Increased biomass yield from Delaware Bay oysters (Crassostrea virginica) by alternation of planting season

The practice of moving oysters from low-salinity to high-salinity areas for improving growth and meat quality has been practiced for well over a century. In the Delaware Bay, the practice was abruptly changed when MSX (Haplosporidium nelsoni) caused large-scale oyster mortality in the higher salinity portions of the bay. Similar disruptions occurred in Chesapeake Bay and other areas. In time the Delaware Bay, the oyster industry learned how to operate around the disease, but in early 1990s, Dermo (Perkinsus marinus) began to cause serious mortality on transplanted oysters. Despite the historic and continuing movement of oysters within and between estuaries, there is little published scientific literature indicating optimum conditions for transplantation. We investigated the effects of transplantation from a low-salinity seed bed to a typical higher salinity leased ground. The transplants were designed to evaluate an early, the traditional spring, and two fall transplant dates on the subsequent disease levels, growth, and survival of the oysters in three size classes: market, submarket, and small. Environmental and oyster disease data suggest we conducted the experiment under nearly worse-case conditions, high Dermo, and low food (chlorophyll). There were no significant differences associated with the timing of transplant. We did not record significant growth on any size oyster and disease caused mortality exceeded 50% for early transplants. Smaller oysters experienced greater mortality than market size individuals. Despite these conditions, meat dry weight nearly doubled within 1 to 2 mo after transplant in all but the March transplant. Under these disease and environmental conditions the only economic gain would be from the doubling of the meat weight and associated better meat quality. No gain can be expected from submarket oysters growing into the market size classes.