Wind creates a natural bubble curtain mitigating porpoise avoidance during offshore pile driving

During offshore wind farms construction, abundance in harbour porpoise (Phocoena phocoena) is known to be negatively affected. From 2011 to 2013, extensive passive acoustic monitoring was conducted during research projects accompanying the construction of two wind farms in the German North Sea. Using C-PODs, we studied the effect ranges of pile driving disturbance on acoustic porpoise detections to test how these may change with different wind speeds. We found that disturbance radii highly depended on the prevailing wind speed during construction with further reaching effects at lower wind speed. Disturbance effects reached to 16 km at wind speed of 2m/s and to 10km at wind speed of 5m/s. With increasing wind speed, more air bubbles in the upper water layer may lead to greater mitigation of piling noise, thereby reducing disturbance radii for porpoises. Alternatively, increasing wind may increase high frequency noise due to sediment movement in the water, which could decrease the signal to noise ratio of ...