Not so long ago, Maryland had so many oyster shells that Eastern Shore residents used them to pave driveways.

But that began to change in the 1980s, when oyster harvests began their slide to today's historic lows. Instead of harvests in the millions, watermen are lucky to catch around 100,000 bushels a season.

Today, one of the biggest problems in reviving oyster populations is an acute lack of shells with which to build new habitat. But a new effort is recycling shells off dinner plates at restaurants or catered affairs.

Oyster restoration requires massive amounts of shell to create habitat, as well as a smaller amount of pristine shell on which to place the oyster spat so it will grow.

"The amount of work we can do is dependent upon how much shell we can get," said Mike Naylor, director of the Maryland Department of Natural Resource's shellfish program. "Planting an acre of bottom takes thousands of bushels of shells. How many thousands depend on how deep you want the shell to end up."

For decades, the DNR dredged for the less-pristine shells in an area off Poole's Island in the upper Chesapeake Bay. But two years ago, the Coastal Conservation Association, an organization that represents sport fishermen, challenged the state's dredging permit application to the Army Corps of Engineers, arguing that the dredging disrupted an important fishing area by stirring up too much mud and sediment.

As a result of the controversy, the DNR did not pursue the permit. The agency is now trying to get permission to dredge oyster shells from Man O'War Shoal in the Patapsco River, but a decision has not been made.

Until then, the DNR will continue to buy shell from the Bay's few remaining shucking houses. (Virginia used to be a source, but now the Old Dominion State is keeping its shell.) The Oyster Recovery Partnership, a nonprofit organization that promotes oyster restoration in the state, has been working with The University of Maryland Center for Environmental Sciences' Horn Point Hatchery to plant a billion oysters a year, and it's looking to more than double its capacity when Horn Point gets a new setting dock facility in the next couple of years.

While the DNR awaits word on its permit, the Oyster Recovery Partnership has found a source of the clean shells on which it sets the spat-area restaurants and caterers that previously had been throwing them away.

The partnership launched the shell recycling program in March, after an 18-month pilot program with a few participating restaurants. Now, it has more than two dozen restaurants in Baltimore; Washington, D.C.; and Annapolis participating.

The program started when oyster shuckers George Hastings, Vernon Johnson and Paul Bartlett decided they shouldn't simply throw away oyster shells after they were done shucking them at bull roasts and catering halls. They called Oyster Recovery Partnership Executive Director Stephan Abel, who loved the idea.

At first, the shuckers took the shell to Horn Point themselves. But that became untenable, as they had events every night. So, Abel arranged to have large containers in three locations in Baltimore that are near major catering facilities. Instead of a two-hour drive to Cambridge, the shuckers could just drive a few minutes to one of the bins, and Abel would send someone to pick them up when the bins were full.

The shuckers' idea got Abel thinking about restaurants. Last year, he went door-to-door, asking noted seafood restaurants for their shell.

"None of them turned me down," Abel said. "Within minutes, they were like, 'Yeah, we're on board. What do we need to do?'"

The participating restaurants range from sustainability advocates such as the "farm-to-table" Woodberry Kitchen to chains like the upscale Oceanaire Seafood Room near Baltimore's Inner Harbor, which has 11 locations nationwide.

Ben Erjavec, executive chef at Oceanaire, is now good for about eight buckets a week, each with a few hundred shells in it. Abel said Erjavec was skeptical in the beginning, but the chef is now a convert.

"Until it got brought to our attention, we were kind of oblivious to it. Then, we kind of jumped on it," Erjavec said. "We wanted to be able to give back to the Bay."

Erjavec lets the customers know about the recycling program and the importance of oysters with a note on the menu.

Abel said the program is netting 25,000 shells a week just from the participating restaurants, which will result in 250,000 planted oysters.

Hundreds of additional bushels are collected weekly when bull and oyster roasts are in season. When Horn Point ramps up to 2 billion oysters with its new setting pier, Abel said, he will need about 200,000 bushels of shell a year.

Two more major catering operations are coming on board, and he plans to expand into Ocean City and Kent Island. Right now, developer Doug Legum is financing the program; next year, Abel says, he hopes to attract corporate sponsors.

Almost as important as getting the shell, Abel said, is the ability to educate an audience that may not be aware of the state of the Bay and the importance of oysters in the water.

"You're reaching all these people that have no idea the value of what an oyster does," Abel said. "It's recycling. It's sustainable."