At 04:23 UTC on April 1, 2014, a hydrophone attached to the Ocean Networks Canada cabled observatory recorded very unusual sounds from the Eastern Strait of Georgia (depth: 170 m). Click the following audiogram to listen to this recording:

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Audiogram of the unusual recording. Click to listen to this recording on Soundcloud.

Spectrographic analysis confirms that these sounds were not emitted by whale or a ship. The closest sound profiles we have to this unusual recording are those of sonar pings, but they are confirmed not...