Soundscape Assessment of a Deepwater (12 kHz) Multibeam Mapping Survey

Soundscape studies can provide insight into how, and the extent to which, an acoustic environment has changed due to anthropogenic noise-generating activity. Here a soundscape study was conducted to understand the changing sound levels on the Southern California Antisubmarine Warfare Range during a deepwater ocean mapping survey using a 12 kHz Kongsberg EM 122 multibeam echo sounder. The exercise confirmed the expected temporal and spatial dependence of the mapping survey activity contribution to the soundscape. The change in sound levels was closely tied to a narrow angular sector around the mobile survey vessel, which meant the temporal impact at any given location was also confined to a brief time period that the vessel was in the corresponding area. The EM 122 signal was detectable above baseline sound levels in the acoustic records only when the survey vessel was within 17 km of the hydrophone receiver and was clearly and consistently associated with changes in the 12.5 kHz decidecade spectral density levels. The results provide important context for simultaneous works assessing beaked whale foraging behavior during the mapping survey, where no adverse change in foraging behavior was found.