Virginia Spat-on-shell Experiments Hold Promise for Bay's Oyster Population

It is no secret that Chesapeake Bay oysters are in trouble. Years of over-harvesting, disease and poor water quality have decimated populations to the point where their numbers are just one percent of historic levels.

Over the years several different methods have been developed to assist in the rehabilitation of the oyster population. While many of these methods have been successful, recent experiments performed by the Virginia Institute of Marine Sciences (VIMS), Virginia Marine Resources Commission (VMRC) and Virginia's oyster industry demonstrate that “spat-on-shell” oyster production may become a viable and effective process for growing healthy and harvestable oysters in Virginia waters.

The University of Maryland Center for Environmental Science (UMCES) has been utilizing spat-on-shell oyster restoration techniques in the Bay since the mid-1960s. Last year, the UMCES facility produced more than 350 million spat-on-shell, of which 325 million were used in Bay restoration. In 2006, the second year of spat-on-shell programs in Virginia, 25 million spat were produced.

In order to reach maturity, spat need to attach to a solid surface. While rocks and other underwater debris are suitable for oyster growth, spat have higher success rates growing upon other oyster shells.

Using carefully engineered aquaculture procedures, spat are cultured in specialized tanks and allowed to “set” onto oyster shells, or cultch. In a few months the spat, numbering about a dozen per shell, will have grown into tiny oysters no larger than a fingernail. The advantages of growing clusters of oysters together rather than raising and planting single cultures are threefold:

• predation from cownose rays is diminished
• the oysters are able to be planted at a younger stage of their development
• and spat-on-shell colonies provide better reef building characteristics.

VIMS, VMRC and volunteers from Virginia's oyster industry placed 18 sets of spat-on-shell oysters in Virginia waters between July and October of 2006. Locations for the sets varied widely, with sites in Pungoteague Creek and the Coan, Piankatank, Rappahannock and Ware rivers. Set sizes also varied from as little as 127,000 to as many as 3.6 million.

Results so far have been promising with survival rates ranging from 17 to 98 percent. While these numbers are heartening, spat-on-shell production projects should not be viewed as the silver bullet that will solve all of the oyster's woes, but they may be able to help the Virginia oyster populations rebound to higher levels. To find out more about oyster restoration in Virginia, please visit: http://www.vims.edu/.