Harmony Point Research Articles

Aspects of the foraging behaviour of the Antarctic Tern Sterna vittata gaini at Harmony Point, South Shetland Islands

During January and February of 2002 and 2003, we studied the diet of the Antarctic Tern Sterna vittata gaini at two colonies in Nelson Island, South Shetland Islands, by identifying the prey fed to chicks by breeders. The fish Notothenia coriiceps was the main prey in both seasons, followed by the myctophid Electrona antarctica, Antarctic krill Euphausia superba and gammarid amphipods. The contribution of fish to the diet increased as chicks grew older. Fish and amphipods were brought to chicks during the day, whereas adults brought Antarctic krill at sunrise and sunset. Both the duration of the feeding trips and the number of trips per foraging bout varied according to the type of prey caught. Preliminary information suggests that, among other causes, the foraging strategy is strongly influenced by the predation pressure of skuas on chicks. Results are compared with the only two previous study on the diet of the Antarctic Tern at the South Shetland Islands.

The diet of the Antarctic fur seal Arctocephalus gazella at Harmony Point, South Shetland Islands: evidence of opportunistic foraging on penguins?

The analysis of 523 scats collected at Harmony Point, Nelson Island, South Shetland Islands, from January to March in 2001 and 2002, indicated that the diet of non-breeding male Antarctic fur seals Arctocephalus gazella was diverse and composed of both pelagic and benthic-demersal prey. Overall, the Antarctic krill Euphausia superba and fish were the most frequent and numerous prey, followed by penguins, cephalopods (mainly squid) and gastropods. Myctophids represented 86.5% and 65.8% of the fish mass in 2001 and 2002 respectively, with Gymnoscopelus nicholsi being the main prey. Interestingly, penguin remains were present in 39.0% and 31.9% of the samples in 2001 and 2002, respectively and these birds were the main prey by reconstituted mass (74.0% and 76.1% in both seasons). The occurrence of penguins in the diet of A. gazella at Harmony Point is discussed in terms of the foraging strategy employed by seals and the temporal availability of prey.

SEX DIFFERENCES IN DIVING DEPTHS AND DIET OF ANTARCTIC SHAGS AT THE SOUTH SHETLAND ISLANDS

Abstract Sexual differences in maximum diving depths and in the composition of the diet of the Antarctic Shag (Phalacrocorax bransfieldensis) were investigated at Harmony Point, Nelson Island, South Shetland Islands, Antarctica, during the 1995–1996 and 1996–1997 breeding seasons. The mean maximum diving depth estimated by the capillary-tube depth gauge technique was 37.8 m which, when compared with other studies, reflects good food availability in shallow waters around Harmony Point. Females dived significantly deeper than males and also reached the maximum dive depth registered (112.6 m). The analysis of the stomach contents recovered when the individuals with capillary-tubes returned to the nest from foraging trips indicated that males ingested almost exclusively large Notothenia coriiceps specimens, whereas females preyed more intensively on smaller fish. The differences observed suggest that individuals of both sexes partitioned foraging depths and food resources.

Diet of Cape PetrelDaption capenseChicks on South Shetland Islands, Antarctica

The diet of the Cape Petrel was investigated in two localities of South Shetland Islands, Antarctica, over the period January—February 1996. Stomach contents of adults obtained by flushing and regurgitates of chicks were sampled during the chick-rearing period. During the whole sampling period, euphausiids represented the predominant prey in terms of frequency of occurrence, mass and number at Fildes Peninsula, while at Harmony Point, euphausiids and fish components were found in similar proportions in terms of mass and frequency. Myctophiids fish, in particular Electrona antarctica, formed the bulk of the fish component. The analysis of the diet throughout the breeding season showed significant differences in number and mass of the prey items at Fildes Peninsula, while at Harmony Point, there were significant differences also in the occurrence of preys. Considering both localities, although the occurrence of the prey did not vary significantly during the brooding period, there were significant differences in their number and mass. Similar results were found in the post-brooding period between both localities.

Sexual Size Dimorphism in the Antarctic Shag

-Analysis of the morphology of 141 Antarctic Shags (Phalacrocorax bransfieldensis) breeding at Harmony Point (62017'S, 59014'W), South Shetland Islands, and 85 at Danco Coast (64009'S, 60057'W), Antarctic Peninsula, indicated that males are significantly heavier and larger than females. However, there are overlaps in the morphometric variables (mass, culmen, bill, tarsus and wing length, and bill depth and width) between sexes. Two discriminant functions correctly classified 97.8% and 97.6% of the males and females considered to generate them. When the validity of the discriminant functions was checked on other Antarctic Shags breeding at Harmony Point and at Danco Coast, the rate of correct classification remained high. These discriminant functions could be used to sex chicks older than 45-50 days and juveniles. Received 17 November 1999, resubmitted 4 May 2000, accepted 8 May 2000.

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

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.

Lanternfish (Myctophidae) in the diet of the Cape petrel Daption capense at the South Shetland and South Orkney Islands, Antarctica

All of the fish identified in stomach contents and regurgitations of breeding and chick Cape petrels collected during January and February 1996 at Fildes Peninsula and Harmony Point, both in the South Shetland Islands and at Laurie Island, South Orkney Islands, were myctophids, a family never previously reported in the diet of breeding Cape petrels. Electrona antarctica was the most important fish prey, followed by Electrona carlsbergi at Fildes Peninsula, Krefftichthys anderssoni at Harmony Point and Gymnoscopelus braueri at Laurie Island. The absence of Pleuragramma antarcticum in the diet of this petrel, which is considered a P. antarcticum-feeder, is discussed.

The contrasting diet of Harpagifer antarcticus (Notothenioidei, Harpagiferidae) at two localities of the South Shetland Islands, Antarctica

The diet of Harpagifer antarcticus was studied at two localities of the South Shetland Islands, Antarctica. The analysis of the stomach contents of specimens collected in tide pools at Potter Cove, King George Island, indicated that gammarid amphipods (mainly Gondogeneia sp.) were the main prey of this fish, followed by polychaetes, gastropods and isopods. By contrast, the specimens from Harmony Point, Nelson Island, which were recovered from stomach contents of Antarctic shags Phalacrocorax bransfieldensis feeding at depths of 46–110 m, preyed almost exclusively on the Antarctic krill Euphausia superba. These results are discussed and compared with previous studies.

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

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.