In the 6th century CE, a whale called Porphyrios terrorized and sank ships near Constantinople for nearly 50 years.

https://en.m.wikipedia.org/wiki/Porphyrios_(whale)

Porphyrios harassed ships in the waters of Constantinople for over fifty years,[7] though not continuously since it at times disappeared for lengthy periods of time.[4] It most frequently appeared in the Bosporus Strait.[1] Porphyrios made no distinctions in regard to which ships it attacked, recorded as having attacked fishing vessels, merchant ships and warships.[1] Many ships were sunk by Porphyrios, and its mere reputation terrified the crews of many more; ships often took detours to go around the waters where the whale most commonly swam.[4] Emperor Justinian I (r. 527–565), perplexed by the whale attacks and wishing to keep sea routes safe,[11] made it a matter of great concern to capture Porphyrios, though he was unable to devise a means through which to do this.[1][4][12]