Description: The region around the sill of the Filchner Trough outflow (77°S, 36°W) is considered a hot spot, both in terms of biology and physical oceanography. The factors contributing to this oceanic area of enhanced food availability and its relation to physical processes are not yet understood. Animal-borne satellite telemetry of southern elephant seal males, instrumented at King George Island / Isla 25 de Mayo aims to describe the seals' preferred foraging depths around the Filchner Trough in order to elucidate the vertical distribution of prey in relation to the oceanographic features on-site. Recent deployments (2010) represent a follow-up study of an ARGOS satellite telemetry project on elephant seals in 2000. Adult males travelled deep into the winter pack ice of the Weddell Sea along the western continental shelf break until they reached the region of the sill of the Filchner Trough outflow, where they remained in a localized 100 km wide shelf-slope area for several months. The re-instrumentation aims to investigate if males continue to travel to similar areas. The trilateral, long-term observation study of scientists from South Africa, Argentina and Germany is based on a synoptic approach for Marion Island and King George Island / Isla 25 de Mayo.

Description: Marine mammals forage in dynamic environments characterized by variables that are continuously changing in relation to large-scale oceanographic processes. In the present study, behavioural states of satellite-tagged juvenile southern elephant seals (n = 16) from Marion Island were assessed for each reliable location, using variation in turning angle and speed in a state–space modelling framework. A mixed modelling approach was used to analyse the behavioural response of juvenile southern elephant seals to sea-surface temperature and proximity to frontal and bathymetric features. The findings emphasised the importance of frontal features as potentially rewarding areas for foraging juvenile southern elephant seals and provided further evidence of the importance of the area west of Marion Island for higher trophic-level predators. The importance of bathymetric features during the transit phase of juvenile southern elephant seal migrations indicates the use of these features as possible navigational cues.

Description: Satellite-relay data loggers (SRDLs) were deployed on southern elephant seals hauled out at Marion Island as part of the International Polar Year project, Marine Mammal Exploration of the Oceans Pole to Pole (MEOP). We describe the dive behaviour responses of one male elephant seal to changes in oceanographic conditions during two post-moult migrations. The seal concentrated his diving activity in a small area (〈200 square km) in close proximity to the Prince Edward Islands during both migrations. The restricted area utilised by the animal allowed for temporal comparisons in dive behaviour and excluded potential effects associated with changes in geographic position. The SRDLs transmitted a total of 16806 temperature points (1265 temperature profiles). Mean monthly in situ surface temperatures were significantly correlated with remotely sensed (MODIS) SST data for the study area. Surface and subsurface temperatures in the study area remained stable throughout both migrations, but were colder in October 2006 due to an intrusion of a cold, anti-cyclonic feature. Dive depths obtained by the seal were similar between years, though dives were longer during 2007. The differences in dive durations between years were a result of the seal spending more time at depths between 300m and 500m during 2007, when compared to 2006. During the colder period of October 2006, the instrumented seal performed shallower and shorter dives when compared to the rest of the migration period. The seal spent relatively more time near the maximum depths of dives during this period, indicating a likely increase in foraging effort. Our results highlight a link between oceanographic data obtained from seal-borne instrumentation and dive behaviour of elephant seals. This is even more pronounced by deploying tags to the same individual over several consecutive years, which excludes interspecific effects in multiyear comparisons. We furthermore suggest that elephant seals alter their dive behaviour on a fine scale to maximise foraging benefits associated with variations in oceanographic conditions, particularly in proximity to mesoscale features.

Description: Deployments of ARGOS satellite transmitters on 19 post-breeding adult southern elephant seal males at King George Island / Isla 25 de Mayo in November 2013 represent a follow-up study of earlier projects on post-moulting adult males satellite tagged in 2000 and 2010. These previous deployments were constrained by the fact that only a small fraction of the satellite tagged seals could be unequivocally attributed to the local breeding population of the Antarctic Specially Protected Area (ASPA) 132 on King George Island / Isla 25 de Mayo due to earlier permanent marking procedures. As a result, a number of the previous tracks ended at South Georgia towards the breeding season, implying that the tagged seals originated from that breeding colony. The recent tracks represent the first deployments on post-breeding males at the ASPA 132 and they include about 50% of the population of adult males that were present during the breeding period either as harem bulls (n = 3), challengers (n = 7), or isolated males (n = 9) between October and December 2013. Of the 19 transmitters, two failed within the first two weeks after deployment and were disregarded for further analyses. The post-breeding long-distance foraging tracks of the remaining 17 males were primarily oriented along the continental shelf margin towards the Bellingshausen and even Amundsen Seas (n = 12), and shorter tracks along the Bransfield Strait / Mar de la Flota to the North (n = 4) and around the tip of the Antarctic Peninsula (n = 1). This suggests far more south-westerly oriented foraging movements of mature males of the ASPA 132 elephant seal colony than previously assumed. All seals showed extended residence times at specific circumscribed at-sea locations, considered as foraging hot spots. These spots were widely distributed within the aforementioned marine areas and coincide with bathymetric features, such as slopes, bays and troughs.

Description: McIntyre et al. (2011a; Mar Ecol Prog Ser 441:257-272) illustrated a number of relationships between environmental variables and the dive behaviour of satellite-tracked southern elephant seals Mirounga leonina. One of these associations was that seals tended to increase their dive depths and spend less time at targeted dive depths when swimming in warmer waters. Boersch-Supan et al.’s (2012; Mar Ecol Prog Ser 461:293-298) comment on this study suggests that the link described between dive depths and in situ temperature is actually a link between dive depths and prey distribution. We do not dispute this assertion, having discussed this likelihood in McIntyre et al. (2011a). Boersch-Supan et al. (2012) further provide a number of criticisms, based partly on their observations of potential prey distributions within a comparatively small geographic area. We argue that their results are not directly comparable to those presented in McIntyre et al. (2011a) given the limited spatial overlap of the study areas and sparse, small-scale dataset presented. We further provide replies to technical comments by Boersch-Supan et al. (2012) pertaining to our data analyses.

Description: We describe the habitat use of 22 male southern elephant seals (Mirounga leonina) satellite tagged at Marion Island between 2004 and 2008. While a few areas of increased utilization appeared to be associated with areas of shallower bathymetry (such as sea-floor ridges and fracture zones), seals in our study did not target other areas of shallow bathymetry within close proximity to Marion Island. Rather, most elephant seals foraged pelagically over very deep water where much variation was evident in diel vertical migration strategies. These strategies resulted in generally deeper and longer dives than what has been reported for male elephant seals from other colonies. No significant differences were recorded for dive durations or dive depths between adults and sub-adults. However, younger animals displayed a positive relationship between dive durations and age, as well as between dive depths and age, while these relationships became negative for older animals. Mixed model outputs suggested that seals increased their aerobic fitness as migrations progressed, enabling them to undertake longer dives. We conclude that Marion Island male elephant seals exhibit much variability in dive strategy and are seemingly capable of exploiting a range of different prey types occurring in various depth layers.

Description: The potential effects of ocean warming on top predators are largely unknown, though the impact on the distribution of prey in vertical space may have far reaching impacts on diving predators such as southern elephant seals. We used data from satellite-tracked southern elephant seals from Marion Island (46° 54’S; 37° 45’E) to investigate the relationship between their dive characteristics (dive depths, dive durations and time-at-depth index values) and environmental variables (temperature at depth, depth of Tmax below 100m, frontal zone and bathymetry) as well as other demographic and behavioural variables (migration stage, age-class, track day and vertical diel strategy). While other variables, such as bathymetry and vertical diel strategy influenced dive depth, our results also consistently indicated a significant influence of temperature at depth on dive depths. This relationship was positive for all groups of animals, indicating that seals dived to deeper depths when foraging in warmer waters. Female seals adjusted their dive depths proportionally more than males in warmer water. Dive durations were also influenced by temperature at depth, though to a lesser extent. Results from time-at-depth indices showed that both male and female seals spent less time at targeted dive depths in warmer water, and were presumably less successful foragers when diving in warmer water. Continued warming of the Southern Ocean may result in the distribution of prey for southern elephant seals shifting either poleward and/or to increasing depths. Marion Island elephant seals are expected to adapt their ranging and diving behaviour accordingly, though such changes may result in greater physiological costs associated with foraging.

Description: The development of models of marine ecosystems in the Southern Ocean is becoming increasingly important as a means of understanding and managing impacts such as exploitation and climate change. Collating data from disparate sources, and understanding biases or uncertainties inherent in those data, are important first steps for improving ecosystem models. This review focuses on seals that breed in ice habitats of the Southern Ocean (i.e. the crabeater seal, Lobodon carcinophaga; Ross seal, Ommatophoca rossii; leopard seal, Hydrurga leptonyx; and Weddell seal, Leptonychotes weddellii). Data on populations (abundance and trends in abundance), distribution and habitat use (movement, key habitat and environmental features) and foraging (diet) are summarised, and potential biases and uncertainties inherent in those data are identified and discussed. Spatial and temporal gaps in knowledge of the populations, habitats and diet of each species are also identified.