Overview

Harvest

Management

Issues Related to the Commercial Fish Industry

References

Overview

Subsistence fishing for penaeid shrimp was practiced by coastal native Americans (McKenzie et al. 1981). This practice was passed on to early European settlers and remained a subsistence fishery through the Civil War. Limitations of preservation and transportation of shrimp kept the fishery from developing further than supplying local markets during the seasons when shrimp were available (McKenzie et al. 1980). During the period from the Civil War to the late 1940s, shrimp were primarily marketed as a canned product. As refrigeration and rapid transportation became more available, the emphasis shifted to fresh and frozen product. In 1880, the U.S. Bureau of Fisheries began to record landings of penaeid shrimp in the southeastern US, including South Carolina. The primary method of collecting shrimp during this period was through the use of haul seines and cast nets. In the 1890s, the otter trawl, a cone shaped net pulled behind a boat, was developed and its widespread use began between 1910 and 1920. By the late 1920s, the otter trawl, in conjunction with powered vessels, began to efficiently collect large amounts of shrimp (Commercial shrimp landings 1980-1996 ). Since the late 1950s, neither increased effort nor increased efficiency has significantly increased the overall landings of shrimp in SC. This may indicate that the maximum sustainable yield for this fishery was reached during this period (McKenzie et al. 1980).

Commercial and recreational shrimping has a long history in the ACE Basin and in South Carolina (McKenzie et al. 1980; Low et al. 1996). It is South Carolina's principle fishery, with estimated average commercial and recreational shrimp landings of 2.1 million kilograms (4.6 million pounds) per year. The long history of the use of this resource has resulted in extensive economic and social components to this fishery, with families depending on commercial shrimping for generations. The shrimping industry in the ACE Basin is of primary importance to a number of small coastal communities including Bennett's Point, Edisto Beach, and larger towns such as Beaufort. Not only important to those directly and indirectly involved in the fishery, the presence of the fishing community also contributes to the local tourism-based economy.

Commercial shrimp trawling in South Carolina occurs primarily from Winyah Bay to the Georgia border. Currently, trawling is limited to nearshore areas and some areas just inside the coastal sounds and bays. With an exception during World War II, South Carolina bays and sounds were closed to trawling until the early 1950s to minimize impacts on other recreational and commercial fisheries and to protect shrimp in nursery areas. In the mid-1950s, the Department of Natural Resources, then the Wildlife and Marine Resources Division, opened selected sounds to trawling between August 15 and December 15. Restrictions were placed on trawling in rivers and creeks to minimize the harvest of juvenile shrimp that were generally too small to be commercially valuable (Bearden et al. 1985). Penaeid shrimp use this shallow (0-10 meter), mid-range salinity (8-15 ppt) area as their primary nursery habitat. This habitat is common south of Winyah Bay, which may account for the higher abundance of shrimp in this region when compared to areas north of Winyah Bay (McKenzie et al. 1980). The southern sounds of St. Helena, Port Royal, and Calibogue are among the most productive of the South Carolina estuaries (Bearden et al. 1985).

Three species of penaeid shrimp make up the commercial shrimp fishery in South Carolina. White shrimp (Penaeus setiferus, recently renamed Litopenaeus setiferus) and brown shrimp (Penaeus aztecus, recently renamed Farfantepenaeus aztecus) constitute the bulk of the harvested crop. Pink shrimp (Penaeus duorarum, recently renamed Farfantepenaeus duorarum) is less important.

Harvest

In South Carolina, trawlers work in nearshore waters from spring to early winter. In 1996, approximately 1.5 million kilograms (3.4 million pounds) of shrimp, including both white and brown shrimp, were landed in South Carolina with an approximate market value of $12.2 million (South Carolina and Colleton County Commercial Shrimp Landings Data ). Trends in Colleton County shrimp landings are similar to yearly state-wide trends . The Marine Resources Division of the SCDNR monitors shrimp population and size, and uses these data to regulate the shrimp fishery.

Penaeid shrimp are also harvested by recreational users, primarily during the fall shrimp baiting season. Total landings, including those by trawling, recreation and aquaculture for the 1994, 1995, and 1996 seasons were approximately 2.7, 4.5, and 2.3 million kilograms ( 6, 10, 5 million pounds), respectively. Recreational landings during 1994 through 1996 ranged from 21 to 23 percent of the total harvest. In addition, there are a number of commercial aquaculture companies in the ACE Basin area (Recreational landings ). Aquaculture landings range from 8 to 19 percent of the total harvest.

Management

The Penaeid shrimp fishery is managed by the South Carolina Department of Natural Resources, Marine Resources Division through licensing and seasonal opening of the fishery. Commercial fishermen must obtain a trawlers license and a captain's license from the Office of Fisheries Management of the SCDNR. The license requires the fisherman to report landings and other fisheries data to the DNR to assist in management of the fishery.

In addition, as of 1997, the SCDNR has authority to open and close the fishery, based on monitoring activities by the DNR. Penaeid shrimp spawn offshore of the southeastern states during late winter and spring. To protect spawning stocks, commercial fishing is not allowed during this period. Trawling for white shrimp generally begins in May but may be delayed to protect spawning stocks. During especially cold winters, with low adult survivorship, opening of the season may be delayed until after brown shrimp spawn in June.

Issues Related to the Commercial Shrimp Fishery

There are a number of problems and conflicts between the shrimp industry and other resource users. These include competition for shrimp between commercial trawlers and recreational shrimp baiters, conflicts with recreational fishermen over the capture of species such as red drum and spotted seatrout, and the destruction of ecologically important live-bottom areas (Bearden et al.,1985; Whitaker pers comm).

• Changing Land Use and its Impacts in Penaeid Shrimp
  
• Competition between Commercial and Recreational Shrimping
  
• Impact of Trawling on Recreationally Important and Endangered Species
  
• Impact of Trawling on Bottom Habitats
  
• Shrimp Aquaculture Industry

Changing Land Use and its Impacts on Penaeid Shrimp
The shallow tidal marsh habitat is the primary nursery area for juvenile penaeid shrimp. This habitat has, in the past, been altered by filling, draining, dredging and other modifications (McKenzie et al. 1981). Although current regulations provide better protection to wetland areas, the upland areas adjacent to the tidal marsh habitats are still subjected to land uses that may have an impact on shrimp resources (Turner 1977). Alterations to these upland areas, such as increase in the amount of impervious surface, agriculture and silviculture practices, or land clearing may increase the volume of surface water that runs off the land by reducing the storage capacity and retention time for rainwater. The resulting impact to nearby tidal marshes is larger salinity fluctuations, which may reduce the quality of the habitat for penaeid shrimp. This may, in turn, result in reduced abundance due to direct mortality, or movement to other habitats that may be less productive due to increased predation or reduced food supplies.

An additional impact associated with agricultural and urban development is the input of pesticides and other contaminants. Scott et al. (1994) have studied the impacts of pesticides on grass shrimp populations in tidal creeks that have agricultural inputs. Many of the pesticides which are used to kill or inhibit insects (arthropods ), are likely to have a similar impact on non-target arthropod species such as shrimp, that utilize the creeks as nursery areas.

Competition Between Commercial and Recreational Shrimping
During the fall, recreational shrimp baiting occurs from early or mid-September to mid-November (Low et al. 1996). (See related section: Recreational Fisheries: Saltwater Fisheries). During the two-month season, landings by recreational baiters may account for up to half of the shrimp landed during this period. Shrimp baiting may affect commercial fishermen by removing shrimp from the population, therefore reducing the size of the population of shrimp available to commercial trawlers. Because the areas fished inside the estuary by recreational shrimp baiters are closed to commercial operations, commercial fishermen may face some increased effort and cost to harvest shrimp. However, commercial landings have not shown a decrease in landings over the last ten years, during which recreational shrimp baiting has increased. Commercial trawling efforts have little direct affect on recreational shrimping because shrimp in areas open to trawling are unavailable to recreational gear types (primarily cast netting from small boats).

Impact of Trawling on Recreationally Important and Endangered Species
A common concern of recreational fishermen is the mortality of recreationally important species in commercial trawls. Studies conducted by the SCDNR, Marine Resources Division indicate that most of the species of concern are caught in low numbers in trawls (Keiser 1976; Whitaker et al. 1989). The comparatively low abundance of red drum, spotted seatrout, Spanish and king mackerel, and cobia on shrimp trawling grounds and their ability to avoid the trawl nets, result in low catch rates for these species. Two species, spot, Leiostomus xanthurus and croaker, Micropogonias undulatus can be caught in large numbers. For these more abundant species, the required use of bycatch reduction devices (BRD) has significantly reduced their incidental catch in trawls (Delancey, L.D., pers comm).

Endangered species such as the green turtle, Kemp's Ridley, and the threatened loggerhead sea turtle are a seasonal problem. These species are common during the warmer months and are regularly caught by commercial trawlers. The placing of turtle excluder devices (TED) and reducing the tow time have reduced turtle mortality (McKenzie et al. 1981; Crowder et al. 1995). (See related section: Endangered Species.)

Impact of Trawling on Bottom Habitats
Within the ACE Basin, the primary habitats utilized by adult white and brown shrimp are composed of mud, sand, and washed shell. These primarily soft-bottom habitats support epifaunal and infaunal communities composed of shrimp, crabs, clams, worms, and other small invertebrates. Unlike "live bottom" areas, the communities in soft-bottom habitats seem to be less heavily impacted by short term trawling activity (Van Dolah et al. 1991). A comparison of the abundance and diversity of the benthic communities in four areas (two control, two experimental) in St. Helena and Port Royal sounds indicated few impacts that could be linked to trawling activities over a five-month period.

The Shrimp Aquaculture Industry
In addition to the commercial shrimp trawl fishery, there are a number of commercial companies raising shrimp in impoundments and ponds in South Carolina, with a few companies in the ACE Basin (Hopkins 1991). Aquaculture has contributed between 6% and 24% of the total shrimp harvest in South Carolina from 1994 to 1997 (Comparison of Wild and Aquaculture Shrimp Harvesting ). Recent difficulties with shrimp viruses reduced the aquaculture harvest by 50 to 70% during 1996 and 1997.

Extensive vs Intensive Aquaculture
Aquaculture methods include a low density or "extensive" form of culture, where larval shrimp are recruited from the wild by flooding estuarine impoundments during peak periods of larval abundance. Additionally, growers may stock these impoundments with low densities of hatchery-reared shrimp. These operations generally involve minimal equipment and time, depending primarily on natural processes to provide food and adequate water to the growing shrimp. Yields of 500 to 1000 kilograms per hectare (445-890 pounds/acre) are often achieved using these methods. In contrast, intensive mariculture operations require stocking ponds at a high density, providing high quality feed, and maintaining water quality by mechanical mixing of the water and water changes throughout the growing season. Using these methods, yields can be increased to over 6,000 kilograms per hectare (5300 pounds/acre) (Stokes, A. pers. comm.).

Intensive mariculture operations in the ACE Basin are based primarily on an exotic species of shrimp, the Pacific white shrimp (Penaeus vannamei) that is related to the native white, brown, and pink shrimp. Pacific white shrimp grow to a larger size at faster rates and are more disease resistant in culture conditions than the local shrimp species.

Escapement of Non-indigenous Shrimp Species
Of concern to resource managers in South Carolina is the escapement of exotic shrimp species (Wenner and Knott 1992; DeVoe 1992). Concerns center around the possibility of P. vannamei escaping from aquaculture ponds and establishing viable populations in the South Eastern Atlantic. Individuals of this species sometimes escape during the growing season as evidenced by occasional catches in the commercial shrimp trawl fishery (Wenner and Knott 1992). To establish a viable population, this species would have to survive the winter water temperatures, reach sexual maturity, successfully spawn, and the larvae and juveniles would have to find appropriate nursery areas and grow to repeat the cycle. It is unknown at this point if the environmental conditions in South Carolina would support this species. Further research is needed to evaluate the potential for these species to establish populations in this region.

Shrimp Viruses in Aquaculture
One of the issues associated with the importation of exotic species is the possible introduction of diseases into local populations of native shrimp. While the aquaculture industry has attempted to control disease outbreaks in ponds, a number of viruses have become prevalent throughout the shrimp aquaculture industry worldwide. These viruses tend to be difficult to identify, and vary widely in their impact on the host organism. Aquaculture research programs on a local and worldwide scale have been concerned about the effects of viruses on aquaculture operations and on wild stocks of shrimp (Hopkins et al. 1995; Overstreet et al. 1997). The extremely high density in which the shrimp are maintained is conducive to the spread of the disease within the ponds due to close contact, high inoculations of viral particles, and healthy shrimp feeding on sick or dead shrimp (Browdy and Holland, in press). Viral infections with Taura Syndrome Virus (TSV) and White Spot Virus (WSV) in shrimp ponds in the ACE Basin area were the primary causes of the large losses during 1996 and 1997.

The impacts to wild shrimp populations are less clear. The local penaeid shrimp, Penaeus setiferus, has been shown to be susceptible to TSV in laboratory situations (Overstreet et al. 1997). However, there is limited evidence of local wild populations being affected by diseases introduced by aquacultural practices. The limited research on the effects of introduced parasites and diseases on endemic populations of shrimp does not provide a clear indication of the risks involved to wild shrimp populations. In addition to the possibility of introducing viruses through aquaculture, other possible sources of infection include fresh and frozen shrimp imported for the food and bait industries (Browdy and Holland in press), and the release of ballast water from large ships (Carlton 1992). The Marine Resources Division of the SCDNR continues to monitor the quality and status of shrimp farming and the importation of non-endemic species in South Carolina through research and permitting activities.

Author

G. Riekerk, SCDNR Marine Resources Research Institute

References

Bearden, C., R. Low, R. Rhodes, R. Van Dolah, C. Wenner, E. Wenner, D. Whitaker. 1985. A review and analysis of commercial shrimp trawling in the sounds and bays of South Carolina. SC Wildlife and Marine Resources Department Technical Report No. 61.

Browdy, C. L. and A. F. Holland. in press. Shrimp virus risk management: A South Carolina Case Study. Aquatic Nuisance Species Digest.

Carlton, J. A. 1992. Marine species introductions by ships' ballast water: An overview. In: M. R. DeVoe (ed.). Introductions and transfers of marine species. South Carolina Sea Grant Consortium, Charleston, SC.

Crowder, L. B., S. R. Hopkins-Murphy, and J. A. Royle. 1995. Effects of turtle excluder devices (TEDs) on loggerhead sea turtle strandings with implications for conservation. Copeia 4:773-779.

Delancy, L. D. 1997. pers. comm. South Carolina Department of Natural Resources, Marine Resources Division, Charleston, SC.

DeVoe, H. R. (ed.). 1992. Introductions and transfers of marine species. South Carolina Sea Grant Consortium, Charleston, SC.

Hopkins, J. S. 1991. Status and history of marine and freshwater shrimp farming in South Carolina and Florida. p. 17-35. In: P. A. Sandifer (ed.). Shrimp culture in North America and the Caribbean. World Aquaculture Society. Baton Rouge, LA.

Hopkins, J. S., P. A. Sandifer and C. L. Browdy. 1995. Effect of two protein levels and feed rate combinations on water quality and production of intensive shrimp ponds operated without water exchange. Journal of the World Aquaculture Society 26: 93-97.

Keiser, R. K. 1976. Species composition, magnitude and utilization of the incidental catch of the South Carolina shrimp fishery. South Carolina Marine Research Center Technical Report No. 16.

Low, R. A., C. W. Waltz, and D. B. Stone III. 1996. South Carolina marine recreational fishery survey, 1995. Marine Resources Division, Office of Fisheries Management Data Report No. 24:58.

McKenzie, M. D. (ed). 1981. Profile of the penaeid shrimp fishery in the South Atlantic. South Atlantic Fisheries Management Council, Charleston, South Carolina.

McKenzie, M. D., J. V. Miglarese, B. S. Anderson, and L. A. Barclay, (eds.). 1980. Ecological characterization of the Sea Island region of South Carolina and Georgia. Vol. II: Socioeconomic features of the characterization area. U.S. Fish and Wildlife service, Office of Biological Services, Washington, DC. FWS/OBS-79/41.

Overstreet, R. M., D. V. Lightner, K. W. Hasson, S. McIlwain, and J. M. Lotz. 1997. Susceptibility to Taura Syndrome Virus of some penaeid shrimp species native to the Gulf of Mexico and the southeastern United States. Journal of Invertebrate Pathology 69:164-176.

Scott, G. I., M. H. Fulton, D. W. Moore, G. T. Chandler, P. B. Key, T. W. Hampton, J. M. Marcus, K. L. Jackson, D. S. Baughman, A. H. Trim, L. Williams, C. J. Louden, and E. R. Patterson. 1994. Agricultural insecticide runoff effects on estuarine organisms: correlating laboratory and field toxicity testing, ecophysiology assays, and ecotoxicological biomonitoring. Report EPA/600/R-94/004; Report PB94-160678. University of South Carolina, School of Public Health, Columbia, SC.

Stokes, A. 1997. pers. comm. South Carolina Department of Natural Resources, Marine Resources Division, Bluffton, SC.

Turner, R. E. 1977. Intertidal vegetation and commercial yield of penaeid shrimp. Transactions of the American Fisheries Society 106:411-415.

Van Dolah, R., P. H. Wendt, and M. V. Levisen. 1991. A study of the effects of shrimp trawling on benthic communities in two South Carolina sounds. Fisheries Research 12:139-156.

Wenner, E. L. and D. M. Knott. 1992. Occurrence of Pacific white shrimp, Penaeus vannamei, in coastal waters of South Carolina. In: H. R. DeVoe (ed.). Introductions and transfers of marine species. South Carolina Sea Grant Consortium, Charleston, SC.

Whitaker, J. D., L. D. Delancey, and J. E. Jenkins. 1989. A study of the experimental closure of South Carolina's sounds and bays to commercial trawling. Technical Report No. 72. SC Wildlife and Marine Resources Department, Charleston, SC.

Whitaker, J. D. 1997. pers. comm. South Carolina Department of Natural Resources, Marine Resources Division, Charleston, SC.

Perez-Farfante, I. and B. F. Kensley. 1997. Penaeoid and sergestoid shrimps and prawns of the world: Keys and diagnoses for the Families and Genera. Memoirs of the Museum of Natural History 175:1-233.