Assessments of the impact of offshore energy developments are constrained because it is not known whether fine-scale behavioural responses to noise lead to broader-scale displacement of protected small cetaceans. We used passive acoustic monitoring and digital aerial surveys to study changes in the occurrence of harbour porpoises across a 2000 km(2) study area during a commercial two-dimensional seismic survey in the North Sea. Acoustic and visual data provided evidence of group responses to air gun noise from the 470 cu inch array over ranges of 5-10 km, at received peak-to-peak sound pressure levels of 165-172 dB re 1 mu Pa and sound exposure levels (SELs) of 145-151 dB re 1 mu Pa-2 s(-1). However, animals were typically detected again at affected sites within a few hours, and the level of response declined through the 10 day survey. Overall, acoustic detections decreased significantly during the survey period in the impact area compared with a control area, but this effect was small in relation to natural variation. These results demonstrate that prolonged seismic survey noise did not lead to broader-scale displacement into suboptimal or higher-risk habitats, and suggest that impact assessments should focus on sublethal effects resulting from changes in foraging performance of animals within affected sites.
Short-Term Disturbance by a Commercial Two-Dimensional Seismic Survey does Not Lead to Long-Term Displacement of Harbour Porpoises
Title: Short-Term Disturbance by a Commercial Two-Dimensional Seismic Survey does Not Lead to Long-Term Displacement of Harbour Porpoises
November 01, 2013
Journal: Proceedings of the Royal Society B
Publisher: Royal Society
Thompson, P.; Brookes, K.; Graham, I.; Barton, T.; Needham, K.; Bradbury, G.; Merchant, N. (2013). Short-Term Disturbance by a Commercial Two-Dimensional Seismic Survey does Not Lead to Long-Term Displacement of Harbour Porpoises. Proceedings of the Royal Society B, 280, 8.