RPS and project partners Marine Conservation Research (MCR) have been working on a project for the Offshore Renewables Joint Industry Programme (ORJIP) - to test the effectiveness of an Acoustic Deterrent Device (ADD) as a mitigation tool to reduce potential injury to low frequency cetaceans, such as the Minke whale, during offshore construction piling operations. The project, managed by the Carbon Trust, was part of a UK-wide, collaborative programme of environmental research aimed at reducing consenting risks for offshore energy projects.
Minke Whale, ORJIP study
Offshore Renewables Joint Industry Programme Board (ORJIP)
Faxaflói Bay, Iceland
Subsea noise generation by offshore windfarm developments, primarily during pile-driving, has been identified as causing potential risk of injury to marine mammal receptors, and is therefore a significant consideration during the consent process.
The current methodology to reduce the potential for auditory injury to marine mammals in the UK is to utilise a combination of marine mammal observers (MMOs) which keep look out for nearby animals, and passive acoustic monitoring (PAM) which detect marine mammal vocalisations. If marine mammals are detected during pile-driving, work is stopped until they have left the area. This approach is limited during poor visibility and high sea states, and unplanned delays during construction can be a challenge.
ORJIP wanted to assess the use of ADDs, which emit a series of amplified sounds of varying frequency into the marine environment to deter marine mammals from entering predicted injury zones. Previous studies (ORJIP Phase 1) researched the efficacy of ADDs in deterring high frequency cetaceans such as seals and harbour porpoise, however, there has been little research into effective deterrence methodologies for low frequency cetaceans.
Image courtesy of MCA.
A team of researchers spent five weeks in Faxaflói Bay, southwest Iceland, during August and September 2016, tracking the Minke whale. The aim of the study was to understand their behavioural response to an ADD during a controlled exposure experiment (CEE). The team sighted nearly 250 Minke whale over the study period, and of these 46 were tracked. 15 full controlled exposure experiments were completed.
Recordings of the ADD were also taken to characterise the nature of their sound emitted to determine which type and level of deterrent sound Minke whale respond to most.
Data analysis showed that the whales reacted strongly to the ADD, swimming quickly and directly away from the playback site in all 15 CEEs. As a result, we were able to confidently recommend that ADDs be used as an effective mitigation tool to reduce the potential for injury as a result of noise generated during pile driving. We were also able to conclude there was little potential for inducing temporary or auditory injury through exposure to the ADD.
The study methodology and results will be used in future to inform government guidance on the mitigation strategies during the development of marine projects.
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