Krill (Euphausia superba) abundance and Adelie penguin (Pygoscelis adeliae) breeding performance in the waters off the Bechervaise Island colony, East Antarctica in 2 years with contrasting ecological conditions

In 2001 and 2003 small-scale acoustic surveys of Antarctic krill (Euphausia superba) distribution and abundance were conducted offshore from an East Antarctic colony of Adelie penguins on Bechervaise Island (67 degrees 35'S, 62 degrees 49'E) that has been monitored for 15 years. Although the distribution of krill was similar between the two summers, their abundance in 2001 was estimated to be 3 times higher than in 2003. This biomass difference was reflected in the breeding performance of the penguins at the monitored colony. Significant differences were observed between the two seasons in foraging trip duration during chick rearing, breeding success, 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 were only a minor component in 2001. Differences between years were particularly apparent during the late guard to early creche stages of chick rearing, coinciding with the timing of the krill survey. Chick mortality peaked during this period also. Krill demographics showed little difference between the 2 years.

Oceanographically, the two summers differed; in 2003 the mixed layer was fresher and shallower, indicating a delayed melting of sea-ice in the study area when compared to 2001. Satellite observations indicated that the pack-ice directly offshore from the Mawson coast broke out earlier in 2001 and the perennial fast-ice along the coast persisted later in 2003.