Deep-diving odontocetes foraging strategies and their prey field as determined by acoustic techniques

Deep-diving odontocetes (sperm, short-finned pilot, and beaked whales; and Risso’s dolphins) are known to forage at deep depths in the ocean on squid and fish. These marine mammal species are top predators, and for this reason they are very important for the ecosystems they live in; they can affect prey populations and control food web dynamics through top-down effects. Many human marine activities are causing impacts on wild populations of deep-diving odontocetes by emitting noise in their natural environment (i.e., military exercises at sea, shipping, pile driving operations, etc.) that may cause animals to strand ashore. A better understanding of their distribution, foraging habits, and deep-sea habitats they feed in is the key to reducing these impacts through the regulation of noise emissions in areas that represent a good habitat for these species.

The studies I will present in this seminar investigate the foraging strategies of this group of marine mammals and the density and size of their potential prey in the deep ocean using passive and active acoustic techniques. Passive acoustics recorders were used to monitor the foraging activity of deep-diving odontocetes, and the density and size of animals living in deep-sea scattering layers was studied using a DIDSON imaging sonar at multiple stations along the Kona coast of Hawaii. Sperm and beaked whale foraging was found to vary in time and space, as well as the density of potential prey. Future studies should aim at linking the variability of these odontocetes foraging with the variability of prey in the deep ocean.

Speaker: Giacomo Giorli, Univ. of Hawaii