Long-term trends in ambient and anthropogenic noise in central and western Pacific Ocean

Multi-year studies of ambient noise trends are uncommon, yet they can provide information on the level of natural variability in noise to which animals are exposed, as well as an idea of changing noise level trends. To investigate long-term trends in low frequency (<1,000 Hz) ocean ambient noise, recordings were collected at two locations in the tropical Pacific Ocean. One site was in the central Pacific, off Kona on the Big Island of Hawaii (2007-2015), and the other in the western Pacific near Saipan, Northern Mariana Islands (2010-2015). In addition, detailed occurrences of two types of transient anthropogenic noise events, vessel passages and mid-frequency active (MFA) sonar transmissions, were identified in a subset of data. Characteristics of those anthropogenic sounds: duration, received levels, and sound exposure levels were measured. Both sites exhibited relatively low levels of ambient noise characteristic of ships (<100 Hz) compared to levels reported in the eastern North Pacific Ocean. At Kona...