Increasing levels of anthropogenic underwater noise have caused concern over their potential impacts on marine life. Offshore renewable energy developments and seismic exploration can produce impulsive noise which is especially hazardous for marine mammals because it can induce auditory damage at shorter distances and behavioral disturbance at longer distances. However, far-field effects of impulsive noise remain poorly understood, causing a high level of uncertainty when predicting the impacts of offshore energy developments on marine mammal populations. Here we used a 10-year dataset on the occurrence of coastal bottlenose dolphins over the period 2009–2019 to investigate far-field effects of impulsive noise from offshore activities undertaken in three different years. Activities included a 2D seismic survey and the pile installation at two offshore wind farms, 20–75 km from coastal waters known to be frequented by dolphins. We collected passive acoustic data in key coastal areas and used a Before-After Control-Impact design to investigate variation in dolphin detections in areas exposed to different levels of impulsive noise from these offshore activities. We compared dolphin detections at two temporal scales, comparing years and days with and without impulsive noise. Passive acoustic data confirmed that dolphins continued to use the impact area throughout each offshore activity period, but also provided evidence of short-term behavioral responses in this area. Unexpectedly, and only at the smallest temporal scale, a consistent increase in dolphin detections was observed at the impact sites during activities generating impulsive noise. We suggest that this increase in dolphin detections could be explained by changes in vocalization behavior. Marine mammal protection policies focus on the near-field effects of impulsive noise; however, our results emphasize the importance of investigating the far-field effects of anthropogenic disturbances to better understand the impacts of human activities on marine mammal populations.
We would like to thank Bill Ruck, Moray First Marine and colleagues from the University of Aberdeen for assistance with the data collection. We are also grateful to Drs. Nathan Merchant and Adrian Farcas (CEFAS) for the provision of the data on the noise modeling and their valuable comments during the development of this work. The project benefited at all stages from input provided by the scientific steering groups and stakeholder groups established by UK and Scottish Governments to support the work conducted around these regional oil and gas and renewables projects.
Financial support for this study was provided through a series of consortia funded projects that involved the UK Department of Energy and Climate Change (DECC), Scottish Government, Oil and Gas UK Ltd., COWRIE, NatureScot, The Crown Estate, Highlands and Islands Enterprise, Beatrice Offshore Wind Ltd.,
and Moray Offshore Wind Farm (East) Ltd. OFB was funded by the Fundación “la Caixa” (Becas Posgrado, 2015) and their support was greatly appreciated. The authors declare that this study received funding from three commercial developers: Oil and Gas UK Ltd., Beatrice Offshore Wind Ltd., and Moray Offshore Wind Farm (East) Ltd. However, these funding bodies had no input into the study design, data collection, analysis, interpretation of data, the writing of this article or the decision to submit it for publication.
- anthropogenic noise
- renewable energy
- seismic exploration
- acoustic disturbance
- offshore wind farm
- passive acoustic monitoring
- marine mammal
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