Assessing the trophic ecology of fur seals is essential for defining their roles as a top predator in Antarctic marine ecosystems. To this end, we examined the diet of Antarctic fur seals, Arctocephalus gazella , in the South Shetlands. While previous studies have considered the diet of this species at this location in summer, to the best of our knowledge, this is the first study to report on the diet of this population in winter, thus adding essential information on the extent of seasonal variation. A total of 224 scats were collected in the winter 2004 ( n = 118) and summer 2004/2005 ( n = 106) on the coasts of Stranger Point, Isla 25 de Mayo/King George. For the total study period krill ( Euphausia superba ) was the main prey taxon, followed by fish, cephalopods and penguins. During winter Pleuragramma antarcticum was dominant, while myctophids were almost absent. Conversely, in summer Electrona antarctica and Gymnoscopelus nicholsi , followed by P. antarcticum , dominated the fish diet. It is concluded that fur seals centred their foraging activity on a krill community and fish associated with krill aggregations.

To improve the knowledge on the Antarctic fur seal foraging behavior, evaluate whether changes in its diet are associated with changes in prey availability, and evaluate whether fisheries had negative impacts on Antarctic fur seal populations, a total of 1359 scats of non-breeding males were collected in ten consecutive sampling periods between 1994 and 2003 at Laurie Island, South Orkney Islands. Antarctic krill was the most numerous prey throughout the sampling period followed in importance by fish prey. Antarctic krill also predominated by reconstructed mass, except during 1994 and 1998 when penguins were the most important prey, and during 1995 when fish dominated. Among fish, demersal-benthic species (mainly Gobionotothen gibberifrons, Chaenocephalus aceratus and Chionodraco rastrospinosus) dominated the diet except in 1997, 1998, 1999 and 2002 when myctophids (mainly Gymnoscopelus nicholsi and Electrona antarctica) were the most important fish prey. In seasons when fish dominated the diet, the diet was primarily comprised of demersal species. Although our results are in overall agreement with previous studies, the contribution to the diet of the main preys changed throughout the sampling period, probably in parallel with changes in prey abundance. According to historical results on fish consumption, the fisheries carried out in the past have had negative impacts on seal populations from the South Orkney Islands.

The Southern elephant seal (Mirounga leonina) is a major consumer from the Southern Ocean. This species is highly sexually dimorphic and frequently exhibits resource partitioning according to sex and/or age classes. This study analysed the feeding habits of the M. leonina population from Isla 25 de mayo (King George Island) in the spring/summer seasons of 1995/1996–2002/2003. A total of 232 individuals from different sex-age groups were stomach lavaged. The analysis of stomach samples showed that cephalopods were the main prey followed by fish, their frequency of occurrence being 98.1 and 17.9 % respectively. Cephalopods were dominated by the Antarctic glacial squid, Psychroteuthis glacialis, which occurred in 83 % of samples, constituting 57.2 % in numbers and 61.3 % in mass. Octopods were of lesser relevance, occurring in 18 % of samples, but became more important in the diet of male individuals. Juvenile seals fed on a lower variety of cephalopod prey than older ones. This would coincide with the diving pattern characteristic of the different sex-age categories of seals. The predominance of P. glacialis might be associated with the more southerly location of the foraging areas of this population compared to others. Fish were largely represented by the myctophid Gymnoscopelus nicholsi, which occurred in 81.3 % of samples containing otoliths and constituted 76.4 % in numbers and 66.4 % in mass. However, while myctophids may be the dominant fish prey of elephant seals in areas close to the South Shetlands, they would be probably replaced by P. antarcticum as seals migrate towards higher latitudes.

The gut microbiota of mammals underpins the metabolic capacity and health of the host. Our understanding of what influences the composition of this community has been limited primarily to evidence from captive and terrestrial mammals. Therefore, the gut microbiota of southern elephant seals, Mirounga leonina, and leopard seals, Hydrurga leptonyx, inhabiting Antarctica were compared with captive leopard seals. Each seal exhibited a gut microbiota dominated by four phyla: Firmicutes (41.5 ± 4.0%), Fusobacteria (25.6 ± 3.9%), Proteobacteria (17.0 ± 3.2%) and Bacteroidetes (14.1 ± 1.7%). Species, age, sex and captivity were strong drivers of the composition of the gut microbiota, which can be attributed to differences in diet, gut length and physiology and social interactions. Differences in particular prey items consumed by seal species could contribute to the observed differences in the gut microbiota. The longer gut of the southern elephant seal provides a habitat reduced in available oxygen and more suitable to members of the phyla Bacteroidetes compared with other hosts. Among wild seals, 16 'core' bacterial community members were present in the gut of at least 50% of individuals. As identified between southern elephant seal mother-pup pairs, 'core' members are passed on via vertical transmission from a young age and persist through to adulthood. Our study suggests that these hosts have co-evolved with their gut microbiota and core members may provide some benefit to the host, such as developing the immune system. Further evidence of their strong evolutionary history is provided with the presence of 18 shared 'core' members in the gut microbiota of related seals living in the Arctic. The influence of diet and other factors, particularly in captivity, influences the composition of the community considerably. This study suggests that the gut microbiota has co-evolved with wild mammals as is evident in the shared presence of 'core' members.

Rapid climate change recorded in the western Antarctic Peninsula confronts species with less predictable conditions in the marine and terrestrial environments. We analysed the breeding chronology and nesting site selection of gentoo penguins (Pygoscelis papua) at King George Island (Isla 25 de Mayo), Antarctica, during four seasons in which differences in snow presence and persistence on the ground were observed. We recorded an overall delay as well as seasonal asynchrony at the beginning of reproduction for those years with higher snow deposition. A redistribution of breeding groups was also observed. Nevertheless, the population breeding success and chicks’ weight at fledging remained relatively constant, despite the delay in breeding chronology, the increased duration of foraging trips during the guard stage and the decreased weight of stomach contents during the crèche stage. We suggest that the plasticity of their trophic biology, along with the flexibility of their breeding phenology and relocation of breeding groups, may be complementary reasons why gentoo penguin populations in the region have remained stable in spite of the changing conditions currently registered.

Cephalopods play a key role in marine environments as food resources for top predators such as marine mammals and seabirds. However, detailed information on their trophic relationships with Antarctic seals is scarce. The aim of the present study was to examine the cephalopod portion of the diet of adult and subadult Weddell seals, Leptonychotes weddellii, at Hope Bay, Antarctic Peninsula, through the analysis of scats collected during three consecutive summers (2003, 2004 and 2005). Cephalopods occurred in almost 45% of the 217 samples collected during the whole period of study. A total of 662 beaks (358 upper and 304 lower) were removed from scats containing cephalopod remains (n = 93). Octopods were largely dominant in comparison with teuthoids constituting in numerical abundance over 95% of the cephalopod prey. The octopod Pareledone turqueti was the most frequent and dominant prey species representing, respectively, 57.9 and 71.1% in numbers and biomass of cephalopods consumed. Species belonging to the group of papillated Pareledone were second in importance. The results were compared with information from previous dietary studies of L. weddellii at other localities of Antarctica. Based on the examination of the cephalopod prey taxa identified in this study, it is suggested that during the study period Weddell seal individuals foraged mainly on benthic prey resources close to the coast, in inshore waters where octopods were dominant in comparison with pelagic squid.

The analysis of prey overlap among Weddell, Antarctic fur and leopard seals was conducted using fecal samples collected at the Danco Coast, Antarctic Peninsula, in 1998 and 2000. The re-occurrence of prey species was moderate in samples collected in 1998, and low in 2000, and reflects resource partitioning among seal species. Prey species that mostly co-occurred in seals’ diet were the Antarctic krill Euphausia superba, bivalves, and the myctophids Gymnoscopelus nicholsi and Electrona antarctica. A dietary similarity index of prey overlap has been calculated and demonstrates evident fluctuations in pairwise comparisons between the seal species. The highest and lowest values of prey overlap were observed between Antarctic fur seals and leopard seals, and between Weddell seals and leopard seals, respectively. Prey overlap between Antarctic fur seals and Weddell seals was moderate in both seasons.

At least 50% of the world's seal population is distributed in the pack-ice region surrounding Antarctica. Among the Antarctic seals, Lobodon carcinophaga (commonly known as “crabeater seals”) are the most abundant. This is a krill-feeding species, subsisting primarily on Euphausia superba. The occurrence of mummified seals has been documented since 1900 in several Antarctic regions, and different hypotheses about age and what happened to them have been proposed. Taking into account the depletion of 14C concentration in marine waters, we dated a recently deceased and a mummified L. carcinophaga along with a mollusk (Nacella concinna) collected alive from different locations around Antarctica. We discuss their relationship in light of the 14C reservoir. The age obtained for the recently deceased crabeater seals suggests a reservoir age of around 1300 yr for these waters, which is in agreement with the correction value for reservoir age obtained for the same species in the area. We applied this reservoir correction value to the conventional age of 1180 14C yr BP obtained for the mummified seal. The results indicate that the death event probably occurred within the last 100 yr. The age obtained for the mollusk specimen confirms that the correction values of the reservoir effect for the Antarctic continent vary according to geographical location and to the type of sample dated.

An ethogram is a baseline tool in animal behavioral studies. Nevertheless, for the southern elephant seal (Mirounga leonina Linneo, 1758), a species in which males compete for access to females through agonistic encounters, the ethograms that are being used are based on literature reports, in which behaviors are adapted from other species or only mentioned without being described. As a result, some of the behavioral elements of the species are still unknown. Here we present an ethogram of male agonistic behavior obtained from systematic observations during three consecutive breeding seasons in a rookery situated in the South Shetland Islands, Antarctica. It includes 27 behavioral acts, 6 of which have never been mentioned in the available literature for the species. This ethogram was compared to known behavioral inventories for the species. In addition, the frequencies of occurrence of each behavioral act were obtained for the complete set of observed agonistic interactions. A comparison of the use of each behavioral act by males of different social classes was performed. This allowed to characterize the agonistic behavior of each group during the breeding season.

The region around the sill of the Filchner Trough outflow (77°S, 36°W) is considered a hot spot, both in terms of biology and physical oceanography. The factors contributing to this oceanic area of enhanced food availability and its relation to physical processes are not yet understood. Animal-borne satellite telemetry of southern elephant seal males, instrumented at King George Island / Isla 25 de Mayo aims to describe the seals' preferred foraging depths around the Filchner Trough in order to elucidate the vertical distribution of prey in relation to the oceanographic features on-site. Recent deployments (2010) represent a follow-up study of an ARGOS satellite telemetry project on elephant seals in 2000. Adult males travelled deep into the winter pack ice of the Weddell Sea along the western continental shelf break until they reached the region of the sill of the Filchner Trough outflow, where they remained in a localized 100 km wide shelf-slope area for several months. The re-instrumentation aims to investigate if males continue to travel to similar areas. The trilateral, long-term observation study of scientists from South Africa, Argentina and Germany is based on a synoptic approach for Marion Island and King George Island / Isla 25 de Mayo.

We report herein the southernmost record of the Hudsonian Godwit (Limosa haemastica), at two localities inthe Antarctic: Esperanza/Hope Bay (January 2005) and 25 de Mayo/King George Island (October 2008). On both occasionsa pair of specimens with winter plumage was observed.

Seventy-seven immobilizations were carried out on adult male southern elephant seals at Stranger Point, Isla 25 de Mayo (King George Island) using a combination of Zoletil ® (tiletamine and zolazepam) and ketamine in order to obtain biological samples. During 2006/2007, 22 males were immobilized at the beginning of their breeding period (EB), 19 of which were recaptured at the end of breeding (LB). Four were given only once at an unknown stage of breeding (USB) and 18 males were immobilized at the beginning of molting (BM). During 2007/2008, 14 adult males were immobilized at an USB. Zoletil ® was administered using an automatic discharge device, whereas ketamine was injected directly with a syringe, and was used only when the initial sedation was not enough to carry out the programmed sampling. The initial mean dose of Zoletil ® was 1,387 ± 304 mg, which represented 0.60 ± 0.14 mg/kg, range 0.36–1.05, n = 77. In 47 procedures, an average dose of 1.04 ± 0.66 mg/kg of ketamine was added. Mean immobilization time was 34 ± 14 min. In 25 out of the 77 procedures, males showed apnea, which lasted 8 ± 4 min (range 2–15 min). The necessary doses of Zoletil ® and ketamine to attain immobilization differed between stages. For animals taken twice, doses (mg/kg) of Zoletil ® and ketamine were significantly higher at the beginning than at the end of breeding. During molting, the doses of Zoletil ® given were significantly lower than those used during breeding, although the proportion of animals that required ketamine during molting was significantly higher than during breeding. Zoletil ® proved to be a safe immobilizing agent for field work on adult males of this species, given the wide range of doses used without any serious consequences. Furthermore, the addition of ketamine was useful when the initial sedation was not satisfactory or for prolonging the immobilization period in a practical and reliable way.