Squid in the diet of Antarctic fur seals: potential links to oceanographic conditions and Antarctic krill abundance

Understanding how changes in oceanographic conditions affect predators and their prey is fundamental for interpreting variability in natural marine ecosystems. At South Georgia, Antarctic fur seals Arctocephalus gazella are known cephalopod predators and potential indicators of change of regional environment conditions and in prey availability. The cephalopod component of the diet of Antarctic fur seals at South Georgia was assessed using lower beaks found in scats collected over five consecutive years (2009–2013) under known variable oceanographic conditions. In years of unusual warm oceanographic conditions around South Georgia and low Antarctic krill Euphausia superba density, the number of the squid Slosarczykovia circumantarctica increased in the Antarctic fur seal’s diet. Moreover, through stable isotope analysis on beaks, S. circumantarctica exhibited higher δ15N values in years that were associated with an offshore habitat isotopic signature where Antarctic fur seals have been foraging. This study provides evidence of the ecological links between the feeding behaviour of Antarctic fur seals, their main cephalopod prey, Antarctic krill densities and oceanographic condition