UK waters are of international importance for the harbour porpoise, holding one of the highest percentages of animals of any European country. As with other cetaceans, these relatively shy animals use sound both to communicate and to find food, and are therefore particularly sensitive to man-made sounds introduced into the marine environment. These include the pulses of noise that spread out from installing pile-driven foundations during offshore wind farm construction. At the same time, an expansion of renewable energy working within environmental limits is essential to mitigate the long-term impacts of climate change, including to marine ecosystems.
This new report, commissioned by WWF-UK, shows that noise reduction measures can clearly help to reduce the risk of a population decline due to the cumulative impacts of wind farm construction. By identifying the difference in impact between a baseline of no noise reduction and reducing noise under certain scenarios, it shows that if, under the assumptions made in the report, all UK wind farms in the North Sea reduced their noise levels by the equivalent of around 8dB, the risk of a 1% annual decline in the North Sea population can be reduced by at least 92% and up to 96%.
The report also discusses that using noise reduction measures in areas with high porpoise densities will be a more efficient than applying the same measures in areas of lower porpoise densities. This is important, as a possible special area of conservation (pSAC) has recently been identified for the harbour porpoise in the Southern North Sea, which overlaps with several existing or planned wind farm sites. If the equivalent noise reductions took place solely within this pSAC, the risk of a 1% annual decline would still be reduced by up to 66%.
This report demonstrates to us that relatively modest reductions, based on previously tested technologies that are becoming ever more widely used, can reduce the cumulative impact of underwater noise significantly, particularly the impacts of behavioural disturbance. By specifically articulating the relative level of these benefits, using scenarios in the context of the requirements to meet the conservation objectives of the Southern North Sea pSAC, this report is also highly topical given the need to find ways in which offshore wind energy can be generated in harmony with well-managed site protection.