Assessing sonar sound levels from commercial ships : final report / by S. Bruce Martin, Craig Evans, Colleen C. Wilson, David E. Hannay.: T42-27/2021E-PDF

"Transport Canada tasked JASCO Applied Sciences to study the occurrence of sonar sounds in the acoustic data recorded at sample rates of 128 kHz (usable data up to 60 kHz) on the Georgia Strait underwater listening station (ULS) and on the autonomous recorders deployed at Boundary Pass up to October 2019. Sonars were detected in 1.3% of the vessel passages. Three types of sonars were identified: single frequency echosounders, multi-frequency echosounders, and a continuous ultrasonic source. Both types of echosounders had highly directional beampatterns, which means the sounds were directed down towards the seabed and were generally only audible for 2-5 minutes during a vessel passage. High-frequency cetaceans (porpoise) that are directly underneath these sonars are expected to experience a temporary change in their hearing thresholds (TTS). The continuous ultrasonic source occupied the frequency band of 18-26 kHz. It was not directional and was audible 4-6 km from the vessel. High-frequency cetaceans within 1 km of a vessel track are likely to experience TTS, and southern resident killer whales have greatly reduced echolocation ranges for periods of 15-20 minutes during the vessel passage. A key recommendation from this study is to identify this continuous ultrasonic source and prohibit its use in Canadian waters. This analysis should be revisited with the Boundary Pass ULS data, which has usable acoustic data up to 250 kHz"--Abstract, page iii.

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