CCAMLR

This paper was requested by WG-EMM in 1995 (SC-CAMLR-XIV, Annex 4, paragraph 6.49). In the early years of development of the ecosystem monitoring program sea ice data, especially derived from satellite images, was recognised as an important source of information for interpreting changes in monitored predator parameters. Standard methods for collection of environmental parameters were agreed in 1990, and following a pilot study carried out by the Secretariat sea ice data derived from US Joint Ice Centre ice charts were routinely acquired and analysed by the Secretariat from 1993. An alternative source of data, digital images produced by the US National Snow and Ice Data Centre, with a relatively low resolution of 25 km, have been archived and analysed routinely by the Secretariat since 1995 to produce a number of indices of ‘sub area' scale sea ice distribution. Archiving and analysing high resolution satellite images remains the responsibility of national monitoring programs.

Predator data and exploratory fishing in the Scotia Sea have revealed the presence of cephalopod stocks in the Antarctic Polar Frontal Zone (PFZ). This is a vast, remote region where large epipelagic cephalopods aggregate into highly mobile schools making them difficult to locate and sample. We used satellite tagged predators and shipboard acoustics for coarse and fine scale location of cephalopod concentrations, and sampled them with commercial and scientific nets to determine the relationship between cephalopod distribution and mesoscale oceanographic features at the PFZ. Satellite tags were attached to 9 grey-headed albatrosses Diomedea chrysostoma, breeding at Bird Island South Georgia, to monitor foraging at sea in January-March 1994. A foraging area at the PFZ, north of South Georgia, was located, an acoustic survey undertaken and a fixed station established where acoustic targets were found. A net survey was carried out with a commercial pelagic trawl, a rectangular midwater trawl 25 m2 (RMT25), a horizontal multiple plankton sampler and a neuston net. Acoustic layers were targeted and the RMT25 sampled 200 m layers to 1000 m in daylight and darkness. Cephalopods were simultaneously recovered from food samples fed to D. chrysostoma chicks at Bird Island. Two CTD transects, approximately normal to the major current flow, were undertaken across the PFZ and remote-sensed sea-surface temperature images from NOAA polar orbiting satellites were obtained aboard ship. The pelagic trawl sampled a cephalopod community that closely resembled that exploited by D. chrysostoma. The largest and most conspicuous species was the ommastrephid squid Martialia hyadesi which is the most important cephalopod prey species. Net-sampled M. hyadesi had been feeding on crustaceans and mesopelagic fish. The cephalopod community was sampled in a feature, interpreted as a warm core ring, in an area characterised by mesoscale features associated with the bathymetry of the northern end of the Northeast Georgia Rise and near a gap in the Falkland Ridge. The association of these mesoscale features with the bathymetry suggests that they may be predictable foraging locations for the cephalopods and their predators.

The fish component of the diet of black-browed and grey-headed albatrosses at South Georgia was investigated by intercepting 155 meals from adults arriving to feed chicks during February 1986 and 1994. Fish represented 30% and 72% by mass of the diet of black-browed albatrosses and 14% and 60% by mass of the diet of grey-headed albatrosses in 1986 and 1994 respectively. We determined the identity and quantified the contribution (by numbers, size and mass) of fish species mainly by using otoliths (54 representing 9 taxa and 57 representing 17 taxa in black-browed and grey-headed albatross samples respectively). For black-browed albatrosses in 1986 the main fish prey was Patagonotothen guntheri (77% of otoliths, 51 % of estimated fish biomass) and a single large specimen of Icichthys australis (40% estimated biomass), whereas in 1994 Pseudochaenichthys georgianus was the main fish prey (57% of estimated biomass) with Magnisudis prionosa (30%) and Champsocephalus gunnari (12%) also making substantial cpntributions. Grey-headed albatross samples from 1986 were dominated by southern lampreys (40% by number, 79% of estimated biomass), lanternfish (32% of numbers, 9% by mass) and Patagonotothen guntheri (11 % by mass); in 1994 Champsocephalus gunnari (42% by numbers, 24% by mass), Magnisudis prionosa (13% by number, 36% by mass), Muraenolepis microps (90% by number), Pseudochaenichthys georgianus (15% by mass) and lanternfish (18% by number but only 1 % by mass) were the main prey. The importance of Patagonotothen guntheri to both species in 1986 and its absence in 1994 probably reflect albatrosses obtaining it from the commercial fishery, which was active in 1986 but closed in 1994. Otherwise the fish diet of black-browed albatrosses is dominated by krill-feeding fish, characteristic of the waters of the South Georgia shelf. In contrast, the grey-headed albatross diet comprises deeper water mesopelagic species, especially lanternfish., which reflect its affinity for the Antarctic Polar Frontal Zone and associated oceanic upwellings.

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