Southern Elephant Seal Foraging in the Southern Ocean

Twenty three juvenile (8-14 months of age) southern elephant seals (Mirounga leonina L.) from Macquarie Island were tracked during 1993 and 1995. Migratory tracks and ocean areas with concentrated activity, presumed to be foraging grounds, were established from location data gathered by attached geolocation time depth recorders. The seals ranged widely (811-3258 km) and foraging activity centred on oceanographic frontal systems, especially the Antarctic Polar Front and bathymetric features such as the Campbell Plateau region. The seals spent 58.6% of their sea time within managed fishery areas while the remainder was spent on the high seas, an area of unregulated fishing. The Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) areas 58.4.1, 88.2 and especially 88.1 were important and distant foraging areas for these juvenile elephant seals. From fisheries records, diet and the foraging ecology studies of the seals there appears to be little, if any, overlap or conflict between the seals and commercial fishing operations within the regulated commercial areas. However, attention is drawn to the possibility of future interactions if Southern Ocean fisheries expand or new ones commence.

Furthermore...

The dive duration of 16 underyearling (6-12 months old) southern elephant seals Mirounga leonina during their second trip to sea was investigated using geolocating time depth recorders. Underyearling seals had a lesser diving ability, with respect to duration and depth, than adult southern elephant seals. Individual underyearlings dived for average durations of up to 20.3 minutes and depths up to 416m compared to durations and depths of 36.9 minutes and 589m, respectively for adults. Dive duration was positively related to their body mass at departure, indicating that smaller seals were limited to shorter dive durations, perhaps as a result of their lesser aerobic capacity. All seals often exceeded their theoretical aerobic dive limit (average of 22.1 plus/minus 18.1%). The number of dives exceeding the theoretical aerobic dive limit was not related to mass, suggesting that factors other than mass, such as foraging location or prey availability, may have been responsible for the differences in diving effort. Foraging ability, indicated by the ability of the seals to follow vertically moving prey, was positively related to seal mass, indicating that small mass restricted foraging ability. The shorter dive durations of the smaller seals inferred that they had shallower dive depths in which to search for prey, thus restricting foraging ability. Although foraging ability was restricted by size, foraging success was found to be inversely related to mass, the smaller seals gaining a higher proportion of blubber than larger seals during their foraging trips. Thus, despite smaller seals being restricted to shallower depths and shorter durations, their foraging success was not affected.

The fields in this dataset are:

Area
Perimeter
ID
Latitude
Longitude
Time
Percent
CCAMLR
EEZ
Season
Seal
Sex
Age (months)
Days at Sea
Range (km)
Bearing (degrees)
Sea Surface Temperatures (degrees C)
Foraging Areas
Departure Mass (kg)
At sea mass gain (kg)
Rate of mass gain (kg)
Survival estimates
Length (m)
Girth (m)
Dives
Divers per hour
Total Time Diving
% trip diving
Dive Duration
Surface Time
Theoretical Aerobic Dive Limit
Drift

1993年至1995年间，研究人员对来自麦夸里岛的23头幼年南象海豹（Mirounga leonina L.，8~14月龄）开展了追踪监测。通过附着式地理定位时间深度记录仪（geolocation time depth recorder）采集的位置数据，研究人员确定了这些海豹的洄游路径与活动集中海域——这些海域被推测为其觅食场。海豹的活动范围跨度达811~3258千米，觅食活动集中于海洋锋面系统，尤以南极极锋（Antarctic Polar Front）及坎贝尔高原（Campbell Plateau）这类地形地貌区域为核心。这些海豹在海上活动的时间有58.6%处于管理型捕捞海域内，剩余时间则在公海——即无管制捕捞的海域——中度过。南极海洋生物资源养护委员会（Commission for the Conservation of Antarctic Marine Living Resources, CCAMLR）管辖的58.4.1、88.2及88.1号区域（尤以88.1为重），是这些幼年南象海豹重要且偏远的觅食区域。结合渔业记录、海豹食性及觅食生态学研究结果来看，在受管制的商业捕捞海域内，海豹与商业捕捞活动之间几乎不存在重叠或冲突——即便存在，程度也极微。不过需注意，若南大洋捕捞业进一步扩张或开启新的捕捞作业，未来二者之间仍有可能产生交互影响。

此外，研究人员借助地理定位时间深度记录仪，对16头1龄以下（6~12月龄）南象海豹的第二次出海行程中的潜水时长进行了观测。相较于成年南象海豹，1龄以下海豹的潜水能力（包括时长与深度）相对较弱：单只1龄以下海豹的平均潜水时长可达20.3分钟，最大潜水深度为416米；而成年海豹的平均潜水时长与最大深度分别为36.9分钟与589米。潜水时长与海豹出海时的体质量呈正相关，这表明体型更小的海豹潜水时长更短，这可能与其有氧代谢能力较弱有关。所有海豹的潜水时长常常超出其理论有氧潜水极限（平均超出22.1%±18.1%）。超出理论有氧潜水极限的潜水次数与体质量并无关联，这表明除体质量外，其他因素（如觅食位置或猎物可获得性）可能是造成潜水努力程度差异的原因。以海豹追踪垂直移动猎物的能力作为觅食能力的衡量指标，结果显示觅食能力与海豹体质量呈正相关，即体质量更小的海豹其觅食能力受到限制。体型更小的海豹潜水时长更短，这意味着它们的潜水觅食深度更浅，进而限制了其觅食能力。尽管觅食能力受体型限制，但研究发现觅食成功率与体质量呈负相关：在出海觅食期间，体型更小的海豹其体脂储备占比高于体型更大的个体。因此，即便体型更小的海豹被限制在更浅的潜水深度与更短的潜水时长内，其觅食成功率并未受到影响。

本数据集包含以下字段：
区域、周长、编号、纬度、经度、时间、占比、CCAMLR区域、专属经济区（EEZ）、季节、海豹个体、性别、月龄、海上活动天数、活动范围（千米）、方位角（度）、海表温度（摄氏度）、觅食区域、出海时体质量（千克）、海上体质量增量（千克）、体质量增加速率（千克）、存活率估算值、体长（米）、围长（米）、潜水次数、每小时潜水次数、总潜水时长、行程潜水占比、潜水时长、水面停留时长、理论有氧潜水极限、漂移量