Mermaid : A New Computer Algorithm Applied to the Classification of Shellfish Growing Areas of Virginia, USA

Abstract. The Virginia Division of Shellfish Sanitation (DSS) opens and closes harvesting of shellfish areas using the direct-rule-management method, and not the conditional-rule method governed by events such as a rainfall, river flow, river height, or tides. To open and close most shellfish areas, the DSS directly compares the Estimated 90th Percentile of fecal coliform concentrations to the National Shellfish Sanitation Program (NSSP) standard of 31MPN/100 mL for the Membrane Filtration test. In this paper, the authors demonstrate a new Mermaid algorithm and program, which employs aspects of their Pearl formulas developed in previous papers. In the absence of raw data, Mermaid uses DSS calculated data of Geometric Mean and the Estimated 90th Percentile of fecal coliform concentrations to back calculate the arithmetic means and the standard deviations of the sample results; and then using these two parameters calculates the upper limit of Geometric Mean and the upper limit of the Estimated 90th Percentile of fecal coliform concentration. To open a shellfish growing area, both the Estimated 90th Percentile values of the fecal coliform consecrations samples and their Upper limits must appear below the NSSP standard of 31 MPN/100 ml for the Membrane Filtration test. Otherwise, consuming shellfish products harvested under this condition poses a public health risk, which can be avoid by using the Mermaid program.