Adélie penguin foraging behaviour and breeding success
in seasons of contrasting krill availability (Mawson Coast, Antarctica)

Parameters measured under the CCAMLR Ecosystem Monitoring Program (CEMP) for Adélie penguins at the Béchervaise Island CEMP site were compared between seasons of contrasting krill availability. Krill biomass estimates were derived from shipboard surveys carried out within the penguins’ normal foraging range during the 2001 and 2003 breeding seasons. More than three times as much krill was present during the two-week survey period in 2001 than in 2003. Penguin parameters that showed significant differences between the two seasons included A5: foraging trip duration, A6: breeding success and A8: meal mass and dietary composition. Penguins travelled further to forage in 2003 than 2001, stayed away longer and brought back smaller meals. Fish (mostly Pleuragramma antarcticum) contributed significantly to the diet in 2003 but was only a minor component in 2001. Differences between years were particularly apparent during the late guard to early crèche stages of chick rearing, coinciding with the timing of the krill survey. Chick mortality peaked during this period also. The findings illustrate the sensitivity of parameters A5 and A8 to prey availability during the short time scale of the chick rearing period. Data on meal mass and foraging trip duration were combined to provide an index of provisioning rate, analogous to the functional response referred to in predator-prey theory. This showed the expected concave monotonic relationship to krill biomass over the period of investigation. These results are discussed in relation to aspects of foraging behaviour, monitoring programs and management issues.