Use of passive acoustics for estimation of cetacean population density: Realizing the potential

Abstract

The potential of passive acoustic methods to estimate cetacean population density has seldom been realized. It has been most successfully applied to species that consistently use echo-location during foraging, have very distinctive echo-location signals and forage a large fraction of the time, notably sperm whale, porpoise, and beaked whales. Research is needed to eliminate some of the impediments to applying acoustics to estimate the density of other species. For baleen whales, one of the greatest uncertainties is the lack of information on call rates. For delphinids, the greatest uncertainties are in estimating group size and in species recognition. For all species, there is a need to develop inexpensive recorders that can be distributed in large number at random locations in a study area. For towed hydrophone surveys, there is a need to better localize species in their 3-D environment and to instantaneously localize animals from a single signal received on multiple hydrophones. While improvements can be made, we may need to recognize that some of impediments cannot be overcome with any reasonable research budget. In these cases, efforts should be concentrated in improving acoustic methods to aid visual-based transect methods.