Construction and operation of an offshore wind farm on the Swedish part of Kriegers Flak has been assessed with respect to impacts on marine mammals, in the context of an application to increase the size of turbines in the wind farm. The mammals in question are two species of seals, harbour seal (Phoca vitulina) and grey seal (Halichoerus grypus) which are abundant in the waters around Kriegers Flak as well as the harbour porpoise (Phocoena phocoena).

Underwater noise from percussive piling of foundations is likely to be the main source of potential impact from wind farm construction. Percussive pile driving generates very high sound pressures, likely capable of inflicting permanent damage to the hearing of seals and porpoises and has been shown to cause behavioural disturbances at distances of tens of kilometres from the site.

The magnitude of impact was assessed for direct damage (acoustic trauma), hearing loss and disturbance of behaviour and masking. Hearing loss was assessed by considering total cumulated sound exposure levels over the duration expected for piling of one foundation (4.5 hours), taking movements of the animals into consideration.

Impacts can be mitigated by reducing the radiated noise from the pile driving by application of a bubble curtain, currently considered best available technology for reduction of noise radiation. The bubble curtain is expected to reduce the broadband source level of the piling. The reduction in radiated noise means that permanent hearing loss is not expected to occur in either seals nor porpoises. Reduction of radiated noise from piling is also predicted to reduce both impact ranges and duration of the disturbance of behaviour.

It is considered likely that the adjacent Natura2000 area Sydvästskånes Udsjövatten will be impacted during construction of the wind farm. Though through the application of mitigation measures, such as bubble curtains, it is estimated that the impact of the emitted noise can be reduced and thus ensure a potential reduction of mammal habitat loss from 27% to 2.5%.

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For more information, please contact Jakob Tougaard

E-mail: jat@bios.au.dk

Telephone: +45 87158706