I do have one question. You wrote: "We set our grown oysters around the marsh grass near our home on Manklin Creek."

I'm not sure exactly where you place them or if you have created a shell bottom someplace, but here is what Maryland says:

"Oysters prefer to set on the shells of other oysters but other hard, clean substrates are also used. They can't set in mud or sand bottom – they need a hard surface. Oysters will grow to about three inches in three years, unless the water is of low salinity."