Effect of pile-driving sounds on the survival of larval fish (abstract)

In view of the rapid extension of offshore wind farms, there is an urgent need to improve our knowledge on possible adverse effects of underwater sound generated by pile-driving. Mortality and injuries have been observed in fish exposed to loud impulse sounds, but knowledge on the sound levels at which (sub-)lethal effects occur is limited, especially for fish larvae. A device was developed in which recorded pile-driving noise can be reproduced accurately in the frequency range between 50 and 1000Hz, at zero-to-peak pressure levels up to 210 dB re 1μPa2 (zero-to-peak pressures up to 32 kPa) and single pulse sound exposure levels up to 186 dB re 1μPa2s. This device was used to examine lethal effects of sound exposure in common sole (Solea solea) larvae. Different developmental stages were exposed to various levels and durations of pile-driving noise. The highest cumulative sound exposure level applied was 206 dB re 1μPa2s, which corresponds to 100 strikes at a distance of 100 m from a typical North Sea piledriving site. The results showed no statistically significant differences in mortality between exposure and control groups at sound exposure levels which were well above the US interim criteria for non-auditory tissue damage in fish. These findings cannot be extrapolated to fish larvae in general, as interspecific differences in vulnerability to sound exposure may occur. Therefore, controlled exposure experiments are currently being carried out for European sea bass (Dicentrarchus labrax) larvae and will be carried out for herring (Clupea harengus) larvae in the near future.