Performance of an echolocating bottlenose dolphin in the presence of anthropogenic masking noise

Abstract

To study the effects of acoustic masking from anthropogenic noise, bottlenose dolphin (Tursiops truncatus) echolocation performance was assessed in the presence of different masking noise types using Navy relevant source transmissions. Echolocation clicks produced by the dolphin were detected with a hydrophone, then digitized within a phantom echo generator (PEG). The PEG converted the received clicks into echoes, delayed appropriately for the simulated target range. The echoes were then broadcast to the dolphin via a sound projector while masking noise transmissions were held constant. Using an acoustic response and a modified method of constants procedure, the echolocation performance of the dolphin was computed as a function of range between 3 and 17 m. Comparative echolocation performance to different masking noise type categories was analyzed between intermittent and continuous noise, direct path transmissions and multipath exposure, and mid frequency versus high frequency bands. These results expand the limited understanding of biosonar processing capability and signal characteristic alterations used to discriminate and resolve changes in small scale features while exposed to potential noise interference types. [Work supported through the Office of Naval Research.]