Analysis and automatic detection of potential Omura’s whale signals in the Indian Ocean

Abstract

The north Indian Ocean is a rich environment for passive acoustic monitoring of baleen whales including fin and blue whales, with several different populations of blue whales having been identified by recordings of their song type. A signal known as the Diego Garcia Croak (DGC) has been recorded on two hydrophone triads near Diego Garcia that make up part of the International Monitoring System of the Comprehensive Nuclear Test Ban Treaty Organization. The DGC signal was tentatively attributed to a blue whale (Sousa and Harris, 2015) but has recently been linked to the Omura’s whale (Cerchio et al., 2019). In previous work, the DGC has been observed visually on spectrograms and initial time and frequency statistics obtained. In this work, a least squares detector is constructed for the signals and applied to long term recordings from 2002 and 2003. The resulting detections are used to extend previous measurements of the DGC signal, generating a robust characterization of the DGC, including frequency statistics, inter-call intervals, and call lengths. Further, localization methods will be applied to initial time-difference of arrival results and used to explore source level estimation of the DGC signal.