Oyster Reproduction Low; Long-Term Detrimental Effects Predicted on Populations, Harvest Levels

ANNAPOLIS — Oyster reproduction remains at record lows for the second straight year, according to new findings of an annual survey conducted by the Maryland Department of Natural Resources (DNR).

The annual Fall Oyster Survey collects data that is used to determine the Oyster Spat Index. Spat are newly attached oysters that are less than a year old; spat set is a measure of oyster reproductive success and occurs in the summer when oysters reproduce.

While the 2004 index of 6.5 spat per bushel is an increase over last year’s index of 4 spat per bushel, it is among the lowest of the last 10 years. Biologically, an index result below 10 spat per bushel is poor.

A low spat set means that oysters cannot sufficiently build their numbers and overcome the suppressive effects of diseases, which have decimated the state’s native oyster population to a fraction of historic levels. Even in years with high levels of spat set, disease has managed to undermine the population.

The Chesapeake Bay’s native oyster, Crassostrea virginica, was once considered a keystone species of the Bay, serving as a primary contributor to the Bay’s filtration system. They also serve as vital hard bottom habitat for many other Bay organisms, another reason why oyster restoration is a major element of Maryland’s multifaceted and comprehensive approach to improving the water quality of Chesapeake Bay. Over 100 years ago, the oyster population filtered the Bay’s volume in about three days; now it takes approximately 700 to do the same.

“The news of this year’s oyster spat set is discouraging as we move forward in Chesapeake Bay restoration,” said DNR Secretary C. Ronald Franks. “As we look to manage the native oyster populations, we are impeded by the fact that the only areas where oysters reproduce are continually plagued by MSX and Dermo, of which there is no cure. However, we plan to maintain our long-standing comprehensive program to employ various restoration strategies for the native oysters, as well as research other possibilities for restoring oysters to their historic levels.”

The 2003 and 2004 spat sets also demonstrate unique characteristics, aside from being historically low. In 2003 there was a large expanse of the Bay with zero spat set. Since spat are the future of the population, it impaired and will continue to severely impair the ability of these regions to produce abundant oysters.

The 2004 set had a smaller zero spat set zone, but it suffered very low spat sets in the State Seed Areas that are used by DNR to produce abundant young seed oysters for the industry. In 2003 while the index average was lower, higher numbers of spat were seen in select State Seed Areas, thus enabling bar replenishment in Spring 2004. Since before 1960, DNR has planted seed to boost populations on harvest bars, but the virtual set failure in 2004 on the Seed Areas means there will be no seed to plant in April 2005. Not having a Seed Program in 2005 will also impact harvesters, as the harvest bars normally planted with seed will not be replenished this April. The last time this occurred was in 1984.

See the graphics at: Maryland Oyster Spat Summary, 2004

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