Ecology of Weddell seals during winter: Influence of environmental parameters on their foraging behaviour

Studying the foraging strategies of top predators can provide information on both how animals interact with their environment and the distribution of their prey. We studied the winter foraging behaviour of Weddell seals in Adélie Land, East Antarctica, and the influence of abiotic parameters (bathymetry, hydrology, sea ice, light intensity) on their foraging behaviour. A total of six seals were fitted with Conductivity Temperature Depth Satellite Relayed Data Loggers (CTD-SRDL) at Dumont D'Urville (∼67°S, 140°E) during the austral winters in 2007 and 2008. The tags transmitted positions and dive information over 169±31 day, providing a total of 20,400 dive profiles and 2350 CTD profiles. Significant environmental influences on seal diving behaviour and habitat use were detected. Seals dived deeper, longer and increased their foraging effort during the day than at night with intermediate values for twilight. During the winter season the maximum dive depth decreased in association with an increase in dive duration, but foraging effort was unchanged. Seals spent more time at the bottom of their dives in shallow waters associated with relatively smooth bathymetry and dominated by Antarctic Surface Water. Considering the whole winter, Weddell seals tended to favour enriched, warmer and less dense water masses following their seasonal appearance on the shelf (Antarctic Surface Water and Modified Circumpolar Deep Water). Our results are consistent with seals feeding primarily on Pleuragramma antarcticum during winter, tracking their vertical diel migrations and foraging in areas associated with bathymetric and hydrographic features likely to concentrate prey patches.