If I were a pirate with great booty (not to be confused with the female anatomy) why in the hell would I bury it at great depth needing sophisticated engineering to recover. Why even bury it? Pirates lived in the moment and their stolen treasure was at their side on their ship.
The most successful pirates operated under the kings and one queen of Britain. They were given license to attack the Spanish and also had safe harbor in Britain and British territory. But, the crown must be given its share of the booty. It was a hell of a deal for the British Crown. The enemy was Spain. The pirates would finance the adventure against Spain at no cost to The Crown. The pirates kill the enemy and at times bring a warship back as additional booty and the pirates pay you for the privilege of safe harbor.
Free lance pirates spent it as soon as the got it. I doubt seriously they had any 401-Ks to worry about.
It occurred to me after reading this article that they wouldn’t have needed to excavate 130 feet down. They need only lower the treasure into an existing sinkhole and cover it up.
First, a common navigation tactic was sail up the coast of North America before heading towards England because of the currents and winds. Second, the theory is that it could have been from a Spanish fleet. Third and the most plausible theory is that the treasure buried was from a fort from the north and to keep it from the enemy took it to the island and buried it. The reason this theory holds is from the episode they ventured to the fort and found architecture used at the fort used on the island. The swamp is turning out to be man made after all and how the legends went. While it may be true that it was not Pirate booty, but the island was used as cover to hide somethign very valueable.