Characterization of the underwater noise produced by recreational and small fishing boats (<14 m) in the shallow-water of the Cres-Lošinj Natura 2000 SCI.

Recreational boats are a dominant source of underwater noise in coastal areas, but reliable boat noise assessment is generally lacking. Here the Underwater Radiated Noise (URN) of seven recreational and small fishing boats moving at two different speeds was measured in the shallow waters of the Cres-Lošinj Natura 2000 SCI (Croatia). Measurements were undertaken considering the internationally recognized standards and published guidelines for shallow waters. URN was provided in 1/3 octave band spectra and in narrow band spectra, to highlight the tonal components. Engine power and type rather than the boat length and design result to be more predictive of URN. Highest speeds induce highest noise levels only in a very limited frequency range and different boats with similar speed but different engines show a shift in the spectra. Relevance of the achieved results for the tested area is further discussed.