When it comes to the law of the sea, it's not quite as clear cut as "finders keepers."
Whether the treasure is gold coins found in a sunken ship or a crate of goods washed ashore, what's up for grabs depends on where it's found and to whom it belongs.
The process is more Law and Order than Pirates of the Caribbean.
A key question is whether the discovery of goods is deemed salvage or treasure-hunting.
Salvage refers to when someone saves property drifting, lost or abandoned at sea. Under international conventions, the "salvor" is required to return the found goods to the original owner in return for a reward.
Treasure hunting typically means exploration aimed at unearthing antiquities and other valuables from shipwrecks for financial gain.
"Treasure hunting is not necessarily salvage, because salvage is the right to be compensated by the owner where the owner is known and you're in a position to return the property to him," said William Moreira, a Halifax lawyer and former president of the Canadian Maritime Law Association.
"Typically in treasure-hunting cases, that's not so, just because the stuff's been lost for so long that no owner could come forward."
Cases of sunken treasure
Often such deep-sea finds come from companies in the business of trolling the seas for sunken treasures.
U.S. salvage company Odyssey Marine Exploration has discovered several notable shipwrecks.
In February 2009, they revealed that they'd found a prized shipwreck: a British warship that sank 264 years earlier during a storm. The company believes the 175-foot HMS Victory may have four tons of gold aboard.
Two years earlier, the Tampa-based company uncovered a shipwreck in the Atlantic laden with 17 tonnes of gold and silver coins worth an estimated $500 million. The mystery ship, code-named "Black Swan," is believed to be the Spanish galleon Nuestra Senora de las Mercedes y las Animas, which sank off Portugal.
The Spanish government is suing Odyssey in federal court in Tampa to claim the treasure, arguing it never abandoned the shipwreck. The case is pending.
The British government has yet to indicate what action it might take on HMS Victory, but Odyssey says it's negotiating with the government about collaborating on the project.
Location, location, location
Important to both of Odyssey's claims will be where the shipwreck was found. With the 2009 discovery, Odyssey claims it was between 40 and 64 kilometres from England's coast, putting it outside territorial waters. Odyssey still hasn't revealed where it found "Black Swan."
Whether the find lies within a country's territorial waters is a vital consideration in any treasure-hunting case.
The concept of territorial waters is set out in the United Nations Convention on the Law of the Sea. Most countries have a limit of 12 nautical miles (approximately 22 kilometres) from their coastlines, and if Odyssey's treasure ships ventured inside that limit, the company could forfeit its claim to the booty.
Moreira says that's a standard rule.
"Usually, for this kind of case, there's a law saying that [the find] is owned by the government, so if it's in territorial waters, the law of the sea convention comes in and … the state would decide who owns and what compensation [the finder] is entitled to.
Dishonest conduct forfeits all
A common misconception is that finders can keep their discoveries at sea. But under international law, anyone who finds a wreck must report it. Hiding a shipwreck or its cargo is an offence.
The 1989 International Convention on Salvage says the salvor, or finder, "may be deprived of the whole or part of the payment due … if the salvor has been guilty of fraud or other dishonest conduct."
"Dishonest conduct" isn't clearly defined, but if Odyssey unilaterally salvaged treasure from a ship in Spanish waters without consulting Madrid, that definitely counts as fraud, and Odyssey would lose its big payday.
"If one commits fraud, that is dishonesty with intention to deceive, then you become disentitled to whatever you'd otherwise be able to get," Moreira says.
If the find lies in international waters, however, and there's no one to claim ownership, the finder is probably in the clear.