Virginia Institute of Marine Science - Wachapreague
Population Assessment of Eastern Oysters (Crassostrea virginica) in the Seaside Coastal Bays
Project Description as Proposed:
Declines of oyster populations and commercial harvest from the seaside have followed similar patterns, though not as severe, as those in Chesapeake Bay. High prevalence of Dermo disease (Perkinsus marinus) and MSX disease (Haplosporidium nelsoni) coupled with over harvest and habitat destruction have dramatically reduced populations. Nevertheless, there are several promising signs that significant enhancement of the population could be achieved with well conceived restoration efforts. Recruitment rates remain high and rapid growth allows oysters to reach reproductive size prior to disease mortality.
To plan a more a comprehensive and effective restoration effort we need an estimate not only of the current standing stock of oysters, but also of their spatial distribution in the seaside bays. This is easier said than done in the complex of habitats that make up the seaside bays.
Oysters on the seaside are found in a range of habitats e.g., patch reefs in the open lagoons, fringing reefs along the marsh edge, small clumps within the marsh, and on man-made structures, such as bulkheads. In addition, private lease holders create a variety of habitats for planting and rearing oysters that include both subtidal and intertidal habitats. Traditional stock assessment methods have involved only determining the density of oysters on "public" oyster reefs and restoration sanctuary reefs. Arguably, the majority of oysters in the region are not counted by this method. Many oysters appear to be surviving in other situations.
Obtaining reliable estimates of the distribution and abundance of oysters on the seaside are beyond the scope of VMRC's resources and until recently posed several technical challenges. Fortunately, we now possess the tools to develop reliable population and distribution estimates for oysters on the seaside. We will employ aerial observations along with ground-level sub-meter accuracy Global Positioning Systems [GPS], integrated with an ArcView-based Geographic Information System [GIS]), to develop distribution maps and design sub-sampling schemes to obtain accurate estimates of basin-wide distribution and abundance of oysters throughout the entire seaside. This 2-year project will provide spatially-explicit estimates of oyster populations throughout the region that can be used to help guide management and restoration efforts.
We need a reliable, spatially-explicit population estimate for seaside oysters for three reasons:
1)Without a regional population estimate we have no basis for determining if our restoration efforts are successful; we cannot tell if populations are increasing or decreasing, if we do not know how many oyster are there now.
2)This information will help to guide where and how we do oyster restoration on the seaside to maximize success. For instance, if the survey reveals that oysters growing in fringing reefs in small tidal creeks are healthier than those growing in fringing reefs along the margins of large creeks (where they are susceptible to erosion from boat wakes), we could direct more resources towards restoration in these habitats. Similarly, if we determine that isolated clumps of oysters within salt marshes are an important component of the population that are less susceptible to overharvesting, we can direct both restoration and management efforts to enhance and protect these as broodstocks.
3)Oyster harvesting can be more effectively managed on the seaside once we know how many oysters are there and where they are located.
Spatially explicit distribution of C. virginica will be determined in two phases. Currently in the first year of this project (January 2007 through December 2007) we are mapping oyster habitats (shell reefs/beds, marsh, and manmade structures) with progressively finer resolution utilizing: 1-meter geo-referenced aerial images in an Arcview-based GIS; aerial surveys; and field mapping/ground-truthing (by boat and on foot) using sub-meter surveying GPS technology (Trimble XRS/Ranger TsCe). This initial mapping phase includes preliminary data on oyster presence and qualitative density estimates. We will use these maps of oyster habitat types and qualitative density strata to develop an appropriate and rigorous stratified, random sampling design during year 2 of the project. During this second year of the project (January 2008 through December 2008) we will employ quadrate and transect sampling in this design to provide quantitative estimates of the abundance, density and size distribution, of oyster populations on the seaside of the Eastern Shore. Biomass-length relationships will be determined from oysters collected from each of the habitat types. A GIS database will be developed with layers detailing the distribution, abundance, size-frequency and biomass of oysters throughout the seaside.
Mark W. Luckenbach - (757) 787-5816; firstname.lastname@example.org
Project Open - 10/1/07 - 9/30/08; Project Completed
Final Product Received:
Population Assessment of Eastern Oysters (Crassostrea virginica)
in the Seaside Coastal Bays (PDF)
Project Summary Provided by Grantee:
Oyster populations in the seaside bays of Virginia's Eastern Shore have followed a similar pattern of decline as those in Chesapeake Bay. Nevertheless, there are promising signs that the population may be rebounding and that further enhancement could be achieved with well conceived restoration efforts. To plan a more comprehensive restoration effort, estimates not only of the current standing stock of oysters, but also of their spatial distribution in the coastal bays are needed.
The overall objective of this project was to develop a spatially-explicit oyster stock assessment of this region in a Geographic Information System (GIS).
In Phase I of this project Virginia Institute of Marine Science (VIMS) staff used National Wetlands Inventory habitat together with Virginia Base Mapping Project aerial photography and ground truth sampling to develop detailed oyster habitat maps throughout the ~900 km2 region. During Phase II of the project, stratified random samples were collected across all oyster habitats within the region. A total of nearly 46,000 oysters were counted and measured.
The results provide the first quantitative assessment of oyster population abundance on a region-wide scale in the Atlantic bays on the seaside of Virginia's Eastern Shore. Oyster densities ranged from <1" m-2 on unconsolidated mudflats and high marsh environments to over 1,300 m-2 in patch reefs. region-wide, the oyster population was estimated to be 3.2 billion, a number that exceeds the most recent population estimate of 1.8 billion oysters for the entire Virginia portion of Chesapeake Bay. The oyster population in this region was composed of a wide range of sizes representing several year classes that suggest a self-sustaining population with the potential for significant expansion.
Detailed results of this project are included in an extensive final report available through the Virginia CZM Program. An extensive GIS-database was produced from the work and is available through the Coastal Gems website.
The spatially-explicit oyster population GIS product developed through this work provides a valuable tool for guiding fisheries resource management and restoration activities for oysters in this region. Ultimately, the usefulness of this product lies in integrating it with other GIS layers (e.g., hydrological, water quality, disease distributions, recruitment rates) to elucidate the factors affecting oyster distribution and abundance throughout the region. It also provides a baseline against which to measure the success of local restoration efforts and evaluate region-wide changes in oyster populations related to such factors as fishing pressure, disease dynamics and climate change.
Disclaimer: This project summary provides the federal dollars initially awarded to the grantee. Due to underexpenditure or reprogramming of grant funds, this figure may change. For more information on the allocation of coastal grant funds, please contact Laura McKay, Virginia Coastal Program Manager, at 804.698.4323 or email: Laura.McKay@deq.virginia.gov
A more detailed Scope of Work for this project is available. Please direct your request for a copy to Virginia.Witmer@deq.virginia.gov