Photo by Rogue Li
New research into the acoustic impact of offshore wind farms on marine life has produced a series of counterintuitive findings — and raised questions about how well the industry understands its effects on the underwater environment.
PhD candidate and marine biologist Fien Demuynck, of Leiden University, spent years conducting fieldwork along the Dutch-Belgian coast, using sensors to measure how fish respond to wind farm noise. Her research focused on porpoises and their prey — pelagic fish including herring, sprat and mackerel, which swim in the middle of the water column rather than near the seabed.
Fish that would not flee
One of the most striking findings concerns construction noise. Piling — the process of driving steel foundations into the seabed — generates intense noise that can cause temporary hearing loss in fish at distances of up to two or three kilometres. Demuynck had expected fish to swim away. They did not.
“We were baffled,” she told Phys.org. “We don’t know why it is. Piling can be so loud that it can cause temporary hearing loss at distances of two or three kilometers from a wind farm. In the murky North Sea, hearing is an important sense for animals, so you wouldn’t expect it to be in their interest to stay there. Perhaps they do so because they are used to the sounds or have hearing loss from previous piling. Or perhaps they react in another way: for example, by shoaling more tightly. This definitely warrants more research.”
Prior to this, Demuynck had tested whether acoustic deterrents — non-harmful sounds played before piling begins — could be used to move fish away from construction zones. In tank tests, wild herring did respond differently to noise, though the type of sound made little difference. In the open North Sea, however, the fish did not respond to the deterrent at all.
Fewer fish around operational turbines
Once turbines are running, they emit a more constant, lower-level operational hum. Demuynck had expected this to benefit fish, since fishing is prohibited within wind farm boundaries, making them potential safe havens. Instead, she found fewer pelagic fish around the Dutch-Belgian wind farms than in surrounding waters.
One possible explanation: “The mixing of the water layers around the poles might reduce plankton production, the main source of food for these fish,” she said. “But we need further research to confirm this.” The altered current patterns caused by turbine foundations, as noted by Energies Media, may also shift nutrient and sediment distribution across the benthic zone.
For porpoises, the picture may be more positive, turbine structures can attract mussels and other invertebrates, potentially providing a rich feeding ground. But Demuynck cautioned that this too requires further study.
Balancing the green transition
Demuynck was careful not to overstate the negative findings. “Marine animals are already facing the effects of global warming and plastic pollution, and on top of that comes noise from human activity,” she said. “Wind farms help to reduce global warming, and that benefits fish as well. I couldn’t say whether the negative effects outweigh the positive ones for porpoises and pelagic fish. But I do think that with new developments, we should look at their impact on marine life and take steps to limit this.”
Her overarching concern, she explained, is straightforward: “We don’t want animals to become stressed, disoriented or deaf.”
As offshore wind capacity continues to expand rapidly across the North Sea and beyond, Demuynck’s work underlines the need for integrated acoustic monitoring as a standard component of project development, and for the industry to resist treating the ocean as a silent frontier.