Benthic diving in male emperor penguins Aptenodytes forsteri foraging in winter

Abstract

We studied the foraging areas and diving depths of male emperor penguins Apten- odytes forsteri raising chicks at Pointe Geologie, Adelie Land, in relation to bathymetry and sea-ice conditions during the first foraging trip after incubation in August 1996 and 1997. Combining satel- lite-tracking and dive-recording devices on the same penguins allowed individual dives to be localised and related to water depth. The penguins mostly dived in zones less than 300 m deep, where they performed 50% of their dives and spent 54% of their bottom time near the sea floor, on average. Analyses including bathymetry and sea-ice cover for the 2 years suggest that after leaving the colony the penguins targeted the nearest available, fast-ice free shallow shelf waters (<300 m). Once in these areas, the penguins foraged by diving near the sea floor during most of the remaining part of their foraging trip. Day-by-day analysis showed that during this central part of the foraging trip, 68% of the dives ended near the sea floor. The most likely function of these dives appeared to be feeding on benthic or bentho-pelagic prey. Benthic dives were rare during the first and last days of trips, when penguins were apparently in transit. Benthic-feeding is interpreted as a strategy towards predictable prey during a critical stage of the breeding cycle. Shallow areas of the Antarctic conti- nental shelf may be important for some emperor penguin colonies around Antarctica. The importance of the benthic strata for this top predator of the Antarctic shelf ecosystem gives new insights on the trophic networks in the pack-ice during the Antarctic winter.