by Alicia Pimental
February 08, 2011
The number of baby oysters in the Maryland portion of the Chesapeake Bay is at its highest level since 1997, and more young oysters appears to be surviving the effects of diseases, according to a recently completed survey by the Department of Natural Resources (DNR).
Since 1939, Maryland has monitored the status of the oyster population through annual field surveys. The surveys track three critical components of the oyster population: reproduction levels, disease infection levels and annual mortality rates.
The two-month 2010 fall population assessment covered 260 oyster bars and 399 samples throughout the Bay and its rivers. Scientists found 80 baby oysters (called spat) per bushel; about five times the 25-year average of 16.
The increased spat set is an immediate asset to Maryland’s expanded sanctuary program,” said DNR Fisheries Director Tom O.Connell. These protected oysters will grow and reproduce, contributing more oysters to the Bay's sanctuary and surrounding aquaculture and public fishery areas, and providing important ecological benefits such as water filtration and reef habitat.
Oyster spat were also widely distributed throughout the Bay and its rivers. While the largest amounts were in the lower Bay’s saltier waters, where reproduction is typically more successful, a moderate spatfall also occurred in fresher waters that generally have little to no spat sets. Some of these areas included the upper Bay as far north as Pooles Island and the upper reaches of the Chester, Choptank and Patuxent rivers.
Additionally, the frequency and intensity of the oyster diseases MSX and Dermo remains low. Dermo remains below the long-term average for the eighth consecutive year, and MSX has fallen after a spike in 2009. Oyster survivorship, measured by the percentage of living oysters per sample, was 88 percent, the highest level since 1985 and more than double the 2002 level.
"These moderate levels of natural oyster mortalities during recent years may reflect increases in disease resistances among oysters and their progeny that survived the severe disease pressures of the 1999-2002 drought,"said Chris Dungan, manager of oyster disease research at the NOAA Oxford Lab.
Since 2000, DNR, the NOAA Chesapeake Bay Office and the University of Maryland have produced more than 2.5 billion oyster spat in hatcheries and planted then in Maryland waters. The partnership has also reclaimed thousands of acres of buried shells from derelict oyster reefs.
Visit Maryland DNR's website to view the full results of the oyster survey.