Shellfish

A Valuable and Renewable Natural Resource

In Florida, oysters and clams are important aquatic species. The annual value of shellfish to the seafood industry in Florida exceeds 20 million dollars, with as many as 2,500 people employed in the harvesting, processing and distribution of shellfish. Most shellfish harvesting areas in Florida are now classified Conditionally Approved, with management plans calling for temporary closure following rainfall. Freshwater drainage from land introduces contaminants into estuaries where shellfish grow, and as coastal development continues, water quality may be degraded. Sources of pollution include failing septic systems, stormwater runoff, wastewater treatment plant outfalls and discharges from boats.

Involvement of people interested in the commercial and recreational harvest of shellfish and coastal water quality is needed to prevent closure of shellfish beds. Inform and educate yourself, County Commissioners, and State Representatives and Senators. Attend workshops and meeting held by permitting agencies. Proper maintenance of septic systems, zoning to provide for reasonable dwelling density in coastal areas, shoreline vegetative buffers to filter contaminants, retention areas to hold runoff of freshwater, upland disposal of wastewater treatment plant effluent, and installation of pump-out facilities in marinas all provide for improved water quality and continued use of Florida's valuable and renewable shellfish resources.

Shellfish Harvesting

The term "shellfish" in this context is limited to oysters, clams and mussels. Most shellfish thrive in estuaries with mixtures of fresh and saltwater. Shellfish are filter feeders, which means that they get food and oxygen by pumping large quantities of water across their gills.  During feeding, shellfish take in bacteria, viruses and chemical contaminants, and can concentrate these impurities in their digestive systems and tissues over 100 times the levels in the water. Because oysters, clams and mussels are often eaten raw and partially cooked, shellfish harvested from polluted areas are a health hazard if consumed. Diseases resulting from consumption of shellfish harvested from polluted waters include typhoid, hepatitis and salmonellosis.

Interstate Shellfish Sanitation Conference (ISSC) and the National Shellfish Sanitation Program (NSSP)

Because shellfish harvested from polluted water may cause human illness, the sanitary control of the shellfish industry is necessary. Florida is a member of the Interstate Shellfish Sanitation Conference (ISSC), a voluntary, cooperative association of states, U.S. Food and Drug Administration (FDA), National Marine Fisheries Service (NMFS), Environmental Protection Agency (EPA) and shellfish industry. State responsibilities include adopting laws and regulations for the sanitary control of the shellfish industry, formulating comprehensive shellfish harvesting area surveys and adopting control measures to ensure that shellfish are grown, harvested and processed in a safe and sanitary manner. FDA reviews methods for classification and management of shellfish areas proposed by the ISSC, and incorporates those methods consistent with standard health practice into the National Shellfish Sanitation Program (NSSP) Manuals of Operations. FDA is also responsible for the annual review of each state shellfish control program to determine conformity with the NSSP standards and guidelines. NMFS and EPA comment to the ISSC. Shellfish industry responsibilities include commenting to the ISSC Conference, obtaining shellfish from safe sources, maintaining sanitary operating conditions and making records available that document location of harvest and sale of all shellfish. FDA, the Florida Department of Agriculture and Consumer Services (DACS) and shellfish industry fulfill their responsibilities to a high degree, thus ensuring shellfish harvested in Florida are safe and wholesome.

Responsibilities

The Shellfish Environmental Assessment Section (SEAS) in the Bureau of Aquaculture Environmental Services is responsible for classifying and managing Florida shellfish harvesting areas. The goal of shellfish harvesting area classification and management is to provide maximum utilization of shellfish resources and to reduce the risk of shellfish-borne illness. SEAS headquarters is located in Tallahassee; its shellfish laboratory is located in Apalachicola. The section is responsible for the 1,200 bacteriological sampling stations in 39 shellfish harvesting areas, encompassing 1,430,854 acres and are responsible for shellfish classification of the following coastal waters: Panama City office: Florida-Alabama line through East Bay in Bay County on the Gulf coast; Apalachicola office: St. Joseph Bay in Gulf County through Wakulla County; Gainesville office: Horseshoe Beach in Dixie County through Homosassa Springs in Citrus County; Port Charlotte office: Boca Ciega Bay in Pinellas County through Ten Thousand Islands in Collier County; and Palm Bay office: Martin County north to the Florida-Georgia line on the Atlantic coast.

Pollution Sources

Fecal Coliform as an Indicator for Human Pathogens

Many pathogens associated with fecal material are discharged into coastal waters.  Because monitoring for all human pathogens is not feasible, an indicator group of bacteria is used to assess the likelihood that human pathogens are present. Fecal coliform is the indicator group of bacteria used by FDACS. Fecal coliform live in the intestinal tract of warm-blooded animals, and each person excretes approximately two billion of these bacteria per day. Few fecal coliform are pathogenic; however, the presence of fecal coliform bacteria in coastal waters indicates feces from warm-blooded animals is present and human pathogens are likely to also be present.

The Department routinely monitors fecal coliform and water quality parameters at established stations in each of Florida's shellfish harvesting areas. Sub-surface water samples are collected, placed in ice-filled coolers and shipped overnight to a certified laboratory. The analysis for fecal coliform takes 24 hours, and numbers of bacteria are expressed in the units of Most Probable Number (MPN) per 100 milliliters (ml). 

The NSSP has established bacteriological standards for shellfish harvesting area classification. For areas to be classified Approved or Conditionally Approved, the level of fecal coliform in sub-surface water samples must meet the NSSP 14/43 standard. For areas to be classified Restricted or Conditionally Restricted, the level of fecal coliform in sub-surface water samples must meet the NSSP 88/260 standard. 
NSSP 14/43 standard: 
The fecal coliform median or geometric mean must not to
exceed 14 MPN/100 ml, and Not more than 10 percent
may exceed 43 MPN/100 ml.
NSSP 88/260 standard:
The fecal coliform median or geometric mean must not
exceed 88 MPN/100 ml, and Not more than 10
percent may exceed 260 MPN/100 ml.

Adverse Pollution Conditions

Tide, rainfall, river stage and river discharge are evaluated on computer to identify environmental conditions that may have an association with fecal coliform levels in the water.  Equations are developed for each station and used to predict rainfall and river levels when fecal coliform levels equal the NSSP 14 and 88 values. Rainfall or river exceeding these levels are defined as adverse pollution conditions. Conditionally Approved and Conditionally Restricted management plans call for temporary closure of areas for shellfishing during rainfall and/or river adverse pollution conditions. Fecal coliform data at each station is compared to the NSSP fecal coliform standards with respect to adverse pollution conditions to investigate the classification of each portion of shellfish areas as Approved, Conditionally Approved, Restricted, Conditionally Restricted or Prohibited.

Wastewater Treatment Plants and Marinas

It is not appropriate to base shellfish harvesting classification on fecal coliform monitoring in the vicinity of wastewater treatment plants and marinas. Chlorination of wastewater treatment plant effluent under normal plant operation provides a high degree of disinfection, yet unpredictable overflows, incomplete treatment of waste and interruption of chlorination may occur. Discharges from marine sanitation devices are of short duration; hence, collection of samples in the pollution slug is unlikely. Therefore, Prohibited buffer zones are established by calculation or hydrographic study for these types of point pollution sources. 

A buffer zone of considerable size is required to reduce to an acceptable level the two billion fecal coliform bacteria excreted by a single person in one day. Two billion fecal coliform bacteria mixed uniformly into 54 million gallons of clean water results in a fecal coliform density equal to the NSSP standard value of 14 MPN/100 ml. For a hypothetical body of water with a water depth of 5.5 feet, a 300 foot by 300 foot closure is required to dilute feces of a single person to 14 MPN/100 ml.

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