Ambient noise and temporal patterns of boat activity in the US Virgin Islands National Park

• Acoustic recordings were collected on coral reefs in the US Virgin Islands.
• Vessel noise was detected throughout the four-month deployment period.
• This noise contributed to higher sound levels and a downward shift in frequencies.
• The overlap with biological sounds suggests the potential for masking.
• Vessel noise may provide a means to track human activity in marine protected areas.

Human activity is contributing increasing noise to marine ecosystems. Recent studies have examined the effects of boat noise on marine fishes, but there is limited understanding of the prevalence of this type of sound source. This investigation tracks vessel noise on three reefs in the US Virgin Islands National Park over four months in 2013. Ambient noise levels ranged from 106 to 129 dBrms re 1 μPa (100 Hz–20 kHz). Boat noise occurred in 6–12% of samples. In the presence of boat noise, ambient noise in a low-frequency band (100–1000 Hz) increased by >7 dB above baseline levels and sound levels were significantly higher. The frequency with the most acoustic energy shifted to a significantly lower frequency when boat noise was present during the day. These results indicate the abundance of boat noise and its overlap with reef organism sound production, raising concern for the communication abilities of these animals.