Description: The crabeater seal (Lobodon carcinophaga) is the most abundant Antarctic seal and inhabits the circumpolar pack ice zone of the Southern Ocean. Until now, information on important environmental factors affecting its distribution as well as on foraging behaviour is limited. In austral summer 1998, 12 crabeater seals of both sexes and different age classes were equipped with satellitelinked dive recorders at Drescher Inlet (72.85°S, 19.26°E), eastern Weddell Sea. To identify suitable habitat conditions within the Weddell Sea, a maximum entropy (Maxent) modelling approach was implemented. The model revealed that the eastern and southern Weddell Sea is especially suitable for crabeater seals. Distance to the continental shelf break and sea ice concentration were the two most important parameters in modelling species distribution throughout the study period. Model predictions demonstrated that crabeater seals showed a dynamic response to their seasonally changing environment emphasized by the favoured sea ice conditions. Crabeater seals utilized ice-free waters substantially, which is potentially explained by the comparatively low sea ice cover of the Weddell Sea during summer 1998. Diving behaviour was characterized by short (〉90 % = 0-4 min) and shallow (〉90 % = 0-51 m) dives. This pattern reflects the typical summer and autumn foraging behaviour of crabeater seals. Both the distribution and foraging behaviour corresponded well with the life history of the Antarctic krill (Euphausia superba), the preferred prey of crabeater seals. In general, predicted suitable habitat conditions were congruent with probable habitats of krill, which emphasizes the strong dependence on their primary prey.

Description: The region of the Filchner Outflow System (FOS) in the southeastern Weddell Sea is characterized by intensive and complex interactions of different water masses. Dense Ice Shelf Water (ISW) emerging from beneath the ice shelf cavities on the continental shelf, meets Modified Warm Deep Water (MWDW) originating from the Antarctic Circumpolar Current at the sill of the Filchner Trough. These hydrographic features convert the FOS into an oceanographic key region, which may also show enhanced biological productivity and corresponding aggregations of marine top predators. In this context, six adult Weddell seals (Leptonychotes weddellii) were instrumented with CTD-combined satellite relay data loggers in austral summer 2014. By means of these long-term data loggers we aimed at investigating the influence of environmental conditions on the seals' foraging behaviour throughout seasons, focussing on the local oceanographic features. Weddell seals performed pelagic and demersal dives, mainly on the continental shelf, where they presumably exploited the abundant bentho-pelagic fish fauna. Diurnal and seasonal variations in light availability affected foraging activities. MWDW was associated with increased foraging effort. However, we observed differences in movements and habitat use between two different groups of Weddell seals. Seals tagged in the pack ice of the FOS focussed their foraging activities to the western and, partly, eastern flank of the Filchner Trough, which coincides with inflow pathways of MWDW. In contrast, Weddell seals tagged on the coastal fast ice exhibited typical central-place foraging and utilized resources close to their colony. High foraging effort in MWDW and high utilization of areas associated with an inflow of MWDW raise questions on the underlying biological features. This emphasizes the importance of further interdisciplinary ecological investigations in the near future, as the FOS may soon be impacted by predicted climatic changes.

Description: Transects of a Remotely Operated Vehicle (ROV) providing under-shelf ice video footage and hydrographic data were carried out during ANT-Land 2015/2016 via Neumayer Station III. The campaign was conducted in liaison with the research expedition Filchner Ronne Outflow System Now (FROSN) of RV Polarstern (PS96). The ROV deployment at the Drescher Inlet represents a follow-up study of seal investigations carried out during RV Polarstern's expedition PS82 at the Filchner Outflow System and at the Drescher Inlet in 2014. It also complements earlier investigations at these locations initiated in 1986 (PS65, PS48, PS34, PS20, PS17). The ROV was launched from sea ice within the Drescher Inlet. The establishment of an 1.5 to 1.5 m hole in the fast ice at -72.80279 (LAT) -19.23379 (LON) to allow the deployment of the ROV was by far the most time-consuming and physically exhausting effort. Opening of the 1.20 m thick sea ice close to a tidal crack and removing of a 6 m thick platelet ice layer beneath required more than five days. In addition, a full day after each of the two snow drift events was required to re-open the ice hole, and further daily maintenance of between one and four hours required to remove new platelet ice out of the hole. The V8Sii ROV (Ocean Modules) was equipped with two High Definition (HD) video cameras (Kongsberg oe14-502) in the front and one wide-angle camera (Bowtech L3C-550) in the rear. Both HD cameras were complemented with three parallel red lasers providing reference scales of 10 by 10 cm on the videos. The lighting is ensured by four LED lights (Bowtech LED- 2400 aluminium) in the front and one in the back. The ROV had a compass, an orientation sensor, an altimeter (Tritech Micron Echo Sounder), an obstacle avoidance sonar (Tritech Micron), and an Ultra Short Baseline (USBL) system (Easytrak Lite USBL, Applied Acoustics) to determine its exact underwater position relative to a GPS being installed on top of a crane over the ice hole. The USBL transducer was installed at the end of a six meter aluminum pole inside the ice hole. A sledge module bearing a CTD (SeaBird SBE19 plus) and sensors for pH, oxygen, light, fluorescence, as well as a Doppler Velocity Logger (Doppler Velocity Log (DVL) Teledyne RDI Instruments, Explorer PA) for bottom tracking and current measurements was mounted to the underside of the ROV. A mini-dredge and sampling box called Rowski's Bucket Broom (RBB) attached to the upper side of the ROV was available to obtain invertebrate specimens for post hoc morphological and genetic investigations. Setting out and retrieval of the ROV was achieved by an A-framed crane over the hole and coiling of the ROV cable was done by a hand winch, which was placed on a sledge next to the ice hole. All steering equipment was sheltered by a pop-up tent. Two successful dive operations under the ice shelf provided high resolution footage, hydrographic data, and samples of the under shelf ice community at depths of around 80 m. The video footage documents cryo-benthic isopod crustaceans attached head-down to the underside of the shelf ice at 80 m water depth, where they occur in dense aggregations and different life stages. The successful retrieval of invertebrate samples by the ROV allows the first genetic investigation of the corresponding species.