Dogged for decades by overfishing and parasites, the oyster population in Maryland’s portion of the Chesapeake Bay has fallen so low that there’s only one way to save it, a new study says: Halt fishing entirely.

The study by the University of Maryland Center for Environmental Science recommended that drastic step, its author said, because nearly 100 percent of the oyster population has been lost since its peak in the early 1800s and more than 90 percent has been lost since 1980. The declines were based on the oyster population in 2009.

Despite a major effort by the Maryland Department of Natural Resources to increase the population by supersizing oyster sanctuaries and protecting them with tough anti-poaching laws, the study released Wednesday and published in the journal Marine Ecology Progress Series called on the state to ban all harvests by watermen. Maryland’s new effort will add to the $50 million it has already spent in an unsuccessful attempt to restore its bay oyster population.

“The magnitude of the decline raises concerns about potential for continued loss of natural oyster beds throughout much of Maryland waters,” Michael J. Wilberg, the study’s chief researcher, said in a statement. “Therefore, we recommend a moratorium on fishing until reefs and self-sustaining populations are restored.”

Wilberg said the bay oyster has declined so much that even a moratorium might not stop it from disappearing in much of the bay.

Maryland DNR said the state has warded off nearly a quarter of its oyster reefs from fishermen. Watermen have complained that the finest oysters are off-limits. Virginia, which wasn’t the focus of the study, has taken similar steps to protect its oysters.

Nonprofit groups such as the Oyster Recovery Partnership are also working to increase the number of oysters. Last month the group chartered a fishing boat so that corporate investors such as Booz Allen Hamilton and partners such as the Nature Conservancy could watch a boat place nearly 7 million baby oysters into a shallow water sanctuary in Harris Creek off the Choptank River.

As the tour watched, a tugboat used a high-pressure hose to blast mountains of shells into the shallows and onto an oyster reef. Each shell was populated with tiny baby oysters, known as spat, that were bred at the University of Maryland Center for Environmental Science laboratory at Horns Point.

At the lab, adult oysters are coaxed into mating with warm water temperatures. The eggs they fertilize are collected and fed in large tanks. When they develop, the spat look for hard surfaces such as shells to attach.

The partnership collects spent oyster shells from as far away as Louisiana and as near as restaurants in Georgetown as part of the recovery. Waiters bus shells from tables after diners eat the bivalves and place them in barrels.

Oysters aren’t just essential to Maryland’s watermen and the economy. They play a crucial role in filtering pollution that’s fouling the bay. Their shells are a natural habitat for other marine life such as sponges and mussels that also filter pollution.

“We all know we need to increase the oyster population,” said Stephan Abel, the partnership’s executive director. “The Harris Creek planting is the beginning of restoring the river to its historic levels.”

Wilberg said that while efforts by the state and the nonprofit groups are “a big step” forward from previous restoration attempts, “I don’t think that’s enough to restore the population” as fishing and death from parasitic organisms continue to reduce it.

In 1701, European explorers were forced to artfully navigate their ships to avoid grounding them on enormous oyster reefs, the study said. In the late 1800s, 15 million bushels of oysters were harvested. In 1994, the total dropped below 79,000.

Under the stresses of continued fishing, disease and habitat loss, harvests declined 95 percent between 1980 and 2008. At their current level, the study concluded, restoration efforts cannot keep pace.

“There’s a good chance it will continue to decline,” Wilberg said. Extinction of the bay oyster isn’t likely because the species lives along the Atlantic coast, he said. “The question is whether large portions of the bay will not have oysters in the future.”