The impact of underwater noise on the early life stages of fish

‘Anthropogenic underwater noise is at levels that do not adversely affect the marine environment’ is the 11th descriptor to maintain a Good Environmental Status (GES) as defined by the Marine Strategy Framework Directive. Both construction and exploitation of offshore wind farms generate underwater noise in the Belgian part of the North Sea. Sound measurements have been conducted to determine the reference noise level, and the pile-driving and operational noise in BELWIND at the Bligh Bank. Based on the sound pressure level (SPL) peaks, pile-driving caused a sixteen-fold amplification of the background acoustic pressure at 550m, and a threefold amplification during the operational phase. SPL peaks are seen at frequencies ranging from 100 to 1000 Hz for both pile-driving and exploitation, covering the optimum hearing frequency range of fish.
Fish eggs and larvae are dependent on currents for their transport and consequently cannot avoid underwater noise. Vulnerability to noise could influence their recruitment and have a substantial effect on population levels. Hence, a research project has been initiated to unravel the acute and chronic effects of the intense impulse piling sound and the long-term continuous operational sound on eggs, larvae and juveniles of commercial fish such as European seabass (Dicentrarchus labrax), sole (Solea solea) and cod (Gadus morhua). Cage experiments at sea and playback experiments in the lab are planned. Effects on behaviour, physiology, morphology and survival will be monitored and linked to sound parameters. The results of this research will assist in the process of establishing GES noise boundaries.