Norwegian Polar Institute, Polar Environmental Centre, Tromsø, Norway.
PLoS One. 2010 Nov 3;5(11):e13816. 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.
威德尔海的水文学和环流是由南极环极流（ACC）在其东部边缘涌入的环极深海水（CDW）驱动的。在威德尔旋流内部，这种高营养、缺氧的水体的夹带和上升也支持了旋流内部的中层海洋生态系统以及沿南极大陆架丰富的底栖群落。我们使用了电导温度深度卫星中继数据记录仪（CTD-SRDL）来研究水文学变异性、冰盖和季节对南部象海豹在冬季觅食期间在威德尔海东部地区运动和潜水行为的重要性。我们开发了一个模型，将潜水深度描述为当地时间的函数，以解释潜水行为的日变化。在夏季，在无冰的开阔海域觅食的海豹表现出明显的日变化，白天潜水深度达到 500-1500 米，夜间则在 150-300 米深度寻找与 CDW 特征相符的次表层温度和盐度最大值。这种模式在旋流内部的威德尔冷暖和暖区尤为明显，出现在 ACC 中，但在海豹以底栖生物为食的德宁蒙兰大陆架地区却不存在。在冬季海冰覆盖的开阔海域觅食区，日变化几乎不存在，海豹在 500-700 米左右的深层觅食。因此，当象海豹在海洋环境之间移动或响应季节性环境条件时，它们似乎会在觅食策略之间切换。当它们在大陆架上时，它们利用当地丰富的底栖生态系统，而夏季开阔海域的日变化模式可能是对桡足类浮游动物为基础的浮游食物网内强烈垂直迁移模式的反应。这种在不同觅食策略之间切换的行为灵活性可能对南部象海豹适应其环境因气候变化而产生的可变性或系统变化具有重要意义。
