Fish in the diet of the Antarctic shag Phalacrocorax bransfieldensis at Laurie Island, South Orkney Islands

The analysis of 29 stomach contents collected from a colony close to Pirie Peninsula, South Orkney Islands, from 2 January to 18 February 1995, showed that fish were by far the most important prey of the Antarctic shag Phalacrocorax bransfieldensis, followed by octopods, decapods and gammarids. The fish Notothenia coriiceps constituted the bulk of the diet; however, its importance decreased by the end of the study when Lepidonotothen nudifrons was the most important prey. The composition of the stomach contents varied throughout the breeding season according to changes in the chicks' energetic demands; as chicks grew older the adults increased the mass of the loads carried to the nests, preying on larger fish, a phenomenon also observed at the South Shetland Islands. Received: 3 July 1996 / Accepted: 9 March 1997     

The diet of the Antarctic fur seal <Emphasis Type="Italic">Arctocephalus gazella</Emphasis> at the South Orkney Islands in ten consecutive years

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 diet of the Weddell seal <Emphasis Type="Italic">Leptonychotes weddellii</Emphasis> at Laurie Island,South Orkney Islands

The diet of the Weddell seal Leptonychotes weddellii at the South Orkney Islands was investigated by the analysis of 44 and 26 faecal samples collected from the beaches of Laurie Island from May 1999 to January 2000 and from October to December 2001, respectively. The diet was diverse and both pelagic and benthic-demersal organisms were represented in the samples. Fish were the most frequent prey of the samples in both seasons, and fish and krill were the most numerous prey items. Octopods predominated by mass in 1999, whereas krill constituted the bulk of the diet in 2001, a fact that was not observed previously. Among fish, Gobionotothen gibberifrons was largely the species that contributed mostly to the diet, whereas pelagic fish could not be identified in the samples. The results are compared with information from other study areas and discussed in relation to the consumption of krill.     

Triacylglycerol lipase activities in tissues of Antarctic fishes

. The activity of the lipolytic enzyme, triacylglycerol lipase (TAG lipase; E.C. 3.1.1.3) was measured in heart ventricle, liver, oxidative skeletal muscle, and adipose tissue of four species of Antarctic fishes (Chaenocephalus aceratus, Notothenia coriiceps, Trematomus newnesi, Gobionotothen gibberifrons). Estimates of weight-specific activities at 0°C in tissues of the Antarctic fishes were broadly comparable to those reported for temperate-zone fish species assayed at their physiological temperature. Within each species, liver tissue displayed the highest weight-specific activity of TAG lipase in C. aceratus, T. newnesi, and G. gibberifrons, while adipose tissue of N. coriiceps showed the highest activity within that species. Combining these estimates with carefully measured somatic indices of the tissues, permitted assessment of the relative importance of different tissues to overall lipolytic capacity on an organismal level. On this basis, liver tissue displays the greatest capacity of TAG lipase per 100 g body weight in each of the species studied.     

Morphology and diet are decoupled in nearshore notothenoids from King George Island,West Antarctica

Antarctic notothenioid fishes show wide adaptive morphological radiation, linked to habitat preferences and food composition. However, direct comparisons of phenotypic variability and feeding habits are still lacking, particularly in stages inhabiting nearshore areas. To assess these relationships, we collected juveniles and adults of the most common benthic species inhabiting shallow waters off the South Shetland Islands within a similar size range, the plunderfish Harpagifer antarcticus, the black rockcod Notothenia coriiceps, and the marbled rockcod Notothenia rossii. Individual size ranges varied from 44.0 to 98.9 mm standard length (LS) (H. antarcticus), from 95.8 to 109.3 mm LS (N. coriiceps), and from 63.0 to 113.0 mm LS (N. rossii). Notothenioid fish showed different morphospace variability, being larger for H. antarcticus than the other Notothenia species and associated with the position of the posterior end of the operculum, along with the location and relative size of the eye. The evolutionary allometry was low, but the static allometry was much higher, especially for H. antarcticus and N. rossii. The diet was mainly carnivorous, consisting of amphipods and euphausiids. Macroalgae were scarce or totally absent in the gut contents of all species. Only H. antarcticus showed an increase in the prey number and ingested prey volume with fish size. Finally, there was a significant covariation between shape changes and LS in all species (allometric effects), however, not with prey composition, probably due to the small size range or ontogenetic stage and the relative similarity (or lack of contrast) in the benthic environment that they utilized.     

The biology of the icefish Cryodraco antarcticus Dollo, 1900 (Pisces, Channichthyidae) in the southern Scotia Arc (Antarctica)

The icefish Cryodraco antarcticus is common in deeper waters of the southern Scotia Arc and the high-Antarctic zone. A number of biological features of this species are presented, with new information collected from recent scientific surveys of the South Shetland Islands and South Orkney Islands. The species is closely related to Chaenocephalus aceratus, but can be distinguished by a number of meristic characters. The two species are similar in size, colouration and body shape, and have a number of aspects of their life-cycle in common, such as reproduction, length-weight relationship and diet. These two species appear to occupy a very similar niche in the southern Scotia Arc ecosystem. However, Cryodraco antarcticus is less abundant and uses different spatial components of shelf areas, replacing Chaenocephalus aceratus in deeper water and high-Antarctic regions.     

A predatory fungus (Hyphomycetes: <Emphasis Type="Italic">Lecophagus</Emphasis>) attacking Rotifera and Tardigrada in maritime Antarctic lakes

Lecophagus antarcticus, described as a new species of predaceous Hyphomycete of rotifers and tardigrades, was collected from cyanobacterial mats and sediments at shallow lake margins on Signy Island, South Orkney Islands, Antarctica. The new species differs from similar Lecophagus species by larger, more robust vegetative hyphae and by producing septate conidiophore branches or conidiophores as terminals of lateral vegetative hyphae. This is the first report of this genus from either freshwater or polar regions.     

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. Received: 27 August 1997 / Accepted: 17 November 1997     

Seasonal and annual variation in the diet of breeding and non-breeding Wilson's storm-petrels on King George Island, South Shetland Islands

The diet of breeding and non-breeding Wilson's storm-petrels (Oceanites oceanicus) was analysed over four breeding seasons on King George Island, South Shetland Islands, in order to test if there are changes in diet composition within and between seasons. Krill was the most important food item, followed by myctophid fish and amphipods. Breeding birds showed a clear seasonal pattern of diet, with krill decreasing and alternative prey increasing from the incubation to the chick-rearing period. Non-breeders were not found to change their diet composition. The data suggest that Wilson's storm-petrels selectively choose alternative prey to krill in order to meet the nutrient demands of their chicks. In years of low food availability, Wilson's storm-petrels may have a limited option of prey choice.     

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, 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. Received: 7 October 1997 / Accepted: 24 May 1998     

Geographical variation in the diet of the Antarctic fur seal<Emphasis Type="Italic"> Arctocephalus gazella</Emphasis>

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.     

Measurements of buoyancy for some Antarctic notothenioid fishes from the South Shetland Islands

Buoyancy was measured for 258 specimens representing 13 species of adult and sub-adult nototheniids, bathydraconids, and channichthyids from the South Shetland Islands. Measurements were expressed as percentage buoyancy (%B)=W_water/W_air᎒². There were no neutrally buoyant species and mean values for %B were 3.07-6.11%, with channichthyids at the low end and benthic nototheniids and bathydraconids at the high end. All species showed an ontogenetic decrease in %B with increasing body weight. With the exception of Champsocephalus gunnari, there was no sexual dimorphism in %B within this sample. With some exceptions, values for %B were consistent with life-history information. Sub-adult Dissostichus mawsoni were not neutrally buoyant, as are large adults. Notothenia rossii had a significantly lower %B than closely related N. coriiceps. Benthic Gobionotothen gibberifrons had a lower %B than semipelagic Lepidonotothen larseni. Although they exhibit some diversification in life history, the four channichthyids in the sample were similar in %B. Neutral buoyancy is rare in notothenioids and may be confined to a single nototheniid clade.     

Comparison of lipid content and fatty acid composition in muscle and liver of two notothenioid fishes from Admiralty Bay (Antarctica): an eco-physiological perspective

During Antarctic summer, total lipids (g/100 g dry matter) in Notothenia coriiceps (n=18) and Lepidonotothen nudifrons (n=10) were low (6.1 and 4.7 in muscle), which is typical of Antarctic benthic species. The liver of female N. coriiceps was heavier and contained more lipids per dry weight than the liver of males. The fatty acid composition of N. coriiceps and L. nudifrons was dominated by polyunsaturated fatty acids (PUFA, respectively, 44 and 49% of total fatty acids in muscle, 31 and 46% in liver), which included primarily C20:5n-3 (18 and 19% in muscle, 13 and 18% in liver) and C22:6n-3 (15 and 19% in muscle, 12 and 20% in liver). In L. nudifrons, the levels of some unsaturated fatty acids increased with age and size. The high percent unsaturation (PUFA+MUFA, 78 and 80% in muscle, 82 and 80% in liver) is a response to low water temperature (-0.4°C). Fish fatty acid profiles reflect fatty acid profiles of the diet (amphipods, macroalgae and fish).     

Diversity, relative abundance, new locality records and population structure of Antarctic demersal fishes from the northern Scotia Arc islands and Bouvetøya

A primary objective of the ICEFISH 2004 cruise was to collect and study notothenioid fishes from remote localities in the Atlantic sector of the Southern Ocean. Nearly 1 month was devoted to bottom trawling for fishes on the shelf and upper slope (to 1,000 m) areas around Shag Rocks, South Georgia, South Sandwich Islands and Bouvetøya. The focus was on the latter two locations, because their faunas are more poorly known. Eight species were collected at Shag Rocks with Patagonotothen guntheri most abundant; 17 at South Georgia with Lepidonotothen nudifrons, L. larseni and Gobionotothen gibberifrons most abundant; 13 at the South Sandwich Islands with L. larseni, L. nudifrons and G. gibberifrons most abundant; and 11 at Bouvetøya with L. larseni, Macrourus holotrachys and L. squamifrons most abundant. Ten new locality records were established: Shag Rocks (1), South Georgia (1), South Sandwich Islands (5), South Sandwich Trench at 5,350 m (1) and Bouvetøya (2). Total known demersal fish diversity on the shelf and upper slope at Shag Rocks/South Georgia, South Sandwich Islands and Bouvetøya is 42, 31 and 17 species, respectively. To examine population structure in the four most abundant notothenioids at Bouvetøya (L. larseni, L. squamifrons, Notothenia coriiceps and Chaenocephalus aceratus), we examined the ND2 portion of mitochondrial DNA. Chaenocephalus aceratus, N. coriiceps and L. larseni exhibited no significant genetic differentiation in comparison with samples from localities in the Scotia Sea and the Antarctic Peninsula. However, L. squamifrons showed significant genetic differentiation between the South Shetlands and Bouvetøya populations (F _ST = 0.189, P = 0.015). Thus, these data combined with previous studies of two other notothenioids suggest that five of the six notothenioid species at Bouvetøya are not genetically differentiated from other localities in the Atlantic sector of the Southern Ocean. The location of Bouvetøya within the Antarctic Circumpolar Current and the long (1–2 years) pelagic stages of the notothenioids at Bouvetøya may be at least partly responsible for this genetic homogeneity.     

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. Received: 3 July 1996 / Accepted: 2 June 1997     

Comparative study of the effects of the late pack-ice break-off on chinstrap and Adélie penguins' diet and reproductive success at Laurie Island,South Orkney Islands,Antarctica

The effects of ice cover on diet and breeding chronology of Adélie (Pygoscelis adeliae) and chinstrap penguins (P. antarctica) were studied in the colonies located at Point Martin, South Orkney Islands. Reproductive success and diet parameters were measured as described in the CCAMLR Environmental Monitoring Program protocols. It was found that late pack-ice break-off in 1998 resulted in lower reproductive success than in 1999 for chinstrap penguins, while Adélie penguin parameters were rather insensitive. This species has shown to be able to cope with this environmental factor, as suggested by its circumpolar and more southerly range. Significant differences in stomach contents' weights and in the proportion of whole krill were found between ice-covered and open-sea periods within and between years. Foraging trips of both species became longer, resulting in underfeeding of chicks and nest desertion by chinstrap-penguin parents. Simultaneous analysis of reproductive parameters of both species and their diets have proven to be useful in discriminating between variation in reproductive success parameters due to prey accessibility and prey abundance.     

Dietary overlap among early juvenile stages in an Antarctic notothenioid fish assemblage at Potter Cove,South Shetland Islands

To date, studies of food overlap in Antarctic fish have been performed on a mixture of late juvenile and adult stages, leaving the young immature specimens (TL ≤ 10 cm) practically unexplored. We studied diet overlap and potential competition among early juvenile individuals in a coastal notothenioid community at Potter Cove, by analysing the stomach contents of 225 fish of 5 species collected in the summer of 2009–2010. We used frequency of occurrence (F %) and the coefficient “Q” for diet evaluation and the method of Tyler and the similarity index “S” for food overlap. Amphipods of the suborder Gammaridea were the main (Q > 2.900) and most frequent (% F) prey for all species, although Notothenia coriiceps also consumed gastropods of the family Littorinidae, mostly Laevilitorina antarctica. Secondary prey were algae for Notothenia rossii and N. coriiceps, calanoid (pelagic) and harpacticoid (benthic) copepods for Trematomus newnesi and the latter copepods and isopods of the family Munnidae for Lepidonotothen nudifrons. The reoccurrence of prey among fish species was 39.6 % and food overlap between 90 % of species pairs was under 58 %. Because similarly low values of diet overlap were reported for intermediate/advanced juveniles and adults of the same species at the same site, we conclude that there is no difference in the degree of interspecific food overlap and therefore potential competition between the immature and mature fraction of the fish community. Food competition is avoided by resource partitioning along a depth gradient or by different prey species.     

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. Received: 22 December 1997 / Accepted: 6 June 1998     

Inter-annual variability in Chinstrap penguin diet at South Shetland and South Orkneys Islands

Inter-annual variability in the diet of Chinstrap penguins (Pygoscelis antarctica) at Laurie Island (South Orkney Islands) and 25 de Mayo/King George and Nelson Islands (South Shetland) was examined based on stomach contents of adults during the 2002/2003–2006/2007 and 2002/2003–2004/2005 breeding seasons, respectively. Krill (Euphausia superba) dominated the diet as frequency of occurrence (in 100% of samples), number (>99%), and percentage contribution in weight (>94.8%). Other prey items were minor and varied between years. The weight of stomach contents was significantly different. The percentage in weight of whole krill was used to compare the feeding conditions across seasons. It differed significantly at the three sites studied. Distribution of krill size varied among years and localities, showing different krill availability for penguins.