Exploring how vessel activity influences the soundscape at a navigation lock on the Mississippi River.

Vessel sound is now globally recognized as a significant and pervasive pollutant to aquatic life. However, compared to marine environments, there is a paucity of data on sound emitted by vessel activity in freshwater habitats. The Upper Mississippi River (UMR) is home to a diverse array of aquatic life as well as being a key route for barge transportation with 29 locks and dams. In this study, passive acoustic monitoring was conducted at Lock and Dam 19 near Keokuk, Iowa, on the UMR between 20 June - August 28, 2019 to coincide with peak navigation use. There was a significant increase in median sound pressure level (SPL; 50-12,000 Hz) recorded during vessel passages (123 dB re. 1µPa for recreational vessels and 137 dB re. 1µPa for commercial vessels) compared to median background levels (111 dB re. 1µPa). Results provide information on the ambient soundscape at a navigation lock, providing a baseline essential for future studies gauging the effect of anthropogenic sound on aquatic life. Lock 19 has also been identified as a potential site for acoustic deterrent deployment to prevent invasive fish movements. The results of this study can help determine the sound level or frequency deterrents would need to emit, to avoid those currently produced during vessel passage.