Aarhus Universitets segl

No. 433: Geotechnical and geophysical feasibility studies for Energiø Nordsø. Assessment of effects on marine mammals

Kyhn, L.A., Sveegaard, S., Galatius, A., Teilmann, J., Tougaard, J. & Mikaelsen, M. 2021. Geotekniske og geofysiske forundersøgelser til Energiø Nordsø. Vurdering af påvirkning på havpattedyr. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 44 s. - Videnskabelig rapport nr. 433


The Danish Parliament decided in 2020 to establish two so-called energy islands, one in the North Sea and one in the Baltic Sea, southwest of Bornholm. Energinet has been tasked to carry out geotechnical and geophysical surveys in these areas, prior to the conduction of strategic environmental impact assessments and the tendering of concessions for the offshore windfarms to be built near the energy islands. The Danish Energy Agency has asked DCE – National Centre for Energy and Environment, Aarhus University to assess potential impacts of the geotechnical and geophysical surveys on marine mammals as well as on Natura2000 sites appointed for marine mammals. In this report, effects of the geotechnical and geophysical surveys on the relevant populations of harbour porpoise, white-beaked dolphin, minke whale, harbour seal and grey seal are assessed for the North Sea energy island area. A similar assessment has been conducted for the Baltic energy island.


The assessment of potential consequences has been centered on the use of a geophysical sound source (sparker), which was judged to be the most significant source of impact on marine mammals.


The risk of inflicting permanent damage to the hearing of marine mammals (permanent threshold shift, PTS) is limited to the time when the sparker is started prior to the survey within a range of up to 640 m for harbor porpoises and 1400m for minke whales. For harbor-, grey seals and white-beaked dolphins, the maximum range for potential infliction of permanent hearing loss is <50 m. This risk will likely be reduced to insignificant if a suitable soft start mitigation protocol is used.


It is estimated that all assessed species may react to the noise from the survey vessel at distances of up to 11 km. It is assessed that the impact of behavioral changes at a population level for all species is minor.


There are no Natura2000-areas within the range of potential behavioural changes. The impact on Natura2000 areas is therefore assessed as insignificant.