when you have all the pieces of the map put them together and it will show you the hidden island then you have to go get a shovel to dig up the treasure with i haven't found yet
Skullduggery Island.
there is actually pieces of the map that you get on the ports but there is a puzzle you have to do to get them
The bank on Skullduggery Island is the Golden Harbor Bank, located in the Arabic-themed port at the lower right on the island map.
There is a dock at the bottom side of the small island, Skullduggery. The island appears when you have collected all 5 of the pieces of the Treasure Map.
Nothing. Captain Crawfish was there. But you don't exactly do anything on Skullduggery island. You defeat Crawfih on sea.
anywhere on the map
If you ment counterfeit when you said confederate, there IS NO treasure map there. There IS one on SKULLDUGGERY island
Once you have all five pieces of the Treasure Map, the 6th island, Skullduggery, appears on the map. When you acquire a powerful ship, and scare off Captain Crawfish, the Governor will give you the Treasure location and a bone shovel to dig it up. (see related question)
Collect the five map pieces (one on each of the trading islands) and join them to see the sixth island, Skullduggery. Once it appears on the map, you can actually go there, but nothing happens there until the end of the game. (see the related question)
It is the sixth, small island that is foggy. It is the real "Skullduggery island". It is just southeast (down and right) from the Pirate Outpost, and directly west (left) of Golden Harbor. It will appear on the map formed when you collect all five map pieces. (see related question)
Once you have all 5 map pieces, the new island (Skullduggery) appears near the Pirate Outpost. But there is nothing you can do there until you acquire a Phoenix Warbird and defeat Captain Crawfish in battle. Once that is done, return to the governor in Fort Ridley and he will give you the map to the treasure on Skullduggery, and a shovel to dig it up.
it is the island in the middle of the map on the top right corner