This page will have a guide to the treasure map you find in Anotto Bay in Assassin's Creed IV Black Flag
Treasure Map Location
The treasure map itself can be found in Anotto Bay, at coordinates (622,270), on a wooden platform:
Note: You need the Diving Bell to get to the cadaver location
Treasure Map Tool
This is the treasure map you find:
Coordinates indicate (992,422).
Note that the treasure chest itself is NOT located in Anotto Bay (where you got the treasure map from), but rather in Principe:
Dig Site Location
Note: Principe does not unlock until after the sequence 9 memory, Trust is Earned
Set a custom marker around this location at the NW side of the area:
Face these four cannons:
Turn right, and go straight along the wall until you reach a wooden face. Then turn left, and go to the edge, near the corner of a stone tower, dig location is there. See screenshots below to help you find the buried chest:
Reward is 4,000 Reales