The endangered species called the right whale was spotted by fisherman Bob Heil, 77, in the early morning off Juno Beach in Palm Beach County, The Palm Beach (Fla.) Post reported Saturday.
Wildlife officials said a barge crewman at sea took a photo of the whale, allowing experts to confirm it was a right whale.
The North Atlantic Right Whale Consortium says there are just 350 right whales left in the North Atlantic, the Post said.
Right whales can be identified from their distinctive features, said Julie Albert of Marine Resources Council, a non-profit environmental group that tracks right whales. They have no dorsal fin and have short, stubby black flippers, with a tail that is black on both sides.
Internationally protected since 1935, right whales usually give birth during winter months off the coast of central and north Florida and southern Georgia, the consortium said.