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A decision support tool for shellfish management in Mississippi Sound.

ABSTRACT The Eastern oyster (Crassostrea virginica) is an economically important fisheries resource along the US Gulf Coast and the eastern seaboard. In the past few years, Mississippi has ranked second in the country in shellfish production, harvesting an average of 350,000 sacks (~15.8 million kg of oysters) per year. A GIS-based decision support tool was developed to aid the Mississippi Department of Marine Resources in managing shellfish in the state. The tool was designed using the ESRI ArcGis 8.3 Arcview software, which enabled us to integrate GIS data layers (e.g., oyster reef sites) with a program that automatically obtains Pearl River stage (gage height) and rainfall amount data from the USGS and NOAA websites, respectively. The program then compares the data with established area-specific standards and makes recommendations to the shellfish manager on the area(s) that should be closed or opened. The decision support tool is the first tool developed for shellfish management in the US Gulf Coast area. Although it was developed for use in Mississippi, it can be modified for use in other states. It simplifies the shellfish management process and maintains a database of the water quality data and the management actions that have been taken, thereby facilitating data analyses and preparation of reports.

KEY WORDS: oyster management, Mississippi Sound, river stage, precipitation, GIS data layers


The Eastern oyster (Crassostrea virginica, Gmelin 1791) is one of the economically important fisheries resources in the eastern seaboard of the United States and the US Gulf Coast region, and it accounts for more than 60% of all oysters harvested in the United States (Gore 1992). In the past few years, Mississippi has ranked second in the country in shellfish production, and harvested an average of 350,000 sacks (~15.8 million kg of oysters) per year.

Crassostrea virginica inhabits shallow waters in intertidal and subtidal zones, and their survival and production depend chiefly on phytoplankton productivity, flooding, salinity and temperature variations, levels of parasitism by Perkinsus marinus (dermo) and Haplosporidium nelsoni (MSX) and predators (Andrews et al. 1959, Menzel et al. 1957, Soniat et al. 1989, Powell et al. 1995, Jordan 1995). Although C. virginica tolerates a wide range of salinity with lower and upper limits of about 2 ppt and 39 ppt, respectively (Shumway 1996), high salinities and warm temperatures are conditions that favor the major predators and parasites of the shellfish. For example, the conch, Stramonita haemastoma thrives at salinities >12 ppt and can have significant predatory impacts on the oyster population (Butler 1954, Gagliano et al. 1970). Another major cause of mortality of oysters in high salinity areas and during warm months along the Gulf of Mexico is P. marinus, a parasitic protozoan (Ogle & Flurry 1980, Ray 1996, Soniat 1996). The impacts of P. marinus parasite on oysters depend on local as well as regional variations in climatic factors (Powell et al. 1992, Kim & Powell 1998).

Management of shellfish is aimed at enhancing the habitat via cultch planting and cultivation, harvest control, and minimizing the risks to humans of consuming raw contaminated shellfish. Disease outbreaks resulting from the consumption of oysters contaminated by bacterial (e.g., Vibrio vulnificus and Vibrio parahaemolyticus) and viral pathogens (Leonard 2001, see also a review by Rose et al. 2001) have been reported in other states. The levels of these pathogens depend on climatic factors such as water temperature, intensity of solar radiation and precipitation. The latter is usually accompanied by runoff carrying pollutants into coastal waters (Lipp et al. 2001). To reduce the risks of acquiring diseases caused by consumption of contaminated oysters, the United States Food and Drug Administration and the Interstate Shellfish Sanitation Conference (ISSC) formed the National Shellfish Sanitation Program (NSSP) that developed criteria for the protection of shellfish harvesting waters (ISSC et al. 1999). For example, the Mississippi Ordinance 1.016 section requires a shellfish harvesting area to be closed "when the geometric mean of the seawater from compliant sampling stations in the area exceed a fecal coliform most probable number (MPN) of 14 per 100 mL and/or more than 10% of the samples exceed a MPN of 43 for a 5-tube 3 dilution test."

In Mississippi, rainfall amounts and/or Pearl River stage are used as metrics for closing shellfish harvesting areas in Mississippi Sound. Many years of studies indicate that both factors are highly correlated with fecal coliform levels (Chigbu et al. 2004a). Each of the nine conditionally approved shellfish harvesting areas in Mississippi has specific closure criteria. These are monitored by designated MDMR personnel using sources such as telephone, various official reports, internet, as well as by direct observation, as stated in the Ordinance 1.016. The objective of our study is to design a GIS-based decision support tool that will ease the process of shellfish management in the state. Although GIS-based tools and methods have been developed for various projects including, microbial risk assessments (Kistemann et al. 2001a, 2001b), environmental impact assessments (Gustafson et al. 2001, Sahin & Kurum 2002), flood area and damage estimation (Renyi & Nan 2002) and resource management (Webb & Bacon 1999), to our knowledge none is available for use in shellfish management in the US Gulf Coast region.

Study Area

Mississippi Sound has a mean depth at midtide level of 3 m, and is partially separated from the northern Gulf of Mexico by a number of barrier Islands. Within the estuary, water from the Gulf mixes with water that flows in from a number of bayous and rivers. The Pearl and Pascagoula Rivers account for more than 90% of freshwater discharge into the Sound (Eleuterius 1978). The Mobile and Mississippi Rivers sometimes contribute significant freshwater into the eastern and western portions of the Sound, respectively (Orlando et al. 1993). The eastern and western parts of the Sound have more variable and lower salinities than the central part of the Sound. Under most conditions, Mississippi Sound is partially or well mixed because of tidal action and winds (Eleuterius 1978).

Pearl River is about 789 km long and drains an area of approximately 23,000 [km.sup.2] before emptying into the western part of the Mississippi Sound, an area that contains some of the most productive oyster populations in the Southeastern United States (Gore 1992). Studies conducted from June 1973 to February 1975 (Eleuterius 1977) suggested that the area experiences bottom minimum and maximum salinity of 2.0-4.0 ppt and 18.0-22.0 ppt, respectively.

Oyster Management in Mississippi Sound

The Department of Marine Resources manages about 17 natural oyster reefs in Mississippi. About 97% of the harvested oysters in Mississippi come from the reefs in the western part of the Mississippi Sound. Management of the Sound for shellfish harvesting is currently based on Pearl River stage, local rainfall amounts and fecal coliform counts (Table 1). River Stage information is collected directly from the USGS website for specific river gauges. The National Weather Service web-site is monitored for rainfall from three NOAA rain gauge locations: Bay St. Louis, Waveland and Pascagoula, MS.

Historical data on fecal coliform levels during the oyster-harvesting season (typically October to April), have been used by shellfish managers to classify Mississippi Sound into areas designated as Approved, Conditionally Approved, Prohibited, Restricted or Unclassified. Harvesting of oysters for direct consumption is permitted only in areas designated as approved or conditionally approved. At present, nine areas are designated as conditionally approved, each of which has specific opening and closing criteria (Table 1), based on rainfall amounts and/or river stage as outlined in the Mississippi Ordinance 1.016. Beside heavy precipitation, other factors listed in the Ordinance that may result in temporary closures of an approved or conditionally approved area include "a hurricane, flooding, chemical spill, hazardous waste or raw sewage discharge, sinking or grounding of vessels carrying hazardous cargoes, evidence of the existence of marine biotoxins."


The GIS data layers that were used in the tool included the oyster reefs, shellfish management areas, sampling stations for water quality monitoring, Gulf Coast imagery, and the USGS river gauge locations. The tool was designed using the Environmental Systems Research Institute (ESRI) ArcGIS 8.3 Arcview and Microsoft Access. The ESRI package provides the user the capability to use geographic data, as well as a programming environment that integrates Visual Basic for application and the ArcObjects library. Microsoft acts as an external relational database that is used to store the metrics for each of the oyster zones as well as the current and historical gauge measurement and information data. The tool automatically obtains river gauge information from the USGS website:, and the National Weather Service (NWS) precipitation data from the NOAA website: http:// Because the gauge data are ingested from the various websites, they are parsed and stored in the corresponding table in the backend database. On a predetermined time interval, the application is designed to use the current gauge data to decide whether an area should be closed, and then uses data on fecal coliform counts to determine whether the area should be reopened. The fecal coliform information is stored in a separate Access database. The readings are stored in a database at a remote laboratory and then transferred to the cataloging database via an automated E-mail application. The tool was built to run on an IBM compatible with Windows 2000 operating system and the following specifications:

(a) CPU speed of 450 MHz (minimum); 800 MHz or higher is recommended

(b) A pentium or higher processor

(c) Memory/RAM 128 MB (minimum); 256 MB or higher recommended

(d) Swap space 300 MB (minimum)

(e) Disk space of 695 MB FAT32 for the ESRI software, and 300 MB for data storage


The shellfish decision support tool consists of 5 major components, namely, the Shellfish Management, Manual Close, External Conditions, Rules Change and Strategic Management, the functions of which are summarized in Table 2. The display user interface for the tool (Fig. 1) is divided into 5 areas.


Area 1 contains the typical user interfaces found in normal office applications such as MSWord, MSExcel, including "file save, exit, copy and paste," in addition to some ArcInfo 8.2 functionality.

Area 2 contains the graphical user interfaces (GUI) for the Shellfish Management Application. The tool bar has buttons, each of which operates a separate function within the application.

(a) The Shellfish Management function button continually monitors river stage and precipitation and automatically recommends whether an oyster harvesting area should be closed. The program's recommendations are reviewed by the DMR officials who then decide whether to accept or reject the recommendations.

When the data being monitored by the application indicate a status change to a Shellfish Management area, a Shellfish Management Form (Fig. 2) automatically opens. The form has 5 areas that show Program Recommendations, National Weather Service (NWS) data comprising information on rain gauges at Waveland, Bay Saint Louis and Pascagoula, MS and the US Geological Survey (USGS) Pearl River stage data at Pearl River, Louisiana. In addition, the form has a time stamp that shows the latest time that the external data from the gauges were collected from external websites by the shellfish application. Finally, the form has an error message display area. If no value is found for rainfall, an error message will notify the user in the area, and if the value is invalid, it will be presented as "-9999" in the table.


When the program recommendations button is selected from the Shellfish Management Form, the program recommendations form opens (Fig. 3) to allow DMR staff to review the reasons why the application is recommending a status change. The application's recommendation can then be accepted or rejected by the DMR staff.


There are 5 areas on the Program Recommendations Form: (1) Area Tabs; (2) Recommendation; (3) Reason for Recommendation; (4) Reason for Rejection and (5) Process Recommendation.

The area tabs consist of nine separate and distinct tabs; each tab contains information specific for a particular area. If the tab heading is in bold, it indicates the particular area has a recommended status change otherwise, no status change recommendation exists.

The recommendation tab has a title that shows either Recommend Open or Recommend Close, which is associated with check boxes for use by DMR staff to indicate an acceptance or rejection of the application's recommendation. The reason for recommendation tab describes why the application is recommending a change for the area. The reason for rejection tab is for use by DMR officials to record their reasons for rejecting a recommendation made by the tool. The reason will be stored in the database and can be reviewed by the current status or history reports functions. The process recommendation tab is selected to update the display with the current status (whether accepted or rejected). If a status change was recommended and this button is not selected, the display will not reflect the status changes. This tab should be selected after all areas have been reviewed and recommendations are either accepted or rejected. The map display will reflect the changes accepted (e.g., Fig. 4). The program "recycles" every four hours when more information is received from the USGS and NWS websites. If an area is not closed, even though the application recommends it, the area will again be recommended to close when the program recycles in four hours.


(b) The external conditions buttons are used to close and reopen areas for events that are not routinely monitored by the Shellfish Management application. The add external conditions allows an event to be pinpointed on the map with either latitude/longitude coordinates or a mouse-click on the screen. The delete external conditions button removes external conditions, which have been previously established.

When the external conditions buttons are selected, the external conditions form (Fig. 5) opens. This form consists of nine areas: (1) Event Location; (2) Area Name and Present Status; (3) Date/Time; (4) Latitude/Longitude; (5) New Status; (6) Open/Close All Zones; (7) External Condition; (8) Operator Comments and (9) Set Status.


The event location button allows one to identify the location of an event by selecting entered mouse click or entered by coordinate value. The area name and present status button lists all of the areas and their present statuses. The area(s) can be selected by left-clicking the mouse. To select more than one area, hold down the shift key while selecting the area with the mouse. Areas that are selected are highlighted.

The date and time stamp is used to record the time and date that the manual close function is used. This is recorded for the current status and history reports.

The longitude and latitude buttons are used to display the longitude and latitude of where the external conditions symbol is on the map display.

The new status button allows the selection of an open or close status of the areas selected in the area names window. Selection is made by clicking on the arrow, which prompts a drop-down menu with Open and Closed to open.

The Open/Close all zones button allows one to select and close or open all areas in the area names list.

The External Condition button allows for the selection of the type of external condition that has warranted closure of an area.

The Operator Comments area is provided to allow additional comments to be noted. These comments are retained for the report features.

The Set Status button is clicked after all the external conditions have been established to process the decision.

(c) The history report button allows DMR to generate reports of the opening and closing events that have taken place for a particular area, including the reasons for change in status.

(d) The status report button generates a visual and/or a printed report for the current status of each of the shellfish harvesting areas.

(e) The rules change button allows the monthly rule tables to be changed for any of the shellfish harvesting areas. Rainfall amount, river gauge levels, fecal coliform counts, and the values that determine river crest and river rerise can be changed using this function.

When the rules change button is selected, the rules change form (Fig. 6) will open and is used to change the criteria for each shellfish management area to open or close, when approved by the authorized person at DMR. There are 6 areas on the form: (1) Select Area ID; (2) Area Information (for area ID); (3) River Gauge Information; (4) Rain Gauge Information; (5) Area Information (for river crest and rerise) and (6) Form Navigation. The rules change function is password protected.


The select area ID allows one to select the area that requires a change in its rule criteria. The area information shows the area ID and the seasonal condition rule (area classification status).

The river gauge information gives information about the river gauge, such as the agency that it belongs to, as well as the ID, name, and the measurement units. It also has the limit box used to set the maximum height of the river allowed before closing a shellfish area, and the period box used to set the maximum time (in hours). In Figure 6, for example, Area IIC--CA is recommended to close when the Pearl River gauge reaches 12.5 ft.

The rain gauge information gives details about the rain gauge, such as agency, ID and name and measurement units. The limit box within the rain gauge information area is used to set the maximum amount of rain (in inches) allowed before closing a shellfish area. The period box is used to set the maximum time (in hours) of rain accumulation. For example, in Figure 6, Area IIC-CA is recommended to close when the Waveland rain gauge shows that it has rained 2 inches in the last 24 h period.

The area information section displays the values the application uses for river crest and rerise. In addition, the maximum acceptable geometric mean fecal coliform count is set here. The crest value change is used to determine when the application considers a river crest has occurred. It considers the river to have crested if the level has dropped 0.04 ft below the highest river value recorded since closure. The ReRise value is used to set the application's river's rerise condition. The river is considered to have reached a level of "re-rise" (which could indicate a condition to close the area again) if the river stage is 0.15 ft above the level that caused the closure. The acceptable geometric mean area is used to set the maximum value for fecal coliform count allowed to keep a shellfish management area open for harvesting.

The navigation area allows the operator to navigate through the rules change records by clicking on the previous and next buttons on the bottom of the form.

(f) The manual close button, like the external condition function, allows the program to be operated outside of the scope of the shellfish management rules closure recommendations. The rules closure criteria affect only the conditionally approved areas. In contrast, the manual close function allows any area to be closed.

(g) The strategic management button allows for a year-end evaluation of the shellfish harvesting areas, based on calculations of the geometric means of fecal coliform counts. Fecal coliform data of water samples from each area are used by the application to calculate the geometric mean of the fecal coliforms for each water sample station. These results can then be used by DMR to reclassify areas as approved or conditionally approved. An area can be classified as approved "if the bacteriological quality of the water of every sampling station does not exceed a fecal coliform median or geometric mean MPN of 14 per 100 mL, and not more than 10% of the samples exceed an MPN of 43 for a 5-tube 3 dilution test" as presented in the ordinance. An area may be classified as conditionally approved if the area meets approved area standards under certain conditions specified in the areas management plan (e.g., rainfall or river stage at a particular location is less than the maximum allowed for in the management plan).

Area 3 is known as the table of contents, and shows what layers are active in the map display area.

Area 4 consists of tools used to move around the map display area.

Area 5 is the map display area, where the shellfish management areas are displayed. They will be color-coded as to their status.

Fecal coliform reports are used mainly for two reasons with regard to the shellfish management areas. First, recent fecal coliform counts are used in determining whether the shellfish harvesting areas can be reopened after a rise in river stage and/or a rain event. Second, the strategic management function of the application will evaluate all of the fecal coliform counts for an entire season. The counts are then computed and used to re-evaluate if the shellfish management area should be classified as approved or conditionally approved. DMR collects water samples from various stations, which are then analyzed for fecal coliforms at the US FDA approved Gulf Coast Research Laboratory, Ocean Springs, Mississippi. The fecal coliform data are sent to DMR via e-mail. The shellfish management application was designed to perform a semiautomatic ingestion of the newly delivered data into the DMR database and also calculate the geometric mean fecal coliform counts to recommend whether to reopen the reefs.

The Pearl River has much influence on the water quality in the western part of the Mississippi Sound, hence Pearl River stage along with rainfall amount are two important variables that the shellfish management tool monitors for closing shellfish harvesting areas. Pearl River stage varies seasonally (Chigbu et al. 2005a), with a peak in late winter/early spring and a minimum in summer/ early fall. The river stage also varies between years because of the influence of ENSO events on precipitation (Chigbu et al. 2004). Both seasonal and interannual variations in Pearl River stage are accompanied by increased levels of fecal coliforms, which in turn determine the duration that the conditionally approved shellfish harvesting areas are opened for shellfish harvesting. In fact, Pearl River stage explains as much as 90% of the variations in fecal coliform concentrations in the western part of the Sound (Chigbu et al. 2004).

Fecal coliform levels often peak in water after rain events. In Mississippi Sound, fecal coliform levels peak within 48 h of a major local rain event (>0.5 inches), whereas Pearl River stage typically crests within about 96 h of a rain event (Chigbu et al. 2005b). It is therefore, reasonable to use the total amount of rainfall within a period of 24 consecutive hours for determining whether an area should be closed in the shellfish management tool.

To our knowledge this is the first decision support tool developed for shellfish management in the US Gulf coast area. Although it was developed for use in Mississippi, it can be easily modified for use in other states. It is easy to use; it simplifies the process of closing and opening of the conditionally approved shellfish harvesting areas, and it maintains a time series database of the water quality on which closing and opening of reefs are based as well as management actions that have been taken. It thus facilitates data analysis and preparation of reports. The tool was installed and successfully tested at DMR during the 2003/2004 shellfish harvesting season. Plans are underway to adapt the tool for use in other states.


This work is a result of research sponsored in part by the National Oceanic and Atmospheric Administration (NOAA-NESDIS), Department of Commerce under grant #: NA07WA0489 to Jackson State University. The United States Government is authorized to produce and distribute reprints for Governmental purposes notwithstanding any copyright notation that may appear hereon. The views expressed herein are those of the authors and do not necessarily reflect the views of NOAA or its sub-agencies. The authors thank Dr. Abdul K. Mohamed (Dean, College of Science, Engineering and Technology) and Russ Beard (Chief Scientist, NCDDC, Stennis Space Center) for supporting the project.


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(1) Department of Biology, Marine Science Program, Box 18540, Jackson State University, Jackson, Mississippi 39217; (2) Veridian Systems Inc., Stennis Space Center, Mississippi 39529; (3) Mississippi Department of Marine Resources, Bayview Avenue., Biloxi, Mississippi 39530; (4) Trent Lott Geospatial Visualization and Research Center, Jackson State University, Jackson, Mississippi 39217; (5) Department of Physics, Atmospheric and General Science, Jackson State University, Jackson, Mississippi 39217

* Corresponding author. E-mail:

(6) Present address: NOAA Living Marine Resources Cooperative Science Center, University of Maryland Eastern Shore, Carver Hall, Princess Anne, MD 21853

Criteria for closing conditionally approved shellfish harvesting areas

 Area Closing criteria

Area IB-CA 10 ft Pearl River Stage and/or 2 inches rainfall
Area II A-CA 10 ft Pearl River Stage and/or 1 inch rainfall
Area II B-CA 10 ft Pearl River Stage and/or 1 inch rainfall
Area II C-CA 12.5 ft Pearl River Stage and/or 2 inches rainfall
Area II D-CA 10 ft Pearl River Stage and/or 1 inch rainfall
Area III-CA 2 inches rainfall
Area IV-CA 10 ft Pearl River Stage and/or 1 inch rainfall
Area V-CA 2 inches rainfall
Area VIII-CA 0.75 inches rainfall


Main components of the shellfish management tool and
their functions

 Main components Functions

1. Shellfish management * Monitors rainfall and river gauge data and
 compares it to monthly rule criteria for
 each area.

 * Recommends closure of an area when
 certain criteria have reached the
 threshold defined in the Shellfish
 Management Plan.

 * Allows for fecal coliform counts to be
 analyzed, and determines when it is safe
 to re-open an area for oystering.

2. Manual close * Provides DMR officials with the ability to
 allow some other closing conditions such
 as oil spills and hurricanes which are not
 automatically monitored by the

 * When an area has been manually closed,
 it can only be manually reopened.

 * The manual close function prohibits or
 "locks-out" normal operations of the
 shellfish management function for the
 area(s) normally closed.

3. External conditions * Allows DMR officials to close for other
 specified reasons, hence it is similar to
 the Manual close function.

 * Allows latitude and longitude coordinates
 to be associated with the closing event.

4. Rules change * Allows the tool to remain up-to-date with
 amendments to Ordinance 1.016 by
 making it possible for DMR officials to
 change any closing or opening criteria
 (e.g. river stage levels, rainfall
 amounts, geometric mean MPN level) for any
 of the conditionally approved areas.

5. Strategic management * Used for longer term (e.g., 1 year)
 evaluation of the shellfish harvesting
 areas based on fecal coliform counts, in
 order to determine whether a
 re-classification of oyster-harvesting
 areas is necessary.
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Article Details
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Author:McIntosh, Michael
Publication:Journal of Shellfish Research
Geographic Code:1U6MS
Date:Dec 1, 2006
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