THE RELATIONSHIP BETWEEN FORAGING BEHAVIOR AND ENERGY-EXPENDITURE IN ANTARCTIC FUR SEALS

By using time-depth recorders to measure diving activity and the doubl y-labelled water method to determine energy expenditure, the relations hip between foraging behaviour and energy expenditure was investigated in nine Antarctic fur seal females rearing pups. At-sea metabolic rat e (MR) (mean of 6.34 +/- 0.4 W . kg(-1) 4.6 times predicted BMR) was p ositively correlated to foraging trip duration (mean of 4.21 +/- 0.54 days; r(2) = 0.5, P < 0.04). There were no relationships between MR an d the total number of dives, the total time spent diving or the total vertical distance travelled during the foraging trip. There was, howev er, a close negative sigmoidal relationship (r(2) = 0.93) between at-s ea MR and the proportion of time at sea spent diving. This measure of diving behaviour may provide a useful, inexpensive means of estimating foraging energy expenditure in this species and possibly in other ota riids. The rate of diving (m . h(-1)) was also negatively related to a t-sea MR (r(2) = 0.69, P < 0.005). Body mass gain during a foraging tr ip had a positive relationship to the time spent at sea (r(2) = 0.58, P < 0.02) and the total amount of energy expended while at sea (r(2) = 0.72, P < 0.004) such that, while females undertaking long trips have higher metabolic rates, the energetic efficiency with which females g ain mass is independent of the time spent at sea. Therefore, within th e range of conditions observed, there is no apparent energetic advanta ge for females in undertaking foraging trips of any particular duratio n.