This article was featured in Eurofish Magazine 3 2026.
The likelihood of wind farms being built in Estonia’s coastal waters has raised concerns among fishers about the effects of low-frequency continuous noise on herring behaviour. Researchers at the Estonian Marine Institute, University of Tartu have conducted several trials to determine the impact.
Novel large-scale experimental studies were conducted in the coastal sea of Estonia to investigate the potential effects of operational noise from offshore wind farms on Baltic herring—Estonia’s national fish. Multiple extensive wind farm projects are currently in the planning or development phase in western Estonia, but none has so far been constructed. Several stake-holders in Estonia, including the pelagic fish trawling fleet, are concerned about the potential effects of wind farms on fish stocks and fishing. However, relatively little is known about the potential impacts of offshore wind farms on marine life, and especially on fish.
Noise had to be synthesised due to the current lack of wind turbines
The general goal of the study was to conduct approximately 12-hour long continuous noise exposure experiments during periods of the year important for herring—spawning migration, spawning, and feeding. As no offshore wind turbines currently exist in Estonian coastal waters, high intensity low-frequency sound resembling the projected operational noise from a 15-20 MW turbine, was generated with a state-of-the-art underwater speaker. Estonian researchers wanted to know whether and to what extent the generated noise affected freely moving herring schools in the study area. In addition, net-cage experiments were conducted to determine the exact sound level that elicited a behavioural response in herring.
Statistically significant noise effects were detected only in the feeding area experiments; no such effects were found in the spawning migration or spawning area experiments. However, the statistical significance did not mean that herring schools completely left the approximately 16 km² study area due to the noise. The observed effect occurred at distances of up to 300–800 m from the noise source (in water approximately 20 m deep), corresponding to a received noise level of about 117–127 dB re 1 µPa in a one-third octave band at 125 Hz at the mentioned distances. Even within this impact zone, not all fish left the area. In net-cage experiments, it was determined that the sound level that triggers a behavioural response in herring is 118 dB re 1 µPa in a one-third octave band at 125 Hz. This threshold can be used in future impact assessments throughout the Baltic Sea.
No meaningful impact detected but caution is warranted
In conclusion, the experiments conducted in this study did not detect any major negative effects on herring. This means that most fish did not leave the study area due to high noise levels in the study area. However, the obtained results still warrant caution regarding the operational noise impacts of offshore wind farms. This means that some, statistically significant, behavioural effects were evident in experiments conducted by Estonian researchers, especially during the herring feeding period. Also, it is unknown whether the absence or presence of herring behavioural effects from a single sound source found in this study would be the same in the presence of multiple sound sources (an entire wind farm). The effects of long-term noise habituation are also unknown, although Estonian researchers have now conducted the longest continuous noise experiments to date, with no signs of habituation during the feeding period.
Consequently, until better knowledge emerges, a precautionary principle is advised by Estonian scientists—simultaneous construction of multiple wind farms in the Gulf of Riga should be avoided at this time. It is likely that the construction of a single offshore wind farm in the Gulf of Riga would not significantly affect the feeding conditions of herring living in the gulf, as fish could move to other areas if noise effects occur. However, the construction of several offshore wind farms might produce population-level effects due to the cumulative impacts of different wind farms.
Wind farm development should follow precautionary principles
From a fisheries policy perspective, offshore wind development should follow a science-based precautionary approach and safeguard the viability of traditional fishing grounds. Therefore, historically and economically important fishing areas should remain unaffected by wind farms as far as possible or be protected through clear spatial restrictions and effective mitigation measures. Marine spatial planning decisions must be grounded in the best available scientific evidence (including studies on noise impacts) as well as in long-term fishing practices and local fishers’ knowledge, to avoid unjustified harm to fish stocks and coastal communities.
Mehis Rohtla
Estonian Marine Institute
University of Tartu
Joosep Pärn
Ministry of Regional Affairs and Agriculture
