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The energy requirements and prey consumption of the rapidly expanding South Georgia population of Antarctic Fur Seals, Arctocephalus gazella, are estimated, using information on diet, population structure, activity patterns, and energy budgets and variations in these with sex and season. All quantitative information on diet is reviewed. Breeding female Fur Seals mainly take Antarctic Krill, Euphausia superba. This predominates also in the summer diet of males but fish (mainly Champsocephalus gunnari) and squid are also eaten. Fish is more important to males in winter. Life tables are used to determine the proportion of each age-class in the population, and especially to estimate the size of that portion of the immature stock which does not appear ashore. Energy costs of adult males are assessed from attendance data and age-specific weights. Female energy budgets are calculated from extensive data on the duration of periods ashore and foraging trips to sea together with information on activity budgets at sea. Pup energy consumption is calculated from body weight and growth data. A summer food consumption of 1.1 × 106 t is divided between juvenile males (39%), adult females (31%), adult males (22%) and juvenile females (8%). In winter, when females are absent, juvenile (67%) and adult males (33%) consume 0.4 × 106 t. Krill forms 69% of the annual consumption, fish 19% and squid 12%. The main peaks of demand are in October (all adults feeding at sea), January-February (rapidly growing pups being reared) and April—May (most of population, including weaners, feeding at sea). From data on diet and foraging ranges and depths, the main natural competitor of the Antarctic Fur Seal is the Macaroni Penguin, Eudyptes chrysolophus; significant competition with a developed Krill fishery would be expected. Continuing commercial exploitation of fish, especially C. gunnari, may influence male Fur Seal populations, particularly in winter.

Replication studies are essential for evaluating the validity of previous research findings. However, it has proven challenging to reproduce the results of ecological and evolutionary studies, partly because of the complexity and lability of many of the phenomena being investigated, but also due to small sample sizes, low statistical power and publication bias. Additionally, replication is often considered too difficult in field settings where many factors are beyond the investigator’s control and where spatial and temporal dependencies may be strong. We investigated the feasibility of reproducing original research findings in the field of chemical ecology by performing an exact replication of a previous study of Antarctic fur seals (Arctocephalus gazella). In the original study, skin swabs from 41 mother-offspring pairs from two adjacent breeding colonies on Bird Island, South Georgia, were analyzed using gas chromatography-mass spectrometry. Seals from the two colonies differed significantly in their chemical fingerprints, suggesting that colony membership may be chemically encoded, and mothers were also chemically similar to their pups, hinting at the possible involvement of phenotype matching in mother-offspring recognition. In the current study, we generated and analyzed chemical data from a non-overlapping sample of 50 mother-offspring pairs from the same two colonies 5 years later. The original results were corroborated in both hypothesis testing and estimation contexts, with p-values remaining highly significant and effect sizes, standardized between studies by bootstrapping the chemical data over individuals, being of comparable magnitude. However, exact replication studies are only capable of showing whether a given effect can be replicated in a specific setting. We therefore investigated whether chemical signatures are colony-specific in general by expanding the geographic coverage of our study to include pups from a total of six colonies around Bird Island. We detected significant chemical differences in all but a handful of pairwise comparisons between colonies. This finding adds weight to our original conclusion that colony membership is chemically encoded, and suggests that chemical patterns of colony membership not only persist over time but can also be generalized over space. Our study systematically confirms and extends our previous findings, while also implying more broadly that spatial and temporal heterogeneity need not necessarily negate the reproduction and generalization of ecological research findings.

Evaluating how populations are connected by migration is important for understanding species resilience because gene flow can facilitate recovery from demographic declines. We therefore investigated the extent to which migration may have contributed to the global recovery of the Antarctic fur seal (Arctocephalus gazella), a circumpolar distributed marine mammal that was brought to the brink of extinction by the sealing industry in the eighteenth and nineteenth centuries. It is widely believed that animals emigrating from South Georgia, where a relict population escaped sealing, contributed to the re-establishment of formerly occupied breeding colonies across the geographical range of the species. To investigate this, we interrogated a genetic polymorphism (S291F) in the melanocortin 1 receptor gene, which is responsible for a cream-coloured phenotype that is relatively abundant at South Georgia and which appears to have recently spread to localities as far afield as Marion Island in the sub-Antarctic Indian Ocean. By sequencing a short region of this gene in 1492 pups from eight breeding colonies, we showed that S291F frequency rapidly declines with increasing geographical distance from South Georgia, consistent with locally restricted gene flow from South Georgia mainly to the South Shetland Islands and Bouvetøya. The S291F allele was not detected farther afield, suggesting that although emigrants from South Georgia may have been locally important, they are unlikely to have played a major role in the recovery of geographically more distant populations.

High-density SNP arrays developed for humans and their companion species provide a rapid and convenient tool for generating SNP data in closely-related non-model organisms, but have not yet been widely applied to phylogenetically divergent taxa. Consequently, we used the CanineHD BeadChip to genotype 24 Antarctic fur seal (Arctocephalus gazella) individuals. Despite seals and dogs having diverged around 44 million years ago, 33,324 out of 173,662 loci (19.2%) could be genotyped, of which 173 were polymorphic and clearly interpretable. Two SNPs were validated using KASP genotyping assays, with the resulting genotypes being 100% concordant with those obtained from the high-density array. Two loci were also confirmed through in silico visualisation after mapping them to the fur seal transcriptome. Polymorphic SNPs were distributed broadly throughout the dog genome and did not differ significantly in proximity to genes from either monomorphic SNPs or those that failed to cross-amplify in seals. However, the nearest genes to polymorphic SNPs were significantly enriched for functional annotations relating to energy metabolism, suggesting a possible bias towards conserved regions of the genome.

Although heterozygosity-fitness correlations (HFCs) are widely reported in the literature, most studies use too few markers to allow the proximate mechanisms to be convincingly resolved. Two competing hypotheses have been proposed: the general effect hypothesis, in which marker heterozygosity correlates with genome-wide heterozygosity and hence the inbreeding coefficient f, and the local effect hypothesis, in which one or more of the markers by chance exhibit associative overdominance. To explore the relative contributions of general and local effects in a free-ranging marine mammal population, we revisited a strong HFC found using 9 microsatellite loci for canine tooth size in 84 male Antarctic fur seals Arctocephalus gazella (Hoffman JI, Hanson N, Forcada J, Trathan PN, Amos W. 2010. Getting long in the tooth: a strong positive correlation between canine size and heterozygosity in the Antarctic fur seal Arctocephalus gazella. J Hered.). Increasing the number of markers to 76, we find that heterozygosity is uncorrelated across loci, indicating that inbred individuals are rare or absent. Similarly, while the HFC based on overall heterozygosity is lost, stochastic simulations indicate that when an HFC is due to inbreeding depression, increasing marker number invariably strengthens the HFC. Together these observations argue strongly that the original HFC was not due to inbreeding depression. In contrast, a subset of markers show individually significant effects, and these are nonrandomly distributed across the marker panel, being preferentially associated with markers cloned from other species. Using basic alignment search tool searches, we were able to locate 94% of loci to unique locations in the dog genome, but the local genes are functionally diverse, and the majority cannot be linked directly to growth. Our results suggest that inbreeding depression contributes little if at all to the relationship between heterozygosity and tooth size but that instead the primary mechanism involves associative overdominance. These findings contribute to a growing body of evidence suggesting that general effects are likely to be uncommon in natural populations.

High density single nucleotide polymorphism (SNP) arrays allow large numbers of individuals to be rapidly and cost-effectively genotyped at large numbers of genetic markers. However, despite being widely used in studies of humans and domesticated plants and animals, SNP arrays are lacking for most wild organisms. We developed a custom 85K Affymetrix Axiom array for an intensively studied pinniped, the Antarctic fur seal (Arctocephalus gazella). SNPs were discovered from a combination of genomic and transcriptomic resources and filtered according to strict criteria. Out of a total of 85,359 SNPs tiled on the array, 75,601 (88.6%) successfully converted and were polymorphic in 270 animals from a breeding colony at Bird Island in South Georgia. Evidence was found for inbreeding, with three genomic inbreeding coefficients being strongly intercorrelated and the proportion of the genome in runs of homozygosity being non-zero in all individuals. Furthermore, analysis of genomic relatedness coefficients identified previously unknown first-degree relatives and multiple second-degree relatives among a sample of ostensibly unrelated individuals. Such “cryptic relatedness” within fur seal breeding colonies may increase the likelihood of consanguineous matings and could therefore have implications for understanding fitness variation and mate choice. Finally, we demonstrate the cross-amplification potential of the array in three related pinniped species. Overall, our SNP array will facilitate future studies of Antarctic fur seals and has the potential to serve as a more general resource for the wider pinniped research community.

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 by around 400 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 organization.

Intra-population variation in diving behaviour of lactating Antarctic fur seals (Arctocephalus gazella) was studied at the Kerguelen Archipelago (49°07'S, 70°45'E) during the austral summers of 1998–2000. Dive data were successfully recorded for 112 seals equipped with time-depth recorders during 117 foraging trips. All seals displayed bouts of diving activity and the nocturnal foraging behaviour typical of otariids preying on pelagic fish and squid. Mean dive depth (53 m) was considerably deeper than recorded for this species at other sites. Four diving behaviour groups were identified: (1) deep divers (n=60); (2) shallow-active divers (n=45); (3) shallow divers (n=9); (4) daytime divers (n=3). The distribution of trips assigned to the various behavioural dive groups varied significantly between years. Antarctic fur seals at Kerguelen exhibit flexible diving strategies both within and between populations in response to changes in environmental conditions and prey availability. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00300-001-0339-6.

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 18th and 19th century sealers. Molecular genetic data from over 2,000 individuals sampled from all eight major breeding locations across the species’ circumpolar geographic distribution, show that at least four relict populations around Antarctica survived commercial hunting. Coalescent simulations suggest that all of these populations experienced severe bottlenecks down to effective population sizes of around 150–200. Nevertheless, comparably high levels of neutral genetic variability were retained as these declines are unlikely to have been strong enough to deplete allelic richness by more than around 15%. These findings suggest that even dramatic short-term declines need not necessarily result in major losses of diversity, and explain the apparent contradiction between the high genetic diversity of this species and its extreme exploitation history.

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.

The Antarctic fur seal (Arctocephalus gazella) is an abundant Antarctic otariid. Here, we present the complete mitochondrial DNA sequence of this species, which includes 13 protein-coding genes, 22...

Vol. 86: 15-30, 1992 l MARINE ECOLOGY PROGRESS SERIES Mar. Ecol. Prog. Ser. Published September 3 I Distributions and predator-prey interactions of macaroni penguins, Antarctic fur seals, and Antarctic krill near Bird Island, South Georgia George L. Hunt, ~ r ' Dennis ~einemann'.', Inigo ~ v e r s o n ~ 'Department of Ecology and Evolutionary Biology, University of California. Irvine, California 92717, USA 'British Antarctic Survey, Natural Environment Research Council, High Cross Madingley Road, Cambridge CB3 OET, United Kingdom ABSTRACT: We studied the distributions, abundances and interactions of macaroni penguins Eudyptes chrysolophus, Antarchc fur seals Arctocephalus gazella, and their zooplankton prey, m particular Antarctic krill Euphausia superba, near Bird Island, South Georgia, South Atlantic Ocean, in February 1986. Simultaneous surveys of marine birds, Antarctic fur seals and Antarctic krill were conducted along a series of transects radiating from the breeding colonies of the vertebrate predators. We examined the relationships between the distributions of predators and their prey with respect to the abundance of krill in the water column and marine habitats near the colonies. Antarctic fur seals and macaroni penguins showed positive correlations with Antarctic krill density across a wide range of spatial scales. Because krill was abundant close to the colony and predator densities decreased with distance due to geometry, distance from colony was a confounding variable. When the influences of distance and direction on predator abundance were factored out, we were able to demonstrate an additional influence of Antarctic krill abundance at measurement scales between 10 and 100 km for Antarctic fur seals and for macaroni penguins at the scale of 70 to 100 km. Water depth was an important correlate of Antarctic krill and Antarctic fur seal abundances but not of the abundance of macaroni penguins. We found no evidence that the fur seals or macaroni penguins were concentrating their foraging for krill in the vicinity of the shelf-break. INTRODUCTION Students of marine birds and mammals have sought to describe and understand the at-sea distributions and abundances of these organisms (e.g. Laws 1977, Brown 1980, Hunt & Schneider 1987, Hunt 1990). In early studies, the measurement of prey abundance at appropriate scales was not feasible, and investigators relied on the measurement of physical features of the ocean to describe the marine habitats used by birds and mammals. The implicit assumptions in these studies were that prey availability varied between the habitats described, and that birds or mammals selected those habitats where prey were most profitably acquired. The possibility of making continuous meas- urements of prey distributions and abundances now ' Present address: Manomet Bird Observatory, PO Box 936, Manomet, Massachusetts 02345, USA O Inter-Research 1992 permits the study of the relationships between predator and prey abundance over a variety of spatial scales. Quantitative studies of the relationships between the at-sea dstribution and abundance of marine mammals and the distribution and abundance of their prey are few, possibly due to the generally low at-sea densities of marine mammals. At the scale of tens to hundreds of km, there is evidence that marine mammals concen- trate where their prey is predictably abundant (e.g. Brodie et al. 1978, Nerini 1984, Oliver et al. 1984, Au & Pitman 1986). In the Antarctic, there have been no quantitative studies of the joint pelagic distributions of marine mammals and their prey. Inferences concerning the coincidence of the distributions of the great whales and Antarctic knll Euphausia superba have been attempted (Harmer 1931, Hardy & Gunther 1935, Mac- kintosh 1965, Laws 1977, Everson 1984), but these studies lacked simultaneous determination of prey resources (see also Plotz et al. 1991, Ribic et al. 1991).

The efficiency with which individuals extract energy from their environment defines their survival and reproductive success, and thus their selective contribution to the population. Individuals that forage more efficiently (i.e., when energy gained exceeds energy expended) are likely to be more successful at raising viable offspring than individuals that forage less efficiently. Our goal was to test this prediction in large long-lived mammals under free-ranging conditions. To do so, we equipped 20 lactating Antarctic fur seals (Arctocephalus gazella) breeding on Kerguelen Island in the Southern Ocean with tags that recorded GPS locations, depth and tri-axial acceleration to determine at-sea behaviours and detailed time-activity budgets during their foraging trips. We also simultaneously measured energy spent at sea using the doubly-labeled water (DLW) method, and estimated the energy acquired while foraging from 1) type and energy content of prey species present in scat remains, and 2) numbers of prey capture attempts determined from head acceleration. Finally, we followed the growth of 36 pups from birth until weaning (of which 20 were the offspring of our 20 tracked mothers), and used the relative differences in body mass of pups at weaning as an index of first year survival and thus the reproductive success of their mothers. Our results show that females with greater foraging efficiencies produced relatively bigger pups at weaning. These mothers achieved greater foraging efficiency by extracting more energy per minute of diving rather than by reducing energy expenditure. This strategy also resulted in the females spending less time diving and less time overall at sea, which allowed them to deliver higher quality milk to their pups, or allowed their pups to suckle more frequently, or both. The linkage we demonstrate between reproductive success and the quality of individuals as foragers provides an individual-based quantitative framework to investigate how changes in the availability and accessibility of prey can affect fitness of animals.

The fur seal, Arctocephalus gazella, population at Mossman Peninsula (Laurie Island) was studied from 1985 to 1987. Weekly counts were carried out at a 4 km bachelor haul-out beach from December through June. Maxima of 2 240, 2 787 and 5 196 juvenile and adult males were counted during March of the respective years. Census data indicate an increase in the non-breeding population of 13.5% between 1985–1986 and 46.5% between 1986–1987.

(1) Quantitative studies of predator-prey interactions depend on a knowledge of their spatial dynamics and behaviour. Studies on marine vertebrates have hitherto been precluded by the difficulty of acquiring the relevant data. (2) Continuous records of diving depths of female Antarctic fur seals on 3-8 day feeding trips to sea from South Georgia were analysed in conjunction with data on diel changes in the abundance and distribution of their main prey, krill. (3) In 36 complete days foraging by seven seals, 75% of 4273 dives were at night. Dives then were consistently shallower (dive depth < 30 m) than in daytime (mostly 40-75 m). (4) This closely matched changes in the vertical distribution of krill, nearly all of which was below a depth of 50 m from 09.00-15.00 h, with substantial quantities above 40 m only between 21.00-06.00 h. (5) Although over 40% of krill in the water column at any time of day was below 75 m, only 3% of dives exceeded this depth. We suggest that because krill migrate vertically fur seals are able to exploit them most efficiently during shallow dives at night.

Lotka's equations summarizing population dynamics can be approximated by functional models of the survivorship and reproductive curves, incorporating three stages of survival and reproduction, respectively. An abbreviated form uses a single reproductive parameter and two survival values. Survivorship and reproductive curves were fitted to data on northern fur seals (Callorhinus ursinus), domestic and feral sheep, white-tailed deer (Odocoileus virginianus), grizzly bears (Ursus arctos), African buffalo (Syncerus caffer), free-ranging horses, and fin whales (Balaenoptera physalus). Data for 10 species suggest a useful relationship between senescence parameters. A bias due to senescence may lead to serious underestimation of survival rates. Observed annual rates of increase of 18-20% for feral horses, 16% for southern fur seals (Arctocephalus gazella), and 60% for white-tailed deer are compatible with observed population parameters. 43 references, 11 figures, 3 tables.