Follow the food: Effects of fish and zooplankton on the behavioral ecology of baleen whales

Abstract

Active acoustics were used to collect information on the type, distribution, and abundance of baleen whale prey species such as zooplankton and fish at fine spatial (sub-meter) and temporal (sub-minute) scales. Unlike other prey measurement methods, scientific echosounder surveys provide prey data at a resolution similar to what a predator would detect in order to efficiently forage. Data from several studies around the world shows that differences in prey type or distribution result in distinctly different baleen whale foraging behaviors. Humpback whales in coastal waters of Australia altered their foraging pattern depending on the presence and abundance of baitfish or krill. In Southeast Alaska, humpback whales foraged cooperatively or independently depending on prey type and abundance. Humpback whales in the Northwest Atlantic with multiple prey species available foraged on an energetically costly (and presumably rewarding) species. The vertical and horizontal movements of North Atlantic right whales in Cape Cod Bay were strongly correlated with very dense aggregations of copepods. In all of these cases, active acoustics were used to estimate numerical densities of the prey, which provides quantitative information about the energy resource available to foraging animals.