NC State Extension Publications

What Shellfish Are Grown in North Carolina, and How Are They Grown?

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Oysters and clams are the primary shellfish grown through mariculture in North Carolina (Figure 1). Aquaculture refers to the human-managed growth of aquatic species, and mariculture refers to the human-managed growth of aquatic species in marine waters. To learn more about shellfish mariculture in North Carolina, watch Careers in Mariculture produced by North Carolina Sea Grant. Those who produce shellfish through aquaculture practices are referred to as growers, “aquaculturalists,” or “mariculturalists.” Shellfish raised by mariculture are initially grown in facilities on land, known as “hatcheries,” and then raised in open estuarine waters, which are brackish. The government owns these open estuarine waters, so mariculturalists in North Carolina lease the waters from the government in order to run their operations. Additionally, under certain environmental conditions, both wild and aquacultured shellfish are susceptible to contamination, creating potential risks for those who consume shellfish. For these reasons, shellfish mariculture is highly regulated.

Oysters have a tear-drop shape. Clams are compact and rounded.

Figure 1. Two main types of shellfish are grown in North Carolina: (a) oysters and (b) clams. Growers produce them in brackish waters they lease from the government.

What Is a Shellfish Lease?

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Shellfish growers can apply for one or more leases through the NC Division of Marine Fisheries (NC DMF). Leases give shellfish growers permission to grow and harvest shellfish in a particular area of the seafloor along the North Carolina coast. There are three main types of leases (Figure 2). They are: (1) a lease to grow and harvest shellfish on top of a bed of oyster shells or rocks on the seafloor (called “shellfish bottom leases”), (2) a lease to anchor floating cages containing shellfish to the seafloor (called “water column amendment leases” or “suspended leases”), and (3) a lease to grow shellfish in cages on racks anchored into the seafloor (called “racked system leases”). The majority (60 percent) of leased acreage in North Carolina is shellfish bottom leases (Figure 2a; NC DMF 2021). Leases must follow specific standards set by the NC DMF and the National Oceanic and Atmospheric Administration, as well as other local, state, and federal agencies. These standards ensure leases are located in places that will not interfere with wild shellfish reefs, natural seagrass beds, or established recreational activities (such as swimming, paddling); and have a minimal risk of being polluted. It can take six months or more for the lease application to be investigated, and leases are limited to 1/2 acre to 10 acres. You can read more about leases in the North Carolina Shellfish Lease Program 2020 and see current leases along the North Carolina coast through the NC DMF Shellfish Leasing Application interactive tool. To apply for a lease, you must submit an application between March 1 and August 1 (as of 2021). For more information, visit the NC DMF leasing page.

Shellfish growing (a) on the bottom (b) suspended (c) in a rack

Figure 2. The three types of NC coastal shellfish leases allow shellfish to be grown (a) on top of cultch (oyster shells or rocks) on the seafloor, (b) in cages suspended from a floating buoy, and (c) in cages on racks above the seafloor.

What Is a Shellfish Growing Area?

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In North Carolina, each lease is located within a larger geographical area called a shellfish growing area. Shellfish growing areas refer to major regions of the North Carolina coast (such as the mouth of the Newport River or Bogue Sound) that are open to commercial shellfish operations. A map of shellfish growing areas along the North Carolina coast can be found on the NC DMF Shellfish Sanitation Temporary Closure Public Viewer. When harvested shellfish are brought to market, the shellfish grower must label them with their shellfish growing area identification number. This identification number can be used to trace bacterial outbreaks, should humans become sick from eating raw shellfish.

What Is a Shellfish Harvest Closure?

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By applying for and accepting the conditions of a lease, North Carolina shellfish growers have permission to grow and harvest shellfish and sell their catch commercially. This allows customers to safely enjoy oysters and clams. However, shellfish growers are subject to food safety regulations mandated by the United States Food and Drug Administration and the state of North Carolina. These regulations are required because shellfish are filter feeders — they filter seawater to obtain the nutrients they need for survival. While filtering seawater, shellfish can take up bacteria and other pathogens that are not harmful to them, but are harmful to people who enjoy eating them. For example, shellfish can take in and temporarily hold bacteria like Vibrio, Clostridium, Enterococcus, and Salmonella without experiencing any problems, but people eating shellfish containing these bacteria can get sick (Rippey 1994; Rincé et al. 2018; Leight et al. 2018).

To reduce human illness from the consumption of raw and undercooked shellfish harvested in North Carolina, the NC DMF temporarily closes shellfish growing areas after large storms. These storms flush bacteria and other pollution from the landscape into coastal waters where shellfish are harvested (Leight et al. 2016). The amount of rainfall that results in a closure varies, depending on the shellfish growing area and the history of pollution in that area. This temporary halt in harvesting is called a “shellfish harvest closure,” and once it is put into place shellfish harvesting must temporarily stop in the affected shellfish growing area for one or two weeks or longer. The NC DMF will announce closures by posting a “proclamation” on its Polluted Area Proclamations page. Consequently, these closures temporarily limit shellfish growers’ ability to harvest, and ultimately, sell their shellfish.

What Is the Process for Reopening After a Shellfish Harvest Closure?

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After a shellfish growing area is temporarily closed to harvest, the NC DMF continues to monitor the bacterial concentrations of these waters. Once water samples show the concentrations of bacteria related to human illness are below a safe level in a shellfish growing area, the temporary closure is lifted and shellfish growers can resume harvesting there.

Acknowledgments

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Special thanks to Eric Herbst, Frank Lopez, Bryan Snyder, and A.K. Leight for their helpful feedback and comments on this fact sheet.

This work is supported by grant no. 2021-67021-33451 (NRI); 2019-67021-29936 from the USDA National Institute of Food and Agriculture; and R/20-SFA-4 from NC Sea Grant.

References

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Leight, A. K., R. Hood, R. Wood, and K. Brohawn. 2016. “Climate Relationships to Fecal Bacterial Densities in Maryland Shellfish Harvest Waters.” Water Research. 89:270-281. https://doi.org/10.1016/j.watres.2015.11.055

Leight, A. K., B. C. Crump, and R. R. Hood. 2018. “Assessment of Fecal Indicator Bacteria and Potential Pathogen Co-Occurrence at a Shellfish Growing Area.” Frontiers of Microbiology. 9:384. https://doi.org/10.3389/fmicb.2018.00384

North Carolina Division of Marine Fisheries (NC DMF). 2021. “N.C. Shellfish Lease and Aquaculture Permitting Program: Table 1.” Accessed: 06 April, 2021. http://portal.ncdenr.org/web/mf/habitat/enhancement/shellfish-leases

Rincé, A. et al. 2018. “Occurrence of Bacterial Pathogens and Human Noroviruses in Shellfish-Harvesting Areas and Their Catchments in France.” Frontiers in Microbiology. 9:2443. https://doi.org/10.3389/fmicb.2018.02443

Rippey, S. 1994. “Infectious Diseases Associated with Molluscan Shellfish Consumption.” Clinical Microbiology Reviews. 7(4): 419-425.

Authors

Postdoctoral Researcher
Biological & Agricultural Engineering
Assistant Professor
Biological & Agricultural Engineering
Assistant Professor and Extension Specialist
Biological & Agricultural Engineering
Associate Professor and Director, Marine Aquaculture Research Center
Biological & Agricultural Engineering

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Publication date: April 12, 2021
AG-898

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