Alejandro R Carlini

Southern elephant seal movements and Antarctic sea ice

Weaned pups and post-moult female elephant seals (Mirounga leonina) were fitted with satellite transmitters at King George Island (South Shetland Islands) between December 1996 and February 1997. Of the nine adult females tracked for more than two months, three stayed in a localized area between the South Shetland Islands and the South Orkney Islands. The other six females travelled south-west along the coast of the Antarctic Peninsula up to the Bellingshausen Sea. Two of them then moved north-east and hauled out on South Georgia in October. One female was last located north of the South Shetland Islands in March 1998. In total, eight females were again sighted on King George Island and six of the transmitters removed. The tracks of the weaners contrasted with those of the adults. In January, five juveniles left King George Island for the Pacific sector spending about four weeks in the open sea west of the De Gerlache Seamounts. Three of them returned to the tip of the Antarctic Peninsula in June, of which one was last located on the Patagonian Shelf in November 1997. The juveniles avoided sea ice while the adults did not. The latter displayed behavioural differences in using the pack ice habitat during winter. Some females adjusted their movement patterns to the pulsating sea ice fringe in distant foraging areas while others ranged in closed pack ice of up to 100%. The feeding grounds of adult female elephant seals are more closely associated with the pack ice zone than previously assumed. The significance of the midwater fish Pleuragramma antarcticum as a potential food resource is discussed.

Fish prey of southern elephant seals, Mirounga leonina, at King George Island

Abstract. Between November and February in the years 1993/1994 to 1999/2000, 153 southern elephant seals, Mirounga leonina, were stomach lavaged at King George Island. Fish occurred in 16 of 108 stomachs containing food items. Myctophids were the dominant fish prey, contributing 76.6% of the 145 sagittal otoliths found. The most important prey species was Gymnoscopelus nicholsi, which constituted 69% of the otoliths and occurred in 75% of stomach samples. Next in importance was the nototheniid Pleuragramma antarcticum, which occurred in 31.3% of samples and represented 11.7% in numbers. We suggest that while myctophids may be the dominant fish prey of elephant seals in areas close to King George Island, they are probably replaced by P. antarcticum as seals migrate towards higher latitudes where this fish is extremely abundant.

Responses of Pygoscelis adeliae and P. papua populations to environmental changes at Isla 25 de Mayo (King George Island)

As part of a monitoring study of Adélie and Gentoo penguin colonies, birds occupying nests with eggs and chicks in crèches were counted annually from the 1995/1996 to the 2006/2007 seasons at Stranger Point, Isla 25 de Mayo (King George Island), Antarctica. During the study period the Adélie penguin population showed a decrease of 62%. The number of chicks in crèches followed a similar trend, the smallest number occurring in 2002, when it was 63% lower than in 1995/1996. In contrast, the Gentoo breeding population size increased by 68%, while chicks produced increased by 63%. Despite the opposing trends in population size between species, there was a positive relation in their interannual variation, although the extent, and for some years the direction, of the change observed always favoured Gentoo penguins. Breeding success (chicks in crèches/nests with eggs) fluctuated between 0.65 and 1.26 for Adélies and between 0.76 and 1.27 for Gentoo penguins, and did not differ significantly between species. The similar breeding success of these species suggests that the contrasting population trends observed were driven by factors operating over winter. We suggest that current changes in environmental conditions may affect adult birds of both species during the previous winter with different intensity but in a roughly similar way, but that juvenile survival of both species and thus the recruitment of new breeders might be affected differentially, with a much lower survival rate of juvenile Adélie penguins.

Geographical variation in the diet of the Antarctic fur seal Arctocephalus gazella

The diet of non-breeding male Antarctic fur seals Arctocephalus gazella was investigated at different localities of the Antarctic Peninsula (Cierva Point and Hope Bay), South Shetland Islands (Deception Island and Potter Peninsula) and the South Orkney Islands (Laurie Island), by the analysis of 438 scats collected from January to March 2000. The composition of the diet was diverse, with both pelagic and benthic-demersal prey represented in the samples. Antarctic krill Euphausia superba was the most frequent and numerous prey at all the study sites except at Cierva Point, followed by fish, penguins and cephalopods. Antarctic krill also predominated by mass, followed by either fish or penguins. Fish were the second most important prey by mass at the Antarctic Peninsula whereas penguins were the second most important prey by mass at the South Shetland and South Orkney Islands. Among fish, Pleuragramma antarcticum was the most important species in the diet of the Antarctic fur seals at the Antarctic Peninsula whereas Gymnoscopelus nicholsi predominated at the South Shetland and South Orkney Islands. The results are compared with previous studies, and the possibility of implementing monitoring studies on the distribution/abundance of myctophids and P. antarcticum based on the analysis of the diet of the Antarctic fur seal is considered.

Cephalopod diet of the southern elephant seal, Mirounga leonina , at King George Island, South Shetland Islands

In the summer of 1995/96, 25 southern elephant seals, Mirounga leonina, were stomach lavaged at Stranger Point, King George Island, South Shetland Islands. Cephalopod remains were present in 72% of the individuals sampled (n = 18). Seven species of squid and three of octopus were identified. The squid Psychroteuthis glacialis was the most important prey in terms of numbers (77%), biomass (80.8%) and frequency of occurrence (94.4%). Next in importance in terms of mass was the squid Alluroteuthis antarcticus (7.8%) in the diet of females and the octopodid Pareledone ?charcoti in the diet of males (13.2%). Females preyed on a wider variety of squid taxa than males (7 vs 3) but octopodids occurred only in stomach contents from males. The predominance of P. glacialis in the prey of the South Shetland Islands elephant seals can be explained by the southerly location of the foraging areas of this population compared to South Georgia, Heard and Macquarie islands, where the diet of southern elephant seals has previously been analysed. Psychroteuthis glacialis is the predominant squid in waters close to the Antarctic continent.

The diet of the Antarctic fur seal Arctocephalus gazella at Harmony Point, Nelson Island, South Shetland Islands

Abstract The diet of non-breeding male Antarctic fur seals (Arctocephalus gazella) was investigated at Harmony Point, Nelson Island, South Shetland Islands, by the analysis of 18 and 33 scats collected during February 1996 and 1997 respectively. Overall, fish were the most frequent prey (74.5%) and predominated by mass (54.4%), whereas krill predominated by number (94.2%). This coincides well with the pattern observed in 1997, but in 1996 krill was the most important prey by number and mass (50.2%). The importance of the remaining taxa represented in the samples (octopods, hyperiids and bivalves) was negligible. Among fish, myctophids represented 85.2% of the fish mass, with Gymnoscopelus nicholsi and Electrona antarctica being the main prey. These two species predominated in 1997, whereas the channichthyid Cryodraco antarcticus and the nototheniid Gobionotothen gibberifrons were dominant in 1996. The importance of the myctophids as prey of the Antarctic fur seal is discussed.

Mass transfer from mothers to pups and mass recovery by mothers during the post-breeding foraging period in southern elephant seals (Mirounga leonina) at King George Island

Abstract Mass transfer from mother to pup during the lactation period, and mass recovery for the same females during the foraging period were measured in the southern elephant seal at King George Island, Antarctica. During the 19.2 ± 0.9-day lactation period measured (which represented 87% of the entire nursing), females lost a mean mass of 10.56 ± 1.76 kg/day (n = 27), while their pups gained a mean mass of 5.27 ± 1.1 kg/day. There was a correlation between daily body weight gain in pups and daily weight loss by their mothers. Pup weaning mass was positively related to maternal post-partum mass. Serial samples showed that weight losses by females and gains by their pups were not linear over lactation, but showed lower values at the beginning and at the end of lactation. During the 60.5 ± 6.2-day foraging phase between the end of lactation and molt, females gained 2.21 ± 0.65 kg/day (n = 12), or 54% of the mass lost during nursing. Growth rates reported here are higher than those reported in other breeding sites. However, the ratio of body mass loss by females to gain by their pups was similar, suggesting that higher growth rates and greater weaning mass at South Shetland are due to a higher mean weight of females on arrival at this breeding site. The foraging period was shorter and the mass gained greater than those measured at South Georgia; this could be related to relatively shorter distances to foraging areas.

Adult male southern elephant seals from King George Island utilize the Weddell sea

Abstract Adult male southern elephant seals instrumented in 2000 on King George Island (n = 13), travelled both to the north (n = 2) and to the east (n = 6) of the Antarctic Peninsula. Five males remained within 500 km of the island focusing movements in the Bransfield Strait and around the Antarctic Peninsula. Sea surface temperatures encountered by these animals showed little variation. While animal trajectories appeared unaffected by sea ice cover, areas of shallow depths were frequented. Three males moved as far as 75°S to the east of the Peninsula with maximum distances of more than 1500 km from King George Island. They travelled into the Weddell Sea along the western continental shelf break until they reached the region of the Filchner Trough outflow. Here the sea floor consists of canyons and ridges that support intensive mixing between the warm saline waters of the Weddell Gyre, the very cold outflow waters and ice shelf water at the Antarctic Slope Front. The need for re-instrumentation of adult males from King George Island is highlighted to investigate whether males continue to travel to similar areas and to obtain higher resolution data.

Predation on cephalopods by Antarctic fur seals, Arctocephalus gazella, at two localities of the Scotia Arc, Antarctica

Abstract The cephalopod remains from 206 Antarctic fur seal (Arctocephalus gazella) scats collected at Mossman Peninsula, South Orkney Islands (n = 105) and at Stranger Point, South Shetland Islands (n = 101) contained 148 beaks (57 lower and 91 upper). The lower beaks were sorted and measured. Identification of 33 of the lower beaks that were collected at Mossman Peninsula revealed two squid species, Brachioteuthis ?picta (n = 26) and Psychroteuthisglacialis (n = 7), with lower rostral lengths (LRL) of 2.0–3.5 mm, and 1.0–2.5 mm, respectively. Identification of 15 of the lower beaks collected at Stranger Point revealed the same squid species, with the LRL of B. ?picta ranging from 3.0–3.4 mm (n = 9), and that of P. glacialis from 2.0 to 3.5 mm (n = 6). Estimated squid sizes and wet masses indicate that Antarctic fur seals feed on the small sub-adult squid which inhabit the surface layers. We have compared the squid diet estimated for the seals with that reported for its congeners in lower latitudes and other Antarctic seals, and conclude that cephalopods do not form an important food resource for Antarctic fur seals.

The diet of the Weddell seal Leptonychotes weddelli at Harmony Point, South Shetland Islands

Abstract A total of 41 faeces and 5 vomits of the Weddell seal Leptonychotes weddelli was collected at Harmony Point, Nelson Island, South Shetland Islands, from 14 January to 1 February 1996. The diet indicated by the remains in the samples was diverse and comprised both pelagic and benthic-demersal species. Fish were the most frequent (95.7%) and numerous prey (46.2%), but molluscs were the most important by mass (65.8%). Octopods, mainly Pareledone charcoti, constituted the bulk of the diet (63.1% by mass), but the importance of the remaining molluscs was negligible. Otoliths represented 510 fish of which 491 were identified as belonging to 5 species: Gymnoscopelus nicholsi, Electrona antarctica, Lepidonotothen nudifrons, Gobionotothen gibberifrons and Nototheniops nybelini. The myctophid Gymnoscopelus nicholsi was the most important fish prey, and the contribution of benthic-demersal species was low. However, the importance of that fish was over-estimated since 96% of the specimens were obtained from the five vomits analysed. The biases associated with the faecal analysis technique are discussed.