Debusschere, E.

Deneudt, K.

Norro, A.

Reubens, J.

Rumes, B.

Open Marine Archive

The influence of pile driving noise on 
Harbour Porpoises
Bob Rumes1, Elisabeth Debusschere², Jan Reubens², Alain Norro1 & Klaas Deneudt²
1 Royal Belgian Institute of Natural Sciences, OD Nature, MARECO, Brussels, Belgium ²Flanders Marine Institute, Oostende, Belgium 
email: Bob.Rumes@naturalsciences.be
The harbour porpoise (Phocoena phocoena) is the most common marine mammal in the Belgian part of the North Sea and is protected byboth national and EU law. In the North Sea, the harbour porpoise is considered under threat because of high bycatch levels and increasingnoise pollution. Impulsive pile driving noise originating from the construction of offshore wind farms has been shown to affect porpoises upto distances of 20 km from the noise source. Driven by high porpoise densities in Belgian waters, a pile driving ban is in force from the startof January up to the end of April. However, The Netherlands have the Borssele offshore wind farm at only one kilometre away from theBelgian offshore wind farm zone, and do not enforce such an embargo. Considering the high mobility of harbour porpoises, there is a needfor improved insights into the impact of pile driving noise on porpoises which can serve as a basis for an objective evaluation of therespective legal regimes.
ACKNOWLEDGEMENTS
The data for this study were obtained from the RBINS wind farm monitoring programme and Flanders Marine Institute (VLIZ), Belgium(2015): LifeWatch observatory data: passive acoustic network (CPOD) for Cetacean detection.
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STUDY SITE
RESULTS & DISCUSSION
From May 16th to September 22nd 2016 a hydraulic hammer was used to drive 51 steel monopile foundations up to 39 meters into the seafloor at the Nobelwind wind farm located on the Bligh Bank in Belgium. 
STUDY DESIGN
Before, during and after this period, porpoise activity was recorded using passive acoustic monitoring (C-PODs), at various distances from the construction site (2 – > 30 km) and underwater noise levels were recorded using moored hydrophones. 
DATA ANALYSIS
The data were analysed using CPOD.exe software version 2.044. Of the four levels of confidence (quality) of the data, only high and moderate click train quality was used, with the species filter set to harbour porpoise. Data were graphically analysed using Excel and R studio.
Anchor weights
Acoustic release C-POD
Buoys
Displacement
In the vicinity of the pile-driving activities (1–10 km) porpoise detections decreased prior to the start of piling, resulting in an increased waiting time between detections. This decrease in detections can be observed up to 48 hours after pile-driving was completed.  
This is in line with results from the German Bight (Brandt et al., 2016) and suggests that increased work vessel traffic acts as a deterrent prior to the start of pile-driving. 
Seasonal pile-driving restriction
In the southern part of the North Sea, harbourporpoise densities show a seasonal pattern with pronounced increases in spring and, to a lesser extent, in late summer to early autumn (Haelterset al., 2016). As a result, in Belgium pile-driving can not take place between January 1st and April 31st. At VG2, PAM detections decreased near the end of this restriction period, weeks prior to the start of hydraulic piling. Pile-driving at Nobelwindended at the onset of the autumn peak. 
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Spatial extent of displacement
In order to test whether we could observe the spatial extent of harbour porpoise displacement we grouped the C-PODs in three distance classes (1-10, 10-20 and 20-40 km) and compared porpoise detections 48h prior, immediately after and 24h after piling at these locations. In contrast to previous studies (Brandt et al., 2016, Dähne et al., 2013), no significant differences were observed at these distances although it is likely that this is due to insufficient data (resulting from the loss of  several moorings). 
Piling vessel @ Nobelwind wind farm (July 2017)                  Nobelwind construction area (red) and             Passive acoustic monitoring-chain                                  Harbour porpoises (Phocoena phocoena)C-POD locations (black)  © Solvin Zankl
REFERENCESBrandt M, Dragon A, Diederichs A, Schubert A, Kosarev V, Nehls G, Wahl V, Michalik A, Braasch A, Hinz C, Ketzer C, Todeskino D, Gauger M, Laczny M, Piper W (2016). Effects of Offshore Pile Driving on Harbour Porpoise Abundance in the German Bight: Assessment of Noise Effects. (p262)Dähne M, Gilles A, Lucke K, Peschko V, Adler S, Krügel K, Sundermeyer J, Siebert U (2013) Effects of pile-driving on harbour porpoises (Phocoena phocoena) at the first offshore wind farm in Germany. Environmental Research Letters 8Haelters J, Rumes B, Vanaverbeke J, Degraer S (2016). Seasonal and interannual patterns in the presence of harbour porpoises (Phocoena phocoena) in Belgian waters from 2010 to 2015 as derived from passive acoustic monitoring.
Porpoise detection positive minutes per day at VG2 (green) and Gootebank (blue) with indication of pile-driving period (red).
To be continued…in the environmental monitoring report offshore wind - 2017
Lz-p 196 dB re 1µPa @ 1000 m
Corresponding to Max. Lz-p 196 – 168 dB re 1µPa*  
Corresponding to Max. Lz-p 168 – 159 dB re 1µPa*  
Corresponding to Max. Lz-p 159 – 151 dB re 1µPa*  
* Preliminary data based pile-driving of Nobelwind H03  
bpnsVG2 bpnsGootebank
INTRODUCTION


The influence of pile driving noise on harbour porpoises

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