Ecological Restoration

Oysters are currently at historic low abundance due to disease-related mortality, habitat degradation, reduced water quality and harvest pressure. Based on recent scientific review of restoration alternatives for the native oyster in Chesapeake Bay, the ecological restoration team works with our many partners to optimize ecological benefits and enhance population recovery while minimizing costs. We work closely with our partners to rehabilitate degraded habitat using natural oyster shell and/or alternate substrates and to target the planting of hatchery-produced oysters. Please explore this page to learn more about our restoration activities.


Targeted Restoration

Recent bottom survey data, oyster population surveys and water quality data along with historical oyster bar locations are used to help determine the best sites for restoration. Knowing the salinity patterns in a tributary allows us to select a restoration approach that appropriately addresses disease and recruitment issues for each tributary. Although successful recruitment occurs in higher salinities, oysters there may be subject to greater disease pressure. Conversely, oyster populations in lower salinities experience less disease pressure but are recruitment-limited and may suffer from freshet mortality. Many partners, including federal and state agencies, non-profit organizations and educational institutions are involved in completing any one project.

Facing a Shell Shortage

Oyster shell, either new (shucked) or from buried deposits, is the predominant and preferred cultch for oyster habitat projects in the Bay. From 1960-2006, the dominant source of shells for restoration was dredged shells from buried deposits in the Upper Bay. More recently, permit issues and reduced sites with buried shell available are limitations to the use of dredged shell. Recycling shell from shucking houses, restaurants, festivals and the public is currently being utilized for restoration. Improving degraded oyster habitat across large areas will require more shell than is available.

Alternative Substrates

Because of the shortage of oyster shell, Maryland is using alternate substrates to rebuild degraded oyster bars. Clam shell, mixed shell (clam, conch and whelk), fossil oyster shell from out-of-state and granite are some options to provide a firm base for the placement of spat-on-shell. These materials have proven effective not just as a base for spat on shell, but also for the settlement of natural oyster larvae.

Oyster Hatcheries

In order to meet the demands of an aggressive restoration agenda and a rapidly growing Marylanders Grow Oysters program, Maryland must have access to large quantities of oyster larvae (over 2 billion per year) for restoration. Larvae produced in hatcheries are released into large tanks, which are filled with shells. The larvae settle upon the shells creating spat-on-shell (baby oysters), which is then planted on various restoration sites. 

 Image of spat-on-shell.

(Photo credit:

Restoration Projects

Tributary-Scale Projects

As a part of the 2014 Chesapeake Bay Watershed Agreement, Maryland committed to restoring oyster populations in five tributaries in Maryland’s portion of the Chesapeake Bay by 2025. The tributaries chosen for restoration are Harris Creek, Little Choptank, Tred Avon, Upper St. Mary’s and Manokin Rivers.

Small-Scale Projects

In a December 15, 2017 press release, DNR announced the intention to design and develop oyster management plans for restoration efforts in sanctuaries in addition to the five tributaries. Specifically, the press released stated the Nanticoke and Severn rivers would have plans developed to determine how the strategic use of state investment and resources could restore oyster populations, using planted seed, shell and spat to spur natural oyster growth and reproduction.

In a September 5, 2018 press release, DNR announced the intention to study and survey existing state oyster sanctuaries in Anne Arundel County, including the Severn River Sanctuary and to work with the local watershed associations to maximize the restoration potential in the tributaries.