Exploitation of the marine environment by two sypatric albatrosses in the Pacific Southern Ocean

The marine habitat exploited by black-browed Diomedea melanophyrs and grey-headed albatrosses D. chrysostoma breeding at Campbell Island, New Zealand, was studied using satellite telemetry. Data were analysed in relation to the bathymetry and sea-surface temperature of the foraging zones. Black-browed albatrosses spent 55% of their time on the Campbell Plateau but also carried out long foraging trips to the Polar Front and Antarctic Zone at a distance of over 2000 km. They relied heavily on juvenile Micromesistius australis, a schooling fish, during foraging trips to the shelf but over oceanic waters the squid Martialia hyadesi was the main prey item. Grey-headed albatrosses spend 71% of their time foraging over the deep waters of the Polar Frontal Zone where M. hyadesi comprised over 90% of the mass of prey taken. No satellite-tracked birds fed over the shelf, but data from the duration of foraging trips and dietary analysis suggests that shelf-feeding is important for this species. Significant inter-species differences in the time spent in neritic and oceanic zones show that black-browed albatrosses were reliant primarily on shelf resources while grey-headed albatrosses are primarily oceanic feeders. In addition, the 2 species overlapped little in the zones used over oceanic waters, with black-browed albatrosses feeding in more southerly waters than grey-headed albatrosses. However, both species fed on M. hyadesi when foraging in association with the Polar Front.