Passive acoustic monitoring of biological and anthropogenic sounds at America’s first offshore wind farm

Abstract

Cape Wind, situated in Nantucket Sound, Massachusetts, is poised to become America’s first offshore windfarm. Our objective is to establish baseline (pre-construction) sound levels of human and biological activity, including diel and seasonal variability of various sound types, at the construction site and three nearby comparison sites. Acoustic recorders have been deployed since April 2012, recording on a 10% duty cycle (sample rate: 80 kHz). Biological contributions to the local soundscape are primarily fish sounds, with the dominant signal likely being cusk eel (Family Ophidiidae) calls. These calls, which are composed of stereotyped pulses with an average bout duration of 3.3 ±0.8 s and mean peak frequency of 1030 ±200 Hz, show both seasonal and diel variation. Dense choruses were detected during summer (July), but limited activity occurred in the fall and winter. During vocal periods, detections occurred throughout the day but peaked near dusk. Vessel traffic also showed diel and seasonal trends, with peaks during the daytime and in the summer, which indicates that boat activity can be tracked acoustically. These trends in biological and anthropogenic activity provide key baseline records for evaluating the influence of windfarm construction and operation on a local US soundscape.