Nord Stream 2 recently constructed a gas pipeline through the Swedish part of the Baltic Sea. During the environmental impact assessment (prior to construction) particular focus was paid to the possible negative impacts on harbour porpoises. Harbour porpoises in the Baltic Proper are distinct from porpoises in the Western Baltic; the population size is very low and the status is assessed as critically endangered. In the summer months, the Baltic Proper population of porpoises aggregate in the Natura2000 area Hoburg’s Bank and Midsjöbanks likely for breeding and nursing, which designates it as critical habitat. The pipeline route discussed in this report was constructed through this area.
In the impact assessment, it was clear that underwater noise was the only real concern with respect to impact on porpoises. The most significant sources of underwater noise were considered to be the pipe laying vessel and support ships, and particularly noisy single activities including rock placement before the pipe is laid down and trenching of the pipe into the sediment.