The Channel Islands National Marine Sanctuary (CINMS) and the surrounding waters are
considered an urban coastal environment, yet home to a diversity of marine organisms. Understanding the
interactions between human activity and the marine ecosystem is vital to its sustainability. In our study, we
investigated the acoustic environment in the region, focusing primarily on the addition of anthropogenic
sound produced by commercial ship traffic. Our study used a passive, broadband, high-frequency acoustic
recording package (HARP) to record ambient noise levels and the contribution of noise from commercial
ship traffic to the acoustic environment. Recorded ship sound levels were identified using ship-passage
records known as Automatic Identification System (AIS). Our analyses of ambient noise levels from July
to October 2007 showed elevated levels of 15–25 dB in the 10–150 Hz frequency band when ships were
nearby (