| Summary: | Acoustic harassment devices (AHDs) are commonly used as mitigation devices during construction of offshore wind farms, to deter marine mammals and thus protect them from hearing damage caused by pile driving noise. However, especially for seals, it is not well known how effective this method is. Here we investigated whether a simulated acoustic harassment device sound (12 kHz pure tone pulses at random intervals, SL=165dB re 1μParms) in the water affected the behaviour of harbour seals (Phoca vitulina) on land at a haul-out site in Kattegat, Denmark. The seals could not hear the AHD sounds when hauled-out, but the hypothesis was that hauled-out seals could react indirectly by responding to changed behaviour of seals in the water around the haul-out site. We quantified reactions of seals on land by counting the total number of seals and the number of seals with their heads lifted before acoustic signals were presented and again 10 minutes into the exposure period. The results show that the number of hauled-out seals were unaffected by the acoustic harassment device, whereas a larger proportion of seals were alert during exposure, possibly indicating awareness that something unusual was happening in the water.
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