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

摘要

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 changes in regional environment conditions and 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 5 consecutive years (2009-2013) under known variable oceanographic conditions. In years of unusually warm oceanographic conditions around South Georgia and low Antarctic krill Euphausia superba density, the number of squids Slosarczykovia circumantarctica increased in the seals' diet. Moreover, stable isotope analysis of beaks showed that S. circumantarctica exhibited higher delta N-15 values in years that were associated with an offshore habitat (lower delta C-13 values) where Antarctic fur seals had 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 conditions.