Shellfish Aquaculture

Commercial marine shellfish aquaculture in the U.S. is practiced to some degree in all coastal states, although the states of Washington and Louisiana lead in production.  Oysters, mussels, shrimp, and clams combined for 16,000 metric tons produced in 2005 (source: Fisheries of the United States 2006, National Marine Fisheries Service).  Although shellfish aquaculture is a minor proportion of U.S. fisheries, the economic impacts are distributed in mostly rural coastal towns.  Many shellfish operations are small, with just a handful of employees. 

Most shellfish are grown on the bottom, on long lines, racks and bags, stakes, or simply scattered on the sediment surface.  On the West Coast, most bottom culture is in intertidal areas, but the East and Gulf Coasts have more subtidal bottom culture.  Hanging culture from rafts or other floating structures is a less-common method that allows for much denser growing conditions, due to the three-dimensional structure.

Filter feeding bivalves provide many habitat benefits.  They filter up to several gallons of water per day, removing plankton and contaminants from the water column.  They also provide a three-dimensional structure ideal for invertebrates, juvenile finfish, and many other species.  The NOAA Restoration Center actively supports restoration of native shellfish, based on the habitat benefits, and has funded over a hundred shellfish restoration projects around the country.

However, there can be negative habitat impacts resulting from commercial shellfish culture, in addition to the benefits.  Mechanical harvest or maintenance of shellfish beds can disrupt benthic habitats, including submerged aquatic vegetation.  Although dredge harvest is often limited to the very surface layer of the benthos, if the tines of harrows or teeth of a dredge harvester dig too deep into the benthos, it can break up the rhizome matrix of eelgrass, making recovery difficult.  Because of potential impacts to marine resources, NOAA Fisheries is currently consulting with the Corps on NWP 48, under the Endangered Species Act and the Magnuson Fisheries Conservation and Management Act.  In addition, NOAA works with the commercial shellfish industry to develop best practices, and supported the Pacific Coast Shellfish Growers in developing their Codes of Environmental Practice.