Acoustic Deterrent Devices to safeguard marine mammals during offshore construction
The Offshore Renewables Joint industry Programme (ORJIP), with funding from innogy, Ørsted, and Statoil has successfully concluded a study to examine the effectiveness of using Acoustic Deterrent Devices (ADDs), as a protection method for minke whales during offshore windfarm construction.
The research project, managed by the Carbon Trust confirmed that minke whales showed a clear response to the tested ADD, demonstrating the effectiveness of the technology in protecting this important species.
Previous studies have demonstrated that ADDs effectively deter seals and harbour porpoises, however, until now there has been little research into the use of ADDs as a deterrent for minke whales. As minke whales are an important species in UK waters, the ORJIP study was set up to address this knowledge gap. The objective was to increase confidence in ADDs and specifically improve the techniques for safely deterring marine mammals during offshore wind construction. During the field research whales were observed to display a clear and sustained movement away from the ADD deployment site, adopting faster swim speeds with more directed movement.
During the construction of wind farms, where percussive pile driving is required for foundation installation, increased underwater noise levels are generated. The detection of marine mammals is currently carried out by marine mammal observers posted offshore, or passive acoustic monitoring (PAM). If a marine mammal is detected close to an offshore wind construction site, piling activity will not commence until it is deemed that there are no longer marine mammals within the predefined zone.
TEMPORARY WHALE EXCLUSION
The ability to use active acoustic systems to create a temporary safety exclusion zone around the turbine is a useful addition to the suite of mitigation options for wind farms developers. In particular, it increases confidence that marine mammals are adequately protected when operating in harsh conditions or poor visibility, and also avoids the need to unnecessarily delay construction operations.
In a joint statement innogy, Statoil & Ørsted said: “This valuable research complements the extensive measures already undertaken by the industry to protect marine mammals, including working closely with organisations such as Natural England and the Marine Management Organisation as well as undertaking extensive environmental studies before progressing with construction on individual projects. This is an important project and we have proactively engaged and supported the ORJIP ADD programme in order to ensure our projects look after the safety of these important species. We are pleased to see that these trials have increased the evidence base proving the efficacy of ADDs in deterring marine mammals.”
Olivia Burke, manager of the ORJIP ADD project at the Carbon Trust said, “The results from this research are really exciting and are a result of many organisations working together to help shed light on this important area. The findings will help increase industry and regulator confidence in the use of ADDs to actively manage the protection of marine mammals during the piling phase of construction.”
Tracking results demonstrated that focal minke whales responded to ADDs at distances which could prevent injurious effects of subsea noise. The study revealed that the selection of appropriate ADDs for mammals with different hearing frequencies and appropriate deployment periods for the underwater environment were important considerations to ensure successful ADD deployment.
This research was undertaken by RPS Energy and MCR on behalf of the ORJIP programme and has improved the current evidence base available on the reaction of marine mammals to ADDs, helping to reduce the knowledge gap and support the use of ADDs as an effective mitigation measure to reduce the potential for injurious effects from piling. This could also reduce the number of personnel deployed to monitor marine mammal presence offshore to minimise health and safety risks as the industry continues to grow.
A total of 246 minke whales were sighted, of which 46 focal whales were tracked. Focal follows including successful ADD deployment were carried out on 15 occasions. In all 15 deployments, the focal animal moved away from the ADD deployment site following activation of the unit.
The study site was located in Faxaflói Bay, southwest Iceland, selected as it is a summer feeding ground for minke whales therefore ensuring a high whale population density. Researchers worked from the specialist cetacean research vessel Song of the Whale and a secondary smaller vessel to ensure minimal disturbance. The Lofitech ADD device was chosen for the research as it had the greatest body of scientific evidence demonstrating efficacy at deterring other marine mammals. Video range tracking (VRT) was employed to measure minke whale response to ADDs during the Control Exposure Experiments.
By Jake Frith
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