It takes the current oyster population one year to filter the bay water. Stimulated by increases in water temperature to 18-20 degrees C, oysters generally spawn from May through September in Chesapeake Bay. Eggs hatch into free-swimming larvae that settle to the bottom two to three weeks after hatching. Growth rates can be affected by temperature, food quantity, salinity, and parasitic infection. Shell growth usually occurs in the spring and soft body tissue growth occurs after spawning.
Oysters usually enter the market three to five year after spat settlement.
Landings have declined dramatically since that time and continue to show a downward trend. During the past 30 years, oyster harvest in Maryland ranged from 3.2 million bushes in 1973 to 124,000 bushes in 1993. In Virginia, the harvest of market oysters ranged from 1.9 million bushels in 1964 to 64,500 bushels in 1993. The baywide oyster stock can be characterized as severely depleted. Recent expansions of the range of oyster diseases, MSX and Dermo, past harvesting practices and low dissolved oxygen levels are primarily responsible for the population's current status.