The 52-hertz whale

In the late 1980s, marine biologists started picking up a strange 52 Hz pitch. It was identified to be the call of a whale, but the frequency is very unusual – blue whales call at 10–38 Hz, and fin whales call at 20 Hz.

It seems to be the call of an individual whale, and the sound has been detected every year since, but its species couldn't be determined so far. Researchers think it could be a blue whale/fin whale hybrid, or that the animal could be malformed. Because there is only a single whale emitting this call, it has been called the "world's loneliest whale".