Chesapeake Oyster Population Less Than One Percent of Historic Levels

September 6, 2011

Solomons, Md. (August 31, 2011) – According to recent research, published in the journal Marine Ecology Progress Series (Vol. 436), the oyster population in the upper Chesapeake Bay has been estimated to be 0.3% of population levels of early 1800s due to overfishing, disease, and habitat loss.

The population of oysters in Maryland’s portion of Chesapeake Bay is approximately 0.3% of pre-harvest levels.  Even with these low population levels mortality due to fishing continues to be substantial at approximately 25% of the population per year since 1980. Harvesting oysters not only reduces the population but also degrades the habitat since oyster shells provide the primary habitat for future generations.  Suitable oyster habitat in Maryland’s portion of the Bay has declined by about 70% since 1980.  In addition, two oyster diseases, Demo and MSX, thrive during drought periods when salinities in the Bay increase causing natural mortality to increase.

The University of Maryland Center for Environmental Science (UMCES) research team, led by Dr. Michael Wilberg developed population models based on data from a long-term scientific survey of oysters conducted by Maryland Department of Natural Resources and harvest from reefs in Maryland waters.  Their approach provides estimates of abundance, fishing mortality, and mortality from other sources, such as disease.

“The collapse of eastern oysters in Maryland waters of Chesapeake Bay is among the largest documented declines of a marine species,” said Michael Wilberg.  “The magnitude of the decline raises concerns about potential for continued loss of natural oyster beds throughout much of Maryland waters.  Therefore, we recommend a moratorium on fishing until reefs and self-sustaining populations are restored.”

“While our study highlights the dire situation of oysters in the upper portion of Chesapeake Bay, there is still cause for optimism for some level of rehabilitation,” adds Wilberg. " In the absence of a moratorium, reductions in fishing should improve the prospects of population recovery.  Maryland has made positive steps toward conserving oysters by increasing the area that is off limits to fishing and increasing support for aquaculture."

Conservation measures have recently been enacted by the state of Maryland to protect more oyster reefs. Maryland has one of last oyster fisheries that relies upon wild populations and not aquaculture.  However, Maryland has enacted new regulations making it easier for oyster aquaculture to be established.  Additionally, the UMCES Oyster Culture Facility produces hundreds of millions of spat annually with the vast majority placed on sanctuary reefs that serve as nursery grounds for the entire population.

The University of Maryland Center for Environmental Science is the University System of Maryland’s environmental research institution. UMCES researchers are helping improve our scientific understanding of Maryland, the region and the world through five research centers – Chesapeake Biological Laboratory in Solomons, Appalachian Laboratory in Frostburg, Horn Point Laboratory in Cambridge, Institute of Marine and Environmental Technology in Baltimore, and the Maryland Sea Grant College in College Park.


Media Contact: David Nemazie, 443-496-0187