Underwater noise from wind turbines can affect marine life. FOI research shows how fish are disturbed and what kind of noise affects them most.
Mathias Andersson, biologist and research scientist at FOI, has studied how fish in Öresund are affected by the noise from the Lillgrund wind farm between Malmö and Copenhagen.
- Öresund is of course a generally noisy environment. We have compared the noise from Lillgrund with the sounds from the normal shipping traffic in the area, says Mathias Andersson.
The group of scientists who have studied the acoustic underwater environment in Öresund consists of both acoustics specialists and biologists. This is the first time that the acoustic noise from an entire wind farm has been charted and compared with the ambient noise of normal shipping traffic. Fish hear over a lower frequency spectrum compared with humans and the noise from a wind farm lies within this spectrum. But it is not only this low frequency noise that can disturb them.
-Wind turbines also emit a sharp audible tone from the gearbox that is transmitted down into the water through the tower and the foundations. It is this tone that differs most markedly from the day-to-day noise from shipping. There is currently very little information about how fish are affected by this tone but we may assume, based on other studies looking at birds and humans, that a loud sharp tone can be stressful,” says Mathias Andersson.
This tone that cuts through the noise is theoretically audible to fish at a distance of several kilometres. The research team has constructed a virtual model of the wind farm. From this one can see how much sound is generated by each individual wind turbine and how much is generated by them all collectively.
-But so far we have not seen fish being scared away by the noise. Some agitation has been observed, mainly in fish frequently moving about in the area, for example migrating eels on their way to spawn in the Sargasso Sea. Further studies are needed to determine whether or not the increased level of noise in the area of the wind farm does have an adverse effect on fish.
Fish have inner ears and some have swim bladders which function as an eardrum. Those fish that have a swim bladder hear better than those that do not have them. In order to find out how fish hear, the scientists construct an audiogram by placing electrodes on the heads of fish and then see how they react to different sounds and frequencies.
The report about sea noise in Öresund is published by Vindval through the Environmental Protection Agency and the Energy Agency. FOI carried out the study in collaboration with Stockholm University.