Use methods to dampen underwater noise emissions (e.g. bubble curtains, screens)
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
Activities that produce large amounts of underwater noise, such as seismic airgun surveys, pile driving, dredging, explosives and sonar, may disturb or cause auditory injury to marine and freshwater mammals (Gordon et al. 2003, Bailey et al. 2010). Various methods may be used to dampen underwater noise emissions. This may involve surrounding the sound source with devices to absorb energy, such as screens or physical barriers, bubble curtains (a ‘curtain’ of air bubbles), hydro-sound dampeners (nets with gas-filled balloons and foam attached), cofferdams (insulated sleeves) or a combination of these measures (Verfuss 2014).
Bailey H., Senior B., Simmons D., Rusin J., Picken G. & Thompson P.M. (2010) Assessing underwater noise levels during pile-driving at an offshore windfarm and its potential effects on marine mammals. Marine Pollution Bulletin, 60, 888–897.
Gordon J., Gillespie D., Potter J., Frantzis A., Simmonds M.P., Swift R. & Thompson D. (2003) A review of the effects of seismic surveys on marine mammals. Marine Technology Society Journal, 37, 16–34.
Verfuss T. (2014) Noise mitigation systems and low-noise installation technologies. Pages 181–191 in: Federal Maritime and Hydrographic Agency, Federal Ministry for the Environment, Nature Conservation & Nuclear Safety (eds.) Ecological Research at the Offshore Windfarm alpha ventus: Challenges, Results and Perspectives. Springer, Wiesbaden.
Supporting evidence from individual studies
A before-and-after, site comparison study in 2010–2013 at seven wind farm construction sites in the North Sea, Germany (Brandt et al. 2018) found that using bubble curtains or screens resulted in harbour porpoise Phocoena phocoena detections within 15 km decreasing less compared to before pile driving than at sites without bubble curtains or screens. Compared to 24–48 h before pile driving, porpoise detections at distances of 0–15 km from piling sites decreased less during pile driving with bubble curtains and screens (0–5 km: 63%; 5–10 km: 23%; 10–15 km: 17%) than during pile driving without curtains or screens (0–5 km: 80%; 5–10 km: 55%; 10–15 km: 50%). In 2010–2013, pile driving was carried out at seven wind farm sites with or without bubble curtains (air bubbles released from a hose on the sea floor) or screens (double-wall screen filled with air). One site constructed all of 30 foundations with screens. Five sites constructed most foundations with bubble curtains (30–79 with; 1–11 without), and one site constructed most without (1 with; 80 without). All seven sites also used acoustic deterrents (pingers and seal scarers) prior to pile driving and ‘soft-start’ procedures. Acoustic data loggers attached to moorings recorded porpoise echolocation clicks at multiple locations at all seven sites 24–48 h before and during each of 581 pile driving events.Study and other actions tested