Shellfisheries
Crab Studies:
In the late 1960s, when many of Maryland's fisheries were more productive than now, there was concern about possible effects of the thermal discharge from the Calvert Cliffs Nuclear Power Plant (then under construction) on the blue crab (Callinectes sapidus) population in Chesapeake Bay waters adjacent to the plant. This led to a series of studies of blue crab population size and structure from 1968 to 1983, and was the only one of the four major fishery- independent surveys to sample the population with crab pots. Although these studies detected no adverse effect of the power plant on numerous parameters of the local crab populations during those 16 years, they have been conducted for an additional 22 years (38 years total), knowing that these data would provide valuable information for both crab scientists and fishery managers. Long-term fishery-independent data sets of at least 10-15 years are important in understanding the dynamics of commercially valuable populations, but such data sets are uncommon. Changes in a population over 3-5 years may be meaningful, but because of relatively short duration, it is often difficult to show statistical significance unless these changes are large. Long-term data sets, however, may enable an investigator to attach significance to more subtle changes. This data set indicated changes that appeared to be undesirable for the crab fishery and possibly for the population itself, long before it reached its present length. Data from the Calvert Cliffs pot survey along with data from three other fishery-independent surveys have been critical to conducting accurate assessments of blue crab stocks in Chesapeake Bay.
Oysters:
Maryland oyster (Crassostrea virginica) landings have declined dramatically during the last 20 years due to harvesting and disease. To manage around the diseases caused by Perkinsus marinus (dermo) and Haplosporidium nelsoni (MSX) and to restore and enhance affected Chesapeake Bay oyster populations, the Maryland Oyster Roundtable Oyster Recovery Action Plan (1993) established Oyster Recovery Areas (ORAs) in several Chesapeake Bay tributaries. The Patuxent River is one of these; in 1986 oyster landings exceeded 96,000 bushels, but by 1993 none was harvested. During the 1998-99 oyster season, limited commercial harvesting resulted in landings of 5600 bushels (MDDNR 2001). Presently, however, harvests are small throughout the state, and a sudden large increase is unlikely. In an effort to better understand this resource, a number of studies are ongoing. Experimental oyster studies conducted during recent drought conditions resulted in extremely high mortalities of a standard strain of native oyster. To determine if survivorship can be improved, we are presently evaluating the performance of two disease-tolerant varieties of native oyster against a standard strain in field experiments in the Patuxent River by examining growth, mortality and dermo disease acquisition rates and status. Additional oyster work involves surveying sanctuaries and managed reserves using both scuba divers and patent tongs to determine oyster density, size and dermo disease status. Another study, now in its 28th year, involves work with MD Department of Natural Resources scientists to determine the accumulation of certain radionuclides by oysters near the Calvert Cliffs Nuclear Power Plant. We are hopeful that some of the information generated by these efforts will aid in restoring the oyster population to an increased fraction of its former size, to improve both the fishery and its ecological function.
