Diet and Energy Budget of the Antarctic Fur Seal, Arctocephalus gazella, at South Georgia

• Main Authors: Doidge, D. W., Croxall, J. P.
• Format: Book Part
• Language: English
• Published: Springer Berlin Heidelberg 1985
• Subjects: Antarctic; The Antarctic; Antarc*; Antarctic Fur Seal; Antarctic Fur Seals; Antarctic Krill; Arctocephalus gazella; Eudyptes chrysolophus; Euphausia superba; Macaroni penguin
• Online Access: https://oceanrep.geomar.de/id/eprint/34040/; https://oceanrep.geomar.de/id/eprint/34040/7/773.pdf; https://doi.org/10.1007/978-3-642-82275-9_73

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.