Analysis of the stomach content of the blue-eyed shagPhalacrocorax atriceps bransfieldensisat Nelson Island, South Shetland Islands

摘要

Stomach contents of 40 specimens of the blu0e-eyed shagPhalacrocorax atriceps bransfieldensiswere sampled at Nelson Island, South Shetland Islands, in January 1994. The analysis of the diet showed that fish were by far the main component, followed by octopods, polychaetes and gammarids.Notothenia coriicepspredominated in frequency (58) and in weight (65), whereasNototheniops nudifronswas the most important species by number (47). The comparison with data published on pellet analysis of shags from the same colony gave similar results. However, although the methodology used in the present study requires more time in the field, it reduces the errors that arise from the examination of regurgitated casts, such as those due to erosion by digestion or loss of the otoliths through the gastrointestinal tract. The observation of 8 nests filmed continuously during 24 h showed that the members of the pairs alternate foraging and make 3–5 foraging trips per individual per day. The activity started as 0700 hours and finished at 2200 hours, and the mean duration of the trips was 73 mi