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.     

How important are pelagic preys for the kelp gull during chick-rearing at the South Shetland Islands?

An analysis of pellets regurgitated indicated adult kelp gulls (Larus dominicanus) on the South Shetland Islands consumed predominantly intertidal prey, whereas previous studies at Antarctic Peninsula sites have reported kelp gulls consuming predominantly pelagic species. The pellets collected at Nelson Island during the chick-rearing period indicated that the limpet Nacella concinna was their most frequent prey, followed by carrion, gammariids, snails and krill. Fish were scarcely represented. Also, regurgitated stomach contents of chicks showed that limpets and carrion were the most frequent food items, accounting for 70% of the mass. However, gammariids were particularly important by number. Significant differences were observed in the overall comparison of the diet as reflected by the two sampling methods. In general, the importance of pelagic prey was negligible when compared to intertidal or scavenged prey. Our results differ greatly from those reported for the Antarctic Peninsula, where chicks were almost exclusively fed with the pelagic fish Pleuragramma antarcticum. These differences could be related to the abundance of pelagic resources in southernmost latitudes, and/or to the presence of more extensive intertidal foraging areas at the South Shetland Islands. Received: 7 October 1996 / Accepted: 14 July 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.     

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     

Penguins, fur seals, and fishing: prey requirements and potential competition in the South Shetland Islands, Antarctica

Antarctic and sub-Antarctic seabirds, marine mammals, and human fisheries concentrate their foraging efforts on a single species, Antarctic krill (Euphausiasuperba). Because these predators may have a significant effect on krill abundance, we estimated the energy and prey requirements of Adelie (Pygoscelisadeliae), chinstrap (Pygoscelisantarctica), and gentoo (Pygoscelispapua) penguins and female Antarctic fur seals (Arctocephalusgazella) breeding on the South Shetland Islands, Antarctica and compared these estimates with catch statistics from the Antarctic krill fishery. Published data on field metabolic rate, population size, diet, prey energy content, and metabolic efficiency were used to estimate prey requirements of these breeding, adult, land-based predators and their dependent offspring. Due to their large population size, chinstrap penguins were the most significant krill predators during the period examined, consuming an estimated 7.8 × 10⁸ kg krill, followed by Adelie penguins (3.1 × 10⁷ kg), gentoo penguins (1.2 × 10⁷ kg), and Antarctic fur seals (3.6 × 10⁶ kg). Total consumption of all land-based predators on the South Shetland Islands was estimated at 8.3 × 10⁸ kg krill. The commercial krill fishery harvest in the South Shetland Island region (1.0 × 10⁸ kg) was approximately 12% of this. Commercial harvest coincides seasonally and spatially with peak penguin and fur seal prey demands, and may affect prey availability to penguins and fur seals. This differs from the conclusions of Ichii et al. who asserted that the potential for competition between South Shetland predators and the commercial krill fishery is low. Received: 26 August 1997 / Accepted: 16 December 1997     

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     

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.     

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     

Inter-sexual differences in Antarctic fur seal pup growth rates: evidence of environmental regulation?

We investigated the variation of Antarctic fur seal (Arctocephalus gazella) pup growth rates in response to sex, breeding season and duration of both maternal foraging trip and attendance bouts. Data were collected during five consecutive rearing seasons at Cape Shirreff, the most important breeding colony in the South Shetland Islands, Antarctica. Our results showed significant interannual and sexual variations in pup growth rates. Male pups grew significantly faster than female pups during 2000, 2001, 2002 and 2004 seasons, whilst during 2003 no difference was found. The interannual variation in pup growth rates was correlated with the interannual fluctuation in maternal foraging trip and attendance bouts. There was a significant effect of pup sex and maternal foraging trip duration on pup growth rates, which varied between years having foraging trip duration a major effect during 2003, when females spent more time at sea and interestingly on that year there were no sexual differences in pup growth rates. The effect of attendance bout on pup growth rates was not significant. Diet analysis showed that Antarctic krill (Euphausia superba) was the most frequent prey item during the study period. Analysis of krill size distribution showed a significant difference in krill length, during 2003, when A. gazella preyed upon the smallest sizes of krill. In this study, sex was the most important factor on pup growth rates, but when prey availability seemed more limited, there are longer foraging trips and shorter attendance bouts the sex factor became less significant.     

Diet of Antarctic fur seals Arctocephalus gazella at the Danco Coast,Antarctic Peninsula

The diet of non-breeding male Antarctic fur seals, Arctocephalus gazella, was investigated at the Danco Coast, Antarctic Peninsula, by the analysis of 31 and 149 scats collected from January to March 1998 and 2000, respectively. Overall, fish and krill, followed by penguins and squids, were the most frequent prey and constituted the bulk of the diet. The importance of the remaining taxa represented in the samples (octopods, gastropods, bivalves, isopods, polychaetes and poriferans) was negligible. Among fish, channichthyids constituted the bulk of the diet, with Chionodraco rastrospinosus and Chaenodraco wilsoni, followed by the nototheniid, Pleuragramma antarcticum, being the main prey. The myctophid, Electrona antarctica, was the most frequent and numerous fish prey. The results are discussed and compared with those reported for the South Shetland Islands, the closest area for which similar information is available.     

Diet and diving behaviour of European Storm Petrels Hydrobates pelagicus in the Mediterranean (ssp. melitensis)

Capsule Unlike Atlantic populations, which feed on krill, Mediterranean populations feed mainly on pelagic fish Gymnammodites cicerellus.

Aims To determine the diet and dive depth of the Mediterranean subspecies of European Storm Petrels Hydrobates pelagicus melitensis.

Methods Analysis of regurgitates of adults arriving at the colony for chick feeding and by determination of dives depth using the capillary tube method.

Results The main prey is Gymnammodites cicerellus, a pelagic fish. Storm Petrels dive for their prey and can reach up to 5 m in depth. They also make short foraging trips just outside the colony where they capture Opossum Shrimps Misydacea.

Conclusions European Storm Petrels in the Mediterranean exploit pelagic fish which are taken by diving. This contrasts with the Atlantic populations which feed mainly on krill. Mediterranean birds also feed on Opossum Shrimps Mysidacea during short foraging trips made at night just outside the colony. Differences in diet between long and short foraging trips may be because adults have to forage for both themselves and their chicks.     

Diet of the Antarctic starry skate Amblyraja georgiana (Rajidae, Chondrichthyes) at South Georgia (Southern Ocean)

Stomach contents were identified from 206 Antarctic starry skate (Amblyraja georgiana) that were collected during three groundfish surveys (September 2007, April 2008 and January 2009) at South Georgia, Southern Ocean. The diet of A. georgiana varied with skate size and between years. Preferred prey included fish (particularly for larger individuals) and Antarctic krill, Euphausia superba, as well as amphipods, polychaetes and other benthic fauna. The skate A. georgiana appears to be an opportunistic predator, and the clear presence of Antarctic krill in this demersal predator’s diet may indicate a benthic habit of this euphausiid species, which has hitherto mainly been considered as occupying a purely pelagic niche.     

The diet of the Antarctic fur seal<Emphasis Type="Italic"> Arctocephalus gazella</Emphasis> 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.     

Daily activity and minimum food requirements during winter for gentoo penguins (Pygoscelis papua) in the South Shetland Islands, Antarctica

Estimates of daily activity and consequent demand for food during winter are scarce for many polar seabirds, yet essential for assessing constraints on foraging effort, demand for food, and potential competition with local fisheries. We affixed archival temperature tags to gentoo penguins (Pygoscelis papua) from two colonies in the South Shetland Islands to measure the frequency, timing, and duration of foraging trips and to estimate minimum food requirements during winter. Foraging trip frequencies ranged from 0.85 to 1.0 trips day⁻¹ and were positively correlated with day length. Early winter foraging trips more closely matched day length than late winter foraging trips. The data suggest that individuals maximize foraging time during the early winter period, likely to recover body mass following the breeding season and molt. The more attenuated response of foraging trip durations to increasing day length in late winter may be related to differences in local resource availability or individual behaviors prior to the upcoming breeding season. Minimum food requirements also exhibited a seasonal cycle with a mid-winter minimum. On average, minimum food requirements were estimated at 0.70 ± 0.12 kg day⁻¹. Extrapolated to the regional population of gentoo penguins, winter food requirements by gentoo penguins were equivalent to roughly 33% of annual krill catches by commercial fisheries in the South Shetland Island region over the past decade. Current expansion of the gentoo population and the krill fishery in the southern Scotia Sea warrants continued monitoring of gentoo penguins during winter.     

Fluoride content of Antarctic marine animals caught off Elephant Island

Summary A number of marine animals were collected off Elephant Island (South Shetland Islands) and analyzed for fluoride (mg/kg wet weight). In fish muscle from six Antarctic species the content was low (approx. 2) not exceeding the content of fishes from other waters. In bone-tissue a concentration of 616–1207 was found. In some benthic living animals the amount of fluoride (determined in the whole body) was different depending on the species investigated. Low amounts of approx. 10 were encountered in a pycnogonid, an octopodid and a polychaet. Very high values of 200–600 were determined in isopods, amphipods, ophiuroids and asteroids, these concentrations exceeded sometimes the value found in Antarctic krill.Results of the Antarctic Expedition 1981 of the Federal Republic of Germany with FRV Walther Herwig     

Diet of Cape petrel Daption capense during the post-hatching period at Laurie Island, South Orkney Islands, Antarctica

The diet of Cape petrel Daption capense was investigated at Laurie Island, South Orkney Islands (60°46^′S, 44°42^′W), Antarctica, in the period January–February 1996. Stomach contents of adults and regurgitate of chicks were sampled during the post-hatching period. The analysis showed that during the whole sampling period Antarctic krill and fish represented the predominant preys in terms of frequency of occurrence, forming nearly 35.8% and 64% by mass, respectively. The species Electrona antarctica was the most frequent fish prey. Amphipods were present in lower numbers and cephalopods were detected in the diet, but in a very small proportion. Diet composition in terms of frequency of occurrence, mass and number is compared with results of previous studies. Received: 27 September 1996 / Accepted: 22 February 1997     

The diet of Antarctic fur sealsArctocephalus gazella during the breeding season at South Georgia

 The diet of lactating female Antarctic fur seals Arctocephalus gazella at South Georgia was investigated during the pup-rearing period (January/March) of 1991–1994. Antarctic krill Euphausia superba was the main prey item, occurring in 88% of all scats (n=497), whereas fish occurred in 47% and squid in 5% of all scats. There was considerable intra- and inter-annual variation in the characteristics of krill taken by fur seals. The distribution of krill sizes taken suggests that fur seals are not actively selecting particular sizes of krill and, therefore, that the krill in the diet reflects the krill available around South Georgia. The absence of group 3 krill (44–48 mm in length) in the South Georgia area, as indicated by their absence in the diet of seals, is suggested as a possible reason for low availability of krill and the subsequent reproductive failure among krill predators. The frequency of occurrence of fish was much higher than in previous studies; the pattern of fish consumption showed a consistent seasonal pattern in 3 of the 4 years studied. Of the total number of the myctophid Protomyctophum choriodon, the most numerous fish taxon, 98% were taken between early February and the middle of March. Champsocephalus gunnari and Lepidonotothen larseni agg., which both feed on krill, dominated the fish component of the diet outside this period and together constituted 94% of the total estimated biomass of fish consumed. The intra- and inter-annual variability in the diet of Antarctic fur seals emphasise the need for diet studies to be conducted during the entire pup-rearing periods of several years. Received: 15 March 1995/Accepted: 13 May 1995     

Diet and foraging effort of Adélie penguins in relation to pack-ice conditions in the southern Ross Sea

We investigated the diet and aspects of foraging effort among Adélie penguins (Pygoscelis adeliae) breeding at three colonies on Ross Island, in the southwestern Ross Sea – Capes Royds, Bird and Crozier – during the chick-provisioning period of three austral summers, 1994–1995, 1995–1996 and 1996–1997. During the study period, pack-ice cover differed in waters offshore of these colonies, by colony, seasons and year. Diet differed among colonies only slightly. The fish Pleuragramma antarcticum was the most important prey, especially during years or periods within years when little pack ice was present. With respect to krill, which composed the remainder of diet, juvenile Euphausia crystallorophias were consumed predominantly in a year of heavy pack-ice cover; more adult krill were consumed in 2 years when pack ice was sparse. Foraging trip duration differed by colony, season and year and was related directly to distance from the colony to the nearest pack ice. The amount of food brought to chicks increased as trip duration increased, to a point (2 days), but then decreased as duration increased further (up to 4 days). On the basis of data on mass of parents and of meal sizes to chicks, it appeared that on the longest trips more of the food gathered by parents was used for self maintenance; on the longest trips, parents lost body mass. Successful foraging during chick rearing, the period when adult foraging is most intense, appears to depend on the proximity of pack ice to nesting colonies for this penguin species. Received: 1 October 1997 / Accepted: 25 April 1998     

Linking population trends of Antarctic shag (<Emphasis Type="Italic">Phalacrocorax bransfieldensis</Emphasis>) and fish at Nelson Island,South Shetland Islands (Antarctica)

This study aims to provide consistent information to explain the steady declining trend in the number of breeding pairs of Antarctic shag Phalacrocorax bransfieldensis in two colonies on Nelson Island, South Shetland Islands, southern Atlantic sector of Antarctica, which was observed during the 1990s up to the mid 2000s over an overall monitoring period of over two decades. It addresses correspondence between long-term population trends of inshore demersal fish and inshore-feeding Antarctic shags of this area, where an intensive commercial fishery for shag prey once operated. The analysis also includes comparable information on diet (by examination of regurgitated pellets), foraging patterns, and breeding output of shags from the Danco Coast, western Antarctic Peninsula, an area where no commercial finfish fishery has ever existed. Integral study of these parameters there showed that, in Antarctic shags, low breeding success and high foraging effort might imply low recruitment and high adult mortality, respectively, with both factors adversely affecting the population trends of this bird. In line with these premises, the declining trend observed in shag colonies on the South Shetland Islands appears to have been influenced by the concomitant decrease in abundance of two of their main prey, the nototheniids Notothenia rossii and Gobionotothen gibberifrons, due to intensive industrial fishing in the area in the late 1970s. In comparison, no such pattern occurred for the Danco Coast colonies.     

Dietary segregation of krill-eating South Georgia seabirds

The diets of six of the main seabird species (two petrels, two albatrosses, two penguins) breeding at Bird Island, South Georgia were studied simultaneously during the chick-rearing period in 1986. For five species, Antarctic krill Euphausia superba was the main food (39–98% by mass); grey-headed albatrosses took mainly the ommastrephid squid Martialia hyadesi (71%) and only 16% krill. The size of the krill taken was similar between seabird species, although there were small but significant differences between penguins and the other species. Sex and reproductive status of krill, however, was different between all seabird species, reflecting some combination of differences in foraging ranges, selectivity by predators, or differences in escape responses of krill. For the krill-eating species, the rest of the diet varied substantially between species, comprising Martialia and nototheniid fish (blackbrowed albatross and, along with lanternfish, white-chinned petrel), lanternfish and amphipods (Antarctic prion and macaroni penguin), and icefish (gentoo penguin). Long-term data on breeding success and information on diet in 5–10 other years suggest that in 1986 seabird diet and reproductive performance was indicative of a year of good availability of krill around South Georgia. In such circumstances, ecological segregation between krill-eating species appears to be maintained chiefly by differences in foraging range and feeding methods, which are reviewed. This situation is rather different from the few studies of seabird communities elsewhere, where prey type and size are believed to be the main mechanisms of dietary segregation.