A Compendium of the Effects of Marine Pile Driving on Salmonids and Forage Fish, and Advances in Sound Attenuation Technologies

Impact pile driving has been associated with extremely high sound pressure levels, with potential effects to fauna protected under Endangered Species Act and Marine Mammal Protection Act. Regulatory agencies in the United States; the National Oceanic and Atmospheric Administration and the United States Fish and Wildlife Service, have established regulations to ensure these species are protected, including requiring measures to attenuate noise produced during in-water impact pile driving (e.g. bubble curtains). Vibratory pile driving is often considered the key mitigation measure to prevent injury to fish (e.g. barotrauma), and sound-attenuating devices are currently not required by agencies during vibratory pile driving. However, recently published data details observed adverse effects to Pacific herring (Clupea pallasii) during vibratory pile driving, including mortality. Mitigating for noise produced during in-water pile driving comes at a high cost, including implementation of sound attenuating devices, and acoustic and biological monitoring. Currently, the most common method of sound attenuation employed is the bubble curtain. However, bubble curtain noise reduction is minimal, and effectiveness is reduced by factors such as improper deployment and bubble drift in current. Recent advances in sound attenuation technologies show promise in increasing noise reduction levels and in simplifying effective deployment. These developments include double-walled piles and encapsulated bubble systems, with documented noise reduction of up to 50 decibels. These new technologies could play a key role in streamlining monitoring requirements while protecting endangered juvenile salmon and key prey species during both impact and vibratory pile driving