The North Sea is a heavily trafficked area, with major shipping routes crossing its waters, and fisheries, offshore oil rigs, and wind farms populating its waves. All this activity inevitably has an effect on marine wildlife, and scientists are particularly interested in how the harbor porpoise population has fared in the face of such disturbances.
source https://phys.org/news/2021-01-harbor-porpoises-decline-german-north.html
