Marine mammals

The Wozep marine mammal research focuses primarily on learning more about the direct impact of construction and, ultimately, the operation of a wind farm and stating that impact in terms of population size. In addition to the use of models (for both underwater noise and its impact at the population level), numerous field measurements are also made in and near wind farms (including those under construction) and scientific research is conducted into the behaviour of harbour porpoises.

A variety of marine mammals are found in the Dutch section of the North Sea. The harbour porpoise (Phocoena phocoena) and two types of seal, the harbour seal (Phoca vitulina) and the grey seal (Halichoerus grypus)  are the most common species. The North Sea and the coastal zone are used for eating, resting and reproduction.

Harbour porpoises (a small toothed whale species) have very good hearing and they use echolocation to find food, but also for navigation over short distances, avoiding enemies and possibly for communications as well. In addition to echolocation (high frequency), porpoises also use sonar (low frequency). Sonar is probably more useful in shallow areas with slightly undulating slopes. Seals actually track their prey more with their whiskers and visually, but they may also use their hearing.

Marine mammals can be affected by underwater noise, including shipping, seismic surveys, the clearing of ordnance, and the construction and operation of wind farms.

Because these marine mammals have a protected status, Wozep is organising research to determine the possible impact of the construction (as a result of the associated noise) and the presence (as a result of changes in habitat) of offshore wind farms. That information can be used, for example, to draft specific construction requirements in order to limit the disturbance of marine mammals. These construction requirements are set out in the site decision . For example, an acoustic deterrent has to be deployed before pile-driving work in order to drive marine mammals and sensitive fish out of the area. Pile-driving intensity is then built up gradually so that any animals left behind have time to swim away. In addition, strict conditions (in the form of a noise standard) apply with regard to underwater noise production during pile-driving work for the wind turbines.

Use of the study results

The marine mammal research helps to reduce the uncertainties relating to the impact of offshore wind farms on marine mammals. This will result in more accurate  environmental impact assessments for the wind farms in the future. In addition, the extra data will allow for more accurate calculations with the Framework for Assessing Ecological and Cumulative Effects (KEC) of the cumulative effects of wind farms on marine mammals. The KEC is investigating the potential cumulative ecological effects of the wind farms in the southern North Sea at present, as well as of wind farms that are under construction or planned for the future. In addition, a better understanding of the effects will provide a firmer footing for permit requirements that will be included in the site decisions for the wind farms.  An example of a permit requirement of that kind is the establishment of a noise standard to mitigate the effects of pile-driving work for the wind turbines.

Ongoing research

To see how effective these new measures are, Wozep is conducting large-scale research into the construction of wind farms off the coast of Zeeland (Borssele I & II). That includes using acoustic monitoring to track the presence of harbour porpoises in and around the working area. Furthermore, twenty seals (10 harbour seals and 10 grey seals) have been tagged in the Voordelta area  [more about this research]

These tags are used to map out the behaviour of these seals. These studies will provide us with a clearer picture of actual disruption during the construction of a wind farm in which mitigation measures have been implemented.

In addition, studies are also being conducted into the sensitivity of harbour porpoises to sound (at different frequencies) and the effects in the form of behavioural changes and hearing.

List with reports on completed studies