Acoustic Monitoring and In-Situ Exposures of Juvenile Coho Salmon to Pile Driving Noise at the Port of Anchorage Marine Terminal Redevelopment Project, Knik Arm, Alaska

Though nearshore development and installation of overwater structures have been a constant fixture of shorelines in the Pacific Northwest for well over a century, few researchers have evaluated the construction impacts generated from such structures, namely the effects of pile driving noise on juvenile salmon. Recent experiences have documented severe effects to some fish species, but actual data on the short- and long-term effects of pile driving are quite limited.  Rather conservative noise criteria for in-water pile driving have recently been instituted, though criteria are considered interim and evolving as additional data and pertinent information come available. 

Effects to fish from the impact pile driving of large diameter, steel piles have been observed, but the potential effects caused by the driving of sheet piles is unknown.  We conducted acoustic monitoring and live cage exposures of juvenile coho salmon to pile driving noise at the Port of Anchorage. Fish were exposed to the impact and vibratory driving of 30-inch steel sheet piles. We conducted 16 separate test exposures (including far-field reference tests) of juvenile salmon to pile driving and held fish for 48 hours to document delayed mortality or behavioral abnormalities. Caged fish were held from about 1 to 50 meters from the driven pile in a variety of fixed position static tests and more natural exposures, drifting past the driven pile. Acoustic monitoring during tests measured peak sound pressures as high as 195 dB (re 1 µpascal), accumulated sound exposure levels (SEL) as high as 190.6 dB, and a maximum SEL per strike as high as 166 dB. Out of 133 fish exposed to pile driving noise, no immediate or delayed mortalities were observed. Post exposure observations, startle tests, and feeding responses showed no behavioral abnormalities over a 48-hour holding period. After post-exposure observations, 78 exposed fish and 19 reference fish were necropsied and examined for gross internal and external injuries. Three exposed fish and two reference fish showed slight body wall reddening, but all swim bladders were intact and no injuries to the kidney were apparent. Injuries did not correlate with increased noise levels, indicating they were likely caused by pre- or post-exposure handling. Our study indicates that juvenile coho salmon were not affected by peak or cumulative sound exposure to impact or vibratory driving of sheet piles during this investigation, despite inclusion of some unrealistically forced exposures.