The marine mammal, which is distinguished from other types of whale by its enormous head, was found dead a few days later on a beach north of Miami. Authorities are investigating the causes of its death.
The sperm whale, 9m long and weighing 30 tonnes, was still alive when the as-yet-unidentified man was photographed sitting on its back. The pictures also show another swimmer trying to climb up on it.
US federal law bans tormenting marine mammals, as well as interfering with any animal in danger of extinction, alive or dead.