Foraging space of emperor penguins Aptenodytes forsteri in Antarctic shelf waters in winter

To determine the foraging space of emperor penguins Aptenodytes forsteri in winter, 12 females from Auster colony (13400 pairs) were equipped with satellite transmitters and time-depth recorders before departing on their 76 +/- 9 d winter (June to August) foraging trip. The females were also injected with tritiated water (HTO) lo estimate food consumption, and non-instrumented females were stomach sampled upon return to the colony to determine their diet. The same data were collected in August/September from 3 males foraging after :heir 4 mo ,prenuptial and incubation fast. Both females and males foraged in pack-ice within 120 km of the colony along a relatively narrow band of the continental shelf in water depths ranging from 200 to 500 m. Only rarely did penguins leave shelf waters to forage in deeper waters over the shelf break. The size of the general foraging area for females was about 11410 km(2), but 50% of all foraging days were spent in only about 15% (1700 km(2)) of the total foraging area. A female of average mass (25 Ig) hunted for about 6 h d(-1), and consumed 1.8 +/- 0.3 kg of food per foraging day. This indicates that females from Auster consumed in winter about 1520 t, about half of which is likely to have been taken from an area measuring only 60 x 28 km. Males were active for about 10 h d(-1) and consumed about twice as much (3.7 +/-: 1.2 kg d(-1) for a 24 kg male) as the females during the early phase of brooding. The diet of females comprised 72% fish (by mass), 16% squid and 12% Antarctic krill Euphausia superba whereas that of the males comprised 53% fish, 2% squid and 43% krill. Most foraging dives of females (81%) and males (64%) were to <200 m and lasted less about 3 min. Males dived deep (>300 m) more frequently than females (19.8% vs 0.1%) but the number of dives per day was similar for both sexes (27 +/- 14 for winter females, 31 +/- 15 for brood-stage males). The small foraging area, diet composition and prey harvest rates of the females provide indirect evidence of the availability of penguin prey species in the pack-ice off Auster in winter.