AUTHOR=Voß Julika , Rose Armin , Kosarev Vladislav , Vílela Raúl , van Opzeeland Ilse Catharina , Diederichs Ansgar 

TITLE=Response of harbor porpoises (Phocoena phocoena) to different types of acoustic harassment devices and subsequent piling during the construction of offshore wind farms

JOURNAL=Frontiers in Marine Science

VOLUME=Volume 10 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2023.1128322

DOI=10.3389/fmars.2023.1128322

ISSN=2296-7745

ABSTRACT=Before piling of offshore wind farm foundations, Acoustic Harassment Devices (AHDs) are used to drive harbor porpoises out of the area where they could suffer injuries. Until 2017, a combination of pingers and seal scarer devices was prescribed for mitigation purposes in Germany. However, seal scarers led to decreased porpoise detection rates in much larger distances than intended, when 750 m is usually rendered sufficient to avoid injuries. Therefore, devices specifically designed for mitigation purposes, such as the FaunaGuard Porpoise module, were developed and are prescribed since then. These Acoustic Porpoise Deterrents (APDs) aim to keep the animals away from offshore construction sites but should not lead to large-scale disturbance as caused by a seal scarer. Although project-specific evaluations indicated that APDs are highly effective, a cross-project analysis and a comparison with data from previous piling procedures employing seal scarers were still pending. The present study aimed to fill this gap. Between March 2018 and April 2019, harbor porpoise detection rates were monitored acoustically in four offshore wind farm projects using CPODs before, during and after piling at different distances up to 10 km from piling. APD operation led to a significant decrease in detection rates in the vicinity of the device, indicating the displacement of the animals from a small-scale area. All results from the present study indicate that APDs should be used instead of seal scarers for future construction of offshore wind farms, assuming there is no habituation effect. Although this study only covers projects in the North Sea, it is likely that Acoustic Porpoise Deterrents will also work in other areas with similar oceanographic conditions. Given that the extent of disturbance to harbor porpoises is lower when using the Acoustic Porpoise Deterrent compared to the seal scarer, we consider that preferential use of the Acoustic Porpoise Deterrent is a positive improvement to mitigation strategies and an important step forward to a less harmful piling procedure.