A recent Maryland Department of Natural Resources (DNR) report details the significant growth of the oyster population and substantial progress toward the state’s oyster management goals for the past five years.
The report is part of the department’s commitment to assess the three areas of oyster management—sanctuaries, public fishery areas, and aquaculture—every five years.
In October 2025, DNR released the 2021-2025 Oyster Management Review, which found that the state has met or made positive progress toward its objectives in all three areas.
The review looks back on a highly productive five-year period, which saw the highest averages for Maryland oyster reproduction, habitat availability, and overall biomass in decades, as well as low levels of disease and observed mortality.
Aside from describing positive outcomes for areas of public fishery and aquaculture, the review analyzes the considerable success seen in the state’s oyster sanctuaries, including 33 sanctuaries that are either restored, trending positively, or undergoing restoration, compared to only four areas that are not performing better since being designated as a sanctuary.
Oyster Sanctuaries
DNR set five objectives for sanctuary areas in 2019; the review found that the state has met two objectives and the other three are in progress.
One met objective was the department’s 2025 completion of initial restoration of five large-scale tributary sanctuaries, aligning with the state’s 2014 Chesapeake Bay Watershed Agreement commitment. The other met objective is conserving and protecting oyster habitat and biomass through continued maintenance.
The state is also seeing progress on increasing oyster populations, broodstock (mature oysters that can produce future generations), and oyster biomass (the total weight of oysters in the ecosystem).
Most sanctuary areas showed positive trends in increasing oyster density, and effective restoration techniques have allowed for steady increases in biomass. DNR is continuing to support small-scale and community-based restoration in tributaries throughout the Chesapeake Bay.
The review also describes the state’s 51 oyster sanctuaries based on their performance and restoration status as of 2025. Aside from the five restored sanctuaries, 12 sanctuaries have positive population growth or average densities exceeding 94.2 oysters per square meter on fall survey sampled sites, and another 16 sanctuaries have received or have plans for restoration or plantings.
Four sanctuaries are underperforming and under evaluation for corrective action. The remaining sanctuaries are either set for educational, nonprofit, or laboratory research (five sanctuaries) or lack data because of an inability to sample or have minimal historical habitat (nine sanctuaries).
Oysters are a keystone species in the Chesapeake Bay because they form reefs, creating habitat that fosters an ecosystem, and because they are important for filtering water. Many of the ecological benefits of oysters are most prominent when the shellfish are able to form dense, three-dimensional reefs, which provide habitat for fish and other aquatic life.
Because sanctuaries are permanently closed to harvest, except on aquaculture lease sites, these areas are intended as places where oysters can grow undisturbed. Scientists also hope these sanctuaries will increase the Bay’s overall spawning stock of oysters and facilitate natural disease resistance.
The report reviewed different sanctuary areas based on a number of metrics, including the number of adult oysters (small and market size), the amount of spat (or juvenile oysters), the available habitat, and the observed level of mortality. This data was used to determine a ranking score that compared how sanctuaries were doing relative to other sanctuaries.
The top performing sanctuaries included the St. Marys River, Little Choptank River, Nanticoke River, Harris Creek, Upper Choptank River, Hoopers Strait, and Tred Avon River.
Data used to determine the characteristics and long-term trends in the sanctuaries comes from DNR’s annual Fall Oyster Survey. The results of the 2025 fall survey are published on DNR’s website.
The 2021-2025 Review’s Appendix A includes detailed information about each of the state’s 51 sanctuaries, including tables of sampling data and graphs of trends over time. The full report and appendices are published on DNR’s website.
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