The use of an air bubble curtain to reduce the received sound levels for harbor porpoises (Phocoena phocoena)

Abstract

In December 2005 construction work was started to replace a harbor wall in Kerteminde harbor,Denmark. A total of 175 wooden piles were piled into the ground at the waters edge over a periodof 3 months. During the same period three harbor porpoises were housed in a marine mammalfacility on the opposite side of the harbor. All animals showed strong avoidance reactions after thestart of the piling activities. As a measure to reduce the sound exposure for the animals an airbubble curtain was constructed and operated in a direct path between the piling site and the openingof the animals’ semi-natural pool. The sound attenuation effect achieved with this system wasdetermined by quantitative comparison of pile driving impulses simultaneously measured in frontof and behind the active air bubble curtain. Mean levels of sound attenuation over a sequence of 95consecutive pile strikes were 14 dB (standard deviation (s.d.) 3.4 dB) for peak to peak values and13 dB (s.d. 2.5 dB) for SEL values. As soon as the air bubble curtain was installed and operated, nofurther avoidance reactions of the animals to the piling activities were apparent.