Mesoscale eddies as foraging area of a deep-diving predator, the southern elephant seal

Physical processes, such as mesoscale eddies, play an important role in ocean mixing and concentrating biological productivity, which provides great feeding opportunities for many marine top predators. This study describes the presumed foraging behaviour of southern elephant seals Mirounga leonina within an intense eddy field along the Polar Front in relation to the physical features of the eddies targeted by foraging seals, especially in the vertical dimension. Combining satellite measurements and data from tags deployed on elephant seals, we showed that some seals (10 of 38) preferentially selected the edge of cyclonic structures, generally associated with a high eddy kinetic energy, during intensive foraging phases. Moreover, we observed that elephant seals dived deeper within cyclonic eddies compared with anti-cyclonic structures. The behaviour of seals well illustrates the function of the spin-up of cyclonic eddies, where the upwelling of nutrients occurs at the centre, and high productivity and high concentration of prey occur at the edge. Productivity, aggregation of resources and accessibility of prey associated with cyclonic eddies probably act together to determine the selection of these structures by foraging elephant seals. However, eddies are not the only favourable foraging habitat within the Polar Frontal Zone, and the identification of oceanographic conditions associated with these other foraging zones requires further work.