- Data on the abundance of adult (rod catch) and juvenile (electrofishing surveys) Atlantic salmon were analysed to assess the potential impact of offshore wind farm construction and operation on local stocks.
- Given the available data and assumptions of the models (including choice of treatment and control rivers) no significant effect of wind farm construction was detected on the abundance of either adult or juvenile salmon.
- The findings of this analysis should be interpreted in the context of the limited power of both the rod catch (adult abundance) and electrofishing (juvenile abundance) data to detect change. Specifically, there is a 1 in 5 chance that the wind farm could be depressing Atlantic salmon abundance in potentially affected rivers by as much as 40% without being detected.
- In the current situation, where there is not an opportunity for obtaining greater predevelopment baseline information, the collection of additional electrofishing data does not improve the chances of detecting an effect of the wind farm beyond that already provided by the rod catch data (a freely available resource collated by Marine Scotland Science).
- Given the associated costs, it is suggested that the collection of additional electrofishing data is therefore unwarranted at the present time.
- Given the remaining uncertainty and the (small) improvements in statistical power provided by longer runs of data, it is suggested that the rod catch data should continue to be monitored and assessed.
- If, in the future, rod catch data suggest a substantial decline in adult numbers returning to the rivers to the north-east of the wind farm relative to those on the Irish Sea side, then collection of supplementary electrofishing data may be justified.
- It is recommended that prior to a future offshore development situational-specific power analyses should be performed and a decision made with regard to the amounts and types of data to be collected.