Effects of pile driving on fish larvae: a field experiment

In the Belgian part of the North Sea, different types of windmills were and are being constructed, i.a. monopiles and jackets foundations. The single strike sound exposure levels (SELss), numbers of strikes and construction durations vary between foundation types, but they all generate low-frequency impulsive noise with a similar cumulative SEL during the construction phase.
The exposure of fish eggs and larvae to low-frequency impulsive noise, have received little attention in bioacoustic research, despite the incapability of these ‘passive drifters’ to actively escape the exposure. In The Netherlands, a worst-case scenario assumed 100% mortality for eggs and larvae within the first 400 m, and 14% over 400 m to 1000 m distance. These assumptions, however, have so far not been verified in the field.
One of the aims of the OffNoise project is to verify the validity of these assumptions by conducting field experiments. The first opportunity to conduct an experiment was the piling activity during the construction of the Northwind NV offshore wind farm in June 2013. From the piling platform, sea bass (Dicentrarchus labrax) larvae were lowered into the sea during a piling period of one monopile, at a distance of 40m from the piling source. Two control groups covered the handling effects and noise impact from the platform operation itself. Three repeats were conducted. Simultaneously to each repeat, the underwater sound pressure and particle motion were recorded. Mortality and respiration rates were monitored, surviving larvae were reared in the lab to examine effects on development and growth.