Harbour porpoise responses to pile-driving diminish over time.

Estimating impacts of offshore windfarm construction on marine mammals requires data on displacement in relation to different noise levels and sources. Using echolocation detectors and noise recorders, we investigated harbour porpoise behavioural responses to piling noise during the 10-month foundation installation of a North Sea windfarm. Current UK guidance assumes total displacement within 26 km of pile driving. By contrast, we recorded a 50% probability of response within 7.4 km (95% CI = 5.7-9.4) at the first location piled, decreasing to 1.3 km (95% CI = 0.2-2.8) by the final location; representing 28% (95% CI = 21-35) and 18% (95% CI = 13-23) displacement of individuals within 26 km. Distance proved as good a predictor of responses as audiogram-weighted received levels, presenting a more practicable variable for environmental assessments. Critically, acoustic deterrent device (ADD) use and vessel activity increased response levels. Policy and management to minimize impacts of renewables on cetaceans have concentrated on pile-driving noise. Our results highlight the need to consider trade-offs between efforts to reduce far-field behavioural disturbance and near-field injury through ADD use.

Déclaration de conflit d'intérêts

The authors have no known competing interests. This study was funded by a commercial developer, Beatrice Offshore Wind Ltd. (BOWL). However, the funding body had no input into data collection, data analysis or interpretation, or the writing of the paper. The aims, scope and experimental design of the study were developed by the authors to meet BOWL planning consent conditions. These were agreed by the regulator Marine Scotland Licensing and Operations Team following consultation with statutory advisors represented on the Moray Firth Regional Advisory Group (MFRAG); a stakeholder group that was established by the Scottish Government to oversee the monitoring programme.