Environmental variability and the behavioural dynamics of Antarctic fur seals in the South Atlantic

Variability in the reproductive performance of marine predators may be a result of physical forcing by large-scale oceanographic variability. Time lags, remoteness from the epicentre of a physical process and the simultaneous action of multiple physical processes often mean that it is difficult to link variability in predator performance with specific measurements of oceanographic variability. This study examined variation in the foraging behavior of lactating Antarctic fur seals (Arctocephalus gazella) over 15 years at the island of South Georgia in relation to major indices of southern hemisphere climate variation. Fur seal foraging trip duration was transformed into a normally distributed index of environmental variation. In a multiple regression analysis, the El Niño/southern oscillation index (ENSO) and a measure of the annual sea ice extent both had significant effects on the fur seal foraging index but both had the greatest effect when entered into regression models together. There was also a significant effect of the interaction between the ENSO and sea ice indices on the fur seal foraging index. There was little effect of a krill recruitment index upon the fur seal foraging index, either alone or when in combination with ENSO or sea ice indices. Lagged cross-correlations showed that the ENSO and sea ice indices had strong effects when lagged by one year. This was supported by bivariate correlation between the monthly ENSO means and the fur seal foraging index. These results show that the foraging behavior of fur seals in the Atlantic domain of the Southern Ocean is sensitive to the proximate physical forcing by a combination of physical variability occurring in the central tropical Pacific as well as in the Antarctic.