CCAMLR

1. Estimating food consumption is central to defining the ecological role of marine predators. This study developed an algorithm for synthesizing information about physiology, metabolism, growth, diet, life history and the activity budgets of marine predators to estimate population energy requirements and food consumption.
2. Two species of marine predators (Antarctic fur seal Arctocephalus gazella and macaroni penguin Eudyptes chrsolophus ) that feed on krill in the Southern Ocean were used as examples to test the algorithm. A sensitivity analysis showed that estimates of prey consumed were most sensitive to uncertainty in some demographic variables, particularly the annual survival rate and total offspring production. Uncertainty in the measurement of metabolic rate led to a positive bias in the mean amount of food consumed. Uncertainty in most other variables had little influence on the estimated food consumed.
3. Assuming a diet mainly of krill Euphausia superba , annual food consumption by Antarctic fur seals and macaroni penguins at the island of South Georgia was 3•84 [coefficient of variation (CV) = 0?11] and 8?08 (CV = 0•23) million tonnes, respectively. This was equivalent to a total annual carbon consumption of 0?35 (CV = 0?11) and 0?72 (CV = 0?23) G tonnes year –1 . Carbon expired as CO 2 was 0?26 (CV = 0?06) and 0?65 (CV = 0?19) G tonnes year –1 for fur seals and macaroni penguins, respectively. The per capita food consumption varied depending upon sex and age but, overall, this was 1?7 (CV = 0?22) tonnes year –1 for Antarctic fur seals and 0?45 (CV = 0?22) tonnes year –1 for macaroni penguins.
4. The algorithm showed that the seasonal demand for food peaked in both species in the second half of the breeding season and, for macaroni penguins, there was a second peak immediately after moult. Minimum food demand occurred in both species during the first half of the breeding season.
5. As both Antarctic fur seals and macaroni penguins compete for krill with a commercial fishery, these results provide an insight into the seasons and stages of the life cycle in which competition is likely to be greatest.

The Antarctic fur seal (Arctocephalus gazella) and macaroni penguin (Eudyptes chrysolophus) are sympatric top predators that occur in the Southern Ocean around South Georgia where they are, respectively, the main mammal and bird consumers of Antarctic krill (Euphausia superba). In recent years the population of fur seals has increased whereas that of macaroni penguins has declined. Both species feed on krill of similar size ranges, dive to similar depths and are restricted in their foraging range at least while provisioning their offspring. In this study we test the hypothesis that the increased fur seal population at South Georgia may have resulted in greater competition for the prey of macaroni penguins leading to the decline in their population. We used: (1) satellite-tracking data to investigate the spatial separation of the Bird Island populations of these two species whilst at sea during the breeding seasons of 1999 and 2000 and (2) diet data to assess potential changes in their trophic niches between 1989 and 2000. Foraging ranges of the two species showed considerable overlap in both years but the concentrations of foraging activity were significantly segregated spatially. The size of krill taken by both species was very similar, but over the last 12 years the prevalence of krill in their diets has diverged with nowadays less krill in the diet of macaroni penguins than in that of Antarctic fur seals. Despite a significant degree of segregation in spatial resource use by the study populations, it is likely that the South Georgia populations of Antarctic fur seal and macaroni penguin exploit the same krill population during their breeding season. For explaining the opposing population trends of the two species, the relative contributions of independent differential response to interannual variation in krill availability and of interspecies competition cannot be resolved with available evidence. The likely competitive advantage of Antarctic fur seals will be enhanced as their population continues to increase, particularly in years of krill scarcity.

The present contribution uses data from German surveys in the 1980’ies and the US LTER programme which continuously collected krill demography data since 1993 during the austral summer season in the upstream area of the Elephant Island mesoscale survey. The intention was to compare the recruitment indices derived from these two mesoscale surveys and analyse whether results from mesoscale surveys are representative for a wider region Generally the proportional recruitment indices for one (R1) and two-year old (R2) krill differ substantially between years. However, results were in conformity with the results from other scientific surveys. Recruitment indices showed a significant correlation for age-one-old krill between scientific surveys from the northern Bellingshausen Sea, the Elephant Island area and South Georgia. The correlation becomes weaker for R2 recruitment indices. No correlation was detectable between the krill recruitment of Atlantic and Indian Ocean survey sites. Problems of single-year outliers from Elephant Island are discussed as well as the problem of ‘undersized’ length classes of the age-one-group which occur in the samples of some years.

In marine ecosystems, characterisation of the foraging areas and habitats of predators is a key factor in interpreting their ecological role. We studied the foraging areas of the macaroni penguin Eudyptes chrysolophus at Bird Island, South Georgia, throughout the breeding seasons of 1999 to 2001 using satellite tracking. We investigated differences in foraging ranges and characteristics between different stages of the breeding season, between sexes, between years and between individuals. During incubation, on foraging trips of 10 to 26 d, both sexes travelled long distances from Bird Island (male average = 572 km; female average = 376 km) in a north-westerly direction towards the Maurice Ewing bank; some individuals, particularly males, travelled to forage in the Polar Frontal Zone. In contrast, during the chick-rearing period, both sexes mainly foraged relatively close (average 62 km) to South Georgia over the continental shelf. Foraging trip characteristics differed between males and females during chick rearing: females travelled further on average and on more direct trips. During chick rearing, males and females on longer foraging trips covered greater distances and travelled further from Bird Island. There were no interannual differences in characteristics of foraging trips, although sex differences in some parameters varied between years. The bearings of chick-rearing foraging trips were non-random and most were in a north-westerly direction. Variation, both intra- and inter-individual, in bearings of foraging trips was high. Travel speeds were slower during foraging trips in the chick-rearing period than during incubation, probably relating to the differences in distances travelled. The stage of the breeding season, associated constraints on the penguins at different stages, and sex were important in determining variation in foraging range and characteristics in macaroni penguins, but year and individual effects were relatively unimportant.

Long-term data on the reproductive performance of krill predators at Bird Island, South Georgia where used to produce Combined Standardised Indices (CSI) that reflect processes operating over different time-scales. The output from all three CSIs indicated that in 2002 there were no indications of predators being unable to find sufficient food to provision themselves or their offspring.

A U.S. flagged commercial factory trawler, the Top Ocean, started fishing operations for krill (Euphausia superba) in Area 48 in July, 2000. This fishery has continued and expanded each year since the initial fishing trials. This paper presents information on the development, yields, and decision making processes involved in harvesting krill by the U.S. fishery. Because the Captain of the Top Ocean had no prior experience fishing for krill, anecdotal and historical information served as the initial basis for decision making. Initial fishing trials in 2000 were conducted in Bransfield Strait and north of South Georgia; in 2001, all fishing was conducted off the South Shetland Islands and Bransfield Strait. In 2002, fishing operations were carried out off the Antarctic Peninsula, west of Elephant Island; and northwest of the South Orkney Islands. Information on set locations, effort, yield, catch rates, and the decision making processes involved in prosecuting the U.S. commercial fishery for krill by each month and region fished are summarized. The decision making processes involved during fishing operations were based on several factors, including krill abundance, weather, ice conditions, condition of krill in relation to the target product, and ad hoc information from nearby fishing fleets. High concentrations of krill were found in Bransfield Strait in 2001 while fishing inside the ice edge. The success of the fishery has increased each year due to factors related to the experience of the Top Ocean. Increasing catch rates with time are likely related to the experience of the Captain, as opposed to indices of krill abundance.

Satellite monitoring of sea surface temperatures (SST) off South Georgia (Subarea 48.3) which includes both analysis of real-time data from vessels and buoy stations provides constant information on the temperature conditions of the area. Weekly SST maps constructed from GOES-E and Meteosat-7 daily satellite data are used to develop maps of mean monthly SST and SST anomalies. For quantitative monthly analysis of variations in temperature distribution and SST anomalies in the South Georgia waters in 12.1989/03.1991 and 11.1999/04.2002 we have selected Cells 1 and 2 (2°x2° resolution, centered at 54°S 41°W and 53°S 37°W, respectively). Temperature values of monthly trends of mean SST and SST anomalies in Cell 1 and 2 are calculated with precision of 0.01°C.

Understanding the demographics of Antarctic krill over large scales may be complicated by regional differences in the 11 processes that govern population structure. The influence of regional differences in growth and mortality on population size 12 structure was examined using data on the length–frequency distribution of krill in the Scotia Sea using samples from the South 13 Shetland Islands and South Georgia collected annually from 1991 to 2000. A correction function, which took account of the 14 higher growth rate at South Georgia, produced a consistent similarity in the position of the modal size classes that was not present 15 in the raw data. Optimising the mortality rate, to minimise the differences in the growth corrected length–frequency distribution, 16 suggested a higher mortality rate at South Georgia that the South Shetlands. The intra-specific variations in growth and mortality 17 rates are consistent with published values and with other Euphausiids species. Having accounted for the demographic plasticity, it 18 is apparent that strong recruitment of the smallest size class of krill is represented in both populations simultaneously. It appears 19 that first-year krill are advected into different regions of the Scotia Sea where the resultant population size structure is determined 20 by regional differences in growth and mortality. The majority of the commercial harvest of krill in the Antarctic occurs in a 21 relatively small number of regional fisheries within the Scotia Sea and is managed using population models based on a single set 22 of demographic parameters. Where substantial differences in these parameters exist between fishing areas, the calculation of 23 catch limits should take these differences into account.

Adélie (Pygoscelis adeliae) and chinstrap penguins (P. antarctica) are morphologically and ecologically very similar, have very similar diet and breed sympatrically in the Scotia Arc from the South Sandwich Islands to the Antarctic Peninsula. To investigate how these two species co-exist, their foraging distribution and diet were studied during the chick-rearing period at Signy Island, South Orkney Islands during the breeding seasons of 2000 and 2001. Satellite tracking data from of 19 Adélie penguins and 24 chinstrap penguins were used to compare foraging distributions. In both years the diet of both species was exclusively Antarctic krill (Euphausia superba) of the same size range. In a year of low prey availability (2000), there was a statistically significant segregation of foraging areas between the two species, however, in a year of normal resource availability (2001) there was no such segregation. There was a significant difference in the foraging areas used by Adélie penguins between years but not for chinstrap penguins. Adélie penguins foraged significantly farther (mean 100 km) from the colony than chinstrap penguins (mean 58 km) in 2000 but not in 2001 (mean 58 km and 35 km respectively). In 2000, the breeding success of Adélie penguins was 51% lower than the long-term mean compared to 15% lower in chinstrap penguins. Both species achieved above average breeding success in 2001. The changes in foraging distribution and breeding success suggest that in years of low resource availability, chinstrap penguins may be able to competitively exclude Adélie penguins from potential inshore foraging areas. Current trends in climatic change and possible effects on ice distribution and krill abundance suggest that conditions could become less favourable for Adélie penguins than chinstrap penguins in areas where both species occur.