Seabird associations with mesoscale eddies: the subtropical Indian Ocean

We investigated seabird-eddy associations in subtropical waters of the southern Indian Ocean during a summer (January) cruise from Amsterdam Island to Western Australia. To determine habitat associations and to enable predictions about foraging strategies, we related the distributions of satellite altimetry data (sea surface height anomalies) to the 3 most abundant taxa in the study area: terns (sooty Sterna fuscata and bridled S. anaethetus) and shearwaters (wedge-tailed Puffinus pacificus) were significantly more common and numerous within convergence zones. However, a step-wise logistic regression model revealed that these seabirds were more strongly associated with other habitat variables, including the distance to breeding colonies and warm sea surface temperature conditions. Great-winged petrels Pterodroma macroptera were widely scattered and did not show associations with convergences or divergences. These contrasting results highlight the need to consider smaller-scale hydrographic features, such as frontal systems, when quantifying seabird associations with mesoscale eddies. Large-scale patterns of ocean circulation and mesoscale variability also seem to play a critical role in determining the extent of seabird-eddy associations. In contrast with previous studies, which have focused on dynamic frontal regions and energetic current systems, we surveyed a region of weak mesoscale variability north of the Subtropical Convergence zone.