What is Skullduggery Island about?

The theme of Poptropica's 13th island, Skullduggery Island, is to help the port of Fort Ridley stave off the looting attacks by the dreaded Captain Crawfish.

You obtain a ship and then trade among the islands to build your wealth, buying ever-larger ships and crews. Finally you can battle and defeat Captain Crawfish, and return the Buried Treasure to Fort Ridley.