The Competing Roles of Vessels, Wind and Waves in Oregon’s Shallow Water Coastal Soundscape

A variety of marine species rely on sound for important life functions including communication, navigation, foraging, prey avoidance, territorial defense and attracting a mate. Favorable acoustic conditions can improve the efficacy of these activities, bolstering the health of marine ecosystems across a wide range of species. Despite its importance as a highly bio-diverse, environmentally and economically vital ocean area, little information is known about the baseline levels and characteristic variability in ocean sound within the nearshore, open waters of the Pacific Northwest (PNW) coastline of the U.S. From 2017 – 2019, during the months of June – October, two autonomous underwater hydrophones were deployed off the central Oregon coast at 20 m depth recording low to mid-frequency (10 Hz – 13 kHz) acoustic data. One hydrophone was placed off South Beach (SB) in an area of high vessel activity near the entrance to one of Oregon’s busiest ports, the Port of Newport, while the other hydrophone was deployed 17 km to the north in the state designated Otter Rock Marine Reserve (OR), an area dominated by natural sound processes. The SB hydrophone recordings exhibited wideband diel variations in sound levels generated by a range of vessels sizes. Substantially larger increases in sound levels (up to 18 dB) were observed during sport fisheries openings, where an order of magnitude increase in vessel use of the port occurred. Additionally, sound levels at both sites were affected by thermally controlled, daily increases in wind speeds common during the summer months along the PNW coast. Empirically derived relationships between local wind speeds and sound levels during periods devoid of vessel noise were used to remove the contribution of wind to the ambient acoustic conditions and highlight variability associated with vessel radiated noise in both areas. Furthermore, the contribution to low frequency (10 Hz – 1 kHz) sound levels from acoustic energy radiated by nearby surfzone dissipation processes was characterized for comparisons with wind and ship-generated noise. Comparisons between the acoustic spectra from 2 stations experiencing the same environmental conditions emphasizes the temporally dependent signature of anthropogenic use and its effects in urban verses naturally dominated coastal soundscapes.