Different systems are used during different phases of the clam’s life. There are three phases involved in farming hard clams: 1) the hatchery phase, 2) the nursery phase, and 3) growout. In the hatchery phase broodstock is induced to spawn, fertilization occurs, and larvae are allowed to grow until they reach the pediveliger stage. Tanks are typically used during the hatchery period. (Lorio and Malone 1995; Kraeuter and Castagna 2001). These can be flow-through, recirculating, or semi-recirculating. Raceway culture can be used briefly during the nursery stage after clam seed leave the hatchery but before they are placed in the field for growout (Kraeuter and Castagna 2001). However, raceways are only used temporarily, depend on saltwater, and have gentle flows (HBOI 2004), therefore having little environmental impact. Floating nursery trays can be used in the nursery stage as well (Lorio and Malone 1995). The trays have a continuous water flow, which can be a horizontal or an upward flow (Kraeuter and Castagna 2001). Once the clams reach about 12 mm, they are ready for planting. Hard clams are almost exclusively raised on bottom, in muddy/sandy substrate (Kraeuter and Castagna 2001). The clams are covered in sediment, with protective mesh covering on top. Recently, some farmers in Florida and Georgia have been growing out their Hard clams in a “soft bag,” which is a pillow-like container constructed of nylon mesh material (HBOI 2004; Kraeuter and Castagna 2001). Outside of Florida, this remains a relatively uncommon practice as growth to market size seems to be stunted (Kraeuter and Castagna 2001).

Grow-out densities are approximately 50 to 75 seed clams (7 to 15 mm) per square foot (Lorio and Malone 1995), although density can be as high as 150 per square foot according to Kraeuter and Castagna (2001). If the clams are not growing quickly, farmers will clear some out to lower density (Kraeuter and Castagna 2001). There have been no density-related problems in Hard clam aquaculture operations.

Controls on farm locations vary by state, region, and often by locality. Some of the permitting agencies include: the State Division of Fish and Wildlife in Rhode Island, The Division of Marine Fisheries in Massachusetts, the State Department of Agriculture’s Aquaculture Division in Connecticut, and the Department of Environmental Conservation (DEC) in New York. In most areas, it appears that it is often difficult to obtain submerged lands leases. For example, in Florida, submerged land leases are available only in areas where other resources are absent, such as sea grasses, reefs and wild shellfish beds that are of economic importance (HBOI 2004).

No feed is used during the bulk of the animal's life. Some algae may be added to seawater during the hatchery stage (Lorio and Malone 1995). In one method the algae is raised in the hatchery by filtering seawater and then warming it to create an algal bloom. In another method, unicellular algal cultures are reared and added to the clam water at .5-1 L per 50 clams per day at 10x10^5 cells/mL. The preferred alga is the Tahitian Isochrysis. (Kreeuter and Castagna 2001)

No feed is used.

No feed is used.

No feed is used.

Treatment of effluent is not necessary because supplemental feed is not used to farm hard clams (Kraeuter and Castagna 2001).

Clams improve water quality by filtering out algae and other plankton, reducing levels of nitrogen, phosphorous, other nutrients and suspended solids (Downey, pers. comm. 2004).

Antibiotics may be used during the short nursery stage, but are not used throughout most of the animal's life (Lorio and Malone 1995). This is primarily a research practice, and is rarely used in commercial production (Kraeuter, pers. comm. 2004).

No controls are necessary for effluent from hard clam operations. However, water quality for growout areas is monitored by the National Shellfish Sanitation Program and local agencies, and contamination from PSP or bacterial outbreak leads to area closures (Downey, pers. comm. 2004).

Farming this species does not create waste.

The hard clams that are available in the U.S. market are all raised within the species native range, predominantly from Massachusetts to Florida. While introductions have occurred on the West coast and in Europe, they have not been commercially successful. There are major hard clam farming operations in Taiwan, but these clams do not enter the U.S. market (Kraeuter and Castagna 2001). However, "escape" is common in clams, as they are broadcast spawners that are mature at one to two years of age (NYSC 2002). "Escape" via broadcast spawning may help to repopulate natural beds that have been impacted by overfishing and/or disease though.

QPX (Quahog Parasite Unidentified) is a disease that effects Hard clams in the northeastern states. It was first discovered in New Brunswick in 1969, and has since appeared in populations throughout the northeast. There have been no outbreaks south of Virginia. QPX infects farmed clam beds generally about a year after planting. When seed from a southern state (i.e., Florida, North Carolina) is moved to the north, the clams are far more susceptible to the disease than clams grown from seed that originates from the north. Scientists speculate that this is because the disease does not exist in the south, and therefore the clams have not built up resistance to it. It remains unknown what the infection source is. QPX is not found in hatcheries, indicating that the source is in the wild, and that the disease is transmitted from wild populations to farmed populations. Outbreaks in farmed populations do not seem to amplify the disease in wild populations (Kraeuter, pers. comm. 2004).

Hard clams are also affected by the ubiquitous Vibrio spp., which can lead to clam fatalities. Vibrio infections can be treated with antibiotics, but states caution against this because of increased resistance to the antibiotics. The best way to combat Vibrio in hatcheries is to improve cleanliness (Kraeuter and Castagna 2001). Hatcheries only monitor their seed for disease if they are to be shipped to another state, so there is no assurance that contaminated seed will not be planted, nor is there any way to prevent the spread of the disease from farms once the clams are planted.

This farmed species is a native mollusk in most areas where it is raised. In most places where it has been introduced, the introductions have not been invasive, leading only to small, localized populations which are not of commercial significance (Kraeuter and Castagna 2001).

As wild populations have been somewhat decimated, planted clams do not compete with wild populations, but complement them, and since the broodstock is not genetically different than the wild populations, the planted clams are unlikely to compromise genetic integrity (Shumway, pers. comm. 2004).

The National Shellfish Sanitation Program (NSSP) coordinates water quality standards and the transfer of shellfish between states. Water quality regulation is necessary to ensure that the market product is not harmful to human health. Monitoring interstate shellfish transfers is important in preventing the spread of disease and invasive species between different locales. When the NSSP was created in 1988, many areas were immediately closed for harvest due to water quality problems, such as parts of Cape Cod. State and local agencies responsible for fisheries management (including the State Division of Fish and Wildlife in Rhode Island, The Division of Marine Fisheries in Massachusetts, the State Department of Agriculture’s Aquaculture Division in Connecticut, and the Department of Environmental Conservation (DEC) in New York) must comply with NSSP regulations (Kraeuter and Castagna 2001). These agencies are responsible for issuing permits, overseeing leasing of beds, exercising control over uncertified areas, monitoring water quality and classifying areas along NSSP guidelines.

Hard clam farms occur in intertidal and subtidal zones of bays and other protected areas.

Hard clam dredging may occur, depending on state regulations. Dredging appears to be a less frequent harvesting method then tonging or raking the area for clams; where dredging occurs it is probably over a limited area. Rake types commonly used to harvest Hard clams include the bullrake, shinnicock rake or oversized clam rake (Kraeuter and Castagna 2001). Dredging does not occur when clams are raised in trays (Lorio and Malone 1995; SRAC 1995). Since dredging appears to be very limited, points were not subtracted here.

Hard clam farms in the United States generally improve water quality by reducing the potential for eutrophication and helping the recovery of wild stocks. In addition, clam farms provide enhance habitat structure. The mesh nets that are used to protect the clams become a substrate for macro-algal and other fouling communities, and thus act like a low lying reef and become home for many additional species. The presence of the mesh may also stabilize the bottom, thereby enhancing the area for reestablishment of submerged aquatic vegetation (Kraeuter, pers. comm. 2004).

Hard clam farms generally use nets as predator deterrents. A commonly used net is made of light density polyethylene, and is secured to the ground by laying heavy tubing around the edges or burying the edges under the substrate. These nets need to be checked regularly to ensure that they remain sealed. (Kraeuter and Castagna 2001) These nets are not known to harm or kill wildlife (Shumway, pers. comm. 2004).

Seeds come exclusively from hatcheries.