Passive Acoustic Monitoring (PAM) technologies are commonly used to monitor echolocating marine mammals around tidal energy devices. However, the detection efficiency of PAM instruments can be hindered by a variety of factors (e.g., signal attenuation, flow noise, ambient noise) inherent to high flow environments that can vary with deployment depth, and can impede monitoring efforts. While previous work indicated that conventional hydrophones that record raw pressure time series data may be preferrable for monitoring harbour porpoise in tidal channels, where these technologies should be deployed for effective monitoring (i.e., at the sea surface or on the sea floor) remains an unresolved issue.