Winter foraging hotspots of Weddell seals (Leptonychotes weddellii) in the southern Weddell Sea

The marine region off the Filchner Trough in the southern Weddell Sea is characterized by the continuous outflow of "supercooled" Ice Shelf Water (ISW) originating from the Filchner-Ronne Ice Shelf. The interaction of ISW with the Warm Deep Water (WDW) of the Weddell Gyre circulation is assumed to convert the Filchner region in an oceanographic “hotspot” that may also show enhanced productivity and corresponding high abundances of marine top predators. Since climate models project an increased melting of the Filchner-Ronne Ice Shelf for the twenty-first-century induced by redirected warm water currents, this “hotspot” may soon undergo rapid environmental transformations. Recent investigations, therefore, aimed at an integrative food web analysis of the poorly studied Filchner Outflow System (FOS). In this context, Weddell seals (Leptonychotes weddellii) are important and abundant top predators, which are known to inhabit the FOS perennially. Since information on movements, habitat use and foraging behaviour of top predators at the FOS is scarce, Weddell seals (n = 6) were tagged with CTD-combined satellite-relayed dive loggers (CTD-SRDLs) during the interdisciplinary research expedition PS82 of RV Polarstern in 2013/2014. A series of linear mixed effects models was applied in order to investigate effects of environmental factors (e.g. bathymetry, hydrography, light intensities) on the diving behaviour of Weddell seals during austral winter. This enabled an insight into the seals’ vertical habitat use. Indices for foraging effort were used to identify preferred foraging depths, which leads to inferences about prey preferences and distribution. Preliminary results revealed that certain areas in the FOS can be regarded as foraging “hotspots” characterized by long residence times and high foraging effort. Overall, this study enhances our understanding of Weddell seals as part of the FOS food web. This is of special interest, as the FOS food web is already threatened by climatic changes.

Promotor(s) & Supervisor: Horst Bornemann
Thesis Institute: Alfred Wegener Institute

ISCED Categories

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0588 - Scientific modelling", "0521 - Ecology", "0522 - Conservation and environmental management