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30th November 2021

The impact of shadow flicker or pulsating shadow effect, caused by wind turbine blades, on Atlantic salmon (Salmo salar)

As the need for onshore wind energy expands, such climate adaptation measures may have unintended and potentially significant influences on how fish respond when situated next to rivers or streams. The aim of this project was to examine evidence of potential impacts of shadow flicker, from wind turbine blades, on Atlantic salmon in the context of species conservation management and climate mitigation strategy in Scotland. Our current understanding of the possible effects of shadow flicker on Atlantic salmon was investigated by reviewing the available literature (peer-reviewed and grey from national and international sources) for existing studies of a similar or relevant nature. Various databases and web-based search engines were used to identify these studies, relevant information was extracted and summarised, and potential impacts across the salmon’s lifecycle identified. There was no direct evidence available, either from laboratory experiments or studies of wild fish, that describe the effects of shadow flicker on Atlantic salmon or any other fish species. Based on the available literature, and our expert opinion, there is currently insufficient evidence to support or refute any biological or ecological impact of shadow flicker on Atlantic salmon. The review has highlighted a lack of basic understanding of the role light patterns may play for Atlantic salmon in rivers and further research is recommended. At present there is no evidence to support any change to related policy guidance. However, under the precautionary principle, some advice for best practice might be advised to prevent shadow flicker being cast on river surfaces. Where appropriate, potential mitigation methods were identified that could reduce any impacts on Atlantic salmon should impacts of shadow flicker on fish be demonstrated in the future.