He said the allure of treasure hidden under the sea seemed to blind the public to the ethical implications. “If these guys went and planted a bunch of dynamite around the Sphinx, or tore up the floor of the Acropolis, they’d be in jail in a minute,” Mr. Crisman said.

Anticipating such comments, John Morris, the chief executive of Odyssey, said in a statement: “We have treated this site with kid gloves, and the archaeological work done by our team out there is unsurpassed. We are thoroughly documenting and recording the site, which we believe will have immense historical significance.”

Robert W. Hoge, a curator at the American Numismatic Society in New York, questioned the secrecy surrounding the discovery and said that while it might be perfectly legitimate, the findings would have been better preserved in the hands of archaeologists.

“Whenever these finds are made by treasure hunters, their first thought is to sell instead of preserving,” Mr. Hoge said. “They need to make money because they’re a corporation with enormous expenses. They’re not there to preserve history.”

The find, which was announced on the same day that the publicly traded Odyssey held its annual stockholder meeting, came four years after the company found thousands of coins worth $75 million after excavating the Republic, a steamship lost in 1865 off Savannah, Ga. The company, which had reported losses for 2005 and 2006, saw its stock rise almost 81 percent to $8.32 by the time the market closed on Friday.

This year, Odyssey received permission from the Spanish government to resume a search that had been suspended on the wreck of the Sussex, a British warship that sank in the Mediterranean in 1694 with a cargo of coins that may be worth billions of dollars.

The company has not disclosed the methods or equipment it used in the Black Swan find.

The largest documented previous find occurred in 1985, when the treasure hunter Mel Fisher found the Nuestra Señora de Atocha, a Spanish galleon that sank off the Florida Keys in 1622. The treasure included thousands of silver coins worth more than $400 million.