Mermaid: A Shellfish Sanitation Model Providing Additional Metrics for the Classification of Shellfish Growing Areas of Virginia (USA), Managed by the Direct Rule Method

The Virginia Department of Shellfish Sanitation (VDSS) manages shellfish growing areas using the Direct Rule method, by directly comparing the Geometric Mean and Estimated 90th Percentile of fecal coliform concentrations to the U.S. National Shellfish Sanitation Program (NSSP) standard. The agency closes the area to harvest if fecal coliform concentrations exceed the NSSP limit and the area is not reopened until concentrations fall below the NSSP limit. The VDSS originally used the NSSP 3-Tube test (14/49 Standard), and transitioned to the NSSP Membrane Filtration Test (MFT, 14/31 Standard) in August 2007. In this article we focus on a VDSS 13-plus year dataset of fecal coliform concentrations from 127,320 water samples collected from 2,193 sampling stations in 103 shellfish growing areas located in Virginia’s state waters. Our goal is to introduce a new shellfish sanitation model, Mermaid, which provides additional metrics to the NSSP statistical procedures for managing shellfish growing areas under the Direct Rule method, using calculated datasets, with uniform and mixed samples. We also examine if the additional metrics, which are based on the upper limits of Estimated 90th Percentile values of fecal coliform concentrations, increase the health safety of harvested shellfish managed under the Direct Rule method. Keywords: Aquaculture, Computer software, Decision support system, Diagnosis, Fecal coliform, Sanitation model, Shellfish harvesting