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

A review of the available literature relating to the impact of shadow flicker on freshwater fish, with a particular focus on Atlantic salmon in rivers. This may, depending on the evidence delivered, inform policy in relation to the placement of wind turbines in areas adjacent to rivers in the Scottish context.

Onshore windfarms have become a common sight within the Scottish countryside and may impact freshwater environments and the fish that they support in a number of ways. These include changes to water quality caused during construction and drainage, or damage to vulnerable freshwater habitats (such as gravels used by fish for spawning) during stream and river crossings. The issue of shadow flicker or pulsating shadow effects is a potential impact which has not been investigated with regard to the placement of onshore wind turbines but has been raised in respect to its potential impact in offshore installations. New turbines and the installation of larger turbines during the repowering of established sites, may have the potential to impact Atlantic salmon (Salmo salar). A species which is already undergoing significant declines throughout its natural range, and a feature within Special Areas of Conservation (SACs), may be adversely impacted by shadow flicker. This literature review will inform regulators and others as to whether this is an issue, whether it is not, or whether more targeted research is needed. It cuts across a range of policy areas, including renewable energy, climate change and conservation of features within designated sites and wider fisheries management.


Project Objectives

• Review the current literature on ‘shadow flicker’ on freshwater fish with a particular focus on Atlantic salmon; 

• Use examples from the literature to provide insights into the actual biological impact that these may have on Atlantic salmon in rivers; and 

• Suggest ways in which this issue, should it be shown to be significant, can be mitigated or used to inform wind turbine placement near rivers.


Research Questions to be answered through this project:

1.  What are the potential biological and ecological impacts/responses of shadow flicker on Atlantic salmon at an individual level at each life stage within a river system?

2.  Do Atlantic salmon habituate to repeated disturbance and may that increase susceptibility to other pressures, such as predation risk?

3. Can the impact of flicker be extrapolated to the whole Atlantic salmon population of an affected river?

4. Are there ways in which this issue can be successfully mitigated?





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