Long term changes in the diet of the South Georgia Shag Phalacrocorax georgianus at the South Orkney Islands

CASAUX R,; BERTOLIN M.; BORRELL V.; PUJADAS J.

Buenos Aires

Congreso; Scientific Committee on Antarctic Research Open Science Conference; 2010

Scientific Comittee on Antarctic Research

A total of 784 pellets of the South Georgia Shag Phalacrocorax georgianus werecollected at Pirie Peninsula, South Orkney Islands, from the 1995/96 to the 2008/09 breedingseasons. The analysis of the samples indicated that shags preyed predominantly on fishwhereas the remaining preys (octopods, bivalves, snails and polychaetes) contributed little tothe diet. Among fish, benthic-demersal species from the families Nototheniidae andHarpagiferidae predominated in the diet. Overall, Gobionotothen gibberifrons, Nototheniacoriiceps, Lepidonotothen nudifrons and Harpagifer antarcticus were the most frequent fishprey. Lepidonotothen nudifrons, followed by H. antarcticus and G. gibberifrons, was the mostabundant prey whereas N. coriiceps, followed by L. nudifrons and G. gibberifronspredominated by mass. The contribution to the diet by mass of G. gibberifrons, L. nudifrons,N. coriiceps, T. newnesi and H. antarcticus fluctuated in 2-4 years cycles. The length of thefish consumed varied in the different years. The largest fish were ingested in 2002 whereasthe smallest ones in 1995. Within species there were also significant differences in the lengthof the N. coriiceps, H. antarcticus, G. gibberifrons, L. nudifrons and T. newnesi specimenseaten in the different years.