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In animal ecology, a question of key interest for aquatic species is how changes in movement behavior are related in the horizontal and vertical dimensions when individuals forage. Alternative theoretical models and inconsistent empirical findings mean that this question remains unresolved. Here we tested expectations by incorporating the vertical dimension (dive information) when predicting switching between movement states (\"resident\" or \"directed\") within a state-space model. We integrated telemetry-based tracking and diving data available for four seal species (southern elephant, Weddell, antarctic fur, and crabeater) in East Antarctica. Where possible, we included dive variables derived from the relationships between (1) dive duration and depth (as a measure of effort), and (2) dive duration and the postdive surface interval (as a physiological measure of cost). Our results varied within and across species, but there was a general tendency for the probability of switching into \"resident\" state to be positively associated with shorter dive durations (for a given depth) and longer postdive surface intervals (for a given dive duration). Our results add to a growing body of literature suggesting that simplistic interpretations of optimal foraging theory based only on horizontal movements do not directly translate into the vertical dimension in dynamic marine environments. Analyses that incorporate at least two dimensions can test more sophisticated models of foraging behavior.

Numerous studies have reported correlations between the heterozygosity of genetic markers and fitness. These heterozygosity–fitness correlations (HFCs) play a central role in evolutionary and conservation biology, yet their mechanistic basis remains open to debate. For example, fitness associations have been widely reported at both neutral and functional loci, yet few studies have directly compared the two, making it difficult to gauge the relative contributions of genome‐wide inbreeding and specific functional genes to fitness. Here, we compared the effects of neutral and immune gene heterozygosity on death from bacterial infection in Antarctic fur seal (Arctocephalus gazella) pups. We specifically developed a panel of 13 microsatellites from expressed immune genes and genotyped these together with 48 neutral loci in 234 individuals, comprising 39 pups that were classified at necropsy as having most likely died of bacterial infection together with a five times larger matched sample of healthy surviving pups. Identity disequilibrium quantified from the neutral markers was positive and significant, indicative of variance in inbreeding within the study population. However, multilocus heterozygosity did not differ significantly between healthy and infected pups at either class of marker, and little evidence was found for fitness associations at individual loci. These results support a previous study of Antarctic fur seals that found no effects of heterozygosity at nine neutral microsatellites on neonatal survival and thereby help to refine our understanding of how HFCs vary across the life cycle. Given that nonsignificant HFCs are underreported in the literature, we also hope that our study will contribute toward a more balanced understanding of the wider importance of this phenomenon. In this study, we investigated the correlation between the heterozygosity of functional and neutral microsatellite markers on an immune‐related fitness trait in Antarctic fur seal pups. We conclusively determined that neither class of marker explained a significant proportion of fitness variation photo credit, the picture was taken by Rebecca Nagel.

Although the genetic basis of color variation has been extensively studied in humans and domestic animals, the genetic polymorphisms responsible for different color morphs remain to be elucidated in many wild vertebrate species. For example, hypopigmentation has been observed in numerous marine mammal species but the underlying mutations have not been identified. A particularly compelling candidate gene for explaining color polymorphism is the melanocortin 1 receptor (MC1R), which plays a key role in the regulation of pigment production. We therefore used Antarctic fur seals (Arctocephalus gazella) as a highly tractable marine mammal system with which to test for an association between nucleotide variation at the MC1R and melanin‐based coat color phenotypes. By sequencing 70 wild‐type individuals with dark‐colored coats and 26 hypopigmented individuals with cream‐colored coats, we identified a nonsynonymous mutation that results in the substitution of serine with phenylalanine at an evolutionarily highly conserved structural domain. All of the hypopigmented individuals were homozygous for the allele coding for phenylalanine, consistent with a recessive loss‐of‐function allele. In order to test for cryptic population structure, which can generate artefactual associations, and to evaluate whether homozygosity at the MC1R could be indicative of low genome‐wide heterozygosity, we also genotyped all of the individuals at 50 polymorphic microsatellite loci. We were unable to detect any population structure and also found that wild‐type and hypopigmented individuals did not differ significantly in their standardized multilocus heterozygosity. Such a lack of association implies that hypopigmented individuals are unlikely to suffer disproportionately from inbreeding depression, and hence, we have no reason to believe that they are at a selective disadvantage in the wider population. We sequenced the melanocortin 1 receptor (MC1R) of 70 wild‐type and 26 cream‐coloured Antarctic fur seals and identified a recessive loss‐of‐function mutation clearly associated with cream coat colour. In order to evaluate whether homozygosity at the MC1R could be indicative of low genome‐wide heterozygosity, we also genotyped all individuals at 50 polymorphic microsatellite loci and found no difference in standardized multilocus heterozygosity between wild‐type and cream‐coloured individuals. Such a lack of association implies that hypopigmented individuals are unlikely to suffer disproportionally from inbreeding depression and thus do not appear to be at a selective disadvantage in the wider population.

Until recent events, the Antarctic was the only major geographical region in which high pathogenicity avian influenza virus (HPAIV) had never previously been detected. Here we report on the detection of clade 2.3.4.4b H5N1 HPAIV in the Antarctic and sub-Antarctic regions of South Georgia and the Falkland Islands, respectively. We initially detected H5N1 HPAIV in samples collected from brown skuas at Bird Island, South Georgia on 8th October 2023. Since this detection, mortalities were observed in several avian and mammalian species at multiple sites across South Georgia. Subsequent testing confirmed H5N1 HPAIV across several sampling locations in multiple avian species and two seal species. Simultaneously, we also confirmed H5N1 HPAIV in southern fulmar and black-browed albatross in the Falkland Islands. Genetic assessment of the virus indicates spread from South America, likely through movement of migratory birds. Critically, genetic assessment of sequences from mammalian species demonstrates no increased risk to human populations above that observed in other instances of mammalian infections globally. Here we describe the detection, species impact and genetic composition of the virus and propose both introductory routes and potential long-term impact on avian and mammalian species across the Antarctic region. We also speculate on the threat to specific populations following recent reports in the area. High pathogenicity avian influenza virus has a wide host range and has been detected across a large geographic area. Here, the authors present evidence of spread to the Antarctic and sub-Antarctic regions, with signs of clinical infection and positive virus detection in birds and elephant seals.

Climate change will affect Antarctic krill Euphausia superba, krill-dependent predators, and fisheries in the Southern Ocean as areas typically covered by sea ice become ice-free in some winters. Research cruises conducted around the South Shetland Islands of the Antarctic Peninsula during winters with contrasting ice conditions provide the first acoustic estimates of krill biomass, habitat use, and association with top predators to examine potential interactions with the krill fishery. Krill abundance was very low in offshore waters during all winters. In Bransfield Strait, median krill abundance was an order of magnitude higher (8 krill m−2) compared to summer (0.25 krill m−2), and this pattern was observed in all winters regardless of ice cover. Acoustic estimates of krill biomass were also an order of magnitude higher (~5 500 000 metric tons [t] in 2014) than a 15 yr summer average (520 000 t). Looking at krill-dependent predators, during winter, crabeater seals Lobodon carcinophagus were concentrated in Bransfield Strait where ice provided habitat, while Antarctic fur seals Arctocephalus gazella were more broadly distributed. Krill overwinter in coastal basin environments independent of ice and primary production and in an area that is becoming more frequently ice-free. While long-term projections of climate change have focused on changing krill habitat and productivity declines, more immediate impacts of ongoing climate change include increased risks of negative fishery−krill−predator interactions, alteration of upper trophic level community structure, and changes in the pelagic ecology of this system. Development of management strategies to mitigate the increased risk to krill populations and their dependent predators over management timescales will be necessary to minimize the impacts of long-term climate change.

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.

1. Energy expenditure is an important component of foraging ecology, but is extremely difficultto estimate in free-ranging animals and depends on how animals partition their timebetween different activities during foraging. Acceleration data have emerged as a new way todetermine energy expenditure at a fine scale but this needs to be tested and validated in wildanimals.2. This study investigated whether vectorial dynamic body acceleration (VeDBA) could accuratelypredict the energy expended by marine predators during a full foraging trip. We alsoaimed to determine whether the accuracy of predictions of energy expenditure derived fromacceleration increased when partitioned by different types of at-sea activities (i.e. diving, transiting,resting and surface activities).3. To do so, we equipped 20 lactating northern (Callorhinus ursinus) and 20 lactating Antarcticfur seals (Arctocephalus gazella) with GPS, time-depth recorders and tri-axial accelerometersand obtained estimates of field metabolic rates using the doubly labelled water (DLW)method. VeDBA was derived from tri-axial acceleration, and at-sea activities (diving, transiting,resting and surface activities) were determined using dive depth, tri-axial acceleration andtravelling speed.4. We found that VeDBA did not accurately predict the total energy expended by fur sealsduring their full foraging trips (R2 = 036). However, the accuracy of VeDBA as a predictorof total energy expenditure increased significantly when foraging trips were partitioned byactivity and when activity-specific VeDBA was paired with time-activity budgets (R2 = 070).Activity-specific VeDBA also accurately predicted the energy expenditures of each activityindependent of each other (R2 > 085).5. Our study confirms that acceleration is a promising way to estimate energy expenditures offree-ranging marine mammals at a fine scale never attained before. However, it shows that itneeds to be based on the time-activity budgets that make up foraging trips rather than beingderived as a single measure of VeDBA applied to entire foraging trips. Our activity-basedmethod provides a cost-effective means to accurately calculate energy expenditures of fur sealsusing acceleration and time-activity budgets, that can be transfered to studies on other species.

Allee effects play an important role in the dynamics of many populations and can increase the risk of local extinction. However, some authors have questioned the weight of evidence for Allee effects in wild populations. We therefore exploited a natural experiment provided by two adjacent breeding colonies of contrasting density to investigate the potential for Allee effects in an Antarctic fur seal (Arctocephalus gazella) population that is declining in response to climate change-induced reductions in food availability. Biometric time-series data were collected from 25 pups per colony during two consecutive breeding seasons, the first of which was among the worst on record in terms of breeding female numbers, pup birth weights and foraging trip durations. In previous decades when population densities were higher, pup mortality was consistently negatively density dependent, with rates of trauma and starvation scaling positively with density. However, we found the opposite, with higher pup mortality at low density and the majority of deaths attributable to predation. In parallel, body condition was depressed at low density, particularly in the poor-quality season. Our findings shed light on Allee effects in wild populations and highlight a potential emerging role of predators in the ongoing decline of a pinniped species.

1. The degree of individual specialization in resource use differs widely among wild populationswhere individuals range from fully generalized to highly specialized. This interindividualvariation has profound implications in many ecological and evolutionary processes. A recentreview proposed four main ecological causes of individual specialization: interspecific andintraspecific competition, ecological opportunity and predation.2. Using the isotopic signature of subsampled whiskers, we investigated to what degree threeof these factors (interspecific and intraspecific competition and ecological opportunity) affectthe population niche width and the level of individual foraging specialization in two fur sealspecies, the Antarctic and subantarctic fur seals (Arctocephalus gazella and Arctocephalustropicalis), over several years.3. Population niche width was greater when the two seal species bred in allopatry (low interspecificcompetition) than in sympatry or when seals bred in high-density stabilized colonies (highintraspecific competition). In agreement with the niche variation hypothesis (NVH), higherpopulation niche width was associated with higher interindividual niche variation. However, incontrast to the NVH, all Antarctic females increased their niche width during the interbreedingperiod when they had potential access to a wider diversity of foraging grounds and associatedprey (high ecological opportunities), suggesting they all dispersed to a similar productive area.4. The degree of individual specialization varied among populations and within the annualcycle. Highest levels of interindividual variation were found in a context of lower interspecificor higher intraspecific competition. Contrasted results were found concerning the effect ofecological opportunity. Depending on seal species, females exhibited either a greater or lowerdegree of individual specialization during the interbreeding period, reflecting species-specificbiological constraints during that period.5. These results suggest a significant impact of ecological interactions on the population nichewidth and degree of individual specialization. Such variation at the individual level may bean important factor in the species plasticity with significant consequences on how it mayrespond to environmental variability.