Crabeater seal diving behaviour in eastern Antarctica

Abstract

Southern Ocean waters are highly productive and contain important food resources for many indigenous predators, including humans. Management of these resources has fallen under the regulation of the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR), which has identified a suite of predators as indicator species for monitoring ecosystem fluctuations, including crabeater seals. For crabeater seals to fulfil this role, however, they must respond predictably to fluctuations in krill distribution and abundance. Here, we investigated the validity of using the diving behaviour of this species as an indicator of krill distribution and abundance. We used behavioural data collected from 23 crabeater seals fitted with satellite-linked time-depth recorders off eastern Antarctica to quantify habitat use as a function of the amount of time they spent within geographic regions with varying environmental characteristics. This was then linked with diving behaviour in those regions. By integrating geographic location and diving parameters, we demonstrated that habitat use and foraging behaviour within eastern Antarctic waters fluctuated in response to seasonal and spatial environmental variability. Our attempts to use oceanographic variables to develop models of crabeater seal habitat use and behaviour demonstrated real limitations in inferring behaviour from a simple set of environmental factors, but we identified ocean depth and the proximity to the ice edge as factors influencing seasonal habitat use and diving behaviour. Whilst our understanding of the influences driving crabeater seal distribution has improved as a result of telemetry studies, it would appear premature to infer cross-species patterns in distribution and abundance with krill given the low predictive power of models derived in the present study. Furthermore, the dynamic and regionally variable use of pelagic habitat by this widely abundant Antarctic predator has important implications for the estimation of crabeater seal biomass.