Timing and context of dolphin clicks during and after mine simulator detection and marking in the open ocean

Abstract

ABSTRACT Two dolphins carrying cameras swam in the ocean as they searched for and marked mine simulators – buried, proud or moored. As the animals swam ahead of a boat they searched the ocean. Cameras on their harness recorded continuous sound and video. Once a target was detected, the dolphins received a marker to take to the simulator's location. During search and detection, dolphins made almost continuous trains of varying interval clicks. During the marking phase, shorter click trains were interrupted by periods of silence. As the dolphins marked simulators, they often produced victory squeals – pulse bursts that vary in duration, peak frequency and amplitude. Victory squeals were produced on 72% of marks. Sometimes after marking, or at other times during their long swims, the dolphins produced click packets. Packets typically consisted of two to 10 clicks with inter-click intervals of 7-117 ms followed by a silence of 223-983 ms. Click packets appeared unrelated with searching or marking. We suggest that the packets were used to improve signal to noise ratios for locating a boat or other distant object. Victory squeals produced when marking the targets suggest to us that the dolphins know when they have succeeded in this multipart task.