CCAMLR

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 ommastrephids 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 (black-browed 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.

Fatty acid signature analysis is based on the conservation and unique signatures of fatty acids in the marine food chain and it may be useful in determining the composition of seal diets or in detecting changes in diets. We apply fatty acid signature analysis to milks collected from Antarctic fur seals at South Georgia during the perinatal period (n= 19) and subsequently during early (n=11), mid (n=11), and late (n=8) foraging trip intervals, and demonstrate its use in detecting shifts in prey intake which correspond with changes observed in diving and foraging behavior during a poor food year (austral summer 1990/1991). In lactating otariid females, milk fatty acids secreted during the perinatal fast are derived largely from blubber mobilization and thus likely resemble an integration of dietary fatty acids consumed during the fattening period prior' to parturition, whereas milk fatty acids secreted during foraging trip intervals are derived primarily from immediate dietary intake during the lactation period. To compare groups, we used methods of classification and regression tree (CART) analysis in S-plus, which allows the statistical interpretation of complicated fatty acid patterns containing up to 70 variables per observation. The fatty acid signature of perinatal milks was significantly different (0/19 missclassification rate) from all other milks and late attendance (0/8 missclassification rate) was correctly distinguished from early and mid attendance (1/22 missclassification rate). Our results confirm that adult female fur seals have a distinctly different diet prior to parturition while away from breeding grounds and likely switch to a diet of krill during lactation. Additionally, at least in a poor food year, fur seals do not feed exclusively on krill throughout lactation but rather begin to shift to a diet of teleost fish during late attendance. These findings were consistent with independent 1990/1991 scat data and indicate that fatty acid signature analysis promises to be a valuable tool in trying to understand aspects of foraging ecology in free-ranging pinnipeds.

The diet of the Antarctic Prion Pachyptila desolata was examined using food samples regurgitated by adult birds during five breeding seasons at Bird Island, South Georgia. In all years the diet was mainly crustaceans, with a small proportion of myctophid fish and trace amounts of cephalopods. Antarctic krill Euphausia superba was the dominant prey item in three years and was replaced by calanoid copepods, especially Rhincalanus gigas and Calanoides acutus, in two years of low krill abundance. Differences in the prey species taken and observations of foraging behaviour suggest that in years of low krill availability Antarctic Prions forage closer inshore, taking copepods by filtering surface water through their palatal lamellae. By switching to feeding on copepods Antarctic Prions are apparently able to maintain a comparable level of reproductive success, unlike most other krill feeding species which suffer much reduced reproductive performance in years of reduced krill availability.

The body composition, milk consumption, and growth efficiency of Antarctic fur seal (Arctocephalus gazella) pups were measured over three consecutive lactation periods (1990-1992) at Bird Island, South Georgia. The body composition of pups differed between the sexes; whereas for any given age females were lighter than males, they had proportionately higher body lipid reserves than males. Milk consumption was determined on 388 occasions in 177 pups. Mean estimates of milk consumption ranged from 2.5 to 3.2 kg (42-53 MJ) during the 6-day perinatal period and from 2.9 to 3.6 kg (49-68 MJ) during the 1- to 2-day maternal attendance periods (feeding bouts). There were no differences in milk consumption between the sexes in any year. Both per-bout and per-day milk consumption increased steadily with age before decreasing significantly in the last 30-40 days of lactation. Per-bout milk consumption was positively related to the duration of the maternal foraging trip and attendance cycle, and both per-bout and per-day milk consumption were related to pup mass. Pups of both sexes consume the same amount of milk, but males direct more of their milk consumption into lean tissue growth than females, which accumulate greater adipose stores. Therefore, mass and mass changes may not be appropriate parameters for investigating differential maternal investment between the sexes in otariid pups.

The diet of the diving petrels Pelecanoides georgicus and P. urinatrix was studied during 1986 (P. georgicus) and 1987 (both species) by lavaging adults as they returned to feed chicks on Bird Island, South Georgia. The diet of both species was dominated by crustaceans. in particular euphausiids (mainly Euphausia superba and some ThysCll1oessa), which contributed 47-76% of the biomass of crustaceans in the diet of P. georgicus. and copepods, which contributed 71 % of the biomass of crustaceans in the diet of P. urinatrix. Calanoides acutus was the most numerous copepod in the diet of both species; however, Rhincocalamus gigas was more common in P. urinatrix than in P. georgicus. The dominant amphipod in the diet of P. georgicus, Primo macropa, was absent from the diet of Pelecanoides urinatrix, in which Themisto gaudichaudii (rare in Pelecanoides georgicus) dominated. Dietary differences were maintained in the period (2 weeks of a total of 10 weeks) when both species were simultaneously rearing chicks. Knowledge of the prey species and of the diving abilities and foraging habits of diving petrels suggests that at South Georgia Pelecanoides urinatrix feeds closer inshore and dives deeper than Pelecanoides georgicus.

The diet of king penguins, Aptenodytes patagonicus, rearing chicks was studied during three consecutive austral winters (1990, 1991 and 1992) at Crozet Islands. The mean stomach content mass of the 47 samples was 503 g. Percentages of wet and reconstituted masses showed that both fishes (66 and 36%, respectively) and squid (34 and 64%) are important components of the winter diet. Juveniles of the demersal onychoteuthid squid M oroteuthis ingens form the bulk of the cephalopod diet, and this was the main prey by reconstituted mass (57%). Myctophid fish (lantern-fishes) accounted for most of the fish diet, constituting together 32 % by mass. The three main species of myctophids eaten in summer by king penguins were either very rare in winter (Electrona carlsbergi) or accounted for a smaller proportion of the diet (Krefftichthys anderssoni = 1.5% by mass and Protomyctophum tenisoni = 4.6%). Five other myctophids, which are rarely consumed in summer, contributed 24% of the diet by mass in winter (Gymnoscopelus piabilis = 18.1, Lampichthys procerus = 2.4%, G. nicholsi = 1.3% , and M etelectrona ventralis and Electrona subaspera = 1.0%). The greater diversity of prey in winter suggests a more opportunistic feeding behaviour at a time probably marked by a change in prey availability. Both the known ecology of the fish and squid prey and the barely digested state of some items suggest that in winter breeding adults forage in the outer shelf. upper slope and oceanic areas in the close vicinity of the Crozet Islands to feed their chicks. Finally, using king penguins as biological samplers, the present work provides novel data on the previously unstudied mesopelagic/epibenthic marine community in waters surrounding the Crozet Islands. Seventeen myctophid fish have been identified to species level. These include several poorly known species in the southern Indian Ocean. The occurrence of small, nearly intact, cephalopods in the diet of king penguins suggests that spawning grounds of four squid species may be located near the Crozet Archipelago.

Seasonally breeding predators, which are limited in the. time available for provisioning young at a central location, and by the fasting abilities of the young, are likely to maximize energy delivery to the young by maximizing the rate of energy delivery averaged over the whole period of investment. Reduction in food availability or increased foraging costs will alter the optimal behavior of individuals. This study examined the behavioral adaptations of a diving predator, the Antarctic fur seal to increased foraging costs during lactation. One group of mothers (n = 5, treatment) was fitted with additional drag to increase the cost of transport in comparison with a control group (n = 8). At the scales of the individual dives, the treatment group made more shorter, shallower (

Based on historic data as provided by the World Ocean Atlas 1994, the general climatic background for temperature, salinity and silicate is given for the area between the Fa1kland (Malvinas) Islands and the Antarctic Peninsula Region. A data set sampled during December 1996 in the Elephant Island Plateau Region by RV POLARSTERN, is compared to the climatic background data, and to more recent data as collected by German research vessels in this region. By means of a new interactive software water mass boundaries are outlined which reveal the approximate location of the Weddell-Scotia Confluence. Vertical distribution of oceanographic parameters temperature, salinity and density is discussed. Geopotential anomaly charts, referenced to 0/300 dbar reveal the general flow as given by the geostrophic part of the circulation. Compared to krill abundance data, the thermal and the dynamic fields indicate some correlation in the distribution of biotic, and abiotic parameters. Analysis of time series data at a station site to the north of Elephant Island, point at slow seasonal oscillations of the water mass boundary between the Weddell Sea waters and the Southeast Pacific Surface waters, the Weddell-Scotia Confluence.
The paper reiterates a recommendation as given in a previous SC-CAMLR paper by the same author, to do a co-operative analysis of data sampled throughout the years in the Elephant Island Plateau Region. With the new modem software as described in this paper, handling of large data bases becomes very easy.