Propagation characteristics of underwater noise from operational offshore wind farms and assessment of potential auditory interference risk to fish

IntroductionWith the rapid expansion of offshore wind power, the potential impact of underwater noise from operational wind farms on marine organisms has attracted increasing concern. MethodsTo investigate the acoustic characteristics of underwater noise from wind farms, this study measured underwater noise data from an operational wind farm in the Nanpeng Island area of Yangjiang, Guangdong, and analyzed its time-frequency and spectral characteristics. ResultsThe results indicate that the acoustic energy in the study area was primarily concentrated at low frequencies below 1000 Hz. Distinct wind turbine noise characteristics were observable at both 2 m and 5 m water depths, and noise levels exhibited a decreasing trend with increasing distance from the wind farm. The wind turbine noise exhibited discrete spectral features, with peak center frequencies mainly distributed at 31.5 Hz, 63 Hz, 160 Hz, and 630 Hz. Outside the wind farm, only the 31.5 Hz and 63 Hz peak bands were prominent. However, within the farm, owing to the proximity of a greater number of operating turbines, all peak frequency bands were more pronounced, and an additional peak emerged around the 250 Hz band. Furthermore, by comparing the underwater noise spectra with fish auditory sensitivity curves, a preliminary assessment was conducted to determine the species-specific spatial extent of potential noise perception: the auditory threshold of the large yellow croaker was exceeded only within the wind farm at frequencies around 380 Hz; the threshold for the green grouper was exceeded at a distance of 500 m from the wind farm; the threshold for the pearl gentian grouper was exceeded at 5.5 km; and the Japanese seabass, having the lowest auditory threshold, had its threshold exceeded at all monitoring stations. DiscussionThe findings of this study provide a data reference for assessing the acoustic environmental impact of offshore wind farms and for planning integrated "wind-fishery" development.