Effects of hydrographic variability on the spatial, seasonal and diel diving patterns of southern elephant seals in the eastern Weddell Sea

• Published in: PloS one Vol. 5; no. 11; p. e13816
• Main Authors: Biuw, Martin, Nøst, Ole Anders, Stien, Audun, Zhou, Qin, Lydersen, Christian, Kovacs, Kit M
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 03.11.2010; Public Library of Science (PLoS)
• Subjects: Algorithms; Analysis; Animal behavior; Animal Migration - physiology; Animals; Antarctic Circumpolar Current; Antarctic Regions; Aptenodytes; Benthic environment; Biological activity; Biology; Circadian Rhythm - physiology; Climate change; Copepoda; Deep water; Diet; Diving; Diving - physiology; Diving behavior; Ecology/Behavioral Ecology; Ecology/Marine and Freshwater Ecology; Ecosystem; Ecosystem biology; Ecosystems; Entrainment; Environmental changes; Environmental conditions; Fatty acids; Feeding; Feeding behavior; Feeding Behavior - physiology; Female; Fish; Food chains; Food webs; Foraging behavior; Geography; Global temperature changes; Hydrography; Ice cover; Leptonychotes; Male; Marine; Marine and Aquatic Sciences/Biological Oceanography; Marine and Aquatic Sciences/Physical Oceanography; Marine ecology; Marine mammals; Measuring instruments; Migration; Mirounga; Mirounga leonina; Models, Biological; Museums; Nototheniidae; Ocean circulation; Ocean currents; Oceanography; Oceans and Seas; Oxygen; Pelagic zone; Pleuragramma antarcticum; Polar environments; Salinity; Sea ice; Seals; Seals, Earless - physiology; Seasonal variability; Seasons; Studies; Summer; Switching; Temperature; Time Factors; Time of use; Upwelling; Variability; Variation; Water circulation; Water Movements; Antarctic Regions; Norway; Antarctica; Southern Ocean; PSE, Antarctica, Dronning Maud Land; PS, Antarctic Ocean, Antarctic Circumpolar Current; PSW, Weddell Sea; PSE, South Indian Ocean, Weddell Gyre
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0013816

Weddell Sea hydrography and circulation is driven by influx of Circumpolar Deep Water (CDW) from the Antarctic Circumpolar Current (ACC) at its eastern margin. Entrainment and upwelling of this high-nutrient, oxygen-depleted water mass within the Weddell Gyre also supports the mesopelagic ecosystem within the gyre and the rich benthic community along the Antarctic shelf. We used Conductivity-Temperature-Depth Satellite Relay Data Loggers (CTD-SRDLs) to examine the importance of hydrographic variability, ice cover and season on the movements and diving behavior of southern elephant seals in the eastern Weddell Sea region during their overwinter feeding trips from Bouvetøya. We developed a model describing diving depth as a function of local time of day to account for diel variation in diving behavior. Seals feeding in pelagic ice-free waters during the summer months displayed clear diel variation, with daytime dives reaching 500-1500 m and night-time targeting of the subsurface temperature and salinity maxima characteristic of CDW around 150-300 meters. This pattern was especially clear in the Weddell Cold and Warm Regimes within the gyre, occurred in the ACC, but was absent at the Dronning Maud Land shelf region where seals fed benthically. Diel variation was almost absent in pelagic feeding areas covered by winter sea ice, where seals targeted deep layers around 500-700 meters. Thus, elephant seals appear to switch between feeding strategies when moving between oceanic regimes or in response to seasonal environmental conditions. While they are on the shelf, they exploit the locally-rich benthic ecosystem, while diel patterns in pelagic waters in summer are probably a response to strong vertical migration patterns within the copepod-based pelagic food web. Behavioral flexibility that permits such switching between different feeding strategies may have important consequences regarding the potential for southern elephant seals to adapt to variability or systematic changes in their environment resulting from climate change.