Passive acoustic monitoring reveals seasonal trends and primary contributors to the low frequency ambient soundscape of the Cordell Bank National Marine Sanctuary

Samara Haver1, Zoe Rand2, Leila Hatch3, Danielle Lipski4, Robert P Dziak5, Jason Gedamke6, Joseph Haxel7, Scott A Heppell8, Jaime Jahncke9, Megan McKenna10, David Mellinger11, William Oestreich12, Lauren Roche1, John Phillip Ryan13 and Sofie M. Van Parijs14, (1)Oregon State University, CIMERS, Newport, United States, (2)Oregon State University, Department of Fisheries and Wildlife, United States, (3)NOAA Office of National Marine Sanctuaries, Scituate, United States, (4)Cordell Bank National Marine Sanctuary, Point Reyes Station, CA, United States, (5)NOAA, Pacific Marine Environmental Laboratory, Newport, United States, (6)NOAA Fisheries, Office of Science and Technology, Silver Spring, United States, (7)NOAA Newport, Newport, OR, United States, (8)Oregon State University, Corvallis, OR, United States, (9)Point Blue Conservation Science, Petaluma, CA, United States, (10)National Park Service Natural Sounds and Night Skies Division, CO, United States, (11)NOAA/OSU Cooperative Institute for Marine Resources Studies, Newport, United States, (12)Stanford University, Hopkins Marine Station, Department of Biology, Pacific Grove, CA, United States, (13)MBARI, Moss Landing, United States, (14)Northeast Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Woods Hole, United States
Passive acoustic monitoring of ocean soundscapes can inform those tasked with protecting marine resources about the status of a marine ecosystem. In 2015, the National Oceanic and Atmospheric Administration (NOAA) established a long-term, continuous, low-frequency (10 Hz – 2 kHz) passive acoustic monitoring site in the Cordell Bank National Marine Sanctuary (CBNMS). CBNMS is managed by NOAA and located offshore of the central U.S. west coast. The southern portion of the sanctuary includes access waters to the busy ports of San Francisco and Oakland, while the western deep waters are exposed to ship traffic transiting up and down the west coast. The California Current flows southward along the coast in this area, and the annual upwelling of nutrient-rich deep ocean water supports a diverse community of marine animals, including several protected species of large baleen whales that feed in and near CBNMS. Passive acoustic data recorded in CBNMS supported the hypothesis that both large vessels in the shipping lanes accessing San Francisco Bay and vocalizing baleen whale species contribute to the lower frequency ambient soundscape of CBNMS. Sound levels fluctuated by month, with the highest levels in the fall (September-November) and lowest levels in the summer (June-August). Throughout the year, very low-frequency (10 Hz – 100 Hz) sound levels were the most variable. Large vessels and whales overlap in their contributions to total ambient levels within this range; however, vessel contributions were more omnipresent, while seasonal peaks were associated with vocalizing blue, fin, and humpback whales. This first characterization of low-frequency ambient sound levels in CBNMS establishes initial baselines for an important component of this site’s underwater soundscape. Standardized monitoring of soundscapes, over time and in comparison to other protected sites, directly supports NOAA’s ability to evaluate and report on conditions within National Marine Sanctuaries.