Maryland sees long-term increase in oyster abundance

Annapolis, Md. — The population of Maryland’s oysters has grown significantly in the past 20 years, according to the results of the latest benchmark stock assessment for the species.

The Maryland Department of Natural Resources and the University of Maryland Center for Environmental Science recently released the summary results of the stock assessment.

“Good news for oysters is good news for the Chesapeake Bay,” DNR Secretary Josh Kurtz said.

“This stock assessment shows that oysters have made important progress during the past two decades. That’s a testament both to our continued investment in oyster restoration and our careful management of the oyster fishery. These findings will help guide management decisions during the next several years.”

MORE COVERAGE FROM PENNSYLVANIA OUTDOOR NEWS:

Shapiro signs bill lifting Pennsylvania’s Sunday hunting ban

Steve Piatt: Sometimes, it’s best to turn the attention from turkeys to trout

Turns out Pennsylvania’s Presque Isle bass are color-sensitive

The stock assessment analyzed the status of the population of eastern oysters, the keystone species that also holds important economic and cultural value for the Chesapeake Bay region, from 2005 to 2024.

After a low point in 2005, shortly after oysters had been decimated by disease, the mollusks have increased in the following two decades.

The stock assessment’s summary results give insight into multiple aspects of the oyster population and oyster fishery.

As overall oyster abundance increased in Maryland’s portion of the Chesapeake Bay, researchers found positive population growth at many oyster restoration sanctuaries as well as decreased fishing pressure in harvest areas compared to the previous stock assessment completed in 2018.

Overall oyster abundance has increased

The stock assessment estimated that more than 12 billion oysters live in Maryland’s waters of the Chesapeake Bay in 2024, including about 7.6 billion adult oysters and over 5 billion spat, or juvenile oysters. The assessment estimates there were only 2.4 billion adult oysters in 2005.

Mike Wilberg, a professor at the University of Maryland Center for Environmental Science who led the assessment, said the increase is likely driven by three main factors.

“The first one is that we have had some good spatsets,” he said. “The second one is that natural mortality rates, or particularly disease, hasn’t been as bad as it was in the 1980s and 1990s. And then the last one is that the department has maintained restrictions on harvesting that have allowed the oysters that are in some of these areas to continue to survive and reproduce.”

The 2025 stock assessment is the second major stock assessment conducted on the eastern oyster in Maryland.

The state’s Sustainable Oyster Population and Fishery Act of 2016 requires DNR and University of Maryland to conduct a benchmark stock assessment every six years, as well as update assessments in intervening years.

Benchmark stock assessments take account of available data from multiple sources to arrive at mathematical models for the status of fishery.     

A major source of data is DNR’s fall oyster survey, which monitors the oyster population at sites across Maryland’s waters of the Chesapeake Bay every year. In 2005, the survey began collecting additional data to acquire a measure of oyster density that can be expanded  to estimate the number of oysters in larger areas of known oyster habitat throughout Maryland’s portion of the Bay.

That change in methodology is why the 2025 stock assessment focused on the years after 2005, Wilberg said.

The 2025 stock assessment also considered data from Maryland’s Bay bottom survey, sonar surveys, plantings, patent tong surveys, harvest reports, peer-reviewed studies, and even the state’s “Yates survey” that mapped oyster bars starting in 1906.

The latest stock assessment found a considerable increase in oyster abundance from the 2018 stock assessment, because of both continued growth of the population and improved methods to analyze the population, such as the additional dredge data, Wilberg said.