Summary
The foraging behaviour of Adélie penguins Pygoscelis adeliae was studied simultaneously at Shirley Island (SI, 110° E) and at Petrel Island (PI, 140° E) in approximate conjunction with the ship-based krill survey conducted on board the RSV Aurora Australis. Acoustic and trawl data were collected near both study sites, albeit at the end of the penguins breeding season. The distances travelled by Adélie penguins from Shirley Island were significantly greater than those travelled by penguins from Petrel Island (SI 31 - 144 km; PI 6 - 79 km). Mean foraging trip durations and mean maximal distances travelled were also significantly different between colonies (duration: SI guard 55 ± 32 h, crèche 113 ± 17 h; PI guard 32 ± 9 h, crèche 25 ± 7 h; distance: SI guard 182 ± 135 km, crèche 353 ± 93 km; PI guard 100 ± 42 km, crèche 86 ± 28 km). All penguins foraged over the continental shelf or the shelf-break and not in oceanic waters. The percentage distribution of dive depths was similar at both colonies; nearly 70 % of all dives were to < 35 m. Trawls from the ship contained krill Euphausia superba and E. crystallorophias near SI but only E. superba near PI. Biomass measurements showed that near SI 61 % of krill biomass occurred at 63 - 97 m but the penguins dived to this depth range only 12 % of their time; near PI 83 % of the biomass was found from 43 - 63 m and 20 % of dives reached these depths. The diet of the SI penguins consisted mainly of E. crystallorophias (51 - 53 % by mass), while penguins from PI ingested large amounts of both euphausiids (27 - 38 % E. superba, 22 - 39 % E. crystallorophias). At SI, the remainder of the diet consisted of fish, mainly Pleuragramma antarcticum (26 - 30 %), and amphipods (< 1 %). Similarly, at PI, fish contributed 19 - 37 % to the penguins diet and amphipods constituted 1 - 3 %.