CCAMLR

To investigate the role of sea ice cover on penguin populations we used principal component analysis to compare population variables of Adélie (Pygoscelis adeliae) and chinstrap (Pygoscelis antarctica) penguins breeding on Signy Island, South Orkney Islands with local (from direct observations) and regional (from remote sensing data) sea ice variables. Throughout the study period, the Adélie penguin population size remained stable, whereas that of chinstrap penguins decreased slightly. For neither species were there significant relationships between population size and breeding success, except for an apparent inverse density-dependent relationship between the number of Adélie breeding pairs and the number of eggs hatching. For both species, no general relationship was found between either population size or breeding success and the local sea ice conditions. However, the regional sea ice extent at a particular time prior to the start of the breeding season was related to the number of birds that arrived to breed. For both species, this period occurred before the sea ice reached its maximum extent and was slightly earlier for Adélie than for chinstrap penguins. These results suggest that sea ice conditions outside the breeding season may play an important role in penguin population processes.

Samples of Antarctic krill collected from six seabird species and Antarctic fur seal during February 1986 at South Georgia were compared to krill from scientific nets fished in the area at the same time. The length-frequency distribution of krill was broadly similar between predators and nets although the krill taken by diving species formed a homogeneous group which showed significant differences from krill taken by other predators and by nets. There were significant differences in the maturity/sex stage composition between nets and predators; in particular all predator species showed a consistent sex bias towards female krill. Similarities in the krill taken by macaroni (offshore feeding) and gentoo (inshore feeding) penguins and differences between krill taken by penguins and albatrosses suggest that foraging techniques were more important than foraging location in influencing the type of krill in predator diets. Most krill taken by predators were adult; most female krill were sexually active (particularly when allowance is made for misclassification bias arising from predator digestion). Because female krill are larger, and probably less manouverable than males, the biased sex ratio in predator diets at this time of year may reflect some combination of selectivity by predators and superior escape responses of male krill. Overall, adult, sexually active female krill, forming 40 % by number of the local krill population, may comprise 60 - 70 % by number and 75 - 88 % by mass of the krill taken by their main seabird and seal predators at South Georgia at the time of peak local demand in February.

Using stomach lavage samples from macaroni penguins (Eudyptes chrysolophus Brandt) breeding at Bird Island, South Georgia and concurrent net samples caught within the penguin foraging range, we examined the potential selection of different length and maturity stages of Antarctic krill (Euphausia superb a Dana). Using Monte Carlo randomised simulation techniques we also determined the probability of obtaining length-frequency distributions of krill different from that obtained from the net samples. The krill taken by the macaroni penguins differed significantly from those caught in the nets. Small krill (28 to 38 mm) were absent from the stomach samples, whereas large krill (58 to 62 mm) were more abundant. Random sampling using Monte Carlo simulation techniques produced length-frequency distributions that were statistically different from the original distribution of krill caught in nets on 76 out of 100 trials. Nevertheless, these differences were smaller than those found between the penguin samples and net samples. Comparison of krill maturity stages showed that krill taken by macaroni penguins contained three times as many female as male krill, whereas krill caught in nets contained nearly equal proportions. The differences in size and maturity of krill taken by penguins are discussed in terms of aggregated random sampling, prey selection by predators, and evasion by krill of predators and nets. We conclude that the differences are unlikely to be accounted for simply by sampling anomalies; the differences are more likely to relate to penguins selecting larger, nutritionally superior krill, but might also reflect differential escape responses of particular classes of krill when evading penguins or nets.

By using time-depth recorders to measure diving activity and the doubly-labelled water method to determine energy expenditure, the relationship between foraging behaviour and energy expenditure was investigated in nine Antarctic fur seal females rearing pups. At-sea metablic rate (MR) (mean of 6.34 ± 0.4 W • kg–1; 4.6 times predicted BMR) was positively correlated to foraging trip duration (mean of 4.21 ± 0.54 days; r2 = 0.5, P

This paper presents data on the distribution of E. superba in the Atlantic sector and adjacent waters with an emphasis on subregions lying beyond the current fishing grounds of the Scotia Sea. In a number of subregions on the periphery of the Weddell Gyre (both to the north and south), as well as in the coastal waters of the Antarctic continent, the formation of krill aggregations is variable in terms of location of individual aggregations. The main difficulty with starting up a fishery there lies with assessing the variability of krill swarming patterns and the subsequent implementation of knowledge about this variability. This process must be undertaken alongside a program of integrated research directed at assessing variability in krill transportation and areas of swarm formation in the open-ocean environment. The commercial exploitation of krill aggregations in open-ocean areas should occur alongside an increase in the amount of exploratory surveys conducted annually.