ANNAPOLIS, Md.,— Maryland’s oyster population has grown significantly over the past two decades, reaching an estimated 12 billion oysters in the Chesapeake Bay in 2024, according to a benchmark stock assessment released by the Maryland Department of Natural Resources (DNR) and the University of Maryland Center for Environmental Science (UMCES). The assessment, covering 2005 to 2024, shows a fivefold increase in adult oysters since 2005, driven by strong reproduction, reduced disease mortality, and effective management.
The stock assessment, released on Monday, estimates 7.6 billion adult oysters and over 5 billion juvenile oysters, or spat, in Maryland’s portion of the Bay, compared to just 2.4 billion adult oysters in 2005, a low point after disease decimated the population. “Good news for oysters is good news for the Chesapeake Bay,” said DNR Secretary Josh Kurtz. “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.”
Led by UMCES professor Mike Wilberg, the assessment attributes the population surge to three factors. “The first one is that we have had some good spatsets,” Wilberg 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.” These restrictions have allowed oysters to survive, reproduce, and provide habitat. Wilberg noted that improved data collection, including dredge data from DNR’s fall oyster survey, also enhanced the 2024 estimates compared to the 2018 assessment.
The assessment analyzed oyster abundance and fishing pressure across 35 harvest reporting regions. One region exceeded the long-term abundance target, 24 were between the target and cautionary levels, three were between cautionary and the lower limit, and seven were below the lower limit. “The oyster population has been increasing across most of the Bay,” Wilberg said. “There are only a few areas where we have had decreases over the last five years.” He cautioned that reaching long-term targets could take decades.
Fishing pressure has also decreased since 2018, with 29 regions below the target fishing mortality rate in 2023-2024, indicating sustainable harvesting. Four regions, however, exceeded the limit, risking population declines. “This indicates that the fishery is in a better condition than it was when we did our last benchmark in 2018,” Wilberg said. DNR’s adjustments to harvest rules, guided by the 2018 assessment, have contributed to these improvements, according to Chris Judy, director of DNR’s Shellfish Division.
Oyster restoration sanctuaries have seen significant growth. In the Little Choptank sanctuary, the adult oyster population grew from 100 million pre-restoration to 500 million, while Harris Creek increased from 40 million in 2010 to 200 million. The Tred Avon River sanctuary saw a fourfold rise, from 40 million to 175 million. “The three major restoration sanctuaries that are pretty much finished have all been really strong successes,” Wilberg said. These gains, driven by intensive spat plantings, contribute to overall population growth, though the exact impact of restoration versus environmental factors remains unclear.
The assessment, mandated every six years by Maryland’s 2016 Sustainable Oyster Population and Fishery Act, draws on DNR’s fall oyster survey, Bay bottom and sonar surveys, harvest reports, and historical data like the 1906 Yates survey. An independent peer review panel validated the methodology and findings. The full report, due in June, will provide further details to guide DNR’s harvest rule proposals, to be discussed at the Oyster Advisory Commission meeting on June 9.
Oysters, a keystone species with economic and cultural significance, faced near-collapse in the late 1990s and early 2000s, with 75% dying from disease between 1999 and 2002. “From such low points as this, oysters have made significant progress,” Judy said. Ongoing restoration projects, like the Eastern Bay initiative, aim to further bolster populations across sanctuaries, fisheries, and aquaculture.
