Fish prey of Antarctic fur seals,Arctocephalus gazella,during the summer-autumn period at Laurie Island,South Orkney Islands

The fish component in the diet of Antarctic fur seals, Arctocephalus gazella, was investigated at Laurie Island, South Orkney Islands from mid January to April 1988. Fish otoliths occurred in 78.8% of faecal droppings. Most of the otoliths extracted from scats belonged to Myctophid fish (93.4%), mainly Electrona antarctica and Gymnoscopelus nicholsi. These two fish species thus constituted the bulk of the diet. A greater percentage of the otoliths from G. nicholsi (31.1%) in this study were considered suitable for measurement in comparison with 10.3% from scats at Heard Island in 1990 and 11.4% at Macquarie Island in 1988/89. This lesser degree of erosion would suggest that foraging areas of fur seals during this study were closer to land than during previous studies. During the period studied, the commercial fishery around the South Orkneys was not based on Myctophid fish so there was no direct competition for fish between the fur seals and fisheries.     

Fish diet of the Antarctic fur seal,Arctocephalus gazella,in summer,at Stranger Point,King George Island,South Shetland Islands

 In February 1992, 34 faecal samples from non-breeding male Antarctic fur seals, Arctocephalus gazella, were collected at Stranger Point, King George Island, South Shetlands. Fish constituted an important part of the diet, occurring in 90% of those scats containing prey remains. From 1162 otoliths found in the faeces, 1086 were identified to at least family level. Myctophids and nototheniids represented together almost 90% of the fish eaten. The dominant species were Gymnoscopelus nicholsi, Pleuragramma antarcticum and Electrona antarctica, contributing 33.3%, 30.8% and 12.0% of the otoliths respectively. The standard length of these three species was estimated from otoliths with little or no signs of erosion. This study showed that fur seals fed mainly on pelagic fish species that are often associated with krill. These findings are corroborated by fur seal diving patterns. Received: 7 October 1994/Accepted: 5 October 1995     

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     

Interannual variation in the diet of non-breeding male Antarctic fur seals, <Emphasis Type="Italic">Arctocephalus gazella</Emphasis>, at Isla 25 de Mayo/King George Island

The diet of non-breeding male Antarctic fur seals, Arctocephalus gazella, was investigated at Stranger Point, King George Island, through the analysis of scats during three consecutive summer seasons (1996, 1997, 1998). Overall, fish and krill were the most frequent prey occurring, respectively, in an average of 82.9% and 78.8% of samples (n = 131), followed by penguins (22.8%) and cephalopods (17.8%). Myctophids constituted almost 90% of the fish predated, with Electrona antarctica and Gymnoscopelus nicholsi being the most abundant and frequent species consumed. All fish taxa identified were krill feeding species suggesting that seals foraged mainly on a krill and a fish community associated with krill aggregations. However, a seasonal change was observed in the relative proportions of the different prey taxa, with a progressive decrease with time in the occurrence of krill and a concomitant increase of fish, penguins and squid. Possible influence of the strong 1997/98 ENSO event is discussed.     

Fish prey of Antarctic fur seals Arctocephalus gazella at Ile de Croy,Kerguelen

 The composition of Antarctic fur seal prey was assessed through analysis of scats collected in March 1994 on Ile de Croy, Iles Nuageuses. Fish remains predominated in samples, occurring in 95% of droppings. A total of 968 otoliths allowed the identification of 16 fish species. Myctophid fish (12 species) dominated the diet both by number (94% of the otoliths) and by fish reconstituted mass (76%). Three fish species constituted together 87% of the reconstituted mass: the myctophids Gymnoscopelus nicholsi (52%) and G. piabilis (12%), and the channichthyid Champsocephalus gunnari (23%). Prey distribution suggests that during late summer seals forage in upper slope waters in the northeast of the Kerguelen Archipelago. Received:1 March 1996/Accepted: 20 May 1996     

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 Antarctic fur seals, Arctocephalus gazella, at King George Island, during the summer–autumn period

The diet of non-breeding male Antarctic fur seals, Arctocephalus gazella, was investigated at Stranger Point, King George Island, by scat analysis from February to April 1996. Overall, krill and fish were the most frequent prey, occurring in an average of 97% and 69% of samples (n=128), followed by cephalopods (12%). Myctophids constituted almost 90% of the fish predated, with Electrona antarctica and Gymnoscopelus nicholsi being the most abundant and frequent species consumed. All fish taxa identified were krill-feeding species suggesting that seals foraged primarily on krill and opportunistically on fish species associated with krill swarms. A seasonal change observed in the relative proportions of the different fish prey taxa indicates that fur seals spent more time foraging over the shelf in summer and off the shelf in autumn. During the study period, commercial fishing in the area was not based upon any of the fish identified in this study.     

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.     

DIET OF SOUTH AMERICAN FUR SEALS (ARCTOCEPHALUS AUSTRALIS) IN ISLA DE LOBOS, URUGUAY

The diet of Arctocephalus australis was studied through fecal analysis, from September of 1995 to May of 1998, in Isla de Lobos (35°01'50"S-54°53'00"W), Uruguay. A total of 539 scats analyzed indicated that the weakfish ( Cynoscion guatucupa ), the cutlasfish ( Trichiurus lepturus ), the anchoveta ( Engraulis anchoita ), the anchovy ( Anchoa marinii ), and cephalopods were the main prey consumed by these fur seals. Prey richness was higher during January. The diet of A. australis varied between years, apparently related to changes in prey availability. C. guatucupa and E. anchoita decreased while T. lepturus and cephalopods increased from 1996 to 1998. South American fur seals fed on fish ranging in length from 5.4 to 104.8 cm and from 0.7 to 629.9 g in wet mass. However, the mean mass of the main items was never more than 200 g. Observations suggests that A. australis is a trophic generalist with the potential to prey on a wide range of species, although most of the diet is comprised of relatively few species. Fur seals and artisan fisheries both took C. guatucupa , with fur seals taking younger individuals (1–2 yr) than artisan fisheries (> 3 yr).     

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.     

King-size fast food for Antarctic fur seals

The study of scats of adult male Antarctic fur seals Arctocephalus gazella (AFS) revealed occasional frequent capture of penguins. Although AFS adult males have been occasionally reported to kill king penguins Aptenodytes patagonicus at the shore, here we report the first observations of at-sea predation by AFS on adult king penguins in the Crozet archipelago, southern Indian Ocean. During our 20 days survey, we observed 17 penguins attacked and either severely injured or killed and consumed. Only AFS adult males were seen catching king penguins successfully. Some adult females and sub-adults also attempted to catch penguins, either at sea or in land, and so did subantarctic fur seals Arctocephalus tropicalis individuals. Our results confirm the ability of fur seals to catch and predate large seabirds, even at sea.     

Prey of the Antarctic fur seal <Emphasis Type="Italic">Arctocephalus gazella</Emphasis> at Marion Island

The prey of Antarctic fur seals, Arctocephalus gazella, was investigated through scat analysis at Marion Island from 1996 until 2000. A total of 25 different prey species were identified from scats, of which 21 were fish, 1 crustacean and 3 cephalopods. Fish were by far the main prey item, occurring in 96.1% of samples, followed by crustaceans (2.7%) and cephalopods (1.2%). Fishes from the family Myctophidae (Gymnoscopelus piabilis, Electrona carlsbergi, G. fraseri and E. subaspera) were the most abundant prey (97.2%) every year, while those from the families Notothenididae, Paralepididae, Notosudidae, Microstomatidae and Gempylidae were present in small numbers. G. piabilis, E. carlsbergi, E. subaspera and G. nicholsi contributed the most in terms of biomass to the diet. Significant seasonal differences existed in the diet when comparing summer and winter. G. piabilis, K. anderssoni, P. bolini and P. choriodon dominated in summer as opposed to E. carlsbergi, E. subaspera, G. fraseri and G. nicholsi that dominated in winter. The fish varied in size and mass, from the small K. anderssoni to the large Paranotothenia magellanica. Cephalopods and the crustacean Nauticaris marionis, in very low numbers and in winter, appeared in the scats, but not in all years of study. Unidentified penguin remains rarely turned up in scats.     

Foraging habitats based on the diet of female northern fur seals (Callorhinus ursinus) on the Pribilof Islands, Alaska

Scats (fecal samples) collected between 1987 and 2000 on northern fur seal Callorhinus ursinus rookeries of St Paul ( n =2968) and St George Islands ( n =1203), Alaska, were used to examine the relationship between breeding sites and food habits of adult female seals. On the basis of the frequency of occurrence (FO) and per cent minimum number of individual prey (%MNI) in scats, juvenile walleye pollock Theragra chalcogramma and gonatid squid Gonatopsis borealis/Berryteuthis magister and Gonatus madokai/Gonatus middendorffi were the dominant prey species consumed overall. Other primary prey (FO>5%) included Pacific sand lance Ammodytes hexapteus , Pacific herring Clupea pallasi , northern smoothtongue Leuroglossus schmidti , Atka mackerel Pleurogrammus monopterygius , Pacific salmon ( Oncorhynchus spp.) and other squid of the Gonatus genus. We identified five rookery complexes from a cluster analysis of the FO of primary prey in scats. Rookery complexes were separated geographically and each was further defined by characteristic patterns in the representation of prey types typically associated with specific hydrographic domains. Diet differences were observed among rookeries on the north and south side of St George Island and on the east, south and south-west side of St Paul Island. The rookery clusters observed in this study provide evidence of resource partitioning among adult female northern fur seals and have important implications for fur seal conservation and management.     

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 composition and biomass consumption of harbour seals in Telemark and Aust-Agder,Norwegian Skagerrak

ABSTRACT

To explore ecosystem dynamics and functions it is vital to obtain knowledge on predator–prey relations. Harbour seals are piscivorous predators that can come into conflict with fisheries. Recently, as the Skagerrak and Kattegat population of harbour seals has increased, claims have emerged that seals are depleting coastal cod populations. The diet of harbour seals in Norwegian Skagerrak was investigated based on otolith identification from scats. The overall seal diet included 20 different fish species/groups. The most important prey (combined index Q _i ) were haddock/pollack/saithe (32.7%), genus Trisopterus (Norway pout/poor cod/bib, 12.5%), plaice (12.4%) and herring (10.0%). Plaice also had the largest biomass (24.1%). Gadoids and pleuronectids comprised 88.6% of the diet (combined index Q _i ) and 87.1% in terms of biomass. Cod constituted 0.7% (combined index Q _i ) of the overall diet and 2.3% in terms of biomass. Fish length estimates showed that seals generally prefer small fish below minimum allowed landing size. Estimated total amount of fish consumed was 315 tons per year and was dominated by non-commercial species. Annual cod consumption was an estimated 7.1 tons, representing 5% of annual cod landings, suggesting that competition between local fisheries and harbour seals is limited.     

Summer diet of leopard seals (<Emphasis Type="Italic">Hydrurga leptonyx</Emphasis>) in Prydz Bay,Eastern Antarctica

The diet of male and female leopard seals (Hydrurga leptonyx) was investigated in Prydz Bay, Eastern Antarctica. A total of 70 scats, 1 regurgitate and 3 stomach contents were collected, during the austral summer, between November 1999 and March 2002. Eight prey species were identified, including birds, mammals, fish and invertebrates. Adelie penguins (Pygoscelis adeliae) were the main prey item and crabeater seals (Lobodon carcinophagus), benthic and pelagic fish, amphipods and krill were found to supplement the diet. Cephalopods did not occur in the diet. Crabeater seals were still being captured well after weaning, and were found in the diet of both male and female leopard seals.     

The diet of the subantarctic fur seal Arctocephalus tropicalis at Marion Island

Scats of subantarctic fur seals Arctocephalus tropicalis at Marion Island were collected from 1996 to 2,000, to examine temporal variability in the diet, factors affecting the variability and how the diet differed from that of the Antarctic fur seal A. gazella in the same period. For A. tropicalis, 19 prey species, of which 18 were fish and one a cephalopod, were identified in 213 scats. Fish were the main prey, occurring in 98.1 % of scats, whereas the cephalopod was present in only 1.4 % of scats. Amongst fish species, Myctophidae were most abundant, with Gymnoscopelus piabilis, G. fraseri and Electrona carlsbergi being the commonest prey items. Other fish families present in the diet in small numbers were Channichthyidae, Paralepididae, Nototheniidae, Microstomatidae and Notosudidae. Fish eaten ranged in size from Protomyctophum bolini and Krefftichthys anderssoni of standard length (SL) 25 mm to a single Dissostichus eleginoides of SL 249 mm. Differences in the diet existed between summer and winter. However, prey type accounted for most variability in the diet. In previous studies based on scats, a dominance of fish in the diet of A. tropicalis was also found at Possession Island (Iles Crozet), Amsterdam Island and Macquarie Island, but the dominant prey species differed between the various localities, also suggesting that prey availability is a major determinant of diet. At Marion Island, from 1996 to 2000 the diet of A. gazella comprised similar prey to that of A. tropicalis, but the proportional contribution of prey types differed in instances.     

Feeding habits of three seal species at the Danco Coast, Antarctica: a re-assessment

The analysis of prey overlap among Weddell, Antarctic fur and leopard seals was conducted using fecal samples collected at the Danco Coast, Antarctic Peninsula, in 1998 and 2000. The re-occurrence of prey species was moderate in samples collected in 1998, and low in 2000, and reflects resource partitioning among seal species. Prey species that mostly co-occurred in seals’ diet were the Antarctic krill Euphausia superba, bivalves, and the myctophids Gymnoscopelus nicholsi and Electrona antarctica. A dietary similarity index of prey overlap has been calculated and demonstrates evident fluctuations in pairwise comparisons between the seal species. The highest and lowest values of prey overlap were observed between Antarctic fur seals and leopard seals, and between Weddell seals and leopard seals, respectively. Prey overlap between Antarctic fur seals and Weddell seals was moderate in both seasons.     

The diet of Weddell seals in McMurdo Sound, Antarctica as determined from scat collections and stable isotope analysis

The diet of adult and juvenile Weddell seals (Leptonychotes weddellii) in McMurdo Sound, Antarctica, was determined from both scat and stable isotope analyses, to ascertain if foraging behavior varied with age, season, or diving pattern. Scats were collected over 6 years and recovered hard parts identified. Stable carbon and nitrogen isotope values were determined for seal blood samples and potential prey items and used to identify primary prey species and assess trophic interactions. Pleuragramma antarcticum remains were recovered from between 70 and 100% of the scats, and there was little evidence for inter-annual or age-specific variation in foraging behavior. However, stable isotope and dive data analyses indicated that while most seals foraged predominantly on pelagic fish and squid, some juveniles concentrated on shallow benthic Trematomus spp. Combining these three methods permitted firm conclusions about diet and foraging behavior to be drawn. Received: 10 June 1997 / Accepted: 8 November 1997