Echolocation activity of harbour porpoises, Phocoena phocoena, show seasonal artificial reef attraction despite elevated noise levels close to oil and gas platforms

Harbour porpoises frequently alter their behaviour in response to underwater sound from shipping, seismic surveys, drilling and marine renewables. Less well understood is the response of porpoises to sounds emitted from oil and gas (O&G) platforms during routine operations.
The responses are not easily predictable as platforms can act simultaneously and to varying degree as a source of disturbance through noise and attraction through an artificial reef effect with increased prey abundance and diversity.
To investigate the presence and feeding behaviour of harbour porpoises around platforms, autonomous acoustic loggers were placed for up to 2 years, at 21 stations 0-25.6 km from the largest platform in the Danish North Sea.
Harbour porpoises were detected at all distances year round in two distinct seasonal activity patterns. During July-January, porpoises were attracted to the platform as indicated by high foraging activity within 800 m of the platform. Echolocation activit...