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The original was posted on /r/todayilearned by /u/Content-Proposal9630 on 2024-10-29 22:18:44+00:00.

Original Title: TIL there is a whale known as the 52-hertz whale (also known as 52 Blue) of an unidentified species that has never been sighted, but has been heard and known to exist since the late 1980s. There was also a feature length documentary about it that Leonardo DiCaprio was an executive producer for.