Cuvier’s Beaked Whale Tracks in Southern California

Cuvier’s beaked whales (Ziphius cavirostris) are difficult to study due to infrequent sightings and their deep-diving behavior. In Southern California, they are a species of concern based on habitat overlap in a naval test range and their sensitivity to naval sonar. One approach to studying their behavior is to use arrays of hydrophones to localize and track individual beaked whales emitting echolocation clicks. We collected over one year of broadband acoustic recordings on small aperture (~1 m) volumetric arrays of four hydrophones at two different sites offshore of the coast of Southern California, a region with a considerable presence of Cuvier’s beaked whales. We detect their echolocation clicks on each hydrophone in an array, then determine the relative time of arrival of the clicks. Each relative arrival time pattern is associated with a unique direction of arrival, allowing us to determine the direction of an echolocating whale in relation to the array. When the clicks are detected on multiple arrays, directions are cross-fixed and the location of an animal can be determined. Sequential locations can be used to form 3-dimensional tracks. Tracks are insightful to determine a number of signal characteristics, such as source sound pressure level, beam directionality, and click temporal patterns as well as a number of animal behaviors including swim speed, group size, group coordination, and foraging depth. These features can be combined to assess habitat use and behavioral response to stimuli in addition to density and abundance of the species.