Sound propagation in the experimental canal.

<p>We measured mean spectrums of each boat recording (A – Lowe Boat, B – Polar Kraft, C – Action Craft, D – Parker Boat) at various distances (1 m, 5 m, and 10 m) from the underwater speaker. At 1 m from the speaker, the playback boat sound was a mean SPL of 15 to 28 dB re 1 µPa less than original recording depending on which boat sound was playing. At 5 m from speaker, the playback boat sound was not detectable from ambient sound in the canal probably because the sound attenuated rapidly due to the shallow water and soft mud substrate on the sides and bottom of the mosquito ditch.