Piling the first steel tube (conductor, diameter: 75-90 centimetres) to a depth of about 50 to 80 metres below the seabed is the loudest sound source during drilling operations. The impact can be limited by various techniques that reduce underwater noise to standards that do not harm marine mammals, including:
- drilling or vibro-driving the conductor instead of pile driving it
- using bubble screens
During the seismic survey, underwater noise is generated by the use of so-called ‘air guns’. When the ‘soft-start’ technology is used, marine mammals are encouraged to swim away from the seismic source at the beginning of the survey. Experience in the last five years indicates that the use of this technology can exclude temporary or permanent hearing damage of these animals. Research has shown that within a few hours after the seismic survey is completed, the marine mammals return. Special attention is paid to avoiding impact on the calves born between April and August. No seismic surveys will be carried out during this period.