Annual Oyster Survey Shows Decreases in Mortality, Reproduction

Oyster mortality fell for the fifth straight year in 2007, but oyster reproduction was poor throughout most of Maryland’s portion of the Bay, according to a recently released survey by the Maryland Department of Natural Resources (DNR).

The annual oyster survey evaluates the health and population of oyster bars in Maryland. For the 2008 survey, DNR biologists used a dredge to assess more than 1,800 oysters from 282 oyster bars.

“Preliminary results from 2008 indicate that reproduction was poor throughout most of the bay, with the exception of the lower eastern shore areas of Tangier Sound, Honga River and the Little Choptank River,” said Mitch Tarnowski, DNR fisheries biologist.

Despite low reproduction, oyster mortality from the diseases MSX and Dermo appeared to be relatively low for the fifth year in a row. While not harmful to humans, MSX and Dermo have lead to the death of up to 90 percent of oysters in some areas.

Both diseases thrive in higher salinities. As a result, disease affects oysters the most during dry years, when lower than normal river flows cause higher than average salinity in the Bay. Though summer 2007 was dry, oyster disease levels were not as high as in previous dry years.

“Oyster mortality in 2006 and 2007 were the two lowest years since the 1980s,” said Mike Naylor, Director of DNR’s Shellfish Program. “It’s too early to know if this is a trend, but this is a very positive development that we will be monitoring carefully.”

DNR has conducted the annual oyster survey each fall since 1939. Biologists use a dredge to monitor natural oyster bars, oyster sanctuaries, seed production and planting areas, and dredged and fresh shell plantings.

For more information about the 2008 oyster survey, including historical mortality graphs, visit DNR’s website.