Marine foraging and annual fish consumption of a south polar Skua population in the maritime Antarctic

Abstract

Pelagic fish are an important component of Antarctic food webs but few quantitative data exist on energy transfer from fish to seabirds for the Seasonal Pack-ice Zone. We studied a local population of south polar, skuas Catharacta maccormicki during a whole breeding cycle and estimated its entire annual food consumption. The lengths of foraging trips suggested that skuas foraged in an area of 817 km2 of coastal waters around the breeding site. Their fish prey consisted almost entirely of two pelagic species, Electrona antarctica and Pleuragramma antarcticum, with individual mean energy contents of 28.62 and 30.26 kJ/g dry weight and body masses of 4.6 and 10.9 g, respectively. Total energy budget estimates of the entire south polar skua population resulted in 3 and 5 tons of pelagic fish caught per season (1994 and 2001, respectively), wherein a single breeding pair raising two chicks requires approximately 115.7 kg E. antarctica and 24.4 kg P. antarcticum. Our study suggests that the pelagic fish in coastal areas are highly important for surface feeding seabirds in the maritime Antarctic.