In a move aimed at restoring the Chesapeake Bay's depleted oyster population, Gov. Martin O'Malley will announce this morning a major expansion of the state's existing patchwork of oyster sanctuaries, according to sources, setting aside large stretches of rivers to protect the water-filtering shellfish from commercial harvest. 

The governor also is expected to spell out moves intended to boost the state's fledgling oyster aquaculture industry, the source say, identifying new areas around the bay open for leasing by those who want to try growing their own bivalves in floats, as pictured above, or on the bottom.

O'Malley's press office has put out an advisory that he is scheduled to "make an important announcement regarding the health and future of the Chesapeake Bay" this morning at the Annapolis Maritime Museum, on a tributary of the Severn River. Officials declined to provide details, but individuals briefed on the plan said the focus of the announcement is on overhauling the state's historic approach to managing oysters, shifting away from subsidizing the traditional wild fishery in favor of promoting private aquaculture.

A legislative advisory commission recommended those moves last year as the best bet for replenishing the bay's oysters, decimated to just 1 or 2 percent of their historic levels by decades of overfishing, habitat loss and disease.  The panel called for "targeted eoclogical restoration," closing entire rivers or major portions to wild harvest while working to rebuild silted-over oyster reefs and populate them with new bivalves reared in state-run hatcheries.

Earlier this year, Department of Natural Resources officials reported to the advisory commission that they were planning to set aside the entire Severn River as a sanctuary, as well as a large oyster bar in the lower Choptank River and Hoopers Strait in Dorchester County.  A source briefed on the latest plans said the number of sanctuaries to be announced has grown beyond those three, including another in St. Mary's County.

The sanctuaries would significantly reduce the areas open to commercial oyster harvest. State officials have been working to encourage Maryland's watermen to try their hand at growing oysters on leased plots rather than roaming the bay to catch whatever they can find.  Toward that end, the legislature this year approved an overhaul of the state's laws on private leasing of the bay to encourage more aquaculture, and the governor is expected to announce that new areas are open for private growers.

The bay's native oysters have been badly depleted by a pair of parasitic diseases, plus silting over of most of the reefs which they once populated.  Efforts to restore them to date have proven fruitless, and officials studied introducing a disease-resistant Asian oyster before deciding earlier this year that the ecological risks of such a move outweighed the potential benefits.  Scientists have said a revived oyster population could play a major role in restoring the bay, as the bivalves filter sediment and other pollutants from the water and provide habitat for fish and other aquatic creatures.  Experts estimate that the bay's oysters were once so abundant they could filter the bay's water in a few days - while the current number would take a year or more.

Baltimore Sun photos: oyster floats by Glenn Fawcett 2008; watermen by Doug Kapustin 2006