Evidences of Intra-Group Orca Call Rate Modulation Using A Small-Aperture Four Hydrophone Array

Abstract Acoustic emissions are vital to orcas (Orcinus orca) to socialize, hunt, orient, and maintain spatial awareness. In order to better analyze their inter and intra-group communication, we propose a novel protocol that allows us to associate vocalizations with their emitter (individual/matriline). Our approach is based on a low cost small-aperture four hydrophone array fixed near the shore up to a few km away from the orcas’ path, operated in conjunction with visual identification. It was conducted in the summer of 2019 off northern Vancouver Island, Canada, at the research station OrcaLab. A total of 722 calls were extracted and localized in azimuth via the hydrophone array from 3 case studies in which different events took place.We then calculated the Call Rate (CR) for each individual/matriline in order to describe their acoustic activity. Results show that CR is modulated according to the distance of the signaler from the joint group, the presence of another group, and the anthropic pressure (nearby cruise ship). This shows evidence of intertwined calls. This protocol does not interfere with the animals and opens new perspectives towards inter and intra-group communication analysis.