Slow to change? Individual fidelity to three-dimensional foraging habitats in southern elephant seals, Mirounga leonina

Long-term fidelity to foraging areas may have fitness benefits to individuals, particularly in unpredictable environments. However, such strategies may result in short-term energetic losses and delay responses to fast environmental changes. We used satellite tracking data and associated diving data to record the habitat use of nine individual southern elephant seals over 34 winter migrations. By assessing overlap in two- and three-dimensional home ranges we illustrate strong long-term (up to 7-year) fidelity to foraging habitat. Furthermore, a repeatability statistic and hierarchical clustering exercise provided evidence for individual specialization of foraging migration strategies.We discuss the possible influences of stable long-term foraging migration strategies on the adaptability of individual elephant seals to rapid environmental change. Our results further illustrate the need for more long-term longitudinal studies to quantify the influence of individual-level site familiarity, fidelity and specialization on population-level resource selection and population dynamics

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

Habitat-based density models of pack-ice seal distribution in the southern Weddell Sea, Antarctica

Climate variability and changes in sea ice dynamics have caused several ice-obligate or krill-dependent populations of marine predators to decline, eliciting concern about their demographic persistence and the indirect ecological consequences that predator depletions may have on marine ecosystems. Pack-ice seals are dominant ice-obligate predators in the Antarctic marine ecosystem, but there is considerable uncertainty about their abundance and population trends. We modelled the density and distribution of pack-ice seals as a function of environmental covariates in the southern Weddell Sea, Antarctica. Our density surface modelling approach used data from aerial surveys of pack-ice seals collected in the 2013/14 austral summer. Crabeater seals Lobo don carcinophaga, the most numerous pack-ice seal we observed, occurred at the highest densities in areas with extensive sea ice near the continental shelf break, but were almost absent in areas of similar sea ice concentration in the southern extent of the Weddell Sea. The highest densities of Weddell seals Leptonychotes weddelli, which were less abundant than crabeater seals within the pack-ice habitat, were predicted to occur over the continental shelf, near the shelf break. The distribution of both seal species broadly corresponded with the distribution and relative abundance of their main prey (Antarctic krill Euphausia superba and Antarctic silverfish Pleuragramma antarctica) obtained from concurrent ecosystem surveys. Ross seals Ommatophoca rossii and leopard seals Hydrurga leptonyx were not detected at all and are apparently rare within the southern Weddell Sea. These results can contribute to biodiversity assessments in the context of marine protected area planning in this region of the Southern Ocean

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

Effects of Smart Position Only (SPOT) Tag Deployment on White Sharks Carcharodon carcharias in South Africa

We present 15 individual cases of sub-adult white sharks that were SPOT tagged in South Africa from 2003–2004 and have been re-sighted as recently as 2011. Our observations suggest SPOT tags can cause permanent cosmetic and structural damage to white shark dorsal fins depending on the duration of tag attachment. SPOT tags that detached within 12–24 months did not cause long term damage to the dorsal fin other than pigmentation scarring. Within 12 months of deployment, tag fouling can occur. After 24 months of deployment permanent damage to the dorsal fin occurred. A shark survived this prolonged attachment and there seems little compromise on the animal's long term survival and resultant body growth. This is the first investigation detailing the long term effects of SPOT deployment on the dorsal fin of white sharks

Antarctic pack ice seals and oceanographic features at the Filchner Outflow System, southern Weddell Sea

The Filchner Outflow System (FOS) in the southern Weddell Sea is one of the most important areas for deep water formation. Here the outflow of Ice Shelf Water (ISW) of the Filchner Ronne Ice Shelf interacts with Warm Deep Water (WDW) of the Weddell Gyre circulation, resulting in Weddell Sea Deep and Bottom Water production (WSDW, WSBW). The interaction around the sill of the Filchner Trough is thought to result in a physical oceanography "hotspot" that may also aggregate primary and secondary producers, leading to increased abundance of top predators. However, data on top predator abundance for the FOS are scarce. Two aerial surveys over ice-covered sea were carried out to estimate density gradients and the regional abundance of pack ice seals in the FOS. A digital imaging survey with fixed wing research aircraft Polar 6 in November 2013 preceded a helicopter survey from aboard RV Polarstern during January 2014. The Polar 6 survey comprised 11 transects summing to a survey effort of 1,148.44 km. 265 seals were counted on transect lines with a higher encounter rate on transects located further to the west. The helicopter survey allowed seal species to be identified. Twenty-five transects (1,367.61 km) were flown in the FOS region and another six transects (425.54 km) further south within the Filchner Trough. Only two seal species, the crabeater seal (Lobodon carcinophaga) (n = 754) and the Weddell seal (Leptonychotes weddellii) (n = 217), were observed. Distance sampling analysis suggested that the density of seals differed strongly between the two survey regions, with very few seals encountered on transects located in the more southerly Filchner Trough region. A longitudinal density gradient increasing from east to west within the FOS region during January 2014 supported the results obtained from the Polar 6 survey, but failed to support the idea of a top predator hotspot at the sill of the Filchner Trough at least for seals

Editorial Animal Ethics and Ecotourism

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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

Distribution, density and abundance of Antarctic ice seals off Queen Maud Land and the eastern Weddell Sea

The Antarctic Pack Ice Seal (APIS) Program was initiated in 1994 to estimate the abundance of four species of Antarctic phocids: the crabeater seal Lobodon carcinophaga , Weddell seal Leptonychotes weddellii , Ross seal Ommatophoca rossii and leopard seal Hydrurga leptonyx and to identify ecological relationships and habitat use patterns. The Atlantic sector of the Southern Ocean (the eastern sector of the Weddell Sea) was surveyed by research teams from Germany, Norway and South Africa using a range of aerial methods over five austral summers between 1996–1997 and 2000–2001. We used these observations to model densities of seals in the area, taking into account haul-out probabilities, survey-specific sighting probabilities and covariates derived from satellite-based ice concentrations and bathymetry. These models predicted the total abundance over the area bounded by the surveys (30° W and 10° E). In this sector of the coast, we estimated seal abundances of: 514 (95 % CI 337–886) 10^3 crabeater seals, 60.0 (43.2–94.4) 10^3 Weddell seals and 13.2 (5.50–39.7) 10^3 leopard seals. The crabeater seal densities, approximately 14,000 seals per degree longitude, are similar to estimates obtained by surveys in the Pacific and Indian sectors by other APIS researchers. Very few Ross seals were observed (24 total), leading to a conservative estimate of 830 (119–2894) individuals over the study area. These results provide an important baseline against which to compare future changes in seal distribution and abundance