A comparison of prey richness estimates for Weddell seals using diving profiles and image data

Abstract

Diving animals such as seabirds and marine mammals are top predators foraging under water, and play an important role in the marine ecosystems through foraging behavior. Recently developed animal-borne digital video or still cameras have made it possible to directly observe and estimate the prey richness of a foraging patch with simultaneously recorded diving profiles. Optimal foraging theory suggests that patch residence time should be affected both by the time it takes to travel to a prey patch and the richness of the patch. Therefore, diving profiles obtained by animal-borne depth and time instruments may be used to calculate a relative index of the richness of a prey patch used by diving animals in the water column. We tested this hypothesis by comparing the indices of prey richness estimated from both dive profiles and image data using adult female Weddell seals Leptonychotes weddellii at breeding colonies in Antarctica. There was a positive correlation between these 2 values, indicating that dive profiles can be used effectively to calculate a relative index of prey richness at a prey patch used by diving animals. © Inter-Research 2005.