Complementary techniques for robust acoustic identification of individual sperm and beaked whales.

Abstract

Properties of individual clicks and characteristics of click trains provide clues for the passive acoustic identification of individual sperm whales via several complementary techniques. For example, recordings of individual clicks can be clustered according to their shape or spectrum, or entire trains of clicks can be exploited by monitoring the slow evolution of click shapes over time. Cadence analysis studies differences in click‐train rhythms of simultaneously clicking whales. Localization uses bearing, and if possible range, to differentiate individuals. Manual click‐train identification employs both individual click properties and sequence analysis to identify individual whales. When combined, these methods can provide robust identification of individual sperm whales. The application of these techniques to beaked whales is difficult because, compared to sperm whales, beaked whales have lower source level, a narrower beam, and a faster rate of turning. Consequently, click trains on a single sensor have frequent drop‐outs. The above techniques require more sophistication and benefit from closely spaced sensors to fill in drop‐outs. Previous Littoral Acoustic Demonstration Center (LADC) multi‐mooring Environmental Acoustic Recording System (EARS) data are analyzed for beaked whales and an experiment is proposed with greater mooring density to improve individual beaked whale identification. [Research supported by SPAWAR and ONR.]