A treasure hunter was ready to retire. Then he found hundreds of coins.

Mike Penninger, left, Corinne Lea, Nick Amelio and Grant Gitschlag show their finds on a boat near Sebastian. Photo / JP Prouty

Mike Penninger thought his treasure-hunting days might be over. After 30 years of exploring wrecks off the Atlantic coast, surfacing with coins, rings and other artefacts, the 71-year-old Florida diver and boat captain was about ready to hang up the scuba suit.

Then, he and his crew came upon something extraordinary off the coast of Sebastian, Florida: scores of Spanish coins from an infamous 18th-century shipwreck.

“It’s a lot of work,” Penninger said of searching for treasure. “I’m too old. I’m almost 72 and so I’m thinking, ‘I’m done with this.’ The very next day, bam, we get the first 100 coins.”

The crew would ultimately find more than 200 coins during dives between May 30 and June 16. Their discovery dates back more than 300 years to what’s known as the Spanish Treasure Fleet of 1715, the divers said.

Although the silver coins were crusted over and rusty, with faded engravings and tapered edges, Penninger and co-captain Grant Gitschlag were quick to recognise the unusually shaped lumps as treasures.

“We’ve all been doing this long enough that you can tell,” said Gitschlag, 32, of Clinton, Mississippi. “Spanish coins of that era were very distinctive, all irregular shapes. People don’t even think they’re coins because they don’t look like a coin.”

He and Penninger led the expedition on the Lilly May along with divers Nick Amelio and Corinne Lea as subcontracted divers for 1715 Fleet - Queen’s Jewels LLC. The Sebastian-based company was named the custodian and exclusive salvaging company for the shipwreck by the US District Courts, which are responsible for overseeing the distribution of artefacts found on US territory.

The total findings will be distributed between the company and the state by the US District Courts in May.

How much the coins are worth is so far unclear, in part because they haven’t yet been restored from their centuries-long stay at the bottom of the ocean.

“It’s more about the historical value than the cash value,” said 1715 Fleet director Sal Guttuso. “Valuation can be tricky. Usually money values on these items only can be established once the items have been sold, and many of these will not be sold but go into Florida museums and private collections of the finders or owners of our company.”

For treasure divers who scour Florida’s ocean floor during a season that runs from May to September, part of the thrill is the lore behind their finds. Penninger and Gitschlag have uncovered rare pieces together, including a gold ring studded with a large Colombian emerald and large pieces of worked silver in the couple of years that they’ve been diving partners.

On any given day during the season, they might come across broken pottery, iron and bronze fasteners and ship parts. But it’s rare for them to find so many silver coins in one place. Gitschlag described their crew as history lovers and “big nerds”.

“It’s so fun to be the first one to hold [the artefacts] in such a long time, and tied to such an incredible event,” he said.

The 1715 Fleet - Queen’s Jewels found hundreds of coins near Sebastian, Florida, this month. Photo / Grant Gitschlag

The coins were initially loaded on to a pair of Spanish treasure ships that were sailing off the coasts of Florida and Cuba in July 1715 before a hurricane struck, according to the 1715 Fleet Society. The storm destroyed the ships, scattering the gold and silver they carried and killing about 1500 people. The shipwrecks along what is now called the Treasure Coast of Florida occurred during the Golden Age of Piracy – 1690 to 1730 – when hundreds of pirates, including the renowned Blackbeard and Henry Jennings, went to the shores of what would become the Sunshine State.

Some of the first to find evidence of the 1715 shipwrecks were beachgoers walking along Florida’s coast in the early 1900s, from Sebastian down to Fort Pierce, said Ben Costello, president of the 1715 Fleet Society. They found mostly Spanish coins, deducing that the wrecked ships must have come from Spain. Floridians found washed-up treasure over the decades, but it wasn’t until the 1950s when divers joined the effort to find out what was out there.

Divers have made the most progress contributing to the historical record of the wrecks, often by writing up details of what they’ve found. Yet many mysteries remain.

“There’s a lot written about the treasure and what was being transported,” Costello said. “There’s not a lot written about who the people were. Who are some of these people that either died or survived? And what happened to them?”

He added, “We keep pushing for more knowledge and information. I guess our biggest goal here is to not let the story die.”

The company’s latest discovery may contribute to that knowledge. Already, it has expanded the map of how far historians and archaeologists believed the shipwreck’s debris was spread.

“These wrecks have been salvaged for many years, and it gets harder to go out there and find stuff,” Gitschlag said. “When we find stuff that tells you that a big piece of that wreckage came through there, and nobody’s ever been there before, it helps add to that story of how these ships broke apart in that hurricane. It’s just helping us and all the other people out here that do the same thing as us, to know where to look next time.”

Penninger will be among those continuing the hunt. His thoughts of retirement have now faded away.

“It’s harder to go and do this every day,” he said. “But when you find a couple hundred coins, it changes your mindset. So I definitely know we’ll be doing this again next year.”