RPS has been working with project partner Marine Conservation Research (MCR) on the Phase II of a project for the Offshore Renewables Joint Industry Partnership (ORJIP) looking at the effectiveness of Acoustic Deterrent Devices (ADDs) to deter marine mammals from injury zones. The project, managed by the Carbon Trust, is a vital UK-wide collaborative programme of environmental research aimed to reduce consenting risks for wave, tidal stream and tidal range projects.
As a key part of this project RPS has led a study into the efficiency of ADDs for preventing minke whale from approaching too close to offshore site operations. Subsea noise, primarily caused by pile-driving is identified as causing a potential risk of injury to marine mamal receptors, and so is a significant consideration for consenting offshore wind-farm developments. Studies have previously been conducted with reasonable success to analyse the efficiency of ADDs in deterring pinnipeds (seals) and harbour porpoise but do not guarantee that the results would be the same for minke whale whose hearing frequency is in a lower range.
The project results were intended to enable the creation of reliable exclusion zones around an offshore turbine. Following on from an extensive desk top review of 34 ADDs in Phase I of the ORJIP study, the Lofitech ADD was selected to test in the field with minke whale, as this had a proven track record of successfully deterring other marine mammal species.
Fieldwork was undertaken by a research team onboard the specialist research vessel, Song of the Whale in Faxaflói Bay, southwest Iceland for a period of six weeks. Nearly 250 minke whales were sighted, 46 whales were tracked, and 15 whales successfully followed as study subjects to compile a full behavioral dataset of the whales’ behavior in response to controlled exposure to the Lofitech ADD. A secondary, smaller vessel was used to deploy the ADD to ensure minimum disturbance from the vessel itself. The methodology used was a 30-minute pre-exposure period, a 15 minute control period (engine cut), 15 minute exposure at 1 km distance, then a 30 minute post-exposure period to observe reactions after the ADD had been switched off.
The study whales responded quickly with a directional movement away from the ADD and increased swim speed – foraging whales moved erratically pre-deployment, then moved away from the sound in an approximate straight line when it was emitted, slowing their pace after some 30-45 minutes. The study showed that focal whales responded to ADDs by moving to distances which could prevent injurious effects from subsea noise. In addition, predictive noise modelling suggested that the whales were not at risk of injury by the exposure to the ADD itself, even if an individual were exposed at closer distances of 25 m.
As a consequence of the project, the study method and results will be used to inform government guidance on mitigation for marine development and will serve as valuable information for other activities including seismic surveys, unexploded ordnance detonation, and offshore mineral excavation.