Study finds wind turbine noise thins herring schools

A study has found that offshore wind farm noise makes herring schools considerably less dense near the sound source, although the fish can move away from the noise zone and spring spawning was not affected, ERR reported.

Kirke Paris examined in a master’s thesis defended at the University of Tartu how the low-frequency noise associated with offshore wind farms affects herring behaviour. A field experiment found that herring schools were less dense near the noise source, but the initial findings do not show that wind farms would immediately cause major harm to fish.

The research was driven by plans to build large offshore wind farms in Estonia’s coastal waters. Human-made noise in the sea is also increasing because of denser shipping and other marine infrastructure. Paris said it is important to understand how animals perceive their surroundings in order to assess how fish use habitats and move.

The researchers observed the fish in the wild because sound waves may not travel in laboratory conditions in the same way as they do in the sea. An artificial environment can also affect animal behaviour.

“A fish in captivity certainly does not respond to some stressor in the same way as it would in the wild,” Paris said on Vikerraadio’s Ökoskoop programme, explaining the choice of method.

The experiment took place in the Gulf of Riga, in the sea south of Kihnu. Researchers installed a special speaker in the centre of an approximately 16-square-kilometre study area to imitate the operating noise of an offshore wind turbine. They travelled along fixed routes on a research vessel and monitored how densely the fish formed schools in the water column.

The sound played underwater had a frequency of 100 hertz, which is typical of offshore wind turbines. The source level reached 170 decibels during the experiment. Paris said that while this could be a very loud sound for a person in the air, underwater it was more like a low and continuous hum.

When the researchers compared conditions with and without noise, the data showed a clear pattern: herring schools became less dense near the sound source when the noise was present. Not all the fish left the area affected by noise, but the schools were considerably more dispersed.

The experiments showed that the statistically significant effect of the noise extended approximately 350 metres. Paris said that, in the context of a single wind farm, a radius of roughly half a kilometre might not pose a major obstacle to the fish.

“The fish can swim away if it finds the noise unpleasant,” she said.

The situation could change significantly if a wind farm consists of dozens or even hundreds of turbines. In that case, the affected area would expand and the combined effect of numerous generators would become decisive.

The location could be especially critical if large development areas blocked fish access to spawning grounds. Paris stressed, however, that the current study cannot establish that such a disabling effect will definitely occur in the Baltic Sea.