The Chesapeake Bay is the largest estuary in America - the third largest in the world. A century ago it boasted an oyster fishery second to none. Ships reportedly would run aground on its mountainous oyster reefs. No more. The shellfish population has been devastated by overfishing, pollution and development. But, efforts are underway to rebuild the Bay's oyster reefs.
There were once so many oysters in the 300 kilometer-long Chesapeake Bay, Native Americans named the inlet "Tschiswapeki" meaning "Great Shellfish Bay."
"The Bay had been marked by huge underwater reefs built by oysters over thousands of years," says Bill Goldsborough, a scientist with the Chesapeake Bay Foundation - an organization dedicated to restoring the Bay. He says oyster beds began disappearing in the late 1800s as thousands of fishermen dragged their equipment across the reefs.
"Those reefs had been discovered after the Civil War, and they were starting to dredge them ferociously and knock them down all in the name of commerce, harvesting and selling the oysters," he said.
Oyster reefs harbor huge amounts of life. Scores of plants and animals find food and shelter in their nooks and crannies. As the Bay's reefs wore down, that habitat was lost. Further damage came from increasing runoff from coastal farmland, deforestation and development, which silted over the flatter oyster bars, cutting off the creatures' food and dissolved oxygen. Then, in the mid-1900s came the final assault - a pair of parasites.
"Dermo is thought to be a native parasite and MSX is thought to be introduced by a foreign oyster probably around 50 years ago," Mr. Goldsborough says. "Those two parasites and the diseases they cause are sort of like the last few nails in the coffin really. The oyster was suffering from degraded habitat already when the parasites came in."
According to Bill Goldsborough, the deadly parasites along with over-fishing and pollution left the Chesapeake oyster population at one percent of its historical population.
But, rather than give up on the shellfish, environmentalists began a program to restore oysters to the Bay by building new oyster reefs.
To create living reefs, the state of Maryland hired the only shell dredging operation left in the country to dig up old oyster shells mired meters deep under Bay mud and silt.
"The shell deposits we dig are 40, maximum of 50 feet (12-15 meters) thick of just oyster shells with mud in 'em," says Bill Moore who manages the C.J. Langenfelder Dredging Company on Kent Island in the Chesapeake. "The reef itself we take the shells out of are thousands of feet across and 40 feet high."
Mr. Moore says recovering the oyster shells is complicated, requiring huge, heavy equipment.
"This is a hydraulic cutter head dredge," he said. "The cutter head loosens the bottom up. The shells are sucked up through a pump. They go to the top of the dredge where they're washed off and sized. The larger shells we use for oyster propagation."
The clean, large shells are loaded on to a barge and hauled to another area of the Bay - an oyster sanctuary. Then, over the future oyster bar, they're pushed into the water and sink to the bottom. The shells form a hard surface or substrate that scientist Bill Goldsborough says is vital for a baby oyster's survival.
"With our native oysters the sperm and eggs are ejected into the water column and that's where fertilization takes place," he says. "The larvae that are produced are planktonic. That means they drift around in the water for about 2 weeks or so. When they're ready, when they've developed to the point where they're ready to settle onto the bottom, they drop down in the water column and they sort of feel around and try to find a hard substrate and that's key. If they're not able to find that and if they settle on mud and can't find something hard to attach to, then they'll die."
Even oysters not spawned in the Bay need something to grow on before they can be moved to the open water.
"The same thing essentially happens in the hatchery when you're trying to produce oysters to plant out in the Bay," he says. "You can spawn the oysters to produce the larvae, but then you also need to introduce those larvae into a tank with substrate that they will then attach to, and then the substrate is what you move around and that typically is shell."
About 50 million young hatchery oysters are now being laid on Bay reefs each year, and soon that number will double. The ultimate goal is to increase the number of oysters in the Bay tenfold by 2012 - not only bringing back the fishery, but re-creating a healthy estuary.