The European Union had 14.6 gigawatts (GW) of offshore wind installed in 2021, and this is expected to increase by at least 25 times over the next decade. While an expanding renewable energy sector is necessary to replace fossil fuels and slow climate change, this should not come at a cost to Earth’s embattled wildlife.
To date, most offshore wind turbines have been built using stable foundations, such as steel piles driven into the seafloor with large hydraulic hammers, often very large. The noise produced by pile driving can be heard tens of kilometers away from the source as short and sharp jolts such as gunfire.
Sound travels much more efficiently in water than in air. Marine mammals such as whales and dolphins use it to communicate over long distances, sense the environment and locate prey. This dependence on sound makes marine mammals particularly vulnerable to the effects of man-made noise, including the noisy construction of offshore wind farms. Piling can deafen, injure or even kill marine mammals at close range.
The dolphin mutur is the smallest and most common marine mammal species in the North Sea, where EU countries hope to produce 150 GW of offshore wind power by 2050. Like bats, these relatives of whales and dolphins emit clicks almost constantly to find echolocation. This helps them find and identify objects, including food. Acoustic deterrents, small devices that emit sound pulses, are used to scare off marine mammals from places where wind farms are built to protect them from the noise produced by pile driving. But until recently, no one was sure how well these deterrents were working.
University of Aberdeen Lighthouse Field Station and St. My colleagues at the University of Andrews Marine Mammal Research Unit have developed a portable acoustic recorder that can detect the movements of harbor seagulls. Using an array of these recorders while piling on an offshore wind farm in northeast Scotland, we have shown that acoustic deterrents work – dolphins swim away from direct sound pulses, ameliorating the most severe effects of construction at sea.
Fighting with noise
A number of measures have been implemented to minimize damage from offshore wind farm construction. Acoustic deterrent devices, activated before piling begins, are expected to discharge marine mammals from the sea tens to hundreds of meters around the construction site, where noise is expected to cause the most damage. These electronic devices were originally developed for use in the aquaculture industry to deter seals from fish farms.
Despite experimental trials, there is limited evidence to show how well acoustic deterrents work during construction. This is due, at least in part, to the difficulties of working in the marine environment, as well as the difficulties of studying animals that are highly mobile, relatively rare, and live most of their lives underwater and out of sight. These factors make it very difficult to observe how marine mammals respond to certain sounds or disturbances. Fortunately, we were able to turn the muturs’ addiction to sound to our advantage.
Recent advances in passive acoustic monitoring have meant that we can use a voice recorder attached to a small underwater microphone cluster called a hydrophone to study porpoise movements. By measuring small differences in the arrival time of dolphin echolocation clicks in the four hydrophones, we determined the direction in which they echolocated. The echolocation beam of the harbor dolphin is narrow and pointing forward, and based on these findings, we were able to determine the direction in which they were swimming.
We found that when acoustic deterrents were used, the clicks we detected of the muturers indicated they were moving directly away from the construction site. This proves that acoustic deterrent devices can make offshore wind farm construction safer.
We detected responses among harbor dolphins up to 7km from the construction site, suggesting that these deterrent devices could be almost too good at their job. Such a long-distance effect can remove animals from important feeding areas, emphasizing the importance of a balance between preventing injury and minimizing discomfort.
Our portable acoustic recorder can now more accurately determine how they respond to disturbance in a wide variety of habitats, improving protection for marine mammals. It will also allow researchers to measure the effectiveness of measures used to minimize disturbance during wind farm construction or other activities.
Don’t have time to read as much as you want about climate change?
Get a weekly summary in your inbox instead. Every Wednesday, The Conversation’s environmental editor writes Imagine, a short email that delves a little deeper into a single climate issue. Join the 10,000+ readers who have subscribed so far.
This article has been republished under a Creative Commons license from The Conversation. Read the original article.
Isla Graham has received funding from Moray Offshore Wind Farm (East) Ltd. The funding agency had no input on data collection, data analysis or interpretation. The objectives, scope and experimental design of the study were developed by the authors to meet Moray Offshore Wind Farm (East) Ltd planning approval requirements. These were accepted by the regulatory Marine Scotland Licensing and Operations Team, following consultation with legal advisors represented at the Moray Firth Regional Advisory Group (MFRAG), a stakeholder group set up by the Scottish government to oversee the monitoring programme.