Changes in the diet of the South Georgia shag Phalacrocorax georgianus at the South Orkney Islands along four consecutive years

The diet of the South Georgia Shag Phalacrocorax georgianus at Laurie Island, South Orkney Islands, was studied by the analysis of 337 pellets (regurgitated casts) collected during the 1995, 1996, 1997 and 1998 breeding seasons. Demersal-benthic fish were by far the main prey, followed by molluscs (mainly octopods and bivalves) and polychaetes. Harpagifer antarcticus (in 1995 and 1998) and Lepidonotothen nudifrons (1996 and 1997) were the most frequent preys followed by Gobionotothen gibberifrons or Trematomus newnesi. Harpagifer antarcticus, followed by L. nudifrons or T. newnesi, was the most numerous prey in all of the seasons and predominated in mass in 1995 and 1996, followed by Notothenia coriiceps and L. nudifrons. In 1997 G. gibberifrons and N. coriiceps were the species that most contributed to the diet whereas N. coriiceps and H. antarcticus did in 1998. Our results differ from those reported also for the South Orkney Islands in previous studies. These differences could be due to the use of different diet analysis methods and to shags-related and/or fisheries-related changes in the food availability. If assumed that the fisheries carried out in the area affected the structure and abundance of the fish populations, the comparison of our results with historical data may be indicating a recovery of G. gibberifrons in inshore waters around the archipelago.