Carefully located, well- designed oyster, mussel and clam farms could help achieve the goal of expanding U.S. seafood production, while also providing food for health- conscious, environmentally concerned consumers. The U.S. government is currently exploring ways to boost seafood production through aquaculture (i.e., sh farm- ing). Certain types of sh farms have been associated with serious environmental, economic and cultural concerns, including industrial-size nsh facilities in the ocean and international coastal shrimp operations. But some meth- ods of shellsh farming could provide an alternate means to help supplement our seafood supply . Carefully located, well-designed oyster , mussel and clam farms could help achieve the goal of expanding U.S. seafood production, while also providing food for health-conscious, environ- mentally concerned consumers. Benefts oshellfsh arming Oysters, clams and mussels are collectively called “mol- lusks” or “bivalves” (meaning two “doors,” i.e., shells). They eat by ltering microscopic algae and other small particles from the water. No added food is necessary to grow these shellsh. Some other types of sh farms use feeds made from small, wild sh, leaving less food for marine wildlife and coastal communities worldwide that depend on small sh for protein. It can take several pounds of wild sh to grow just one pound of farmed nsh, which means we are using up more sh than we get from farming. This is an inefcient use of important resources, and farming mussels, oysters and clams can avoid this overuse of wild sh. www.foodandwaterwatch.org • 1616 P St. NW, Washington, DC 20036 • [email protected]Farming Oysters, Clams and Mussels
The U.S. government is currently exploring ways to boostseafood production through aquaculture (i.e., sh farm-ing). Certain types of sh farms have been associated withserious environmental, economic and cultural concerns,including industrial-size nsh facilities in the ocean andinternational coastal shrimp operations. But some meth-
ods of shellsh farming could provide an alternate meansto help supplement our seafood supply. Carefully located,well-designed oyster, mussel and clam farms could helpachieve the goal of expanding U.S. seafood production,while also providing food for health-conscious, environ-mentally concerned consumers.
Benefts o shellfsh arming
Oysters, clams and mussels are collectively called “mol-lusks” or “bivalves” (meaning two “doors,” i.e., shells). Theyeat by ltering microscopic algae and other small particlesfrom the water. No added food is necessary to grow theseshellsh. Some other types of sh farms use feeds madefrom small, wild sh, leaving less food for marine wildlifeand coastal communities worldwide that depend on smallsh for protein. It can take several pounds of wild sh togrow just one pound of farmed nsh, which means weare using up more sh than we get from farming. This is aninefcient use of important resources, and farming mussels,oysters and clams can avoid this overuse of wild sh.
www.foodandwaterwatch.org • 1616 P St. NW, Washington, DC 20036 • [email protected]
Bivalve farms do not pollute the surrounding waters withwasted feed, and in some cases, they may even improvelocal water quality since they lter the water as they feed.This is a valuable ecosystem service in coastal waters,most of which are overloaded with nitrogen and variousother nutrients from land-based practices like agricul-ture.1 In fact, reductions in wild populations of lter-feed-ing shellsh have likely contributed to declines in waterquality in some coastal areas.2 Clams, for instance, canhelp clean waters by ltering up to two gallons of waterper hour.3
Additionally, mussel, oyster and clam farms very rarelyuse pesticides, fertilizers, antibiotics or other chemicals intheir operations.4
Background
According to the 2005 aquaculture census, $203 millionworth of oysters, mussels and clams were produced in theUnited States that year.5
Oysters
Oysters are the most widely cultivated of the three mol-lusks in the United States. About 70 percent of oystersgrown in the United States are American cupped oysters(Crassostrea virginica), mostly farmed in the Atlantic (espe-cially Massachusetts) and the Gulf of Mexico (especiallyLouisiana).6 Most of the remaining production comes
from the Pacic cupped oyster (Crassostrea gigas), nativeto Japan, but grown along the Pacic coast from Californiato Alaska, predominantly in Washington.7 U.S. farms alsoraise small quantities of several types of specialty oysters.Oysters are popular raw “on the half shell” (served sit-ting in one side of the shell) at seafood bars, as well assteamed, roasted and fried.
Clams
There are many edible species of clams, but the major-ity of those consumed in the United States are eitherhard clams (Mercenaria mercenaria) or Manila clams
(Ruditapes philppinarum). Hard clams are native to theEast Coast of the United States. The industry has beenespecially successful in Virginia and Florida, followed byConnecticut, Massachusetts and New Jersey in produc-tion.8 Hard clams are sold under different names depend-ing on their size. The smallest (and most valued) are the“littlenecks”; slightly larger are the “topnecks” and “cher-rystones.” Clams larger than these are usually called “qua-hogs” (pronounced co-hogs) or “chowder clams.”9 Manilaclams are native to Asia, but were accidentally introducedto North America in the early 1900s with imported “seed”(i.e., young clams) from Japan. Starting in the 1980s,
increasing demand for the sweet, tender Manila clams ledto a rapidly expanding industry for their cultivation on theWest Coast.10 In the United States, these farms are heav-ily concentrated in Washington State.11 Manila clams aretypically served steamed.12
Mussels
Several types of mussels are cultivated for food, the mostcommon of which in North America is the blue mussel(Mytilus edulis). Mussel farming dates back to at least the13th century13 and is common in Europe, where musselsremain very popular. Despite historically lower demandin the United States, mussels have been steadily gainingrecognition as a delicious, healthy, sustainable seafood.The majority of mussels eaten in the United States arecurrently imported from farms in Canada or New ZealandMussel farms within the United States are located primar-
ily in New England or Washington State, with smallernumbers of farms in California and Alaska.14
Most farmed oysters are produced in a controlled hatcheryenvironment. After they enter a growth stage known asa spat when they reach about the size of a pea, they aretypically transplanted to open-water (non-hatchery) loca-tions to grow to full size.15 Oysters can be grown either on
or off the bottom of the seaoor. In traditional ocean-bedculture, hatchery-grown spat are placed on pieces of driedshell called cultch,16 which are placed on the seaoornear shore and covered with mesh to protect them fromnatural ocean predators. They can also be grown in in-tertidal areas, the region near the shoreline between thelow-water and the high-water marks. There, oysters areexposed to the air during low tides, which helps makecollection easier and protects against predators and thegrowth of fouling organisms. Raising oysters too close tothe sea bottom can create problems, however. The currentis not strong in these areas, so waste may accumulate andsediment may interfere with feeding.17 Collecting bottom-cultured oysters can also disrupt and damage the naturalhabitat, especially if done regularly.
Alternately, cultch (with spat) can be placed inside burlapmesh bags on trestled racks that are set up like shelvesseveral feet above the ocean oor.18 This “rack” or “bagculture” method can be slightly more expensive and re-quires maintenance to ensure oysters are getting enoughoxygen,19 but it makes for easier and more ecologicallyfriendly collection. Additionally, off-bottom techniquesare being developed in Maryland on the Chesapeake
Bay involving oatation devices made from PVC frameson which these racks or bags can be placed. This canmitigate potential negative impacts to the seaoor, andis also thought to cause faster growth. However, growersmust be vigilant about water quality, as the oysters aregenerally raised closer to land where water may be morecontaminated.20
ClamsClam aquaculture typically occurs in three stages: hatch-ery, nursery and grow-out. Because it is generally difcultto collect juvenile clams from the wild, clam farming ona commercial scale requires hatcheries to produce seed.21 Hatcheries use adult clams to produce larvae, whichremain in the hatchery until they reach about 1 millime-ter in size.22 Next, clams are protected from predators ina nursery until they reach about 8 to 10 millimeters insize, which takes several months.23.24 Nurseries can beeither land-based, in locations with access to seawater, oreld-based, in shallow coastal waters using some method
of predator control, like netting. For both eld- and land-based systems, circulating seawater provides the clamswith naturally occurring plankton
Finally, clams are usually grown to market size on shal-low-water coastal plots leased from the state. Clams areplaced on the bottom and covered with protective nettingor held in soft-meshed polyester bags. Once the clamsreach market size, they can be collected by hand-raking,or in the case of “bag culture” (similar to the methodused for oysters, above), the bags can simply be lifted outof the water.25
Why Oyster, Clam and Mussel Farming Is a Good Alternative for…
Fish Farmers Consumers The Planet
• Because chemicals and feed arenot needed, there are low inputcosts
• Mussels can be grown at high den-sities and large-scale mortalitiesfrom disease are rare
• There is less resistance from envi-ronmentalists and concerned con-sumers than with nsh farming
• More sustainable methods canalso be better for production andquality (e.g. oyster oats and rope-
grown mussels)
• These shellsh are low in caloriesand high in protein
• They contain high levels of omega-3 fatty acids, vitamin Cand iron
• Consumers can feel good aboutmaking a sustainable choice
• Compared to imported sea-food, U.S.-grown oyster, clamsand mussels will be carefullymonitored for contamination andsafety
• These “lter feeders” can im-prove water quality by removingpollutants
• They require no added feed,meaning small, wild sh aren’t
depleted to make aquaculturefeed and there is no pollutionfrom uneaten feed
• Bivalve shellsh farmers rarelyuse chemicals in their operations
• Native or established speciescan be used, so wild populations
Although relatively few diseases have been reported inhard clams, there is one hard clam pathogen that hascaused problems for clam farmers north of Virginia,known as QPX for “Quahog pathogen unknown.”26 Thisparasite is not harmful to humans, but does cause largedie-offs of infected clams. QPX is thought to infect adult
clams experiencing stressful growing conditions in high-salinity environments.27 The development of testing meth-ods for QPX has reduced the risk of spreading the disease,but clams should be grown at reasonable densities usinglocal seed to minimize risks.28
Mussels
Mussels are farmed in two basic ways: suspended cultureor bottom culture. Bottom culture usually involves collect-ing native, wild juvenile mussels, called “spat” or “seed,”often through dredging, and re-laying them over sites onthe sea bottom, at lower densities.29 This method yieldsmussels with less meat and also increases the amount of grit,30 which needs to be purged during processing. Thedredging can disrupt the seaoor ecosystem, causinghabitat disturbance and changes in nearby animal andplant life.31
More commonly (and with less disruption of the oceanbottom), mussels are grown in suspended culture, hangingin the water column in mesh bags or on ropes, poles orrafts. Instead of dredging for juveniles, small, wild mus-sels drifting in the water column settle on hanging collec-tors — usually ropes — and are later transferred into long
mesh tubes, known as “socks” or “sleeves,” where theyare grown to market size. Typically, the sleeves are hungfrom a main line held in place with anchors and buoys,known as the “longline” system.* Mussels are collectedafter 18 to 24 months, usually by a mechanized processthat does not damage the ocean bottom.32
Where to Locate Shellfsh Farms
The future success of oyster, clam and mussel farmingdepends on high water quality standards and continuedfrequent monitoring for potential disease and toxicityproblems in local waters. Generally, farmed shellsh areless likely than their wild counterparts to cause paralyticshellsh poisoning (PSP), a contaminant of great concernto consumers. Regulations require that all shellsh farmsmonitor their waters for the plankton that causes PSP. 33
Oyster and clam producers in particular must also be care-ful that the number of shellsh they grow does not becomeso high as to reduce oxygen levels or spread disease. Thereis a built-in disincentive for farmers to grow too densely,because this can result in the illness and/or die-off of shell-sh, which can ultimately decrease protability.34
Industry growth is somewhat constrained by limited suit-able places to grow shellsh.35 Cooperation and com-munication between growers, coastal residents and otherusers is essential for appropriate use of shared coastalresources.
Sites for farms should be chosen carefully to minimizeenvironmental impacts and conicts with other users.Although there have been concerns about the potential forshellsh waste to alter the seaoor and affect the diversityof nearby wildlife, these effects are usually minimal andmostly avoidable when farms are sited appropriately.36 Farms typically are not, and should never be, located oversensitive areas or areas with high natural biodiversity.37
Mussels have traditionally been cultivated in coastalwaters, but in recent years, water quality concerns andincreased coastal activities have led some proponents topush for submerged offshore mussel farms. At these sites,there are fewer conicts for space with other users, andthe product tends to be of higher quality.38 However,there are still many challenges to offshore mussel farm-ing, including the need for improved longline technologyto withstand stronger waves, as well as increased costsand safety risks associated with maintenance and collec-tion.39 Concerns over marine mammal entanglement have
* Not to be confused with longline shing, a shing method in whichmultiple baited hooks are suspended from a oating main line several mileslong.
led to offshore farms equipped with satellite monitoringand ropes with built-in weak links that break away inthe event of animal interactions.40 The absence of a goodregulatory framework for bivalve ocean aquaculture isalso problematic.41
Although pilot projects off the coast of New England havedemonstrated the viability of offshore mussel farms,42 thechallenges are unique and potential impacts must con-tinually be evaluated, especially if the operations are largein scale.
Recommendations
1. State and federal policy regarding marine aquacul-ture should take into consideration the distinctionsbetween bivalve farming and nsh farming. A goodexample of this occurs in Alaska, where open net-
pen nsh aquaculture is banned, but the permittingprocess for shellsh aquaculture has been streamlinedand the regulations claried.
2. Appropriate locations for farms should be chosenbased on careful consideration of ecological, physi-cal and social factors, including proximity to sub-merged aquatic vegetation and potential conictswith other uses.43
3. Suspended or off-bottom culture (ropes, bags, plat-forms, oats) is preferable to bottom culture. When-ever possible, collection of farmed shellsh should bedone by hand — either by pulling from bags, ropes oroats, or via hand-raking. These methods have far lespotential for ecological harm than dredging or suction
dredging, which disrupts the seaoor environmentand can negatively affect plant and animal communi-ties.44
4. Large-scale operations should be approached withcaution, as potential for negative ecological impactsmay be greater with increasing scale.
5. Clam and oyster seed should be purchased from alocal hatchery whenever possible to minimize thepotential for disease transfer from hatchery to growoutwaters.45 Although wild mussel seed is often available,
collection practices should be monitored to ensurethey are sustainable.
6. Controlling the growth of algae and other unwantedspecies on nets should be accomplished using onlynontoxic methods like air-drying, brine, vinegar, fresh-water or brushes.46
1 Lindhal, Odd et al. “Improving marine water quality by mussel farming: a prot-able solution for Swedish society.” Ambio: A Journal of the Human Environment ,vol. 34,2005 at 131.
2 Rice, Michael. “Environmental Effects of Shellsh Aquaculture in the Northeast.”Northeastern Regional Aquaculture Center, University of Maryland (NRAC Exten-sion Fact Sheet 105-2008), 2008 at 1-2.
3 Hadley, Nancy and Loren Coen. “Hard clams: Mercenaria mercenaria, M.campechiensis.” South Carolina Department of Natural Resources. Undated at 1.Available at: www.dnr.sc.gov/cwcs/pdf/Hardclam.pdf
4 Goldberg, R.J. et al. “Marine Aquaculture in the United States: Environmental Im-pacts and Policy Options.” Pew Oceans Commission. 2001 at 14; Flimlin, Gef etal. “Best Management Practices for the East Coast Shellsh Aquaculture Industry.”East Coast Shellsh Growers Association. June 2010 at 3.
5 U.S. Department of Agriculture, National Agricultural Statistics Service. Census of Aquaculture: 2005, Volume 3, Special Studies Part 2, October 2006 at Table 855“Marketable Aquaculture Sales by Species: 2005”
6 Calculations performed by Food & Water Watch, using data from U.S. Depart-ment of Agriculture, National Agricultural Statistics Service. “2005 Census of Aquaculture” at 63-65; Food and Agriculture Organization, Fisheries and Aqua-culture Department. Species Fact Sheet: American cupped oyster, Crassostrea vir- ginica. Undated. Available at www.fao.org/shery/culturedspecies/Crassostrea_virginica/en; information also available from conversations with oyster farmingcompanies on the East and West Coasts, conducted by Food & Water Watch staff in July 2010.
7 FAO. Crossastrea gigas. Fiseries and Aquaculture Department, Species Factsheet.Available at: www.fao.org/shery/species/3514/en; information also availablefrom conversations with oyster farming companies on the East and West Coasts,conducted by Food & Water Watch staff in July 2010.
8 U.S. Department of Agriculture. National Agriculural Statistics Service. Census of Aquaculture: 2005, October 2006 at 63; information also available from conver-sations with oyster farming companies on the East and West Coasts, conducted byFood & Water Watch staff in July 2010
9 Hadley, Nancy and Jack Whetstone. “Hard Clam Hatchery and Nursery Produc-tion.” (SRAC Publication No. 4301) Southern Regional Aquaculture Center.September 2007 at 1.
10 Department of Fisheries and Oceans, Canada. “Manila Clam.” Updated April2009. Available at: www.pac.dfo-mpo.gc.ca/science/species-especes/shellsh-coquillages/clam-palourde/manila-japonaise-eng.htm.
11 U.S. Department of Agriculture. National Agriculural Statistics Service. Census of Aquaculture: 2005., October 2006 at 64.
12 Forristall, April. “Manila clams.” Seafood Business vol. 27, iss. 4. April 2008.13 Goulletquer, P. “Mytilus edulis.” Cultured Aquatic Species Information Pro-
gramme, Fisheries and Aquaculture Department, Food and Agriculture Organiza-tion of the United Nations. 2004.
14 U.S. Department of Agriculture. National Agriculural Statistics Service. Census of Aquaculture: 2005., October 2006 at 64.
15 Louisiana Sea Grant College Program. “Education on the Halfshell: Oyster Cul-ture Cycle.” Page 5-7. Undated.
16 Don Webster. “Oyster Aquaculture Production” in Culture Methods, MarylandOyster Advisory Commission, University of Maryland. November 2007 at 10-11.
17 FAO. “Crassostrea Virginica. Fisheries ad Aquaculture Department Species Fact-sheet. Available at: www.fao.org/shery/culturedspecies/Crassostrea_virginica/en at 5.
18 Spencer, B. E. Molluscan Shellsh Farming, Fishing News Books, 2002 at 232,information also available from conversations with oyster farming companies onthe East and West Coasts, conducted by Food & Water Watch staff in July 2010.
19 FAO. “Crassostrea Virginica. Fisheries ad Aquaculture Department Species Fact-sheet. Available at: www.fao.org/shery/culturedspecies/Crassostrea_virginica/en
20 Don Webster. “Oyster Aquaculture Production” in Culture Methods, MarylandOyster Advisory Commission, University of Maryland. November 2007 at 10-11.
21 Kraeuter, J.N. “Mercenaria mercenaria.” Cultured Aquatic Species InformationProgramme, Fisheries and Aquaculture Department, United Nations Food andAgriculture Organization. 2005.
22 Hadley, Nancy and Jack Whetstone. “Hard Clam Hatchery and Nursery Produc-tion.” (SRAC Publication No. 4301) Southern Regional Aquaculture Center.September 2007 at 3 and 5.
23 Whetstone, Jack et al. “Biology and Culture of the Hard Clam (Mercenaria mercenaria).” Southern Regional Aquaculture Center. August 2005 at 4.
24 Hadley, Nancy and Jack Whetstone. “Hard Clam Hatchery and Nursery Produc-tion.” (SRAC Publication No. 4301) Southern Regional Aquaculture Center.September 2007 at 5.
25 Flimlin, Gef et al. “Best Management Practices for the East Coast Shellsh Aqua-
culture Industry.” East Coast Shellsh Growers Association. June 2010 at 12-13.26 Hadley, Nancy and Loren Coen. “Hard clams: Mercenaria mercenaria, M.campechiensis.” South Carolina Department of Natural Resources. Undated at 1.Available at: www.dnr.sc.gov/cwcs/pdf/Hardclam.pdf
27 Baker, Shirley et al. “Introduction to Infectious Diseases in Hard Clams.” Depart-ment of Fisheries and Aquatic Services, Institute of Food and Agricultural Sci-ences, University of Florida. October 2006 at 2.
28 Barber, Bruce. “A Guide to Bivalve Diseases for Aquaculturists in the Northeast-ern U.S.” School of Marine Sciences, University of Maine. Undated at 9.
29 Goulletquer, P. “Mytilus edulis.” Cultured Aquatic Species Information Pro-gramme, Fisheries and Aquaculture Department, Food and Agriculture Organiza-tion of the United Nations. 2004.
30 Department of Fisheries and Oceans, Canada. “An Economic Analysis of theMussel Industry in Prince Edward Island.” June 2006 at 5.
31 Kaiser, M.J. et al. “Chronic shing disturbance has changed shelf sea benthiccommunity structure.” Journal of Animal Ecology , vol.69. 2000 at 494, 501.
32 Department of Fisheries and Oceans, Canada. “An Economic Analysis of theMussel Industry in Prince Edward Island.” June 2006 at 7 and 9.
33 Food and Drug Administration. “Appendix 5 – FDA and EPA Safety Levels in
Regulations and Guidance.” June 2001. Available at www.fda.gov/Food/Guid-anceComplianceRegulatoryInformation/GuidanceDocuments/Seafood/Fishand-FisheriesProductsHazardsandControlsGuide/ucm120108.htm; information alsoavailable from conversations with oyster farming companies on the East and WesCoasts, conducted by Food & Water Watch staff in July 2010.
34 Ferreira, et al. “Management of productivity, environmental effects and prot-ability of shellsh aquaculture – the Farm Aquaculture Resource Management(FARM) model.” Aquaculture 264, April 2007. [Abstract.]
35 Kraeuter, op cit.36 Crawford, Christine et al. “Effects of shellsh farming on the benthic environ-
ment.” Aquaculture, vol.224. 2003 at 137-139.37 Lewis, Jon and Marcy Nelson. “Investigation of the Benthic Conditions Under
Mussel-raft Farms.” Aquaculture and Environmental Section, Maine Departmentof Marine Resources. 2008 at 7.
38 Holmyard, John. “Potential for offshore mussel culture.” Shellfsh News, No.25.2008 at 19-20.
39 Hoagland, P. et al. “Business Planning Handbook for the Ocean Aquaculture of Blue Mussels.” Marine Policy Center, Woods Hole Oceanographic Institution.September 2003 at 8, 22.
41 Hoagland, P. et al. “Business Planning Handbook for the Ocean Aquaculture of Blue Mussels.” Marine Policy Center, Woods Hole Oceanographic Institution.September 2003 at 24.
42 Ibid at 8.43 Flimlin, Gef et al. “Best Management Practices for the East Coast Shellsh Aqua-
culture Industry.” East Coast Shellsh Growers Association. June 2010 at 18-20.44 Spencer, B.E. et al. “Intertidal clam harvesting: benthic community change and
recovery.” Aquaculture Research vol. 29. 1998.45 Flimlin, Op Cit, at 29.46 Flimlin, Op. Cit., at 36.
About Food & Water Watch: Food & Water Watch is a nonprot consumer organization thatworks to ensure clean water and safe food. Food & Water Watch works with grassroots organiza-tions around the world to create an economically and environmentally viable future. Throughresearch, public and policymaker education, media and lobbying, we advocate policies thatguarantee safe, wholesome food produced in a humane and sustainable manner, and public,rather than private, control of water resources including oceans, rivers and groundwater.
