Responses of bottlenose dolphins and harbor porpoises to impact and vibration piling noise during harbor construction

Abstract

Abstract. The development of risk assessments for the exposure of protected populations to noise from coastal construction is constrained by uncertainty over the nature and extent of marine mammal responses to man-made noise. Stakeholder concern often focuses on the potential for local displacement caused by impact piling, where piles are hammered into the seabed. To mitigate this threat, use of vibration piling, where piles are shaken into place with a vibratory hammer, is often encouraged due to presumed impact reduction. However, data on comparative responses of cetaceans to these different noise sources are lacking. We studied the responses of bottlenose dolphins and harbor porpoises to both impact and vibration pile driving noise during harbor construction works in northeast Scotland, using passive acoustic monitoring devices to record cetacean activity and noise recorders to measure and predict received noise levels. Local abundance and patterns of occurrence of bottlenose dolphins were also compared with a five-year baseline. The median peak-to-peak source level estimated for impact piling was 240 dB re 1 lPa (single-pulse sound exposure level [SEL] 198 dB re 1 lPa 2 s), and the r.m.s. source level for vibration piling was 192 dB re 1 lPa. Predicted received broadband SEL values 812 m from the piling site were markedly lower due to high propagation loss: 133.4 dB re 1 lPa 2 s (impact) and 128.9 dB re 1 lPa 2 s (vibration). Bottlenose dolphins and harbor porpoises were not excluded from sites in the vicinity of impact piling or vibration piling; nevertheless, some small effects were detected. Bottlenose dolphins spent a reduced period of time in the vicinity of construction works during both impact and vibration piling. The probability of occurrence of both cetacean species was also slightly less during periods of vibration piling. This work provides developers and managers with the first evidence of the comparative effects of vibration and impact piling on small cetaceans, enabling more informed risk assessments, policy frameworks, and mitigation plans. In particular, our results emphasize the need for better understanding of noise levels and behavioral responses to vibration piling before recommending its use to mitigate impact piling.

Underwater Noise Emission Due to Offshore Pile Installation: A Review

“…The reasons for this are, most likely, attributed to the fact that noise is less severe when compared to impact piling and vibratory methods of installation are less frequently applied offshore. However, a few studies do exist which try to quantify the noise levels [45,46] and assess the environmental impact [47,48]. Even scarcer are studies which investigate systematically the behavioural response of marine mammals when noise mitigation systems are employed [49,50].…”

Combining ecosystem modeling with serious gaming in support of transboundary maritime spatial planning

“…Little information was available for species-specific functional responses to changing intensities of anthropogenic pressures; however, there is abundant literature to support that these pressures can detrimentally affect marine communities. Anthropogenic noise has been found to affect the foraging and resting behaviours of seals (Mikkelsen et al 2019) and seabirds (Buxton et al 2017) and has been linked to fatal stranding (Forney et al 2017), hearing damage (Ketten 2012), disrupted foraging and reproductive behavior (Gomez et al 2016), and changes to the distributions (Graham et al 2017) of cetaceans. The presence and physical disturbance caused by boats and recreational activities on the water's surface can have short-term effects on marine mammal behavior (Lusseau 2003), lead to displacement (Machernis et al 2018), and increase the risk of physical harm via ship strikes (Redfern et al 2013).…”

Guiding principles for assessing the impact of underwater noise

“…The most direct and comprehensive way to mitigate the risk of acoustic impact on marine species is to reduce the amount of noise pollution emitted at source (noise abatement). For pile driving, alternative piling technologies such as vibratory piling and continuous flight auger (CFA) piling may reduce noise levels emitted (though see Graham et al, ). There are also several noise reduction technologies available, such as big bubble curtains and acoustic barriers that are integrated into the piling rig (e.g.…”