Application of dual frequency identification sonar for the study of deep diving odontocetes prey fields.

A dual frequency identification sonar was used to estimate density and size of potential deep diving odontocetes' prey in deep sea scattering layers in Hawaii. Size distributions data showed a bimodal pattern, with a population of data above the 50 cm of length, possibly big squids, and a population of data below 50 cm, mainly micronekton. The number of animals bigger than 50 cm was correlated with the length of the peak of the frequency distribution. Data suggest that big predators, like squids that constitute prey for beaked, pilot, and sperm whales, are more likely to be found where they have better chance to find micronectonic prey.