New corrections factors for the quantification of fish represented in pellets of the blue-eyed shag Phalacrocorax atriceps

A comparative analysis was carried out on stomach contents and pellets (=regurgitated cast) of the blue-eyed shag or imperial cormorant Phalacrocorax atriceps collected throughout the breeding season at Nelson Island, South Shetland Islands. This allowed to estimate correction factors necessary for the quantification of fish represented in pellets. These factors were obtained for Notothenia coriiceps, Harpagifer antarcticus, Nototheniops nudifrons, Trematomus newnesi, Gobionotothen gibberifrons, Notothenia rossii, Pagothenia bernacchii and Parachaenichthys charcoti whereas Pleuragramma antarcticum, Notolepis coatsi and Electrona antarctica were represented in pellets but not found in the stomach contents. Fish were the main prey and N. coriiceps and H. antarcticus were the dominant species both in mass and number. Observations on behaviour showed that the daily foraging trips per bird increased in number but diminished in duration throughout the breeding season. These trends are related to the increase in the chicks' energetic demands.