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

The region of the Filchner Outflow System (FOS) in the southeastern Weddell Sea is characterized by intensive and complex interactions of different water masses. These hydrographic features convert the FOS in an oceanographic hotspot, 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 dive loggers during austral summer 2014 to investigate the influence of environmental conditions on the seals’ foraging behaviour over winter and identify potential foraging hotspots in the FOS. Weddell seals preferred foraging in shallow areas of the continental shelf (< 700 m), where they presumably exploited the abundant bentho-pelagic fish fauna during both pelagic and demersal dives. Diurnal and seasonal variations in light availability also affected foraging activities. Furthermore, Eastern Shelf Water and modified Warm Deep Water were associated with increased hunting time and foraging effort. Moreover, two areas in the FOS were emphasized as potential foraging hotspots characterized by long residence times suggesting enhanced prey availability. However, the underlying biological principles contributing to these foraging hotspots still remain unclear. This highlights the importance of further ecological investigations as the FOS is already threatened by predicted climatic changes

Distribution and diving behaviour of crabeater seals (Lobodon carcinophaga) in the Weddell Sea

The crabeater seal (Lobodon carcinophaga) is the most abundant seal worldwide and inhabits the circumpolar pack ice zone of the Southern Ocean. Around half of its population is found in the Weddell Sea. By now, information on important environmental factors which affect their distribution as well as on geographic and seasonal differences in diving and foraging behaviour is limited due to the inaccessibility of their habitat. In austral summer 1998, a heterogeneous group of 12 crabeater seals belonging to both sexes and different age classes was equipped with satellite-linked time-depth recorders (SDRs) at Drescher Inlet (72.85°S, 19.26°E) in the eastern Weddell Sea. The transmitters provided data for a duration between 7 and 117 days (mean = 54.9 d). During this time the tagged seals dispersed radially in the Weddell Sea and covered large distances (mean = 1,763 km). To identify environmental variables which influence the distribution of crabeater seals and to predict suitable habitats, a maximum entropy (Maxent) modelling approach was implemented. It revealed that sea ice concentration mattered most in modelling species distribution with increasing probabilities of presence towards the ice edge. However, seals spent an unusually high amount of 64.4% in open waters and were only occasionally found in ice-covered zones during the study period. This is likely to be related to the comparatively low sea ice cover of the Weddell Sea in summer 1998. Although crabeater seals are generally closely associated with pack ice, it seemed to be that they can deal better with open water conditions than previously thought. Further important factors identified by Maxent were surface temperature, water depth and distance to the shelf break. All these four environmental variables are known to influence and determine the distribution of Antarctic krill (Euphausia superba), the preferred prey of crabeater seals. In general, predicted suitable habitats were congruent with probable habitats of krill. Beside geographic locations, satellite-linked data logger record dive data. Diving behaviour in this thesis was characterized by short (>90% = 0 – 5 min) and shallow (>80% = 0 – 72 m) dives. This pattern reflects the typical summer and autumn diving and foraging behaviour of crabeater seals since krill is abundant in the upper 150 m of the water column during summer. Differences between age classes were not evident. In contrast, diving behaviour showed seasonal differences with dives becoming shorter and shallower in autumn. This behaviour corresponds to the biology and ecology of krill which inhabits the under ice habitat during autumn and winter. This shows that both the vertical and horizontal distribution of crabeater seals is closely related to its primary prey

Under-shelf ice foraging of Weddell seals

The Weddell seal (Leptonychotes weddellii) inhabits the Antarctic coastal ecosystem and aggregates in areas characterized by a stable fast ice layer. Due to their extreme diving capabilities, they are able to exploit both pelagic and benthic prey resources. They mainly feed on fishes but occasionally also take cephalopods and crustaceans. Weddell seals instrumented with still-picture camera loggers in the Drescher Inlet, eastern Weddell Sea, detected an unknown cryo-benthic community underneath the floating ice shelf. Images show dense aggregations of invertebrates that likely represent an attractive food horizon for Weddell seals. In this context, we conducted a retrospective analysis of dive profiles collected in the Drescher Inlet to identify favoured hunting depths of Weddell seals and correlate those to the local physical and biological environment. A total of 34 adult Weddell seals were instrumented with dive loggers in the course of six summer field campaigns between 1990 and 2016. An automated broken stick algorithm was used to separate each dive profile into different segments. Segments with a high sinuosity were considered to indicate hunting. Segments characterized by a straight dive trajectories (low sinuosity), were assumed to be transit phases with no hunting activities. A tri-modal distribution of mean hunting depths suggests that Weddell seals concentrated their foraging activities in three depth strata. A peak in hunting depths below 370 m corresponds to the sea floor of the Drescher Inlet, indicating demersal foraging. A second peak between 110 and 160 m matches with the depth of the underside of the floating ice shelf, which suggests shelf ice associated foraging. The third peak probably represents hunting in the pelagic realm. Our investigation highlights the importance of the shelf ice underside as an attractive food horizon for Weddell seals suggesting a re-evaluation of trophic interactions and bentho-pelagic processes in the coastal Antarctic ecosystem

Habitat modelling of crabeater seals (Lobodon carcinophaga) in the Weddell Sea using the multivariate approach Maxent

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 satellite-linked 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

Winter foraging hotspots and habitat use of Weddell seals (Leptonychotes weddellii) at the Filchner Outflow System, southern Weddell Sea

The region of the Filchner Outflow System (FOS) in the southeastern Weddell Sea is characterized by intensive and complex interactions of different water masses. These hydrographic features convert the FOS in an oceanographic hotspot, 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 dive loggers during austral summer 2014 to investigate the influence of environmental conditions on the seals’ foraging behaviour over winter and identify potential foraging hotspots in the FOS. Weddell seals preferred foraging in shallow areas of the continental shelf (< 700 m), where they presumably exploited the abundant bentho-pelagic fish fauna during both pelagic and demersal dives. Diurnal and seasonal variations in light availability also affected foraging activities. Furthermore, Eastern Shelf Water and modified Warm Deep Water were associated with increased hunting time and foraging effort. Moreover, two areas in the FOS were emphasized as potential foraging hotspots characterized by long residence times suggesting enhanced prey availability. However, the underlying biological principles contributing to these foraging hotspots still remain unclear. This highlights the importance of further ecological investigations as the FOS is already threatened by predicted climatic changes

Foraging hotspots of Weddell seals in the southern Weddell Sea

The region of the Filchner Outflow System (FOS) in the southeastern Weddell Sea is characterized by intensive and complex interactions of different water masses. These hydrographic features convert the FOS in an oceanographic hotspot, 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 dive loggers during austral summer 2014 to investigate the influence of environmental conditions on the seals’ foraging behaviour over winter and identify potential foraging hotspots in the FOS. Weddell seals preferred foraging in shallow areas of the continental shelf (< 700 m), where they presumably exploited the abundant bentho-pelagic fish fauna during both pelagic and demersal dives. Diurnal and seasonal variations in light availability also affected foraging activities. Furthermore, Eastern Shelf Water and modified Warm Deep Water were associated with increased hunting time and foraging effort. Moreover, two areas in the FOS were emphasized as potential foraging hotspots characterized by long residence times suggesting enhanced prey availability. However, the underlying biological principles contributing to these foraging hotspots still remain unclear. This highlights the importance of further ecological investigations as the FOS is already threatened by predicted climatic changes

Foraging behaviour of Weddell seals (Leptonychotes weddellii) in connection to oceanographic conditions in the southern Weddell Sea

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

Shelf ice-associated cryo-benthos and environmental features

Incidences of cryo-benthic communities beneath ice shelves are rare and recent discoveries. Combined seal- and ROV-borne imagery and novel sampling technologies allowed for a re-assessment and augmentation of earlier findings on a cryo-benthic isopod community (Antarcturus cf. spinacoronatus), being attached head-down to the underside of floating shelf ice at depths of around 80-150m. The shelf ice-associated cryo-benthos was discovered at Drescher Inlet (-72.83667 -19.15300), Riiser-Larsen Ice Shelf (eastern Weddell Sea). The inlet constitutes a 25km long and between 2 and 4km wide crack in the surrounding shelf ice, which is associated with certain environmental features. Here we compile all available local physical, biological, and biogeochemical data and discuss their relevance in the wider regional context for this faunal hotspot. These include data on shelf, sea and platelet ice, seafloor topography, hydrography and water chemistry, as well as associated pelagic and benthic marine life, in particular affinities of the cryo-benthic isopod community to related fauna occurring in nearby seabed communities using molecular barcoding

The retrospective analysis of Antarctic tracking data project

The Retrospective Analysis of Antarctic Tracking Data (RAATD) is a Scientific Committee for Antarctic Research project led jointly by the Expert Groups on Birds and Marine Mammals and Antarctic Biodiversity Informatics, and endorsed by the Commission for the Conservation of Antarctic Marine Living Resources. RAATD consolidated tracking data for multiple species of Antarctic meso- and top-predators to identify Areas of Ecological Significance. These datasets and accompanying syntheses provide a greater understanding of fundamental ecosystem processes in the Southern Ocean, support modelling of predator distributions under future climate scenarios and create inputs that can be incorporated into decision making processes by management authorities. In this data paper, we present the compiled tracking data from research groups that have worked in the Antarctic since the 1990s. The data are publicly available through biodiversity.aq and the Ocean Biogeographic Information System. The archive includes tracking data from over 70 contributors across 12 national Antarctic programs, and includes data from 17 predator species, 4060 individual animals, and over 2.9 million observed locations

The retrospective analysis of Antarctic tracking data project

The Retrospective Analysis of Antarctic Tracking Data (RAATD) is a Scientific Committee for Antarctic Research project led jointly by the Expert Groups on Birds and Marine Mammals and Antarctic Biodiversity Informatics, and endorsed by the Commission for the Conservation of Antarctic Marine Living Resources. RAATD consolidated tracking data for multiple species of Antarctic meso- and top-predators to identify Areas of Ecological Significance. These datasets and accompanying syntheses provide a greater understanding of fundamental ecosystem processes in the Southern Ocean, support modelling of predator distributions under future climate scenarios and create inputs that can be incorporated into decision making processes by management authorities. In this data paper, we present the compiled tracking data from research groups that have worked in the Antarctic since the 1990s. The data are publicly available through biodiversity.aq and the Ocean Biogeographic Information System. The archive includes tracking data from over 70 contributors across 12 national Antarctic programs, and includes data from 17 predator species, 4060 individual animals, and over 2.9 million observed locations.Supplementary Figure S1: Filtered location data (black) and tag deployment locations (red) for each species. Maps are Lambert Azimuthal projections extending from 90° S to 20° S.Supplementary Table S1: Names and coordinates of the major study sites in the Southern Ocean and on the Antarctic Continent where tracking devices were deployed on the selected species (indicated by their 4-letter codes in the last column).Online Table 1: Description of fields (column names) in the metadata and data files.Supranational committees and organisations including the Scientific Committee on Antarctic Research Life Science Group and BirdLife International. National institutions and foundations, including but not limited to Argentina (Dirección Nacional del Antártico), Australia (Australian Antarctic program; Australian Research Council; Sea World Research and Rescue Foundation Inc., IMOS is a national collaborative research infrastructure, supported by the Australian Government and operated by a consortium of institutions as an unincorporated joint venture, with the University of Tasmania as Lead Agent), Belgium (Belgian Science Policy Office, EU Lifewatch ERIC), Brazil (Brazilian Antarctic Programme; Brazilian National Research Council (CNPq/MCTI) and CAPES), France (Agence Nationale de la Recherche; Centre National d’Etudes Spatiales; Centre National de la Recherche Scientifique; the French Foundation for Research on Biodiversity (FRB; www.fondationbiodiversite.fr) in the context of the CESAB project “RAATD”; Fondation Total; Institut Paul-Emile Victor; Programme Zone Atelier de Recherches sur l’Environnement Antarctique et Subantarctique; Terres Australes et Antarctiques Françaises), Germany (Deutsche Forschungsgemeinschaft, Hanse-Wissenschaftskolleg - Institute for Advanced Study), Italy (Italian National Antarctic Research Program; Ministry for Education University and Research), Japan (Japanese Antarctic Research Expedition; JSPS Kakenhi grant), Monaco (Fondation Prince Albert II de Monaco), New Zealand (Ministry for Primary Industries - BRAG; Pew Charitable Trusts), Norway (Norwegian Antarctic Research Expeditions; Norwegian Research Council), Portugal (Foundation for Science and Technology), South Africa (Department of Environmental Affairs; National Research Foundation; South African National Antarctic Programme), UK (Darwin Plus; Ecosystems Programme at the British Antarctic Survey; Natural Environment Research Council; WWF), and USA (U.S. AMLR Program of NOAA Fisheries; US Office of Polar Programs).http://www.nature.com/sdataam2021Mammal Research Institut