Underwater sound modelling of floating offshore wind farms in the Strait of Sicily

Underwater operational noise generated by floating offshore wind farms (FOWFs) has the potential to affect marine animals. The extent of this impact, however, has yet to be investigated. It is therefore important to understand how these new constructions could impact the marine ecosystem. Currently, there are several projects planned to install FOWFs in Italian territorial waters, comprising just a few to hundreds of turbines. In this study, we evaluate the noise produced by three FOWFs that are planned to be built in the Strait of Sicily, an area of particular interest for such developments. The selected FOWFs differ in their sizes, in terms of number of turbines, and in the environmental characteristics of the areas, in terms of bathymetry and seabed substrates. The propagation losses were modelled in decidecade bands using JASCO’s Marine Operations Noise Model (MONM) based on the parabolic equation method for frequency bands from 10 to 800 Hz, combined with BELLHOP beam-tracing model from 1 to 25 kHz. The bathymetry and geoacoustic profiles were taken from EMODnet. The February sound speed profile from Copernicus datasets was applied as this is representative of the expected worst-case scenario (longest propagation ranges) for impacts on marine life. After having modelled the propagation losses, source levels were applied that correspond to the operational noise generated by two aerogenerator flotation types: spar and semi-submersible. Results showed that the sound fields originated by the operating wind farms exceed behavioural disturbance and auditory threshold shift criteria, only within a few hundred meters from the turbines, for all the considered hearing groups. The outcomes are discussed considering the background sound levels and the most up to date marine mammals’ behavioural disturbance and injury thresholds, in the light of the current European guidelines and National regulation.