New Passive Acoustic Monitoring in Monterey Bay National Marine Sanctuary

Abstract

Understanding the marine soundscape is of growing importance to the National Marine Sanctuaries. In the center of Monterey Bay National Marine Sanctuary, a new Passive Acoustic Monitoring (PAM) project has begun. Using the power and communications infrastructure of the Monterey Accelerated Research System (MARS) cabled observatory, we deployed a broadband, digital, omnidirectional hydrophone on Smooth Ridge, near the MARS node (36°42.75'N, 122°11.21'W; depth 891 m). The system has been recording almost continuously since 28 July 2015. Natural biological sound (biophony) dominated long-term spectral average results at frequencies below 50 Hz, showing seasonal patterns in baleen whale vocalizations. Prevalence of blue whale vocalizations during August through October 2015 was succeeded by prevalence of fin whale vocalizations during November 2015 through January 2016. Diel variations (stronger signal at night) were evident for both species. In the high-frequency range, beaked whale clicks have been detected and represent a focus for advancing automated detection and classification methods. Biophonic richness in this soundscape was also indicated by human-expert analysis results for a one-week period, during which biological sound events were detected 86% of the time. Examination of natural physical sound (geophony) has included rainfall and the relationship between wind speed and ambient sound. The first 10 months of data showed that sound levels at 2 kHz followed Wenz curve predictions for wind speeds above 5 m/s. Examination of human-made sound (anthrophony) has included noise from vessel traffic and explosions detonated underwater during fishery operations. This new PAM project is providing extensive information on biophony, geophony, and anthrophony in this deep soundscape, information that is essential to understanding and managing acoustic habitat of the Sanctuary.