Crary bank: a deep foraging habitat for emperor penguins in the western Ross Sea

Abstract

Although most dives of emperor penguins (Aptenodytes forsteri) are less than 100 m, penguins from the Cape Washington colony regularly perform deep dives > 400 m. To evaluate the significance and location of these deep dives of birds on foraging trips from Cape Washington, we report the satellite tracks of three birds. We also review the frequency of deep dives in the 35 of 42 birds that performed deep dives during seven research seasons over 22 years. Records included 83,314 dives, of which 1418 were > 400 m deep (deepest 552 m). Durations of these deep dives ranged from 7 to 13 min, up to more than twice the aerobic dive limit. Inter-deep-dive-intervals (IDDIs) between most deep dives were 10–20 min. The travel routes of satellite-tagged birds showed that all three spent time over Crary Bank, about 100 km from Cape Washington. Dives > 400 m only occurred over Crary Bank in the two satellite-tracked birds that were also equipped with dive recorders. The depths of the dives were consistent with the distribution of the most common, and energy-dense prey item found in their diet, Pleuragramma antarctica. We conclude that significant food resources are located over Crary Bank, accounting for the deep dives and success of birds from Cape Washington, the second largest, stable colony of emperor penguins known.