Influence of Tugboats on the Underwater Soundscape Along the West Coast of Canada

Ambient underwater noise levels have been increasing, leading to concern about the impacts to marine species. Extensive research has been conducted on the changes to ambient noise levels of large commercial vessels and potential mitigation measures. However, little is known about smaller commercial vessels (e.g., tugboats) moving throughout coastal waters and what can be done to decrease their influence on marine species. To understand changes to the ambient noise levels (20–24,000 Hz) when tugboats are present, stationary hydrophones were deployed between August and October at two locations: Cowichan Bay, British Columbia (BC) (2019/2020) and Argonaut Wharf, Campbell River, BC (2021). Log transportation tugboats were assessed in Cowichan Bay and the results show significantly elevated median sound pressure levels (10 dB) when log transport tugs were detected near the estuary where log storage occurs. Even though Argonaut Wharf was used as a site without log transportation tugboats, tugboats were present throughout the study period. Median sound pressure levels were also significantly elevated (6 dB) when tugboats were present in Argonaut Wharf. The results demonstrate the impact that tugboat activities have on underwater soundscapes and are the first step in understanding the impact these activities have on marine organisms and important ecosystems.