Degraer, S.

Dulière, V.

Haelters, J.

Vigin, L.

Open Marine Archive

Towards a model fo r the redistribution o f harbour porpoises 
(Phocoena phocoena) due to pile driving in Belgian waters
Haeltersjan, Valérie Dulière, Laurence Vigin and Steven Degraer
Royal Belgian Institute o f Natural Sciences (RBINS), Operational Directorate Natural Environment, 3de 
en 23ste Linieregimentsplein, 8400 Ostend and Gulledelle 100, 1 200 Brussels 
E-mail: i.haelters@mumm.ac.be
In 2011 the offshore wind farm  at the Thorntonbank, Belgian waters, entered its second phase, with 
the piling o f 49 jacket foundations fo r 48 wind turbines and an offshore high voltage substation. As 
pile driving is known to generate high underwater sound levels, it is im portant to  assess its impacts 
on cetaceans, which depend on the emission and reception o f sound fo r foraging, spatial 
orientation and social interactions. We investigated the effects on the harbour porpoise (Phocoena 
phocoena), the most common cetacean in Belgian waters, by perform ing standardised visual aerial 
line transect surveys before and during the piling phase. One week before piling started, harbour 
porpoises were very common, with average densities o f more than 2 animals.km 2. One week into 
the piling phase changes in density and spatial d istribu tion  clearly suggested harbour porpoise 
displacement due to behavioural responses elicited by repeated, relatively short piling events.
We developed a model o f the expected red istribution o f harbour porpoises after disturbance due to 
pile driving and applied it to  data on harbour porpoise density d istribu tion  prior to  the start of 
piling. Model results o f changes in density and d is tribu tion  showed good agreement w ith 
observations. This approach should be considered a firs t step towards a fu ture prediction o f the 
effect o f piling on harbour porpoises’ d istribution.
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Towards a model for the redistribution of harbour porpoises (<i>Phocoena phocoena</i>) due to pile driving in Belgian waters

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