Over the last decade there has been a growing interest in marine renewable energy production, such as offshore wind power. Construction of these devices can result in very high noise levels, which has raised concerns about the impact on marine species.
In 2006-7, two 5 MW wind turbines were installed off NE Scotland (UK), the first to be installed in water this deep (138 feet). The wind turbines were 16 miles from a Marine Protected Area for bottlenose dolphins. Studies led by Professor Paul Thompson at the University of Aberdeen, Dr. Helen Bailey at the UMCES Chesapeake Biological Laboratory and other collaborators from Talisman Energy (UK) Ltd, investigated these noise levels and impacts on marine mammals. These studies have recently been published in the journal Marine Pollution Bulletin.
The first study recorded the underwater noise produced. This was measured before and during the loudest part of the construction phase when the wind turbines were hammered to the seabed, a process known as pile-driving. “These pile-driving sounds were audible up to 44 miles away and could have caused behavioral disturbance to dolphins up to 31 miles away,” says Dr. Bailey.
In the second study, hydrophones moored to the seabed were used to monitor the presence of dolphins and porpoises by recording their echolocation clicks. Harbor porpoises regularly occurred around the wind turbine site. However, there was some evidence that porpoises did respond to the installation activities. “There was a longer time interval between detections of porpoises during and shortly after the second piling event,” explains Dr. Bailey, “and the number of hours per day that porpoises were detected was significantly lower in 2006, when the core engineering work was carried out, than in 2007.”
These studies indicate that the construction of offshore windfarms can produce noise that travels over large distances and that this can impact marine mammals. This should be considered in site planning and environmental impact assessments.
Dr. Bailey recommends “In order to determine impacts on marine mammals we need baseline data, ideally for a minimum of two years, so that we can differentiate between natural variation and impacts caused by offshore energy. It is difficult to determine the extent of behavioral disruption to marine mammals and other species so we need to take a precautionary approach.”
Such approaches could include developing engineering solutions to reduce the noise levels produced during construction or using alternative construction techniques that generate less noise.
The articles “Assessing underwater noise levels during pile-driving at an offshore windfarm and its potential effects on marine mammals” and “Assessing the responses of coastal cetaceans to the construction of offshore wind turbines”, are available online in the journal Marine Pollution Bulletin.