A master’s thesis defended this spring found that the noise generated by offshore wind farms can cause herring schools to disperse, but the fish can swim elsewhere, and spring spawning is not affected by turbine noise, writes ERR News.
Kirke Paris defended her master’s thesis at the University of Tartu, in which she studied how the low-frequency sound characteristic of offshore wind farms affects the behavior of Baltic herring. A field experiment showed that the density of herring schools was lower near the sound source; at the same time, initial results do not indicate that wind farms cause significant harm to fish.
The choice of the study was determined by practical necessity, as large offshore wind farms are planned in the coastal waters of Estonia. Underwater noise caused by human activities is also increasing. Paris said that understanding how animals perceive their environment is important for understanding how fish inhabit and move around in their environment. The researchers decided to observe the fish in their natural habitat because sound might travel differently in a laboratory setting than it does in the open sea, and artificial environments could also affect fish behavior. Paris noted that fish in captivity would certainly react to stressors differently than they would in the wild.
The experiment took place in the Gulf of Riga, south of Kihnu. A special loudspeaker was placed in the center of an area of about 16 square kilometers that simulated the sound produced by a wind turbine. The researchers traveled in a boat along predetermined routes and measured the density of fish. The sound frequency was the 100 hertz typical of wind turbines, and the sound produced by the loudspeaker reached 170 decibels. Paris said that this corresponds to very loud human speech, but in water it is more like a low, continuous hum.
When comparing conditions with and without sound, a clear trend was evident.
When the loudspeaker was turned on, the density of herring schools in its vicinity decreased. Although not all fish left the area affected by the noise pollution, the schools of herring became visibly more dispersed. The data obtained during the experiment show that a statistically significant noise effect is observed about 350 meters around the sound source. Paris pointed out that a radius of less than half a kilometer does not create a significant obstacle in the context of a single wind turbine, and fish can swim away from it. The situation changes significantly if a wind farm consists of dozens or hundreds of turbines. In this case, the area affected by noise expands, and the combination of noise generated by several turbines simultaneously becomes important. Location becomes especially important if large wind farms block the path to spawning grounds. Paris emphasized that current research does not indicate that this will happen in the Baltic Sea.
In addition to noise pollution, wind farms can affect fish in other ways. For example, sediments raised during construction can reduce underwater visibility. The electromagnetic field created by underwater cables connecting wind farms to land can also interfere with fish’s navigational abilities.
Not all changes caused by wind farms are harmful to marine life, however. The subtle foundations of wind turbines often attract fish, increasing the amount of biomass and available food. No-fishing zones, which are often created around wind farms, can provide fish with a safe haven.
Paris said that fish hearing is much more complex than it might initially seem.
Although marine animals do not have externally visible ears, their inner ears detect changes in sound pressure in the environment. Many species can also detect the movement of water particles. Because fish are such a vast and diverse group, hearing varies greatly between species. Some fish can hear ultrasound, while others can hear infrasound. Most species are better at detecting low frequencies, between 100 and a few hundred hertz. Sound helps fish navigate their environments, forage for food, and avoid predators.
The Baltic herring is likely among the fish with the best hearing in the region. Although the hearing of Baltic herring has not been studied before, there is extensive research on its closely related Atlantic herring.
The field study took place from 2023 to 2025, and the master’s thesis is part of a larger study. Paris conducted her research in the fall, when the fish are more active and concentrate in the bay. Other researchers then continued to observe the behavior of Baltic herring in the spring, in the shallow waters of the Gulf of Pärnu.
It was found that noise does not affect spawning, which is good news for wind farm planning.
Paris plans to continue studying the specific mechanisms of fish perception during her doctoral studies, paying particular attention to the movement of water particles caused by sound.
The researcher pointed out that when assessing the impact of wind farms, more than one factor should be considered, and combinations of different factors should be taken into account. She added that researchers are interested in how sound affects the entire ecosystem, not just one species.
The findings in the study therefore do not mean that wind farms can be built without restrictions at sea. At the same time, there is no reason to fear that the sound created by a single wind farm could immediately destroy the Baltic herring population. It is a very bad idea to fill the entire Gulf of Riga with wind turbines, but smart solutions are necessary.
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