The map is in the Eastern part of the restricted area, in the hollowing. To reach it, you need to dive and swim along the underwater tunnels.
The treasure can be found in the fort on Principe. On the North side of this location, you will find two gun batteries and the square towards past them. The treasure is past the second tower, on the cliff's edge, next to the rocks.
Treasure's Coordinates: 992, 422
The treasure: 4000 regals