Scientific Report of Port-Cros National Park
Anthropogenic underwater noise is widely recognised as a stressor for cetaceans, but current knowledge gaps hinder the efforts to assess and manage acoustic impacts in the Pelagos Sanctuary. The present project aimed at characterising noise from shipping through sound propagation modelling and mapping, and at assessing the potential impacts on cetaceans. The model provides estimates of noise levels throughout the study area with a resolution of 0.5 km. Input data are environmental variables (temperature, salinity, bathymetry and seabed type), a range of frequencies (models of noise spectra emitted by different categories of ships), and the positions of noise sources within the study area (coming from the ship tracking system named AIS for Automatic Identification System). The real-time flow of AIS data is used to feed the real-time noise mapping system that has been set up (www.oceannoisemap.com), while archival data were used to assess noise distribution during summer 2012 (taken as a test period). In the whole study area, average estimated noise levels varied between 80 and 126 dB re 1μPa (rms). Noisier zones were found in the area between continental Franceand north-western Corsica, as well as in north-eastern Corsican waters. In such areas,estimated levels exceeded 100 dB 95 % of time, 110 dB 50 % of time, and 120 dB 5 %of time. Maximum instantaneous levels reached more than 140 dB re 1μPa (rms). Based on known thresholds for the onset of negative effects, our results show that noise levels were sufficient to cause behavioural disturbance to cetaceans. The information gathered represents the first large-scale assessment of noise levels in the Pelagos Sanctuary and can be used as a basis for management purposes.
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