Sex differences in diving depths and diet of Antarctic Shags at the South Shetland Islands

Sexual differences in maximum diving depths and in the composition of the diet of the Antarctic Shag (Phalacrocorax bransfieldensis) were investigated at Harmony Point, Nelson Island, South Shetland Islands, Antarctica, during the 1995-1996 and 1996-1997 breeding seasons. The mean maximum diving depth estimated by the capillary-tube depth gauge technique was 37.8 m which, when compared with other studies, reflects good food availability in shallow waters around Harmony Point. Females dived significantly deeper than males and also reached the maximum dive depth registered (112.6 m). The analysis of the stomach contents recovered when the individuals with capillary-tubes returned to the nest from foraging trips indicated that males ingested almost exclusively large Notothenia coriiceps specimens, whereas females preyed more intensively on smaller fish. The differences observed suggest that individuals of both sexes partitioned foraging depths and food resources.