Harbour porpoise responses to pile-driving diminish over time

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.

Underwater Noise Emission Due to Offshore Pile Installation: A Review

“…The extent of auditory damage depends upon several parameters, i.e., the principal frequency content of the radiated sound, the duration of exposure to high noise levels and the auditory characteristics of the species [36][37][38][39]. Moreover, due to the fact that pile driving activities extend for periods of months, the level of response may also change over time as a result of habituation [40][41][42][43][44].…”

The diel pattern in harbour porpoise clicking behaviour is not a response to prey activity

“…However, the fact that clicks are produced almost continuously and that animals are constantly moving around has made PAM a very important tool for studying this species in the field. It is also widely used to successfully assess the impact on porpoises from many man-made activities, such as noise from coastal wind farms 1 , 16 – 19 and deterrent signals intended to keep them away from gill nets 20 – 24 .…”

Seal Bomb Noise as a Potential Threat to Monterey Bay Harbor Porpoise

“…To date there have been no investigations into the response of harbor porpoises to seal bomb noise, however behavioral response studies on impulsive, low-frequency noise during pile driving associated with windfarm construction (Tougaard et al, 2009Dähne et al, 2013;Graham et al, 2019), seismic airguns (Bain and Williams, 2006;Thompson et al, 2013), and other explosions (Von Benda-Beckmann et al, 2015) may provide valuable insight into response levels. A variety of sound level metrics and behavioral response thresholds have been reported from studies of harbor porpoises exposed to low-frequency, impulsive stimuli ( Table 1).…”