Harbour porpoise responses to pile-driving diminish over time.

Isla M Graham,Tim R Barton,Barbara Cheney,Nathan D Merchant,Paul M Thompson,Saliza Bono,Adrian Farcas

doi:10.1098/rsos.190335

Abstract

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.

Highlights

Recognition of the potential impact of underwater noise disturbance on marine wildlife has resulted in major policy developments affecting the management of offshore activities such as oil and gas exploration and marine renewable developments [1,2,3]
The same covariates with very similar parameter estimates were retained in a model of 24-h response with distance using a subset of piling events (n 1⁄4 9) preceded by a longer 192-h break in piling
Based on the relationship with distance from piling, at the start of the construction period in April there was greater than or equal to 50% chance of harbour porpoises responding to piling in the 24-h period after piling at distances up to 7.4 km from piling

Summary

Introduction

Recognition of the potential impact of underwater noise disturbance on marine wildlife has resulted in major policy developments affecting the management of offshore activities such as oil and gas exploration and marine renewable developments [1,2,3]. This has been driven by concerns for cetaceans, because their behavioural repertoires involve extensive vocalizations and responses to. Data to parametrize important inputs or components of these models, notably dose–response relationships describing behavioural responses to noise exposure [8], are often sparse or absent

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