obtain. Ground-based photogrammetric techniques are less invasive, but inherent limitations make them impractical for many field applications. The recent proliferation of unmanned aerial systems (UAS) in wildlife monitoring has provided a promising new platform for the photogrammetry of free-ranging pinnipeds. Leopard seals (Hydrurga leptonyx) are an apex predator in coastal Antarctica whose body condition could be a valuable indicator of ecosystem health. We aerially surveyed leopard seals of known body size and mass to test the precision and accuracy of photogrammetry from a small UAS. Flights were conducted in January and February of 2013 and 2014 and 50 photogrammetric samples were obtained from 15 unrestrained seals. UAS-derived measurements of standard length were accurate to within 2.01 ± 1.06%, and paired comparisons with ground measurements were statistically indistinguishable. An allometric linear mixed effects model predicted leopard seal mass within 19.40 kg (4.4% error for a 440 kg seal). Photogrammetric measurements from a single, vertical image obtained using UAS provide a noninvasive approach for estimating the mass and body condition of pinnipeds that may be widely applicable.

Phocids routinely fast for extended periods. During these fasts, energetic requirements are met primarily through the catabolism of blubber lipid. To assess whether fatty acid (FA) composition changes during the postweaning fast in northern elephant seals, blubber biopsies were acquired longitudinally from 43 pups at 2.3 ± 1.5 and 55.2 ± 3.7 days postweaning in 1999 and 2000. At weaning, short-chain monounsaturated FA (SC-MUFA, ≤18 carbons) dominated the blubber while saturated FA (SFA) were found in the next highest proportion. The major FA (all ≥1 % by mass) comprised approximately 91 % of total blubber FA. In both years, 18:1n-9 and 16:0 were the most prevalent FA. Major FA mobilized during the fast consisted of polyunsaturated FA (PUFA), SFA, and SC-MUFA. Long-chain MUFA (>18 carbons) tended to be conserved. The fractional mobilization value of 20:5n-3 was the highest, resulting in significant reductions of this PUFA. Although concentrations of some blubber FA changed significantly during the postweaning fast, the general FA signature of blubber was similar at weaning and near the end of the fast. Changes in some FA differed across years. For example, the concentration of 20:4n-6, a minor PUFA, was significantly reduced in 1999 but not in 2000. FA mobilization patterns in northern elephant seal pups are somewhat similar to those reported previously for other fasting phocids and terrestrial mammals, though there are some notable differences. Differences in FA mobilization patterns across mammalian species may be related to differences in diets, geographical distribution, environmental factors, physiological adaptations, and life history stage.

Two major drivers in population dynamics are bottom-up processes, such as environmental factors that affect foraging success, and the top-down impacts of predation. Many populations of marine mammal and seabird species appear to be declining in response to reductions in prey associated with the bottom-up effects of climate change. However, predation, which usually occurs at sea and is difficult to observe, may also play a key role. We analysed drivers of population dynamics of Antarctic fur seals Arctocephalus gazella at Cape Shirreff from 1997 to 2009, including a predator that targets pre-weaned pups and bottom-up environmental effects in an ecosystem particularly sensitive to small changes in temperature. We use Bayesian mark-recapture analysis to demonstrate that although large-scale environmental variability affects annual adult survival and reproduction, first year survival appears to be driving the current decline in this population (as defined by a decline in the annual number of pups born). Although the number of pups increased during the first third of the study, first year survival and recruitment of those pups in later years was very low. Such low survival may be driven by leopard seal Hydrurga leptonyx predation, particularly prior to weaning. Our results suggest that without leopard seal predation, this population would most likely increase in size, despite the observed bottom-up effects of climate changes on adult vital rates. More broadly, our results show how age-targeted predation could be a major factor in population decline of K-selected colonial breeders.

Life-history theory predicts that selection will favor optimal levels of parental effort that balance benefits of current reproduction with costs to survival and future reproduction. The optimal level of effort depends on parental traits, offspring traits, and provisioning strategy. Additionally, how these factors influence effort may differ depending on the stage of reproduction. The relative importance of maternal and offspring traits on energy allocation to offspring was investigated in known-age Antarctic fur seals Arctocephalus gazella across four stages of reproduction, using birth mass and milk-consumption measurements. Maternal traits were important during three of the four stages investigated, with larger females giving birth to larger pups and investing more in pups during perinatal and molt stages. Pup mass influenced maternal effort during the premolt stage, and provisioning strategy influenced postnatal maternal effort at all stages. Energy provided to the offspring during an attendance visit was positively related to the duration of the foraging-trip/visit cycle; however, when investment was controlled for trip/visit cycle duration, the overall rate of energy transfer was similar across trip durations. In addition to strong effects of maternal mass, pup traits affected energy allocation, suggesting that pup demand is important in determining maternal care. These findings emphasize the importance of considering state variables in life-history studies and suggest that timing of measurements of effort in species with long provisioning periods may influence conclusions and our ability to make comparisons of reproductive effort among species.

Little is known about how variation in the pattern and magnitude of parental effort influences allocation decisions in offspring. We determined the energy budget of Antarctic fur seal pups and examined the relative importance of timing of provisioning, pup traits (mass, condition, sex), and weather (wind chill and solar radiation) on allocation of energy obtained in milk by measuring milk energy intake, field metabolic rate (FMR), and growth rate in 48 Antarctic fur seal pups over three developmental stages (perinatal, premolt, and molt). The relative amount of milk energy used for growth was 59.1% ± 8.1% during the perinatal period but decreased to 23.4% ± 15.5% and 26.0% ± 13.9% during the premolt and molt. This decrease was associated with a greater amount of time spent fasting, along with an increase in pup activity while the mother was at sea foraging. Average daily milk intake, pup mass, and condition were all important in determining how much energy was available for growth, but the amount of energy obtained as milk was the single most important factor determining pup growth. While mean mass-specific FMR did not change with developmental stage (range = 1.74-1.77 mL O(2)/g/h), the factors that accounted for variation in FMR did. Weather (wind chill and solar radiation) and pup traits (mass and condition) influenced mass-specific FMR, but these impacts varied across development. This study provides information about the factors influencing how offspring allocate energy toward growth and maintenance and improves our predictions about how a changing environment may affect energy allocation in pups.

Genetic analyses can reliably determine the relationships among putative cases of twins in pinniped species. These studies demonstrate that field observations of nursing twins may often be cases of adoption or foster nursing of unrelated pups. A recent study of Antarctic fur seals ( Arctocephalus gazella ) on South Georgia Island found that only 3 of 11 putative twin cases were truly twins. Here we report results of genetic testing of eight putative cases of twinning (twin siblings and mother) observed at Cape Shirreff (62°27′30″S, 60°47′17″W), Livingston Island, Antarctica. Parentage and relatedness analyses using 18 microsatellite markers confirmed six out of the eight cases as twins and two cases of adoption/foster nursing of unrelated pups. All twins analyzed were dizygotic and in five out of six cases, the twins were likely full siblings (relatedness coefficient, or r xy μ = 0.46, σ 2 = 0.004). In one case, the twins were likely half-siblings ( r xy = 0.17), supporting a previous finding of heteropaternity in Antarctic fur seals. This result suggests that mate infidelity during estrus maybe common in Antarctic fur seals, which has implications for our understanding of this species's mating system. The twinning rate estimated at Cape Shirreff (0.12% or 6 twins per 4,965 births) is consistent with the scarcity of twin births observed in pinnipeds, which is associated with the high cost of nursing multiple pups in these animals.

The use of intrinsic biomarkers to infer the foraging ecology of marine predators has become a common alternative to traditional methods of estimating diets and foraging behavior. In this study we examined the ability of the stable isotope analysis (δ 15 N and δ 13 C) of milk to infer seasonal variations in the diets and foraging habitats of female Antarctic fur seals ( Arctocephalus gazella ) breeding at Cape Shirreff, Livingston Island, Antarctica. We found that the stable nitrogen values of lipid-free milk were correlated with seasonal changes in female diet composition during the lactation period identified from scat collections. While we could not fully quantifying female diets using isotopic analysis, evidence from both scat collections and stable isotope analysis suggest that Antarctic krill ( Euphausia superba ) remained a major dietary item throughout lactation. In addition, these two methods independently highlighted the increasing importance of fish and squid in the diets of females as the season progresses. Furthermore, the isotopic values of milk collected during the perinatal fast suggest that females may be foraging in high productivity areas north of the South Shetland Islands and consume a larger proportion of fish and/or squid prior to parturition. While more confirmatory studies are needed to refine these methods, our results suggests that the δ 15 N and δ 13 C values of lipid-free milk can be used as a proxy to describe the foraging ecology of female Antarctic fur seals prior to and across the lactation period.

The ability of an animal to acquire energy will affect its allocation to offspring and will ultimately influence fitness. This study investigated the relative influence of maternal traits, seasonal demands of pup-rearing, and individual effects on the foraging behavior of 27 female Antarctic fur seals Arctocephalus gazella at Cape Shirreff, Livingston Island, Antarctica during 2 austral summers (2005 and 2006), using time depth recorders. The relationship between foraging and allocation was investigated using pup growth as an indicator of parental investment. While female diving behavior differed between years, trip duration was below the 10 yr mean and did not differ between the 2 years of the study, indicating favorable feeding conditions in both years. Study year and maternal age accounted for a significant amount of the variation in day and night dive characteristics, while maternal mass influenced only parameters related to night dive effort. As the season progressed, females increased their dive effort at night, made shorter daytime dives, with more bout diving. Indi- vidual variability accounted for a significant amount of the variation in all foraging parameters. Females could be assigned to one of 4 behavioral dive groups (high effort, low effort, intermediate effort with high dive rate, and intermediate effort), based on 13 dive parameters although year instru- mented and age appeared to be important in determining group affiliation. Age, mass, year, and trip number influenced diving behavior; however, there was no relationship between foraging behavior and pup growth rate, except in young females.

Krill (Euphausia superba) carapace measurements (length and width; mm) collected from plankton tows in the South Shetland Islands (SSI), Antarctica are used to test the generality of a common discriminant function developed to reconstruct krill length frequencies in Antarctic fur seal diets for the area surrounding South Georgia (SG). Total length and sex ratio of krill in the SSI were overestimated by 5.6 and 154%, respectively, when the SG allometric equations were applied to 3 years (2003–2005) of data. These errors arise and increase as a result of krill population dynamics, specifically recruitment that contributes large proportions of immature krill, misclassified as males by the SG discriminant function. We develop sex-specific regression models based on separate discriminant functions that provide significantly better discriminatory power. However, our analysis indicates that reconstructions of krill sex ratio and length composition in the ocean environment are less reliable in years when the ratio of immature to mature krill is high. For the SSI area, five out of 14 years (35.7%) surveyed (1992–2005) had proportions of immature to mature adult krill ≥ 0.50.

Life-history theory predicts that adults of long-lived species such as seabirds should optimally balance investment in current and future offspring. However, when trying to optimize investment in offspring provisioning, the most energetically costly component of seabird parental care, adults need to contend with large interannual fluctuations in prey availability and hence the cost of chick provisioning. Adults faced with this uncertainty can mechanistically balance parental care by adopting a strategy somewhere along the continuum between maintaining constant investment in foraging effort between years and letting chick provisioning fluctuate or holding chick provisioning constant and varying investment in foraging effort. Using ship-based hydroacoustic assessment of prey, time-depth recorders attached to penguins and land-based observations at the breeding colony, we examined how foraging and reproductive effort in breeding chinstrap penguins Pygoscelis antarctica responded to interannual variation in the abundance of Antarctic krill Euphausia superba in the vicinity of Seal Island, South Shetland Islands, 1990–1992. Regional measures of krill density varied by a factor of 2.5 (47.0, 23.8 and 61.2 g m � 2 in 1990, 1991 and 1992, respectively) and was correlated with annual measures of breeding adult body weight and reproductive performance (breeding population size, duration of chick rearing, chick growth, breeding success and fledgling weight). In contrast, measures of penguin foraging effort (dive depth, dive duration, number of trips day � 1 , trip duration, number of dives trip � 1 and dive rate) did not differ between years. We conclude that chinstrap penguins reduce reproductive success rather than increase foraging effort in response to decreases in prey abundance in a manner consistent with predictions of life-history strategies for long-lived seabirds.

This study examines whether lactating northern fur seals (Callorhinus ursinus) from different breeding sites on the Pribilof Islands in the eastern Bering Sea forage in separate areas. Satellite transmitters were attached to 97 northern fur seal females from nine breeding areas for 119 complete foraging trips during the 1995 and 1996 breeding seasons. Females from St. Paul and St. George islands tended to travel in different directions relative to their breeding site in both years of the study. St. Paul Island females dispersed in all directions except to the southeast, where St. George Island females foraged. Habitat separation was also observed among breeding areas on northeastern and south- western St. Paul Island and to a lesser degree on northern and southern St. George Island. Although foraging direction led to geographical separation among sites, the maximum distance traveled and the duration of foraging trips did not differ significantly among islands in either year. The results of this study document that lactating fur seals from the same site share a common foraging area and that females from different breeding sites tend to forage in separate areas and hydrographic domains. Resume : Notre etude verifie si les otaries a fourrure nordiques ( Callorhinus ursinus) nourricieres habitant les differen- tes aires de reproduction des iles Pribilof dans l'est de la mer de Bering recherchent leur nourriture dans des sites dif- ferents. Des emetteurs satellites ont ete fixes a 97 otaries a fourrure provenant de neuf aires de reproduction, fournissant ainsi des donnees sur 119 excursions completes de recherche de nourriture durant les saisons de reproduction 1995 et 1996. Les femelles des iles St-Paul et St-Georges avaient tendance a se deplacer dans des directions differentes de leur aire de reproduction durant les deux annees de l'etude. Les femelles de l'ile St-Paul se dispersaient dans toutes les di- rections, excepte vers le sud-est, ou les femelles de l'ile St-Georges recherchaient leur nourriture. Des separations d'habitat s'observent aussi entre les aires de reproduction au nord-est et au sud-ouest de l'ile St-Paul et, dans une moindre mesure, entre les aires au nord et au sud de l'ile St-Georges. Bien que la direction des deplacements durant la recherche de nourriture ait entraine une separation des sites, la distance maximale des deplacements et la duree des sorties a la recherche de nourriture n'ont pas varie significativement d'une ile a l'autre durant les deux annees. Ces re - sultats montrent que des otaries a fourrure nourricieres provenant d'une meme aire de reproduction ont tendance a par- tager un meme site de recherche de nourriture et que des femelles provenant d'aires de reproduction differentes tendent a rechercher leur nourriture dans des regions et des domaines hydrographiques separes.

Mitigating direct and indirect interactions between marine predators and fisheries is a motivating factor for ecosystem-based fisheries management (EBFM), especially where predators and fisheries compete for a shared resource. One difficulty in advancing EBFM is parameterizing clear functional responses of predators to indices of prey availability. Alternative characterizations of fishery-predator interactions may therefore benefit the implementation of EBFM. Telemetry data identify foraging areas used by predators and, therefore, represent critical information to mitigate potential competition between predators and fisheries. We analyzed six years (2009-2014) of telemetry data collected at Cape Shirreff, Livingston Island and Admiralty Bay, King George Island, Antarctica, on three species of Pygoscelid penguins and female Antarctic fur seals. In this region, all four species are primarily dependent on Antarctic krill. The tracking data demonstrate local movements near breeding colonies during the austral summer and dispersal from breeding colonies during the winter. We then assessed overlap between predators and the Antarctic krill fishery on a suite of spatiotemporal scales to examine how different data aggregations affect the extent and location of overlap. Concurrent overlap was observed on all spatiotemporal scales considered throughout the Antarctic Peninsula and South Orkney Islands region, including near tagging locations and in distant areas where recent fishing activity has concentrated. Overlap occurred at depths where mean krill densities were relatively high. Our results demonstrate that direct overlap of krill-dependent predators with the krill fishery on small spatiotemporal scales is relatively common throughout the Antarctic Peninsula region. As the krill fishery continues to develop and efforts to implement ecosystem-based management mature, indices of overlap may provide a useful metric for indicating where the risks of fishing are highest. A precautionary approach to allocating krill catches in space would be to avoid large increases in catch where overlap on small spatiotemporal scales is common.

Understanding how population density influences mating systems may lead to important insights into the plasticity of breeding behavior, but few natural systems allow for such studies. Antarctic fur seals (Arctocephalus gazella) provide an interesting model system because they breed in colonies of varying densities. Previous studies have largely focused on a high-density site at Bird Island, South Georgia. Here, 13 highly polymorphic microsatellite loci were used to conduct a genetic analysis of a low-density breeding colony of this species at Livingston Island, approximately 1,600 km south of South Georgia. The majority of adults seen ashore (n = 54) were sampled together with every pup born (n = 97) over four consecutive years. Paternities were confidently assigned for 34 out of the 97 pups. Two out of 23 sampled males accounted for the paternity of 28 % of all pups sampled during the study and 82 % of the pups with an assigned father. Moreover, a full likelihood pedigree inference method assigned a further eight paternities to a single unsampled male seal that is inferred to have held a territory during the season before the study began. The most successful males in our study easily surpassed the previous record for the total number of pups sired per male seal for the species. Furthermore, we identified two triads of full siblings implying that their parents remated in three consecutive years. These findings suggest that territorial male fur seals may achieve greater success in monopolizing access to breeding females when population density is relatively low.

Diving animals offer a unique opportunity to study the importance of physiological constraint in their everyday behaviors. An important component of the physiological capability of any diving animal is its aerobic dive limit (ADL). The ADL has only been measured in a few species. The goal of this study was to estimate the aerobic dive limit from measurements of body oxygen stores and at sea metabolism. This calculated ADL (cADL) was then compared to measurements of diving behavior of individual animals of three species of otariids, the Antarctic fur seal, Arctocephalus gazella , the Australian sea lion, Neophoca cinerea , and the New Zealand sea lion, Phocarctos hookeri. Antarctic fur seals dove well within the cADL. In contrast, many individuals of both sea lion species exceeded the cADL, some by significant amounts. Australian sea lions typically dove 1.4 times longer than the cADL, while New Zealand sea lions on average dove 1.5 times longer than the cADL. The tendency to exceed the cADL was correlated with the dive pattern of individual animals. In both Antarctic Fur Seals and Australian sea lions, deeper diving females made longer dives that approached or exceeded the cADL ( P r 2 =0.54). Australian and New Zealand sea lions with longer bottom times also exceeded the cADL to a greater degree. The two sea lions forage on the benthos while the fur seals feed shallow in the water column. It appears that benthic foraging requires these animals to reach or exceed their aerobic dive limit.

Persistent organic pollutants (POPs), contaminants that may bioaccumulate in upper trophic level organisms, were detected in the milk of a top predator, the Antarctic fur seal (Arctocephalus gazella). Multiparous females had significantly lower concentrations of certain POPs (trans-nonachlor, p,p'-DDE, and several PCBs) in their milk than primiparous females, likely due to the annual lactational transfer of the POP burden from mother to pup. Furthermore, there were significant interannual differences in POP concentrations in multiparous females' milk from five breeding seasons between 2000 and 2011. Decreasing trends in concentrations of certain POPs over the recent decade coincide with declining global emissions, yet atmospheric concentrations in the Antarctic are not always consistent with global trends, suggesting that additional factors may contribute to temporal trends of POPs in fur seals. Climate shifts and corresponding availability of krill over the past decade were not consistent with trends observed in POP concentrations in fur seal milk, suggesting that climate may not be a key factor. Additional mechanisms, such as variability in the geographic ranges of individual seals during overwintering migrations are discussed and should be explored further.

� 0.8 m a � 1 , driven by a mean basal melt rate of 〈wb〉 = 1.3 � 0.4 m a � 1 . Interannual variability was large, associated with changes in both surface mass accumulation and 〈wb〉. Basal melt rate declined significantly around 2000 from 1.8 � 0.4 m a � 1 for 1992–2000 to � 0.75 � 0.55 m a � 1 for 2001–2008; the latter value corresponding to approximately steady-state ice-shelf mass. Observations of ocean temperature T obtained during 2007–2009 by instrumented seals reveal a cold, deep halo of Winter Water (WW; T ≈ � 1.6°C) surrounding WIS. The base of the WW in the halo is � 170 m, approximately the mean ice draft for WIS. We hypothesize that the transition in 〈wb〉 in 2000 was caused by a small perturbation (� 10–20 m) in the relative depths of the ice base and the bottom of the WW layer in the halo. We conclude that basal melting of thin ice shelves like WIS is very sensitive to upper-ocean and coastal processes that act on shorter time and space scales than those affecting basal melting of thicker West Antarctic ice shelves such as George VI and Pine Island Glacier.

Avian yolk fatty acids (FA) composition is influenced by two main factors: maternal diet and genetic factors that regulate FA metabolism. However, due to embryonic developmental requirements, yolk FA are thought to be physiologically constrained and less useful for dietary and trophic studies. We assessed the relative contributions of diet and physiological constraints in determining the yolk FA composition of a marine bird, the gentoo penguin (Pygoscelis papua) by comparing FA signatures of yolks and prey between a captive, controlled- feeding experiment and a wild population. Captive and wild yolk FA signatures differed even though both groups’ yolk lipids were composed primarily of three FA (16:0, 18:0 and 18:1n-9). Differences were due to FA occurring in relatively low abundance, but which mirrored differences in the FA composition of diets. However, yolk FA signatures were correlated across three penguin species suggesting that common developmental constraints can be relatively more important than species-specific differences in diet or egg-laying physiology. While yolk FA are constrained, several minor components of yolk FA are reflective of diets and the calibration coefficients resulting from this study have the potential to be incorporated into predictive models and allow for quantitative dietary and trophic studies using FA analysis of penguin egg yolks.

Top predators integrate resources over time and space, and depending on the particular species they represent, different components of the marine environment. The habitat utilization of top predators has been studied using electronic tags to follow their movements and foraging behavior. In addition, these tags provide information on the physical characteristics of the water column (temperature and salinity) at a scale and resolution that is coincident with the animals' behavior. In addition to data on the animals' behavior, these tags provide physical oceanographic data in regions or at times they cannot be collected using other currently available technologies. These data inform us on how these important top predators are likely to respond to climatic change, as well as about how the Southern Ocean is changing.

Identifying individuals' foraging strategies is critical to understanding the ecology of a species, and can provide the means to predict possible ecological responses to environmental change. Our study combines stable iso- tope analysis and satellite telemetry to study the variability in individual foraging strategies of adult female southern elephant seals (Mirounga leonina). Our hypothesis is that female elephant seals from the Western Antarctica Penin- sula (WAP) display individual specialization in their diets. We captured adult female elephant seals (n = 56, 2005-2009) at Livingston Island (Antarctica), and instru- mented them with SMRU-CTD satellite tags. We collected blood, fur, and vibrissae samples for d 13 C and d 15 N anal- yses. The mean values for all vibrissae were -21.0 ± 0.7% for d 13 C, and 10.4 ± 0.8%, for d 15 N. The individual variability of d 13 C (60%) was more important than the within-individual variability (40%) in explaining the total variance observed in our data. For d 15 N, the results showed the opposite trend, with the within-individual variability (64%) contributing more to the total variance than the individual variability (36%), likely associated with the effect that the fasting periods have on d 15 N values. Most individuals were specialists, as inferred from the low intra- individual variability of d 13 C values with respect to the population variability, with half the individuals utilizing 31% or less of their available niche. We found eight dif- ferent foraging strategies for these animals. Female ele- phant seals from the WAP are a diverse group of predators with individuals utilizing only a small portion of the total available niche, with the consequent potential to expand their foraging habits to exploit other resources or envi- ronments in the Southern Ocean.

Diving behaviour of chinstrap penguins (Pygoscelis antarctica) was studied in four adults brooding chicks on Seal Island, South Shetland Islands, Antarctica. During foraging trips to sea, chinstrap penguins made shallow, short duration dives almost continuously, for the most part within 50 m of the surface. Diving effort was concentrated during the daylight hours (10h00-15h00), although a second peak in effort was seen around midnight (22h00-02h00). These peaks were possibly due to the constraints of visual location of prey, chick provisioning, or the need to take advantage of diurnal changes in krill swarm densities or behaviour. It was estimated that most effort was concentrated 3-20 km from shore. Dive depth and duration averaged 31.0 m (± 26.3m) and 72s(± 36s), respectively. Maximum dive depth and duration were 121m and 180s, respectively.

We demonstrate the first use of marine mammal dive-depth data to improve maps of bathymetry in poorly sampled regions of the continental shelf. A group of 57 instrumented elephant seals made on the order of 2 x 10(5) dives over and near the continental shelf on the western side of the Antarctic Peninsula during five seasons, 2005-2009. Maximum dive depth exceeded 2000 m. For dives made near existing ship tracks with measured water depths H