The Waddell Mariculture Center (WMC) is a field experiment station of the S.C. Department of Natural Resources. WMC was constructed in 1983-84 to develop propagation and farming techniques for marine and brackish water species of finfish, mollusks, crustaceans and plants. In addition to developing techniques for commercial aquaculture, the center produces juvenile fish for use in fishery management and stock evaluation by the Marine Resources Division.
Through cooperative agreements with Clemson University, University of South Carolina and the University of Charleston, opportunities and facilities are made available for graduate research while the universities provide specialized expertise in disciplines such as nutrition, genetics and engineering.
Over the past two decades, WMC has worked with a variety of species including striped bass, white bass and their hybrids, two species of sturgeon, cobia, whiting, red drum, black drum, flounder, seatrout, tilapia five species of marine shrimp, freshwater prawns, hard clams, bay scallops and oysters.
The scope of work varies widely among species, especially in response to grants from the federal government and private businesses.
Depending upon current demands, various systems can be equipped with boilers and heat exchanger, water chilling units and/or varying degrees of filtration and water sterilization. The Center also has large live-feed production areas to produce phytoplankton and zooplankton for intensive larval rearing and bivalve conditioning.
The staff includes thirteen state-supported scientists, biologists and maintenance personnel. Personnel working on grants, temporary personnel and graduate students brings the usual total staff to 20-25. On any particular day, there may also be visiting staff from the Marine Resources Research Institute (MRRI) or the universities.
Much of the South Carolina coast, particularly the southern half, is laced with vast estuaries which create several thousand miles of shoreline along a coast which is only 200 miles long.
Land adjacent to estuaries is expensive, but not unrealistic. Much land adjacent to estuaries is still used for agriculturre and silviculture. However, available tracts of land are often relatively small, perhaps 5 to 10 ha. Most accessible land adjacent to the ocean beaches is developed for recreational and residential use.
Near-shore salinities are typically about 30 ppt with progressively lower salinities up into the estuaries. Farms raising marine species may be as much as 20 miles from the coast. Annual precipitation and evaporation are 105 and 125 cm respectively.
Coastal water temperatures range from about 6 to 12°C during winter to almost 30°C in the summer. Water temperatures are generally above 20°C from mid-April through mid-October.
South Carolina has a long history of seafood production through coastal fisheries. Slowly, utilization of the fishery resources is shifting from commercial harvesting to recreational harvesting. However, the infrastructure for handling commercial quantities of seafood product is still intact. Many of the coastal aquaculture species are also harvested by local fisheries.
The WMC research and development approach can be generalized as follows: (1) adapt existing technology to the environmental and socioeconomic conditions in South Carolina, (2) perform economic and feasibility analyses and identify major constraints to increased profitability, and (3) modify the technology in response to those constraints.
With moderate land costs, land broken up into relatively small tracts, a labor force with skills in advanced agricultural mechanics, reasonable electrical rates, and generous supplies of saltwater, South Carolina is well-suited for intensive pond production technology. The creation of this intensive pond production technology for marine species has been a major research thrust at WMC.
Shrimp production technology for outdoor ponds was producing up to 2,000 kg/ha in the early 1980's when WMC began operations. The Center has been the leader in intensification of pond production technology. By using the right combination of stocking density, feeding rate, aeration rate and water exchange, production as high as 29,249 kg/ha has been demonstrated at WMC. Some commercial farms in the area now routinely target production levels of 10,000 to 15,000 kg/ha.
Shrimp farms in South Carolina import postlarvae for stocking ponds. The demand for postlarvae continues to grow (currently 40 to 50 million per year). There are increasing concerns about availability during the critical stocking season and the health status of imported stocks. Therefore, interest in developing an in-state hatchery is keen.
South Carolina is not the best location for a shrimp hatchery. Water temperatures during the prime hatchery season (February through May) are too cool. Coastal water has high turbidity due to the large expanses of saltwater marsh and the high tidal amplitude. Salinities may be too low if there is unusually high precipitation.
WMC has been working for the past several years to develop cost effective techniques to raise temperature and salinity and remove suspended solids from coastal water to make it suitable for shrimp hatchery use. In the course of development work, WMC produces postlarvae for stocking experimental growout studies and provides excess postlarvae to local shrimp farms.
In addition, technology to produce shrimp broodstock during the limited outdoor growing season and hold them in greenhouse enclosures has been devised. The first shrimp hatchery in the state is being built now. WMC will be supplying the hatchery with high health broodstock and insure that they have access to improved stocks as they become available.
Almost all the shrimp commercially produced in S.C. are Penaeus vannamei, the Pacific white shrimp. There are environmental concerns about the potential impact of escapement of this non-native species into coastal waters. Concerns are magnified if the farmed shrimp carry viruses which have not been found in the local species.
In an effort to alleviate these concerns, much effort has been expended to increase the growth rate of the native white shrimp, P. setiferus. While acceptable production has been achieved (15,000 kg/ha), growth rates are less than that of the Pacific species. However, WMC annually produces Atlantic white shrimp postlarvae for distribution to farmers who want to grow shrimp for the small, but lucrative, live bait market. Other species such as the Caribbean white shrimp P. schmitti, and the black tiger prawn, P. monodon, have also been investigated and comparisons with the Pacific blue shrimp, P. stylirostris, are underway now.
Another approach to resolution of the non-indigenous species issue has been expansion of certified healthy stocks of shrimp for distribution to hatcheries supplying South Carolina farmers. WMC is an multiplication center where high-health shrimp postlarvae from the U.S. Marine Shrimp Farming Program's nuclear breeding facility are grown to broodstock size.
Some shrimp farms target specialty oriental markets for live shrimp. Current research at WMC includes testing various methods for live shipment to reduce transportation costs.
WMC did the pioneering work on pond production of red drum. Yields as high as 24,048 kg/ha were demonstrated before emphasis was shifted away from red drum farming research. Product prices have never drawn much commercialization interest in red drum farming in South Carolina. However, WMC still produces large numbers of red drum juveniles for stock enhancement and fishery management projects.
The hybrid of the striped bass x white bass was first developed by the S.C. Wildlife and Marine Resources Department as part of its freshwater fish hatchery programs. Important recreational fisheries for hybrids stocked into lakes and reservoirs delayed legislation to allow commercialization for several years. The main impact of WMC research on hybrid production has, once again, been development of intensive pond production technology. Harvests of up to 13,640 kg/ha have been demonstrated.
Hybrid striped bass stocked in WMC ponds are spawned at the MRRI lab in Charleston, SC. Work at MRRI has focused on controlled spawning of captive broodstock and elimination of dependence on wild fish.
Striped bass raised in captivity at WMC have been the source of broodstock for the past few years. Currently, white bass are being raised from egg to broodstock size as well. In addition, several combinations of back-crosses of hybrids bred with stripers, white bass or other hybrids are being investigated.
Several species of sturgeon have been cultivated at WMC, especially the endangered shortnose sturgeon. There is interest in market production of sturgeon in other regions. However, the work at WMC was oriented towards development of propagation techniques for use in a stock enhancement program.
Other fish which were briefly cultivated include seatrout and black drum. Seatrout were found to be extremely cannibalistic at the juvenile stage and were not pursued further. Black drum appeared especially easy to reproduce (spawned in a pond) but lacked a viable market.
Currently, WMC is modifying systems and capturing broodstock to begin a flounder culture program. Mullet are being cultured as part of assessments of various polyculture combinations.
Several types of mollusks are, or have been, investigated at WMC. Promising species include hard clams, oysters and bay scallops.
MRRI and WMC have been developing clam farming techniques for many years. This research fostered a very large commercial clam aquaculture venture and several small operations.
The commercial operations use land-based hatchery and nursery facilities with growout in estuarine enclosures. Recent refinements include work on a tidal-powered floating nursery and upwelling nursery silos deployed in ponds.
Final growout of clams in ponds is being investigated as well to see if it is possible to avoid deploying equipment in the estuary all together. Clams in the first pond growout trial are reaching market size in two years at a density of one million per hectare.
Some work has been done on scallop culture in ponds. Scallops were deployed in various net enclosures. Fouling of the netting typically results in high mortality. Releasing scallops free on the pond bottom has not been attempted.
A research emphasis in the past two years has been pond growout of oysters; either as a monoculture crop or polycultured with fish or shrimp. It was found that growth may be very rapid but the oysters need to be supported off the bottom to prevent suffocation. Inexpensive support hardware has been developed and the oyster carrying capacity of ponds is being determined. It appears that the maximum acceptable density is about one million per hectare.
The possible human health risks associated with consumption of oysters grown in ponds must be addressed before the technology can be commercialized. Initial results indicate that pond oysters may be less likely to transmit pathogens to humans than oysters taken directly from the estuary.
In many respects, oysters make an excellent polyculture candidate. The dense algae blooms resulting from intensive feeding of shrimp or fish provide oyster food. The use of oysters to improve water quality from fish and shrimp ponds prior to discharge is being studied.
Oyster polyculture is but one aspect of a larger project which seeks to minimize the environmental impact of coastal aquaculture. Of particular concern is the high biochemical oxygen demand, suspended solids and nutrients of pond effluent. Several approaches to are being investigated including cleaning effluent, minimizing effluent and completely eliminating discharge.
It has been found that intensive striped bass hybrids and shrimp growout ponds can be operated with much reduced water exchange rates without affecting production. Up to 7,000 kg/ha of shrimp and 13,640 kg/ha of fish have been produced with no water exchange except for that which occurs through excessive precipitation. These production levels exceed the average commercial production goals. However, some commercial farms are now targeting higher production and ponds are typically drained at harvest.
One way to increase the production capability of no-exchange systems is through sludge management. Techniques to concentrate sludge in confined deposition areas and automatically remove it have been designed. Alternate disposal options, such as high land application to improve impoverished soil, are being investigated.
For short annual crops like shrimp, it may be possible to rejuvenate water through the fallow winter period and reuse it the next season. Harvesting techniques which do not require that the water be discharged are being developed. In addition to eliminating the harvest effluent, the pond develops a rich community of shrimp forage items through the winter; an aquatic pasture of sorts. The abundant live prey increase shrimp growth rates the following spring.
WMC continues to refine and integrate these various techniques to reduce environmental impacts. A hypothetical sustainable marine aquaculture system based on pond systems with negligible communication with the estuary is being devised. It is hoped that a prototype will be ready for testing within a few years.
WMC research also addresses engineering aspects of aquaculture such as design and maintenance of aquaculture equipment and facilities in the harsh saltwater environment. Ten years of exposure to this environment has taken its toll on WMC facilities and taught some valuable lessons as well. Of particular concern is the aeration equipment required to maintain large super-intensive production ponds.
Aeration equipment on the market is generally suited to freshwater (such as that used in the catfish industry) or very small saltwater units (such as that used in Asian shrimp farms). Specifications and operating procedures for saltwater paddlewheels in the 5 to 10 hp range are being continually refined.
Other engineering projects include sludge handling as part of the environmental impact elimination work and water filtration, water heating work as part of the shrimp hatchery technology development.
Over the past decade, roughly 90 manuscripts have been written and nearly 150 presentations made on work conducted at WMC. A publication list from which to order copies of papers is available.
In addition, WMC provides tours of the facility several times each week. Because of its location near a popular resort area, several thousand tourists from across the country find themselves being introduced to the concepts and practices of aquaculture at WMC.
The Center also has a strong technology transfer program which is integrated with the state agriculture extension services. Personalized assistance is to provided aquaculturists, or potential aquaculturists, within the state. Assistance ranges from site selection and business plan development to daily management recommendations, help with harvesting and securing markets.
The commercial aquaculture scene in South Carolina has grown and changed dramatically over the past decade. For those species discussed above, gross receipts from commercial production were negligible in 1984 but should reach $10 million per year in 1994. WMC constantly shifts its focus in response to both immediate industry concerns and the need to create new business opportunities for the future. Fortunately, the challenges seem as fresh now as they did ten years ago.