Farming Oysters, Clams and Mussels - Food & Water Watch

Farming Oysters, Clams and
Mussels
The U.S. government is currently exploring ways to boost
seafood production through aquaculture (i.e., fish farming).
Certain types of fish farms have been associated with
serious environmental, economic and cultural concerns,
including industrial-size finfish facilities in the ocean and
international coastal shrimp operations. But some methods
of shellfish 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, environmentally
concerned consumers.
Benefits of shellfish farming
Oysters, clams and mussels are collectively called “mollusks”
or “bivalves” (meaning two “doors,” i.e., shells). They
eat by filtering microscopic algae and other small particles
from the water. No added food is necessary to grow these
shellfish. Some other types of fish farms use feeds made
from small, wild fish, leaving less food for marine wildlife
and coastal communities worldwide that depend on small
fish for protein. It can take several pounds of wild fish to
grow just one pound of farmed finfish, which means we
are using up more fish than we get from farming. This is an
inefficient use of important resources, and farming mussels,
oysters and clams can avoid this overuse of wild fish.
Issue Brief • December 2010
Carefully located, welldesigned
oyster, mussel and
clam farms could help achieve
the goal of expanding U.S.
seafood production, while
also providing food for healthconscious,
environmentally
concerned consumers.
www.foodandwaterwatch.org • 1616 P St. NW, Washington, DC 20036 • info@fwwatch.org

Bivalve farms do not pollute the surrounding waters with
wasted feed, and in some cases, they may even improve
local water quality since they filter the water as they feed.
This is a valuable ecosystem service in coastal waters,
most of which are overloaded with nitrogen and various
other nutrients from land-based practices like agriculture.
1 In fact, reductions in wild populations of filter-feeding
shellfish have likely contributed to declines in water
quality in some coastal areas. 2 Clams, for instance, can
help clean waters by filtering up to two gallons of water
per hour. 3
Additionally, mussel, oyster and clam farms very rarely
use pesticides, fertilizers, antibiotics or other chemicals in
their operations. 4
Background
According to the 2005 aquaculture census, $203 million
worth of oysters, mussels and clams were produced in the
United States that year. 5
increasing demand for the sweet, tender Manila clams led
to a rapidly expanding industry for their cultivation on the
West Coast. 10 In the United States, these farms are heavily
concentrated in Washington State. 11 Manila clams are
typically served steamed. 12
Mussels
Several types of mussels are cultivated for food, the most
common of which in North America is the blue mussel
(Mytilus edulis). Mussel farming dates back to at least the
13 th century 13 and is common in Europe, where mussels
remain very popular. Despite historically lower demand
in the United States, mussels have been steadily gaining
recognition as a delicious, healthy, sustainable seafood.
The majority of mussels eaten in the United States are
currently imported from farms in Canada or New Zealand.
Mussel farms within the United States are located primarily
in New England or Washington State, with smaller
numbers of farms in California and Alaska. 14
Oysters
Oysters are the most widely cultivated of the three mollusks
in the United States. About 70 percent of oysters
grown in the United States are American cupped oysters
(Crassostrea virginica), mostly farmed in the Atlantic (especially
Massachusetts) and the Gulf of Mexico (especially
Louisiana). 6 Most of the remaining production comes
from the Pacific cupped oyster (Crassostrea gigas), native
to Japan, but grown along the Pacific coast from California
to Alaska, predominantly in Washington. 7 U.S. farms also
raise small quantities of several types of specialty oysters.
Oysters are popular raw “on the half shell” (served sitting
in one side of the shell) at seafood bars, as well as
steamed, roasted and fried.
Clams
There are many edible species of clams, but the majority
of those consumed in the United States are either
hard clams (Mercenaria mercenaria) or Manila clams
(Ruditapes philppinarum). Hard clams are native to the
East Coast of the United States. The industry has been
especially successful in Virginia and Florida, followed by
Connecticut, Massachusetts and New Jersey in production.
8 Hard clams are sold under different names depending
on their size. The smallest (and most valued) are the
“littlenecks”; slightly larger are the “topnecks” and “cherrystones.”
Clams larger than these are usually called “quahogs”
(pronounced co-hogs) or “chowder clams.” 9 Manila
clams are native to Asia, but were accidentally introduced
to North America in the early 1900s with imported “seed”
(i.e., young clams) from Japan. Starting in the 1980s,

Why Oyster, Clam and Mussel Farming Is a Good Alternative for…
Fish Farmers Consumers The Planet
• Because chemicals and feed are
not needed, there are low input
costs
• Mussels can be grown at high densities
and large-scale mortalities
from disease are rare
• There is less resistance from environmentalists
and concerned consumers
than with finfish farming
• More sustainable methods can
also be better for production and
quality (e.g. oyster floats and ropegrown
mussels)
• These shellfish are low in calories
and high in protein
• They contain high levels of
omega-3 fatty acids, vitamin C
and iron
• Consumers can feel good about
making a sustainable choice
• Compared to imported seafood,
U.S.-grown oyster, clams
and mussels will be carefully
monitored for contamination and
safety
• These “filter feeders” can improve
water quality by removing
pollutants
• They require no added feed,
meaning small, wild fish aren’t
depleted to make aquaculture
feed and there is no pollution
from uneaten feed
• Bivalve shellfish farmers rarely
use chemicals in their operations
• Native or established species
can be used, so wild populations
are not threatened
Production Methods
Oysters
Most farmed oysters are produced in a controlled hatchery
environment. After they enter a growth stage known as
a spat when they reach about the size of a pea, they are
typically transplanted to open-water (non-hatchery) locations
to grow to full size. 15 Oysters can be grown either on
or off the bottom of the seafloor. In traditional ocean-bed
culture, hatchery-grown spat are placed on pieces of dried
shell called cultch, 16 which are placed on the seafloor
near shore and covered with mesh to protect them from
natural ocean predators. They can also be grown in intertidal
areas, the region near the shoreline between the
low-water and the high-water marks. There, oysters are
exposed to the air during low tides, which helps make
collection easier and protects against predators and the
growth of fouling organisms. Raising oysters too close to
the sea bottom can create problems, however. The current
is not strong in these areas, so waste may accumulate and
sediment may interfere with feeding. 17 Collecting bottomcultured
oysters can also disrupt and damage the natural
habitat, especially if done regularly.
Alternately, cultch (with spat) can be placed inside burlap
mesh bags on trestled racks that are set up like shelves
several feet above the ocean floor. 18 This “rack” or “bag
culture” method can be slightly more expensive and requires
maintenance to ensure oysters are getting enough
oxygen, 19 but it makes for easier and more ecologically
friendly collection. Additionally, off-bottom techniques
are being developed in Maryland on the Chesapeake
Bay involving floatation devices made from PVC frames
on which these racks or bags can be placed. This can
mitigate potential negative impacts to the seafloor, and
is also thought to cause faster growth. However, growers
must be vigilant about water quality, as the oysters are
generally raised closer to land where water may be more
contaminated. 20
Clams
Clam aquaculture typically occurs in three stages: hatchery,
nursery and grow-out. Because it is generally difficult
to collect juvenile clams from the wild, clam farming on
a commercial scale requires hatcheries to produce seed. 21
Hatcheries use adult clams to produce larvae, which
remain in the hatchery until they reach about 1 millimeter
in size. 22 Next, clams are protected from predators in
a nursery until they reach about 8 to 10 millimeters in
size, which takes several months. 23 . 24 Nurseries can be
either land-based, in locations with access to seawater, or
field-based, in shallow coastal waters using some method
of predator control, like netting. For both field- and landbased
systems, circulating seawater provides the clams
with naturally occurring plankton
Finally, clams are usually grown to market size on shallow-water
coastal plots leased from the state. Clams are
placed on the bottom and covered with protective netting
or held in soft-meshed polyester bags. Once the clams
reach market size, they can be collected by hand-raking,
or in the case of “bag culture” (similar to the method
used for oysters, above), the bags can simply be lifted out
of the water. 25

Although relatively few diseases have been reported in
hard clams, there is one hard clam pathogen that has
caused problems for clam farmers north of Virginia,
known as QPX for “Quahog pathogen unknown.” 26 This
parasite is not harmful to humans, but does cause large
die-offs of infected clams. QPX is thought to infect adult
clams experiencing stressful growing conditions in highsalinity
environments. 27 The development of testing methods
for QPX has reduced the risk of spreading the disease,
but clams should be grown at reasonable densities using
local seed to minimize risks. 28
Mussels
Mussels are farmed in two basic ways: suspended culture
or bottom culture. Bottom culture usually involves collecting
native, wild juvenile mussels, called “spat” or “seed,”
often through dredging, and re-laying them over sites on
the sea bottom, at lower densities. 29 This method yields
mussels with less meat and also increases the amount of
grit, 30 which needs to be purged during processing. The
dredging can disrupt the seafloor ecosystem, causing
habitat disturbance and changes in nearby animal and
plant life. 31
More commonly (and with less disruption of the ocean
bottom), mussels are grown in suspended culture, hanging
in the water column in mesh bags or on ropes, poles or
rafts. Instead of dredging for juveniles, small, wild mussels
drifting in the water column settle on hanging collectors
— usually ropes — and are later transferred into long
mesh tubes, known as “socks” or “sleeves,” where they
are grown to market size. Typically, the sleeves are hung
from a main line held in place with anchors and buoys,
known as the “longline” system. * Mussels are collected
after 18 to 24 months, usually by a mechanized process
that does not damage the ocean bottom. 32
Where to Locate Shellfish Farms
The future success of oyster, clam and mussel farming
depends on high water quality standards and continued
frequent monitoring for potential disease and toxicity
problems in local waters. Generally, farmed shellfish are
less likely than their wild counterparts to cause paralytic
shellfish poisoning (PSP), a contaminant of great concern
to consumers. Regulations require that all shellfish farms
monitor their waters for the plankton that causes PSP. 33
Oyster and clam producers in particular must also be careful
that the number of shellfish they grow does not become
so high as to reduce oxygen levels or spread disease. There
is a built-in disincentive for farmers to grow too densely,
because this can result in the illness and/or die-off of shellfish,
which can ultimately decrease profitability. 34
Industry growth is somewhat constrained by limited suitable
places to grow shellfish. 35 Cooperation and communication
between growers, coastal residents and other
users is essential for appropriate use of shared coastal
resources.
Sites for farms should be chosen carefully to minimize
environmental impacts and conflicts with other users.
Although there have been concerns about the potential for
shellfish waste to alter the seafloor and affect the diversity
of nearby wildlife, these effects are usually minimal and
mostly avoidable when farms are sited appropriately. 36
Farms typically are not, and should never be, located over
sensitive areas or areas with high natural biodiversity. 37
Mussels have traditionally been cultivated in coastal
waters, but in recent years, water quality concerns and
increased coastal activities have led some proponents to
push for submerged offshore mussel farms. At these sites,
there are fewer conflicts for space with other users, and
the product tends to be of higher quality. 38 However,
there are still many challenges to offshore mussel farming,
including the need for improved longline technology
to withstand stronger waves, as well as increased costs
and safety risks associated with maintenance and collection.
39 Concerns over marine mammal entanglement have
*
Not to be confused with longline fishing, a fishing method in which
multiple baited hooks are suspended from a floating main line several miles
long.

led to offshore farms equipped with satellite monitoring
and ropes with built-in weak links that break away in
the event of animal interactions. 40 The absence of a good
regulatory framework for bivalve ocean aquaculture is
also problematic. 41
Although pilot projects off the coast of New England have
demonstrated the viability of offshore mussel farms, 42 the
challenges are unique and potential impacts must continually
be evaluated, especially if the operations are large
in scale.
Recommendations
1. State and federal policy regarding marine aquaculture
should take into consideration the distinctions
between bivalve farming and finfish farming. A good
example of this occurs in Alaska, where open netpen
finfish aquaculture is banned, but the permitting
process for shellfish aquaculture has been streamlined
and the regulations clarified.
2. Appropriate locations for farms should be chosen
based on careful consideration of ecological, physical
and social factors, including proximity to submerged
aquatic vegetation and potential conflicts
with other uses. 43
3. Suspended or off-bottom culture (ropes, bags, platforms,
floats) is preferable to bottom culture. Whenever
possible, collection of farmed shellfish should be
done by hand — either by pulling from bags, ropes or
floats, or via hand-raking. These methods have far les
potential for ecological harm than dredging or suction
dredging, which disrupts the seafloor environment
and can negatively affect plant and animal communities.
44
4. Large-scale operations should be approached with
caution, as potential for negative ecological impacts
may be greater with increasing scale.
5. Clam and oyster seed should be purchased from a
local hatchery whenever possible to minimize the
potential for disease transfer from hatchery to growout
waters. 45 Although wild mussel seed is often available,
collection practices should be monitored to ensure
they are sustainable.
6. Controlling the growth of algae and other unwanted
species on nets should be accomplished using only
nontoxic methods like air-drying, brine, vinegar, freshwater
or brushes. 46

Endnotes
1 Lindhal, Odd et al. “Improving marine water quality by mussel farming: a profitable
solution for Swedish society.” Ambio: A Journal of the Human Environment,
vol. 34,2005 at 131.
2 Rice, Michael. “Environmental Effects of Shellfish Aquaculture in the Northeast.”
Northeastern Regional Aquaculture Center, University of Maryland (NRAC Extension
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 Impacts
and Policy Options.” Pew Oceans Commission. 2001 at 14; Flimlin, Gef et
al. “Best Management Practices for the East Coast Shellfish Aquaculture Industry.”
East Coast Shellfish 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. Department
of Agriculture, National Agricultural Statistics Service. “2005 Census of
Aquaculture” at 63-65; Food and Agriculture Organization, Fisheries and Aquaculture
Department. Species Fact Sheet: American cupped oyster, Crassostrea virginica.
Undated. Available at www.fao.org/fishery/culturedspecies/Crassostrea_
virginica/en; information also available from conversations with oyster farming
companies 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/fishery/species/3514/en; information also available
from 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 conversations
with oyster farming companies on the East and West Coasts, conducted by
Food & Water Watch staff in July 2010
9 Hadley, Nancy and Jack Whetstone. “Hard Clam Hatchery and Nursery Production.”
(SRAC Publication No. 4301) Southern Regional Aquaculture Center.
September 2007 at 1.
10 Department of Fisheries and Oceans, Canada. “Manila Clam.” Updated April
2009. Available at: www.pac.dfo-mpo.gc.ca/science/species-especes/shellfishcoquillages/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 Programme,
Fisheries and Aquaculture Department, Food and Agriculture Organization
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 Culture
Cycle.” Page 5-7. Undated.
16 Don Webster. “Oyster Aquaculture Production” in Culture Methods, Maryland
Oyster Advisory Commission, University of Maryland. November 2007 at 10-11.
17 FAO. “Crassostrea Virginica. Fisheries ad Aquaculture Department Species Factsheet.
Available at: www.fao.org/fishery/culturedspecies/Crassostrea_virginica/en
at 5.
18 Spencer, B. E. Molluscan Shellfish Farming, Fishing News Books, 2002 at 232,
information also available from conversations with oyster farming companies on
the East and West Coasts, conducted by Food & Water Watch staff in July 2010.
19 FAO. “Crassostrea Virginica. Fisheries ad Aquaculture Department Species Factsheet.
Available at: www.fao.org/fishery/culturedspecies/Crassostrea_virginica/en
20 Don Webster. “Oyster Aquaculture Production” in Culture Methods, Maryland
Oyster Advisory Commission, University of Maryland. November 2007 at 10-11.
21 Kraeuter, J.N. “Mercenaria mercenaria.” Cultured Aquatic Species Information
Programme, Fisheries and Aquaculture Department, United Nations Food and
Agriculture Organization. 2005.
22 Hadley, Nancy and Jack Whetstone. “Hard Clam Hatchery and Nursery Production.”
(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 Production.”
(SRAC Publication No. 4301) Southern Regional Aquaculture Center.
September 2007 at 5.
25 Flimlin, Gef et al. “Best Management Practices for the East Coast Shellfish Aquaculture
Industry.” East Coast Shellfish 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.” Department
of Fisheries and Aquatic Services, Institute of Food and Agricultural Sciences,
University of Florida. October 2006 at 2.
28 Barber, Bruce. “A Guide to Bivalve Diseases for Aquaculturists in the Northeastern
U.S.” School of Marine Sciences, University of Maine. Undated at 9.
29 Goulletquer, P. “Mytilus edulis.” Cultured Aquatic Species Information Programme,
Fisheries and Aquaculture Department, Food and Agriculture Organization
of the United Nations. 2004.
30 Department of Fisheries and Oceans, Canada. “An Economic Analysis of the
Mussel Industry in Prince Edward Island.” June 2006 at 5.
31 Kaiser, M.J. et al. “Chronic fishing disturbance has changed shelf sea benthic
community structure.” Journal of Animal Ecology, vol.69. 2000 at 494, 501.
32 Department of Fisheries and Oceans, Canada. “An Economic Analysis of the
Mussel 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 also
available from conversations with oyster farming companies on the East and West
Coasts, conducted by Food & Water Watch staff in July 2010.
34 Ferreira, et al. “Management of productivity, environmental effects and profitability
of shellfish aquaculture – the Farm Aquaculture Resource Management
(FARM) model.” Aquaculture 264, April 2007. [Abstract.]
35 Kraeuter, op cit.
36 Crawford, Christine et al. “Effects of shellfish farming on the benthic environment.”
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 Department
of Marine Resources. 2008 at 7.
38 Holmyard, John. “Potential for offshore mussel culture.” Shellfish 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.
40 Paul, Walter. “An offshore mussel aquaculture experiment.” Applied Ocean Physics
and Engineering Deparment, Woods Hole Oceanographic Institution. 2000.
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 Shellfish Aquaculture
Industry.” East Coast Shellfish 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 nonprofit consumer organization that
works to ensure clean water and safe food. Food & Water Watch works with grassroots organizations
around the world to create an economically and environmentally viable future. Through
research, public and policymaker education, media and lobbying, we advocate policies that
guarantee safe, wholesome food produced in a humane and sustainable manner, and public,
rather than private, control of water resources including oceans, rivers and groundwater.
Copyright © December 2010 by Food & Water Watch. All rights reserved. This issue brief can be viewed or downloaded at www.foodandwaterwatch.org.