Marine mammals

Efficacy of Acoustic Deterrent Devices

A two phase project to investigate mitigation methods that could deter marine mammals from an offshore wind construction site and in turn, safeguard them from piling noise

During the construction of wind farms, turbine foundations are driven into the seabed using a hydraulic hammer which generates significant levels of underwater sound. At close range this could potentially be harmful to a number of marine mammals.

Currently if a marine mammal is detected close to an offshore wind construction site this delays piling until it is deemed that there are no longer marine mammals within the predefined injury zone. The current method for detecting the mammals is by using marine mammals observers posted offshore, or passive acoustic monitoring. These methods of detection are restricted by sea roughness and daylight hours meaning that visual and acoustic mitigation has limitations.

ORJIP carried a two phase project to investigate and understand the efficacy of mitigation methods that could deter mammals from an offshore wind construction site and in turn, protect them from piling noise.

Marine mammals

Phase 1

Acoustic deterrent devices could enable exclusion zones to be created around the turbine helping to actively mitigate any harmful impact, thus avoiding the need to spot marine mammals from the sea surface and increase certainty that marine mammals are protected when operating in deep water conditions where visibility can be poor.

Phase 1 of the ORJIP study identified and reviewed 34 acoustic deterrent devices and their effectiveness on different marine mammals. The work identified a basic understanding of efficacy of acoustic deterrent devices for harbour porpoise, grey seal, harbour seal, bottlenose dolphin and minke whale and little evidence or no understanding of:

  • Deterrence in offshore environments
  • Long term responses to deterrence
  • Flexibility of effective range

This led to the second phase of the work. The outputs from Phase one can be found here:

Efficacy of Acoustic Deterrent Devices - Phase 2

Phase 2

Stage one of this phase focused on Harbour porpoise, Grey seal and Harbour seal. A literature review gathered evidence on the effectiveness of acoustic deterrent devices using existing evidence.

The outcome of this work, accepted by regulatory bodies, demonstrated that previous studies demonstrated effective deterrence beyond 500m for Harbour porpoise, Grey seal and Harbour seal. As a result acoustic deterrent devices could be used for these species during construction.

However there were still many uncertainties regarding efficacy for other species. Leading to stage 2 of the work where ORJIP carried out in-field testing on the efficacy of acoustic deterrent devices on Minke whale to provide recommendations on their use during construction. Recommendations on the use of Acoustic Deterrent Devices (ADDs) in the offshore wind industry will be provided to inform government guidance on mitigating injury to marine mammals.

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