CCAMLR

The purpose of this paper is to synthesize information on the energetics and food requirements of krill predators that may be in the most direct competition with the krill fishery. These krill predators are the Adélie (Pygoscelis adeliae), chinstrap (Pygoscelis antarctica), gentoo (Pygoscelis papua), and macaroni (Eudyptes chrysolophus) penguins and the crabeater (Lobodon carcinophagus) and Antarctic fur (Arctocephalus gazella) seals. Basal, active, and. reproductive energy ' requirements are compiled for each species. Estimates' of the amount of krill needed . to sustain individuals and/or breeding pairs and population requirements are provided.

Acoustic surveys were carried out in January 1996 within two 100 x 80 km boxes located over the shelf-break to the north-east and north-west of South Georgia. Surveys were conducted from RRS James Clark Ross using a Simrad EK500 echo-sounder operating at 38, 120 and 200 kHz. These surveys were the first in a new five-year British Antarctic Survey programme initiated in part to monitor inter-annual variability in the abundance of the Antarctic krill Euphausia superba in the South Georgia region, and to provide krill biomass estimates for management purposes. Survey box 1 was located to the north-east of Cumberland Bay and encompassed Charlotte Bank, an area where historically whale catches were high and where numerous observations of elevated krill abundance have been made. Box 2 was located to the north of Bird Island, within a foraging area of prime importance for breeding krill predators. Together the two boxes therefore provide data of value to fishery scientists, ecologists and environmental modellers. The acoustic surveys were of randomised design and each nominally constituted 10 randomly spaced parallel transects, 80 km in length, running perpendicular to the major direction of shelf-break in the area; poor weather however necessitated some modification of this plan during the 1996 surveys. All transects were steamed during the hours of daylight in order to avoid biases in krill biomass estimation caused by diel vertical migration. Echoes were integrated in 2 m depth bins from 2 to 250 m below the transducers, over 100 second intervals (≈0.5 km at 10 knot survey speed). Two transects were run per day, and at night net hauls were carried out at a location toward the centre of the previous pair of transects to obtain krill for estimates of length frequency distributions. Weighted mean krill lengths of 29.5 mm for box 1 and 32.0 mm for box 2 were determined. Thresholded (mvbs 120 kHz minimum -100 dB) 120 and 38 kHz echo signal pairs were partitioned using a dB difference technique (δmvbs = mvbs 120 kHz - mvbs 38 kHz) into those attributable to krill (δmvbs between 2 and 12 dB), small zooplankton (δmvbs > 12 dB) and nekton (fish/squid, δmvbs

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.