Southern elephant seals (Mirounga leonina) are apex predators that spend several months at sea feeding over vast areas. Their population trends are related to food availability during winter, which in turn is influenced by environmental conditions; thus, fluctuations in their populations reflect changes in the ecosystems. Although population trends for this species are available for large populations, there are still small colonies for which information is scarce, as is the case for the colony located at Peninsula Potter, South Shetland Islands. At this colony, field censuses of the number of breeding females conducted from 1995 to 2018 revealed an overall decline of 11.9% at an annual rate of 0.6%. However, contrasting trends before and after 2008 were observed. A decrease of 46.5% at an annual rate of 4.6% was registered before 2008, while for the subsequent period (2008–2018) the number of females increased by 64.5% at an annual rate of 5%. A positive association was observed between the extent of sea ice in winter foraging areas and population numbers between 1995 and 2008. The females of this colony feed on the edge of the sea ice, so in years of low sea ice extension the effort required to reach these areas is greater. This could lead individuals to choose to breed in areas closer to their feeding grounds in order to avoid the energetic expenditure of body reserves acquired during winter that would sustain the return trip to their natal colony.

eportamos el primer registro de una bandada de pato picazo ( Netta pep- osaca ) en Punta Elefante, Isla 25 de Mayo/King George, Islas Shetland del Sur, Antártida. Dicha localidad constituye, además, el avistamiento más austral para esta especie. Los ejem- plares fueron observados junto a dos individuos de pato overo ( Anas sibilatrix )

We report the first record of a flock of Rosy-billed Pochard ducks ( Netta pep- osaca ) in the Elephant Point, 25 de Mayo/King George Island, South Shetland Islands, Antarc- tica. This locality also represents the southernmost sighting for this species. The specimens were observed together with two individuals of the Southern Wigeon ( Anas sibilatrix ).

The analysis of blubber fatty acids (FAs) is a useful tool to infer diet of mammals that live in remote regions where year-round studies are difficult. The FA may not be distributed uniformly within the blubber, which can have implications for dietary predictive studies. The aim of this study was to determine the FA composition in the blubber core of the Antarctic leopard seal, Hydrurga leptonyx, and evaluate the potential implications of FA stratification for dietary analysis. The blubber cores of 24 seals were sub-sectioned into outer, middle and inner layers and their FA were compared to those of their potential prey species. A vertical variation in FA composition was found across the whole blubber core of the leopard seal. 17 FAs were found at greater than trace amounts (>0.5%) across all samples and the most abundant were: C18:1ω9, C16:1, C22:6ω3, C16:0 and C18:1ω7, which accounted for approximately 70% of the total FA. Almost all FAs had a continuous gradient through the blubber. Principal Component Analysis confirmed separation between inner and outer layers while the middle layer was a transition. The stratification of the leopard seal blubber was similar to the general pattern observed in a variety of marine species: monounsaturated FA (MUFA) dominated the three layers being more abundant in the outer layer, polyunsaturated (PUFA) and saturated FA (SFA) were more abundant in the inner layer. Polyunsaturated FAs are of dietary origin and SFAs are chemically inert so they can be used as a long-term reserve, which suggest that the inner layer is the site of deposition of the FA obtained from diet. The influence of prey on the composition of the leopard seals' blubber was clearer in the inner layer, although neither outer nor inner layers exactly matched the FA of the potential prey. This suggests that there are other components influencing the FA composition of this predator; therefore, in order to carry out dietary analysis it is important to consider the stratification of blubber and to use the inner layer, where the influence of diet is more evident. This has significant implications for sampling methods in the field.

We evaluated the diet of Adélie (Pygoscelis adeliae) and gentoo (P. papua) penguins at Stranger Point colony (25 de Mayo/King George Island) during different stages of their annual cycle using the stable isotope method and the conventional dietary analyses (i.e. stomach contents). Antarctic krill (Euphausia superba) dominated the diet of Adélie and gentoo penguins in all three studied stages (pre-breeding, breeding and post-breeding). Nevertheless, only in gentoo penguins a shift in the diet was evident from mainly krill during the breeding stage to mixed diet (i.e. krill and fish/squids) during the pre- and post-breeding stages. Results from stable isotopes suggest that Adélie penguins might be foraging in southern localities compared to their congener during the inter-breeding period. Moreover, Adélie penguins showed a large individual variability in foraging habitat during the post-breeding stage. However, our model has predicted that both species exploited similar areas during the breeding season. The results obtained during the chick-rearing stage were compared with the stomach contents of both species obtained during the same season (2011/2012). Our findings provide new knowledge on the feeding ecology and foraging habitats of pygoscelid penguins. They confirm the importance of Antarctic krill during the annual cycle and improve the understanding of life strategies and predator–prey interactions essentially out of the reproductive period, in which the information is very limited. These results can help to establish new management strategies, particularly considering the potential overlap between predators and fisheries.

Abstract The Adélie penguin (Pygoscelis adeliae) breeding population at Stranger Point, King George Island (25 de Mayo), increased in number from 1965/66 until 1980/81 after which it started to decrease almost continuously up to the present. A significant decrease in the number of breeding pairs and chicks crèched was observed between 1995/96 and 2013/14 (75% and 78%, respectively), although the rate of this decrease has slowed since 2006/07. Over the last seven years, larger interannual fluctuations were recorded in the number of breeding pairs and chicks in crèches, as well in the breeding success. The values for the index of breeding success during 2007/08, 2009/10 and 2012/13 were low and this parameter showed higher temporal fluctuation in the period 2007/08 to 2013/14. The reduction in breeding success and the number of chicks reared to crèche will unfavourably impact on future population size at Stranger Point through the reduction of new recruits. Although Adélie penguin population trends on the Antarctic Peninsula are linked to the marine environment variability (i.e. reduction in sea ice affecting the availability of prey), breeding success is also influenced by the amount of snow fall which has increased in recent years.

Southern elephant seals (Mirounga leonina) range widely throughout the Southern Ocean and are associated with important habitats (e.g., ice edges, shelf) where they accumulate energy to fuel their reproductive efforts on land. Knowledge of the fine scale foraging behaviour used to garner this energy, however, is limited. For the first time, acceleration loggers were deployed on three adult southern elephant seals during a translocation study at Kerguelen Island. The aims of the study were to (1) identify prey capture attempts using 2-D accelerometer tags deployed on the head of southern elephant seals, (2) compare the number of foraging dives identified by simple dive depth profiles and accelerometer profiles and (3) compare dive characteristics between prey encounter and non-prey encounter dives. The 2-D loggers recorded depth every second, surge and heave accelerations at 8 or 16 Hz and were carried for periods between 23 and 121 h. Rapid head movements were interpreted to be associated with prey encounter events. Acceleration data detected possible prey encounter events in 39–52% of dives whilst 67–80% of dives were classified as foraging dives when using dive depth profiles alone. Prey encounters occurred in successive dives during days and nights and lasted between tenths of a second and 7.6 min. Binomial linear mixed effect models showed that seals were diving significantly deeper and increased both descent rate and bottom duration when encountering prey. Dive duration, however, did not significantly increase during dives with prey encounters. These results are in accordance with optimal foraging theory, which predicts that deep divers should increase both their transit rates and the time spent at depth when a profitable prey patch is encountered. These findings indicate that this technique is promising as it more accurately detects possible prey encounter events compared with dive depth profiles alone and thus provides a better understanding of seal foraging strategies.

The aim of the present study was to enhance the knowledge of the feeding habits of the juvenile component of the population of Southern elephant seals [Mirounga leonina (Linnaeus, 1758)] from Isla 25 de Mayo, South Shetland Islands, age class whose diet information is scarce. A total of 60 individuals were stomach lavaged in the spring - summer seasons of three consecutive years (2003, 2004 and 2005) of which 53.3 % (n = 32) presented food remnants. The Antarctic glacial squid Psychroteuthis glacialis Thiele, 1921 was the dominant prey taxon in terms of frequency of occurrence (68.7%), numerical abundance (60.1%) and biomass (51.5%), contributing 84.1% to the total relative importance index. Other squid prey species of importance were Slosarczykovia circumantartica Lipinski, 2001 in terms of occurrence (37.5%) and numerical abundance (14%) and Moroteuthis knipovitchi Filippova, 1972 in terms of biomass (16%). All identified cephalopod prey taxa are distributed south of the Antarctic Polar Front, except for the squid Martialia hyadesi Rochebrune & Mabille, 1889 which has a circumpolar distribution associated to the Polar Frontal Zone. No significant differences in the sizes of P. glacialis preyed upon by elephant seals were found between sexes and years. However, significant interannual differences were found in the taxonomical composition of their diet. This would be associated with temporal changes in food availability at the foraging areas of seals, which in turn may have been influenced by changes in oceanographic conditions as a result of the El Niño Southern Oscillation (ENSO) phenomenon that occurred during part of the study period. Furthermore, a differential response of males and females to this temporal variation was observed, with the former being also associated to a predation on octopods. This would suggest a sexual segregation in foraging habits of this species from the early stages of its life cycle.

Rapid changes to climate in the western Antarctic Peninsula region over the last 50 yr, which have led to decreases in the extent and duration of sea ice, are likely to have significant impacts upon the Antarctic ecosystem as a whole. Understanding the behaviour of higher trophic level animals occupying these regions is important, as they may be indicators of changes in prey availability and food-web structure. Leopard seals Hydrurga leptonyx are important components of the Antarctic ecosystem, because they are widespread and adapted to consuming prey at a range of trophic levels. They rely on sea ice for breeding, moulting and as a resting platform. Using tracks of 12 leopard seals, we calculated first-passage times (indicative of the intensity of area-restricted behaviour) and quantified relative habitat use, including both foraging and resting areas, using Cox proportional hazard models, in relation to coastline, bathymetry and sea ice. We also correlated monthly home range size with monthly sea-ice extent. We found that when sea-ice extent was low, leopard seals were restricted to coastal habitat, but that this effect was lost when sea-ice extent was greater. This was supported by the finding that leopard seal home range size decreased as the sea-ice extent decreased. Since leopard seals and other animals that consume krill are likely to be increasingly limited by sea-ice cover if the warming trend continues, we suggest that the krill fishery be restricted to offshore areas to avoid conflict with krill predators.

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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.

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.