Effects of offshore wind farms operational noise on bluefin tuna behaviour

Abstract

The number of offshore wind farms is growing up quickly in the lasts years. Several studies about its environmental acoustic impacts have been developed at the same time the industry expands, most of them related to the high level impulsive noise produced during the pile diving process associated to the construction stage. Nevertheless, the study of the impact of the operational noise of turbines is very limited. In this paper we investigate the behavioural response of Bluefin tuna when exposed to the operation noise of a turbine. We analysed tuna reaction in terms of three parameters: depth of the school, swimming pattern and changes in the swimming direction. The experiment was developedin a fixed commercial tuna cage in the Mediterranean Sea. The usual behaviour of Bluefin tuna in captivity conditions was previously analysed using a continuous monitorization. Variations in depth were observed when feeding boat approaches, which could be interpreted as a consequence of the acoustical stimulus. The turbine noise was acoustically characterized, and reproduced using a broad-band underwater source. To monitor tuna behaviour two echosounders and a video system were simultaneously used. When exposed to short duration noise tuna behaviour does not exhibit clear disturbances. Nevertheless, with long duration emission tuna reacted: school reduced the radio of thecircular swimming region, moved up to the surface and some individuals were disorientated. Tuna seems to be habituated after several repetitions is short time.