|NOAA Science Supports Harris Creek Oyster Project|
The Chesapeake Bay is North America’s largest estuary. The surface area of the Bay and its tidal tributaries is approximately 4,480 square miles—more than twice the size of Delaware. With so much area to choose from, how do experts decide where—and how—to implement oyster restoration projects? By using cutting-edge technology and science.
Rebuilding oyster reefs and oyster populations in the Chesapeake Bay is important for several reasons. Today, due to years of overharvest, diseases, poor water quality, and increased sediment loads, there are less than 1% of the oysters in the Bay that there used to be. Oysters, historically, provided an important commercial fishery on the Bay. Oysters also form reefs that provide habitat for fish and crabs that like to hide among the reefs. Oysters also are filter feeders, so they help clean the Bay’s water.
Because oysters are such an important part of the Chesapeake ecosystem, federal and state agencies set a goal through the President’s Executive Order on Chesapeake Bay Protection and Restoration to restore healthy oyster populations to 20 tributaries by the year 2025.
Oyster restoration efforts, which often feature installing hard features like oyster shells, recycled concrete, stone, or concrete “reefballs” on which baby oysters can grow, all need to be done in areas that meet certain criteria in order to be successful. Oysters need hard Bay bottom for survival, because if it’s muddy—as is the bottom of much of the Bay and its tributaries—newly planted oysters could sink into the mud. Also, oysters need water with sufficient salt and oxygen levels.
As part of a partnership comprised of federal and state agencies, academic institutions, and nongovernmental organizations, NOAA plays important roles: Providing up-to-date science on where in the Bay oyster restoration efforts are likely to succeed—and data on how well those efforts are working.
In order to find these places, the NOAA Chesapeake Bay Office’s field science team uses technology including sonar to map areas in tributaries where agencies agree restoration efforts are needed. The process involves several steps. First, the science team does a broad-scale survey using side-scan sonar of areas in the tributary to determine what kind of bottom—hard, muddy, sandy, or perhaps existing oyster reef—is in place. For example, the graphic above shows what kind of bottom is available in Harris Creek on Maryland’s Eastern Shore.
Once the broad-scale mapping has been analyzed to show what bottom areas are available for potential restoration, a more fine-scale mapping is accomplished. This step zooms in on areas that have characteristics that might support oyster reefs and is undertaken to pinpoint where conditions are best to support restoration and to provide a baseline for future monitoring of reef health. The field science team also does a detailed assessment and produces a map of existing oyster populations so that restoration efforts can be tailored to the conditions and healthy oysters that are already there. The map below shows where live oysters are in Harris Creek, and at what density, in areas of the creek that have oyster shell. The map at left was developed from a population study guided by NOAA’s broad-scale and fine-scale habitat surveys.
The numbers of oysters per square meter are important because a group of federal and state agencies, academic institutions, and other organizations recently agreed on definitions to help guide oyster restorations. The Oyster Metrics Report sets guidelines for what is considered a successful restoration project. If an oyster reef has at least 15 oysters per square meter (but preferably 50), or more, it is considered restored. So to get some of the restorable bottom on the Harris Creek map up to this threshold, it won’t take too much effort; other areas will require more intensive restoration work. Having estimates of oyster density in these areas allows more effective allocation of restoration resources.
Experts agree that getting a critical mass of oysters in one tributary can help oysters in other locations, as well. In producing computer models for the U.S. Army Corps of Engineers to help guide restoration work, scientist Elizabeth North developed a visualization of where oyster larvae—baby oysters—would end up if there were a healthy population of oysters in Harris Creek. Her work shows simulated larvae moving around—and then expanding out of—Harris Creek. The model shows that, depending on water depth and currents, healthy oyster restorations in one area can benefit other areas as well.
Harris Creek was the first tributary selected for restoration by the federal agencies working under the Executive Order. The Maryland Department of Natural Resources, along with partner agencies NOAA and the U.S. Army Corps of Engineers’ Baltimore District, held an open house for people to let them know more about the project in March 2012 at the Chesapeake Bay Maritime Museum in St. Michaels.
Oyster restoration efforts are ongoing in other tributaries around the Bay watershed. For example, the Lafayette River and the Great Wicomoco River, both in Virginia, have been sites of oyster restoration efforts in recent years. These projects started before the Oyster Metrics Report was completed, but oyster restoration partners are using science to survey those areas to see if they meet the Report’s definitions of success.
Building oyster reefs is complex. Using science to guide where to build reefs, how many reefs to build, and to define success helps scientists best apply limited resources. The future health of the Chesapeake Bay oyster population depends on this science.