ALBERT

Description: Long-term temperature and current-meter records from moorings in the northern Canary Basin display strong current events with time scales between one and three months and large vertical scales of several thousand meters. The data are compared to hydrographic surveys in the area that show a meandering subtropical front. The strong current events are found to be related to the passage of the front through the mooring positions. An analysis of composite time series, for selected depths, indicates cases of westward and of eastward propagation of frontal meanders. The frontal pattern is also found in geopotential anomalies inferred from historical XBT data sets, suggesting that the front is a persistent feature of the density field. In two cases strong current events appear to be related to a Mediterranean Water lens.

Description: Giant petrels are the dominant scavenging seabird species in the Sub-Antarctic and maritime Antarctic ecosystems. They consume large amounts of penguin carrion, but also include significant numbers of seals, Antarctic Krill, Euphausia superba, and small petrels in their diets. Using results of detailed dietary studies at Bird Island, South Georgia, and qualitative data for other localities, notable variation in the quantitative impact of Giant petrels on their prey is revealed. Energy budgets of chicks are calculated from data on meal size and feeding frequency at all stages of growth. Differences in energy requirements between the Northern Giant Petrel, Macronectes halli, and the Southern Giant Petrel, M. giganteus, and between male and female chicks, are demonstrated. Published and unpublished data on numbers of giant petrels at known breeding sites are reviewed, and the present world breeding population is concluded to be ca. 8,600 pairs of M. halli and ca. 38,000 pairs of M. giganteus. Using survival and demographic data for South Georgia, total world non-breeding populations of ca. 26,000 and ca. 113,000 birds are calculated for M. halli and M. giganteus, respectively. The energy consumption of these populations in the breeding season is assessed and, taking into account geographical variation in diet, their impact on local ecosystems is evaluated. The approximations and assumptions of these estimates are discussed.

Description: The methods and results of the study of the tropho-dynamic relationships between 2 Diomedea albatrosses and the marine environment at South Georgia are described. They illustrate the technical and theoretical developments necessary to obtain certain empirical data essential for accurate assessments of the role of seabirds in marine ecosystems. Differences in breeding success during eight yr (consistent in D. chrysostoma, more variable in D. melanophris) are linked with important differences in breeding frequencies which affect the size and activities of populations at the breeding sites. Extensive dietary studies, based on sampling adults about to feed chicks, showed major inter-specific differences, resulting in chicks receiving meals of similar size and frequency but of different energy content. The frequency of chick feeding was determined initially by daily and 3-h weighing. Recently automatic equipment has recorded weights every 10 min, giving the frequency and size of meals and resulting digestive performances of the chicks. Experiments involving exchanging chicks between the two species were combined with new methods for analyzing growth curves. They showed that, while there was a species-specific genetic component to growth, the overall rate could be significantly modified by the nature of the diet. The slower growth rate of D. chrysostoma chicks, and the species’ diet, are probably important factors affecting breeding frequency. Adult feeding performance is being studied by devices recording simple activity budgets at sea. Preliminary results are described and projected work linking this with the automatic weighing equipment and with assessment of foraging energy costs is outlined.

Description: The energy requirements and prey consumption of the rapidly expanding South Georgia population of Antarctic Fur Seals, Arctocephalus gazella, are estimated, using information on diet, population structure, activity patterns, and energy budgets and variations in these with sex and season. All quantitative information on diet is reviewed. Breeding female Fur Seals mainly take Antarctic Krill, Euphausia superba. This predominates also in the summer diet of males but fish (mainly Champsocephalus gunnari) and squid are also eaten. Fish is more important to males in winter. Life tables are used to determine the proportion of each age-class in the population, and especially to estimate the size of that portion of the immature stock which does not appear ashore. Energy costs of adult males are assessed from attendance data and age-specific weights. Female energy budgets are calculated from extensive data on the duration of periods ashore and foraging trips to sea together with information on activity budgets at sea. Pup energy consumption is calculated from body weight and growth data. A summer food consumption of 1.1 × 106 t is divided between juvenile males (39%), adult females (31%), adult males (22%) and juvenile females (8%). In winter, when females are absent, juvenile (67%) and adult males (33%) consume 0.4 × 106 t. Krill forms 69% of the annual consumption, fish 19% and squid 12%. The main peaks of demand are in October (all adults feeding at sea), January-February (rapidly growing pups being reared) and April—May (most of population, including weaners, feeding at sea). From data on diet and foraging ranges and depths, the main natural competitor of the Antarctic Fur Seal is the Macaroni Penguin, Eudyptes chrysolophus; significant competition with a developed Krill fishery would be expected. Continuing commercial exploitation of fish, especially C. gunnari, may influence male Fur Seal populations, particularly in winter.

Description: This paper reviews the current state of knowledge of the food habits of the poorly known small cetaceans of the Southern Ocean and presents new information obtained through a study of stranded specimens in Tierra del Fuego. In the Antarctic and Sub-Antarctic, food data are available for only 10 of the 22 species present. Adding to this all the food records known from the South Temperate Zone south of 30° S, there is still no information at all for 5 species (Mesoplodon layardii, M. hectori, M. bowdoini, Cephalorhynchus eutropia and Phocoena dioptrica); that of 8 species is based on fewer than three samples, and more than 10 samples are available for only 2 species (Orcinus orca and Cephalorhynchus commersonii. Since these cetaceans are among the larger animals of the Southern Ocean, their role in the food web of the ecosystem cannot be determined until more information is available.