From Wikipedia

The 52-hertz whale is an individual of unidentified whale species, which has been regularly detected in many locations since the 1980s, calling at the very unusual frequency of 52 Hz. This pitch is much higher frequency than that of the Blue Whale (15-20Hz) or Fin Whale (20Hz), whose migration patterns it is most similar to.[1] It appears to be the only individual with this call, and has hence been described as the world's loneliest whale.