Energy requirements and daily food consumption of crabeater seals in the Antarctic winter pack-ice

Although the most abundant of all mammalian predators in the Antarctic marine ecosystem, crabeater seals are also one of the least understood. The most fundamental question of all - how many are there? - is the focus of an extensive international collaborative program (the Antarctic Pack-ice Seal Program, or APIS). This study supplements APIS by providing additional data on the diving behaviour and food requirements of crabeater seals, that can be used in conjunction with census data to provide information on the role of crabeater seals in the antarctic ecosystem.

Winter densities and distributions of Crabeater seals were collected during 1999. Crabeater seals were most often encountered on the shelf break. The data collected include numbers of seals sighted per hour in relation to the amount of time the ship spent in each 0.5 degree grid square.

This study is the first to describe the winter distribution of crabeater seals (Lobodon carcinophagus) in East Antarctica. The study was conducted in the Mertz Glacier Polynya region from July to August 1999. In total 89 crabeater seals were seen in 26 groups which ranged in size from 1 to 35 animals (mean = 3.2). The mean observed haulout density along a 200m wide strip transect was 0.108 seals per square kilometre, or 0.042 groups per square kilometre. Crabeater seals were not uniformly distributed in the polynya but selected areas of stable ice over shallow (less than 1000m) waters. We used a generalised linear model to assess the relationship of seal distribution to the physical attributes of sea ice concentration, thickness, and ocean depth. We found that ice thickness and ocean depth were the most important determinants of seal distribution. Crabeater seals occurred in areas where the ice affords them a stable haulout platform while allowing them access to Antarctic krill that live directly beneath the ice.

尽管食蟹海豹是南极海洋生态系统中数量最多的哺乳类捕食者，但它们也是了解最少的物种之一。最根本的问题——它们的数量有多少？——是一项大型国际合作项目（南极浮冰海豹项目，Antarctic Pack-ice Seal Program，简称APIS）的研究焦点。本研究通过提供食蟹海豹潜水行为和食物需求的额外数据对APIS进行补充，这些数据可与种群普查数据结合使用，以揭示食蟹海豹在南极生态系统中的作用。

1999年期间收集了食蟹海豹的冬季密度和分布数据。食蟹海豹最常出现在陆架坡折带。收集的数据包括每小时观测到的海豹数量，以及船只在每个0.5度网格单元内停留的时间。

本研究首次描述了东南极洲食蟹海豹（Lobodon carcinophagus）的冬季分布。研究于1999年7月至8月在默茨冰川冰间湖区域开展。共观测到89只食蟹海豹，分为26群，群规模从1只到35只不等（均值=3.2）。沿200米宽条带样线观测到的平均登陆密度为每平方公里0.108只海豹，或每平方公里0.042群。食蟹海豹在冰间湖内的分布并不均匀，而是偏好选择浅水区（水深小于1000米）上方的稳定冰区。我们采用广义线性模型（generalised linear model）评估海豹分布与海冰浓度、厚度及海洋深度等物理属性之间的关系。结果发现，冰厚和海洋深度是影响海豹分布的最重要决定因素。食蟹海豹倾向于栖息在那些既有稳定登陆平台，又能让它们获取冰下南极磷虾的冰区。