Marine mammals rely heavily on sound for foraging, communicating, and navigating. As noise in the ocean increases, their ability to perform these important life functions can be affected. In the past decade, numerous studies have expanded our awareness of the effects of anthropogenic noise on marine life. Improving our knowledge of how sound impacts marine mammals is particularly important in coastal waters where the spatial distributions of vessels and marine mammals overlap, as exemplified by the critical habitat for the endangered Southern Resident killer whale (Orcinus orca). The impacts of small vessel traffic (including the commercial and recreational whale watching that is directed on this population) has been difficult to assess as there is a data gap for small vessel noise emissions. In this study, two autonomous marine acoustic recorders were deployed in transboundary Haro Strait (British Columbia, Canada, and Washington State, USA) from July to October 2017 to measure sound levels produced by whale watching vessels and other small boats. The vessels were categorized into six types: rigid-hulled inflatable boats (RHIBs), monohulls, catamarans, sailboats, landing crafts, and a small boat with a 9.9 horsepower outboard engine. Acoustic data were analyzed according to the ANSI S12.64 (2009) standard for measuring ship noise using JASCO Applied Sciences’ PortListen® software system, which automatically calculates source levels from calibrated hydrophone data and vessel position logs. It is recommended that sounders are turned off when not needed in proximity to killer whales and other cetaceans that use high-frequency sound (e.g., harbour porpoises, Phocoena phocoena, Dall’s porpoises, Phocoenoides dalli, Pacific white-sided dolphins, Lagenorhynchus obliquidens)

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