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An Introduction to Culturing
Oysters in Virginia
Mark W. Luckenbach,
Francis X. O’Beirn
Jake Taylor1
School of Marine Science
Virginia Institute of Marine Science
College of William and Mary
1999
1
Present address: Conservation and Repletion Division, Virginia Marine Resources Commission, Newport News, Virginia.
Acknowledgments
The ideas expressed here are the product of work conducted by the staff of the Virginia
Institute of Marine Science Aquaculture Program, largely since 1989. Mike Castagna con-
ceived of and initiated the program. Administrative support under the VIMS Dean and
Director Frank O. Perkins and his successors Dennis L. Taylor and L. Donelson Wright have
allowed the program to continue. Armistead Williams first pointed us in the right direction
and Linwood Holton, former governor of Virginia and President of Virginia’s Center for
Innovative Technology (CIT), provided not only the financial support of his agency, but
needed encouragement and enthusiasm for our program over the years. Funding support for
the program has come from state funds, Virginia’s Center for Innovative Technology,
NOAA’s National Coastal Resources Research and Development Institute and the National
Marine Fisheries Service. The Tidewater Oyster Gardeners Association contributed to the
printing costs of this brochure. We are especially indebted to Wanda Cohen and Kay
Stubblefield for editorial and production assistance, and to Sylvia Motley and Eileen Horne
for printing.
To obtain a copy of this report contact:
Nancy Lewis Wanda Cohen
Virginia Institute of Marine Science Virginia Institute of Marine Science
Eastern Shore Laboratory Publications Center
Wachapreague, VA 23480 Gloucester Point, VA 23062
Fax: (757) 787-5831 Fax: (804) 684-7573
Phone: (757) 787-5816 Phone: (804)684-7011
email: nlewis@vims.edu email: wcohen@vims.edu
2
Preface
This document is intended to respond to a growing demand for information on
intensive, off-bottom aquaculture of the eastern oyster, Crassostrea virginica, in Virginia and
neighboring coastal states. Over the past few years the number of individuals involved in
intensive oyster aquaculture in Virginia has increased dramatically, and we now estimate that
over 2000 separate off-bottom oyster culture operations are underway within the coastal
waters of Virginia. Individuals involved in this activity include non-commercial gardeners,
traditional watermen and members of the well-established hard clam aquaculture industry. In
addition to growing oysters for personal consumption and marketing, an increasing number
of individuals are participating in the activity to supply oysters for environmental restoration
projects.
This publication represents an attempt to fulfill the need for an introduction to
culturing oysters. The approach described here reflects a strategy which we have been
developing and refining over the past 10 years. It is neither complete nor exclusive. It is
directed towards the culture of C. virginica in areas where the common oyster diseases
Dermo and MSX (caused by the pathogens Perkinsus marinus and Haplosporidium nelsoni,
respectively) are endemic and it includes information for both commercial aquaculturists and
non-commercial gardeners. This publication is revised from a 1997 edition and contains new
information about the status of selective breeding programs, regulations in Virginia related to
oyster aquaculture and non-indigenous oyster species. We have also attempted in this revision
to provide a listing of more reference materials for individuals interested in further reading.
As in the past, our experiences are drawn largely from work in Virginia, but the general
strategy should be applicable in many locations from southern New Jersey south along the
U.S. Atlantic coast.
It is never quite the right time for a publication of this type. Refinements in
techniques and new lessons learned from failures are ongoing. Nevertheless, we offer this in
the hope that it will provide an outline of the major components of culturing oysters in the
region.
3
Historical Perspective During the past few decades oyster
populations in Virginia have been particu-
It is now clear that a prominent feature
larly hard hit by the sustained presence of
of the Chesapeake Bay, and other estuaries
two parasite-induced diseases (MSX
along the U.S. Atlantic coast, were large,
[caused by Haplosporidium nelsoni] and
structurally complex oyster reefs.1,2 These
Dermo [caused by Perkinsus marinus]).
reef environments not only provided
These protozoan parasites have been found
critical habitat for the survival and growth
at record high levels in recent years;
of oysters,3-5 but it is becoming increas-
Dermo has now spread to all public oyster
ingly clear that they were important habitat
beds in Virginia and accounts for 70 to
for other commercial and non-commercial
90% mortality in most.13 Clearly the
species.6-9 Additionally, the oysters and
presence of these diseases present major
other suspension feeders on these reefs
challenges to current efforts to restore wild
likely affected water quality, phytoplank-
populations of oysters and develop oyster
ton abundance and food web structure
aquaculture.
within the Bay and similar estuaries.10-12
Critical features of these reefs included
3-dimensional relief above the seabed, Diseases
interstitial space within the fabric of the Contrary to popular accounts these
reef surface and multiple year classes diseases are not caused by viruses, but
(>10) of oysters. rather by single-celled protozoa. The
The demise of Virginia’s oyster fishery causative agent of MSX is
has been over 100 years in the making. Haplosporidium nelsoni; Dermo results
The initiation of this decline had as much from infections by Perkinsus marinus.
to do with the development of the steam Neither parasite is harmful to humans and
canning process in the 1870’s as it did with no threat is posed by consuming shellfish
pollution and disease. This process made infected with either parasite. P. marinus is
possible the wholesale over exploitation endemic to the area and Dermo disease has
which ultimately led to reduction of likely afflicted oyster populations for a
populations below those capable of coping long time,14 but the origin of H. nelsoni is
with natural threats or sustaining a fishery. less certain.
The virtual elimination of natural oyster Both parasites thrive in salinities above
reef habitat and alteration of population 15‰ and exhibit lowered virulence at
structure to include only a few year classes lower salinities. Below about 10‰
fundamentally changed the nature of the H. nelsoni is eliminated from its host,
resource. while P. marinus persists at lower salini-
ties but does not reach pathogenic intensi-
4
ties. Transporting of oysters infected with been the focus of several researchers who
P. marinus from low salinity to higher have identified variations in disease
salinity (above 15‰) will generally susceptibility in natural populations.18,19
result in rapid disease progression.15-17 The widely used practice of using large,
New infections of both H. nelsoni and old (and presumably, therefore, disease
P. marinus generally occur during warmer resistant) field-collected animals as brood
months with the peak period for new stock by some hatcheries is representative
Dermo infections generally occurring in of this strategy. Problems with this ap-
August and early September in Virginia.14 proach include the unverified nature of
MSX infections can arise from May disease exposure among the brood stock
through September, yet the life cycle of H. and the uncertainty of resistance to both
nelsoni and the mode of infection remain of the major diseases.
unknown. Although observed levels of the Selective breeding programs begin
parasites in oyster tissues are reduced in with natural variation among wild popula-
the wintertime, infections are not elimi- tions and select for desired traits. For the
nated by current “normal” wintertime eastern oyster, development of dual resis-
temperatures.14 The pathology of MSX tance to both Perkinsus marinus (Dermo)
infections can be confined to local out- and Haplosporidium nelsoni (MSX) has
breaks resulting in fast acting and high been the priority. The most successful of
mortality events. Dermo infections tend to these efforts was initiated at Rutgers
be more chronic and result in high cumula- University over 35 years ago. Selected
tive mortality, the levels of which can rival lines of oysters were developed with a
that of MSX. high degree of resistance to MSX.20
These stocks initially proved to be highly
Disease Resistance and susceptible to Dermo and slow growing,21
Selective Breeding Programs but subsequent selection efforts have made
significant improvements in both of these
There is an abiding hope by many that
areas. The current oyster breeding pro-
a disease resistant oyster will someday be
gram, known as CROSBreed (Cooperative
available for both aquaculture and restora-
Regional Oyster Selective Breeding
tion of wild stocks. Research related to
program), is a multi-state cooperative
this goal has generally followed three
effort to further develop and test these
lines: (1) the search for natural strains of
oyster lines. Currently, under the direction
the native oyster which exhibit some
of the Aquaculture Genetics and Breeding
disease tolerance; (2) selective breeding
Technology Center (ABC) at VIMS, this
programs; and (3) investigations with non-
program has developed a hardy strain of
indigenous oyster species. The first has
5
oyster which exhibits good growth rates requiring a comprehensive management
and reduced susceptibility to both MSX approach as described below.
and Dermo in low to moderate salinities One final avenue for acquiring a
(approximately 10-25‰). However, the disease resistant oyster that has received
performance of this strain of oysters in attention in recent years is the use of non-
higher salinity has not yet been estab- indigenous or exotic oyster species. Exist-
lished. CROSBreed oysters have been ing data suggest that at least two other
distributed to commercial hatcheries, and oyster species, the Pacific oyster
seed from these lines may be purchased (Crassostrea gigas) and the Suminoe
from these hatcheries. As discussed below oyster (Crassostrea ariakensis) are less
in the section on Purchasing Seed and susceptible to Dermo and MSX than our
Materials, it is not advisable to publish a native oyster. It is beyond the scope of this
fixed list of seed suppliers which sell this publication to discuss all of the ecological
or any other strain–it would likely be out and legal issues surrounding the importa-
of date by the time the ink was dry. Rather, tion and use of a non-indigenous species.
we provide in the Appendix a list of We note, however, that it is illegal to
contacts within VIMS and other organiza- introduce a non-indigenous species into
tions which should between them be Virginia coastal waters without approval
knowledgeable about seed availability in of the Commissioner of Fisheries and
any given year. similar requirements apply in other coastal
It is important to note that selective states. Given the uncertain state of our
breeding is an ongoing process and that current knowledge of the ecological and
even as one generation of CROSBreed economic consequences of introducing an
oysters has been distributed to hatcheries, exotic oyster species, we think it unlikely
another generation is being developed and that such an action will be approved in the
tested. We fully expect that no one strain near term. New technologies, currently
of oyster will meet all needs and that some under development in the VIMS ABC,
day, as Dr. Standish Allen, Director of the may facilitate the production of reproduc-
ABC notes, “you will be able to purchase tively sterile exotic oyster species and
your oyster seed from a catalog, selecting speed approval of their use in aquaculture.
the seed most appropriate for your envi- Presently, however, the native oyster is the
ronment and farming practice.” Selective only game in town. Fortunately, by follow-
breeding programs are, however, unlikely ing the few simple steps in the strategy
to develop the “perfect oyster” and dis- outlined below it is generally possible to
eases likely will remain a significant issue, culture the native oyster to market size,
even in disease endemic waters.
6
Overview of the Strategy Managing around disease - The
second component of our strategy for
Growing native oysters in the presence
culturing oysters is to manage around the
of these diseases requires an integrated
diseases. One approach is to grow oysters
strategy which emphasizes (1) brood stock
in low salinity sites. Below 10‰
selection, (2) management around disease
Haplosporidium nelsoni does not persist
and (3) rapid growth to harvest size. All
and, while Perkinsus marinus can survive
too often attempts to culture oysters have
at these salinities, it does not cause mortal-
focused on just one of these components to
ity. Raising oysters throughout the entire
the exclusion of others; for instance, the
growing cycle in low salinity can be an
development of a “super” disease resistant
effective means of avoiding disease, but it
oyster or a particular containment system
results in a very watery tasting oyster
for holding oysters off the bottom.
which is generally regarded as less desir-
Brood stock selection - The foregoing
section discussed the importance of brood able. Moreover, oysters grown at some low
stock selection programs and described salinity sites are at risk of mortality from
one such program (CROSBreed). We freshets.
stress again that, while disease tolerant A temporal approach to managing
oyster lines have been developed, it is around diseases, particularly Dermo, can
unlikely that a fully disease resistant oyster be effective. June through early September
will ever be realized. A more realistic is the period within Virginia during which
scenario is that continuing small improve- new infections of P. marinus generally
ments in the disease tolerance of oyster occur and existing infections intensify.14
stocks will enhance the success of inte- By avoiding exposure to the pathogen
grated approaches to oyster culture. during the early stage of seed production,
The most important point for the oyster it is possible to limit oysters to a single
culturists with respect to brood stock disease exposure period (summer) during
selection is to ensure that seed is pur- the culture cycle. As noted above, this
chased from a hatchery which has used the level of exposure to P. marinus is gener-
best available brood stocks, by which we ally not sufficient to cause mortality in
mean oysters with a proven record of good hardy oyster stocks. Seed producers may
growth and survival in disease endemic dramatically reduce the risk of P. marinus
areas. As the evaluation of wild stocks exposure by spawning oysters in late June
from different regions and breeding pro- to early August (so that the seed do not go
grams progress, we expect that the best into overboard nurseries until the major
disease threat has passed).
available stocks will change and, as noted
above, may become site specific.
7
Box 1
F a ll S eed
1 F all Þ 1 W inter Þ 1 Sp ring Þ 1 S um m er Þ 2 F all Þ 2 W inter Þ 2 S p rin g Þ 2 S u m m er
st st st st nd nd nd nd
go od p oor good poo r goo d p oor go od poo r
g ro w th g ro w th gro w th gro w th gro w th g row th g ro w th gro w th
d isea se ex p o su re d isease exp o sure
H a rv e st H arv est
S p rin g S eed
1 S p rin g Þ 1 S u m m e r Þ 1 F a ll Þ 1 W inte r Þ 2 S p ring Þ 2 S u m m e r
st st st st nd nd
g o od poor g o od p o or g o od poor
g ro w th g ro w th g row th g ro w th g ro w th g row th
d isease exp osure d isease exp o sure
H a rv e st
Over the past 10 years we have advo- harvestable size prior to succumbing to
cated a strategy whereby oyster culturists disease. Among the many examples of
purchase fall seed. That is, oyster seed successful oyster culture in Virginia over
spawned in July or even early August and the past 10 years, have been several cases
moved to nursery facilities when the threat of alternative approaches to the fall seed
of disease exposure is reduced. This strategy. Spring seed, spawned as early as
strategy maximizes the number of growing
seasons prior to reaching two disease Box 2. Idealized growth curve for
cultured oysters using fall seed. Middle
exposure seasons (see Box 1). We define
line represents average growth at a good
growing seasons as the fall (September - growing site; upper and lower lines
November) and spring (March - May) represent excellent and poor sites,
periods during which oysters in Virginia respectively, within the expected range.
generally experience the greatest growth 100
and disease exposure seasons as June
through August. Each of these periods are, 80
Shell length (mm)
however, approximations and variations
are observed both spatially and temporally. 60
The use of fall seed is predicated on
achieving very rapid growth during the 40
first fall season (see Box 2). In our experi-
ence, failure to achieve this results in 20
small oysters (less than 35 mm) entering
the winter months and a much reduced 0
Aug Dec Apr Aug Dec Apr
likelihood that oysters will reach
8
March, has successfully been used by
Box 3 Highlights of the strategy:
numerous growers. While this approach
• Purchase disease-free seed produced
provides for fewer growing seasons prior from the best available brood stock
to two disease exposure seasons (see Box • Select a good growing site
1), it does avert the risks posed entering • Protect oysters from predators with
the winter with small oysters. We have appropriate meshes
• Keep meshes clean and unobstructed
generally observed this strategy to work at • Harvest oysters as soon as they are
sites where very high growth rates are large enough
achieved, such as the high salinity envi-
ronments of the Atlantic side of the East- floats. The principal behind this approach
ern Shore, permitting growth to harvest is that both the quantity and quality of the
size in 14 months or less. Further, some food available to the oyster is improved
individuals have had success growing when suspended in the water column.
oysters which were spawned during May Unfortunately, there are no strict guide-
or June and placed in the field during July. lines with respect to the best position in
Successful use of these summer seed the water column to place the oysters.
would appear to require a culture site with Often raising the oysters as little as 6
only modest disease exposure risk. For the inches above the bottom is sufficient to
oyster culturist it is most important to reduce the amount of suspended sediments
ensure that the seed you purchase is which they must filter and improve their
disease free at the time of the purchase growth rates, but performance is very site
and that they were produced from the best specific and depends on the bottom type,
available brood stocks. water depth and food availability. Place-
A final aspect of temporal disease ment of oysters in racks or bags in the
management is to harvest oysters before intertidal can have advantages which
they enter their second summer when P. include access to oysters, fouling control
marinus infections are likely to intensify and predator protection; however, ex-
and the oysters succumb to Dermo. It is tended exposure reduces the feeding time
better to eat a 2½ inch oyster in April than available for oysters and reduces growth
to wait a few months for it to grow larger rates. If intertidal culture sites are used,
and lose it to disease. oysters should be placed in the low inter-
Grow them fast! - The third component of tidal to reduce exposure to extremes of
the strategy is rapid growth to harvest size. heat and cold.
This has generally been achieved in off- The quantity and quality of food
bottom culture, in which oysters are available to oysters can vary considerably
suspended above the bottom in bags or between locations and is a function both of
9
the hydrodynamics at a site and the abun- the most desirable for everyone. Recently
dance of phytoplankton in the water. At a number of different modifications of this
present the best approach for an oyster system has become commercially avail-
grower with access to more than one site is able.
to experiment with different areas to The important features of any system
determine the site which affords the best for maintaining oysters in off-bottom
growth. Others confined to a single loca- culture are (1) adequate predator protec-
tion may have to evaluate different seed tion, (2) minimal flow obstruction, (3)
stocks and handling strategies in order to ease of maintenance and handling, and (4)
maximize oyster growth and survival. low cost. Additionally, it may be neces-
Oyster growth rates are also dependent sary, depending upon location, to consider
upon salinity. Below 10‰ oyster growth the impediments of navigation or aesthet-
rates are generally reduced compared to ics associated with the structures.
higher salinities; some stocks show inter- Taylor Float
mediate growth rates at salinities between The Taylor float, so called because
10 - 20‰ and highest growth rates at high much of the design and original testing
salinities, but that may be a function of was done by Jake Taylor, is constructed of
heritage. As noted above, we expect that 4 inch diameter PVC pipe and galvanized
oyster seed bred for selected salinity wire (Box 4). The float is approximately 2
regimes may be available in the near ft x 8 ft x 1 ft deep and is of sufficient size
future. to grow 1,500 to 2,000 oysters to market
size. Lightweight, schedule 20 PVC drain
Containment Systems pipe works as well as the more expensive
schedule 40 pipe. Sizes of the pipe and
A wide range of options are available
the number of fittings are shown in Box 4.
for maintaining oysters off the bottom,
The mesh cage of the float is generally
each combining advantages and disadvan-
constructed of 1 inch square, double-
tages. Published methods include the use
dipped, 16 gauge galvanized hardware
of fixed racks, floats and suspended
cloth, cut and folded as shown in the
bags—e.g. the flexible belt22 and the chub
figure. The plastic-coated form of this wire
ladder system.23 No single method will
generally sells for about 20% more than
work for everyone and no single method
the un-coated, but that is more than offset
guarantees success. Each grower must
by an extended life, especially in high
consider characteristics of the growing site
salinity sites. The wire cage is then at-
and his or her handling capabilities. We
tached to the PVC float using 14.25"
describe a particular containment system
cable ties.
below, but do not mean to imply that it is
10
Box 4. Schematic of Taylor float construction and approximate materials cost.
Materials for 1 Taylor float: Approximate Cost
[ 10' x 4' double-dipped 16 gauge vinyl coated wire, 1" x 1" squares .................................. 15.90
[ (2) 10' lengths of 4" schedule 20 gauge PVC pipe. .............................................................. 6.70
[ (4 ) 4" schedule 20 gauge PVC 90o elbows .......................................................................... 5.00
[ (20) 14 ¼" black plastic cable ties ....................................................................................... 2.70
[ 1"x 3"x 8' wood strip for lid ................................................................................................. 1.85
[ 3' x 8' filter cloth for lid ........................................................................................................ 1.00
[ Gray PVC glue & PVC cleaner ............................................................................................ 1.00
[ 24" #8 crab pot line .............................................................................................................. 0.60
[ ½" stainless steel hog rings ................................................................................................... 0.50
[ Miscellaneous ....................................................................................................................... 2.00
Total $37.25
Some tips for making floats
/ The wire is generally purchased in 100 ft rolls which may actually vary in length by several inches.
Roll out your wire first and measure the total length before cutting. That way if the roll is a little short,
you can spread those missing inches among the cuts and still get 10 floats per roll.
/ Clean and glue the pipe joints well. Water in your pipes can sink the float!
11
It is important to attach zinc bars as Virginia. One involves using plastic mesh
sacrificial anodes to this mesh to reduce in the place of galvanized. Plastic has the
corrosion and extend the life of the float. advantage of not corroding, but is more
Oyster seed which are too small to be expensive, provides less rigidity and offers
retained within the 1 inch mesh may be more surface area for fouling. The PVC
placed inside mesh bags (described below) pipe may, of course, be cut to any size to
which are then placed within the float. As fit the needs of individual culturists and
the sizes of the oysters increase, the mesh some non-commercial oyster gardeners
size of the bags should also be increased have chosen to work with half-sized
and the densities of oysters reduced. Also, Taylor floats, which are constructed by
a ½ inch mesh liner made of thin plastic reducing the longest segments of pipe
(sold as bird netting to protect fruit trees) (shown in Box 4) from 95 inches to 47.5
may be placed within the float and at- inches.
tached with cable ties. This liner is inex- Advantages of this containment system
pensive, adding only approximately $1.00 include low materials cost and sturdy
to the cost of a float. design. The open mesh of the wire float
We have investigated several lid provides limited surface area for fouling
options for this float including ¼ inch and permits good water flow. Disadvan-
thick plywood lids, wire mesh, shade cloth tages include the cumbersome size and
and no lids. Performance of different lid need for a hoist to retrieve the floats when
options varies with location and opinions they are full of oysters. Further, in some
about the best type of lid vary between locations the use of these floats may be
culturists. Lids have been found to be restricted by navigational or aesthetical
useful in restricting the growth of concerns.
macroalgae in the floats and reducing Again, we do not wish to imply by
predation by otters and seagulls. However, presenting designs for the Taylor float here
barnacle and oyster settlement may be that this is the preferred containment
greater under lids and seagulls roosting system for all growers. In fact, we expect
(with the associated problem of that this system will be replaced in the
elevated fecal coliform bacteria levels) near future by any number of improved
may be greater on floats with lids. Indi- designs. For the present, however, we
vidual culturists will need to experiment receive a large number of requests for the
with the use of lids at their site to deter- design specifications and this manual is
mine their value. intended in part to meet those requests.
Several modifications to this basic
design have been used by growers in
12
Constructing the mesh bags and liner: purchased in small quantities from some
vendors. Cut 9 ft x 3 ft sections and secure
1/16" mesh bags- Fiberglass window it to the inside of the float using cable ties.
screen can be purchased in 4 ft x 100 ft The liner should extend 6 inches up the
rolls. Cut 18-inch x 24-inch sections and sides of the float and be secured at the top
sew two panels together with monofila- with cable ties.
ment line, double stitching along three
sides. After placing oysters in the bag, seal Box 5. Side view of Taylor float.
by stapling 2 ¾ inch x 18 inch wood strips
together on the open side; adding 2 addi-
tional wood strips along the bottom of the
bag provides additional strength to the
bag.
1/8" mesh bags- Plastic mesh may be
ordered from several aquaculture supply
vendors in flat and tubular forms. The
latter are much better for constructing
bags. The standard dimensions of a roll of Purchasing Seed and
1/8 inch tubular mesh are 36 inches x 200 Materials
ft. Each roll makes about 100 24-inch x
The question most commonly posed to
18-inch bags. One end of the bag should
us is, “Where do I get seed?” Given our
be closed with ½” stainless steel hog rings,
foregoing discussion of the importance of
and the other end with cable ties.
using good quality, disease-free seed, this
is obviously a critically important ques-
3/8" mesh bags- These bags can be
tion. Unfortunately, it is impractical to
purchased individually from aquaculture
respond to that question here. Oyster seed
supply companies or rolls of tubular mesh
are sold by a number of commercial
can be purchased. Each bag measures 40
hatcheries along the U.S. Atlantic and Gulf
inches x 20 inches. The one open end can
coasts, but their availability and quality
be closed with cable ties.
can vary annually. Any list which we
might provide at the time of this writing
½” liner- Liners are constructed from
would be quickly out of date and give the
very thin mesh which is sold as bird
perception of endorsing some hatcheries
netting to protect fruit trees It generally
and excluding others. Similarly, purchas-
comes in 3000 ft x 14 ft rolls, but may be
ing materials to construct floats or other
13
containment systems can be done through culturists and gardeners start with the
a number of sources. larger seed.
The Virginia Shellfish Growers Asso- 1. Obtain required permit (see section
ciation, a trade group which represents on Regulations below).
many of the shellfish culturists in the 2. Securely moor floats in the water.
Commonwealth, counts among its mem- 3. Place 15 - 20 mm seed oysters in
bers most of the shellfish hatchery opera- 3/8" mesh bags at a density not
tors. You can contact them to get more exceeding 2500 oysters/bag and
information about seed supplies from their place no more than 2 bags/Taylor
members. Further, the private, non-profit float. [Numbers will vary in other
Chesapeake Bay Foundation is actively floats]. The best time to initiate this
involved in working with oyster culturists step is in late September after the
in Virginia and Maryland, often coordinat- greatest threat of P. marinus infec-
ing seed purchases and holding float tion has passed. Remember to
construction workshops. Finally, in Vir- start with disease-free seed from
ginia there are a number of oyster garden- good brood stock.
ing clubs which have been organized to 4. After 2 - 6 weeks, depending upon
facilitate information exchange, as well as growth rates, remove oysters from
seed and materials purchases. The appen- the bags and place into a float with
dix provides contacts or initial points of ½" mesh lining. Densities within
inquiry for contacting each of these the float should not exceed 2000
groups. animals. Alternatively, some
growers prefer to keep oysters in
Procedures @- inch mesh bags throughout
We recognize that there can be more the culture cycle. If this is done,
than a single approach to culturing oysters densities should be reduced to
in this region, but offer this basic sequence approximately 600 oysters/bag
of steps as a starting point. The steps and and 2 - 3 bags/float.
5. Over the next 6 - 18 months main-
the oyster densities are given for oyster
tain the oysters and floats in good
culture using the Taylor float, because we
are most familiar with this system, but the condition (see below) and harvest
basic approach can be followed using oysters as soon as they are large
other systems. Modifications based upon enough to eat! The oysters will
grow at varying rates and leaving
using smaller seed are outlined below in
large oysters within the float will
Box 6. We recommend that beginning
slow the growth of the remaining
14
ones. {Note: This suggestion is vary between sites and between seasons
made with Virginia growers in mind. and years at individual sites. Regular
Other states may have regulations inspection of the floats and bags is re-
regarding minimum harvest sizes quired to judge when cleaning is needed.*
for aquacultured oysters. In all The principal cause of fouling is
cases growers should abide by marine organisms which settle from the
Health Department regulations plankton and attach to the floats, bags and
regarding the certification of their oysters. Most of these organisms can be
growing waters.} removed by washing with water (fresh or
Box 6 provides a summary of the steps salt) and scrubbing with a stiff brush.
involved, including those for starting with High pressure washing is sometimes
small seed. required to remove firmly attached organ-
isms, but care must be taken when using
Box 6. Number and size of mesh bags high pressure washers not to damage small
and oysters used in a Taylor float. oysters.
2500 2-3 mm oysters/ 1/16" mesh bags; 2 In some locations the settlement of
bags/float for approximately 2-4 weeks barnacles, mussels and even oysters onto
2500 6-12 mm oysters/ 1/8" mesh bag; 2 bags/ the floats can be a particular problem,
float for approximately 2-4 weeks since these organisms are not easily
2500 15-20 mm oysters/ 3/8" mesh bag; 1 bag/ washed off. If detected early enough, these
float for approximately 2-4 weeks animals can be cleaned off using a brine
1500 -2000 20-50 mm oysters/float with ½” dip24,25 (described below in the section
mesh liner for approximately 5-8 mo. about flatworms). It is especially important
1500 -2000 50-75 mm oysters/float without that a brine dip only be used with oysters
liner for approximately 3-8 mo. greater than 5 mm, since smaller oysters
will suffer mortality from the procedure.25
Maintenance and Care Predators and Other
Maintaining an oyster garden is a little Associated Organisms
like caring for a vegetable garden. It is a
Predators ranging from flatworms to
lot easier if you stay on top of a few
river otters may be found associated with
relatively simple tasks! Analogous to
off-bottom cultured oysters, but not all
weeding a tomato patch, the bags and
floats that are holding oysters must be *If oysters are retained in bags throughout the
cleaned periodically. The frequency with grow-out period, we recommend that you flip the
bags every 2-3 weeks to remove excess sediment
which this clean-ing must be done will and re-distribute the oysters.
15
animals pose a threat to the oysters. Distin- water another hour before being placed
guishing between those organisms which back in the float.
eat or otherwise harm oysters and those Another treatment is to raise the bags
which do not is important. A complete above the low water mark so they are
accounting of the organisms associated exposed to the sun at low tide. This
with cultured oysters is beyond the scope method should kill the flatworms but not
of this document, but a few common the oysters, but is subject to variation in
examples are given below. success depending upon weather conditions.
Flatworms - The oyster leech or oyster Clam worm - This polychaete worm
flatworm, Stylocus ellipticus (formerly (Nereis succinea) is usually the most
Eustylochus ellipticus) can be a very common worm associated with cultured
significant predator on small oysters. In oysters in the region. It is generally 1 - 3
Virginia S. ellipticus generally invades cm in length, segmented and has numerous
oysters in late spring or early summer, small appendages running the length of the
though occasionally late summer infesta- body on each side. Usually light pink to
tions will occur. This animal is usually no reddish brown in color, this worm is easily
larger than 25 mm, flat and thin with spotted crawling across the shells of
irregular margins and it lacks the “centi- oysters. Fortunately, this animal does not
pede looking” appendages seen on the pose a threat to oysters and the oyster
common clam worm. It can be green, culturist need not be concerned with them.
yellowish brown, or salmon in color with a Crabs - There are a variety of crabs
whitish branching intestine that can be which may be associated with oyster
seen through the skin. Flatworms prey on cultivation and most should be viewed as
barnacles and small oysters and can be predators. The blue crab (Callinectes
devastating to a crop of cultured oysters if sapidus) is a voracious predator on oysters
left untreated. and care should be take to exclude them
The preferred treatment for flatworm from the bags and floats. Several species
infestation is a brine dip. The bags with of mud crabs (Panopeous and related
oysters should be left out of water for genera) also feed on small oysters. During
about one hour before the dipping to make mid to late summer in this region several
sure all oysters are closed. A brine solu- of these crabs, especially the blue crab,
tion is made by dissolving 25 pounds of settle out of the plankton and into bottom
salt in 10 gallons of estuarine water in a habitats. At this time the small crabs may
plastic trash can. Each bag is dipped into pass through meshes as small as ½ inch
the brine solution for five minutes with and grow rapidly to a size capable of
agitation. The bags are then left out of consuming oysters. It is important, there-
16
fore, to regularly inspect floats and bags Epifauna - Organisms that are found
and remove any crabs. attached to hard substrates (including
In high salinity environments in the oysters, mesh bags and floats) are known
area hermit crabs (genus Pagurus) are as epifauna. Many are benign and only
common. Though some of these crabs can impact the aesthetic appeal of the oysters.
grow to a size capable of eating small Others may compete with the oysters for
oysters, they generally do not pose a threat food resources and may cause a reduction
to cultured oysters and can in fact be put to in water flow (and hence food) through the
beneficial use. Small hermit crabs, those containment/culture system.
found in shells 1 - 2 cm in length, can be Barnacles are hard-shelled crustaceans.
added to the inside of 3/8 inch mesh bags They generally attach in large numbers and
to help control the fouling. They will can compete with oysters for space and
graze on small animals and plants which food. They can be eliminated by aerial
settle onto the bag and obstruct water flow. exposure if identified early enough, but
Do not add hermit crabs to bags with large individuals must be physically
smaller seed as they may consume small removed with a scraper. Care must be
oysters. taken when handling floats or oysters
Grass shrimp- Often the most common covered with barnacles as they are abra-
organisms associated with oyster floats are sive.
small grass shrimp (Paleomonetes pugio Sea Squirts (Sea Grapes) are com-
and P. vulgaris). These animals do not monly found in higher saline waters. They
pose a threat to the oysters and may be resemble grapes with siphons. They can be
ignored. eliminated by either scraping-off or aerial
Snails - In high salinity areas oyster exposure for 1-2 hrs (depending on the air
drills (Urosalpinx cinerea and Eupleura temperature).
caudata) are major predators on oysters. Hydroids are ‘algae-like’ colonial
Fortunately, they are seldom found in off- animals. They can be found in large
bottom floats or trays and the few which do numbers particularly on the surface of the
manage to invade a float are easily removed mesh bags or the float. They can result in
by hand. The common periwinkle (Littorina reduced flow into the culture structure and
littorea), which is usually observed on the can be removed by washing with freshwa-
stems of salt marsh cord grass, feeds on ter allied with scrubbing with a brush.
small fouling organisms. Adding a dozen or Aerial exposure will also result in them
so periwinkles to the inside of the bags being dried out and subsequent brushing
containing oysters will reduce the fouling will remove them.
and help keep meshes cleaner.
17
Other bivalve species in the form of growers in other states should check local
mussels and ark shells may settle on or in regulations). Rapidly grown oysters tend to
the culture systems. They pose no real have thin shells with a high meat content.
threat unless they are extremely abundant. We recommend harvesting cultured oys-
Vigilance is the key to determining their ters at relatively small sizes 2¾ - 3 inches
numbers and whether action is necessary. in shell length. This reduces crowding in
Mussels can be removed only by picking the floats and allows the remaining oysters
them from among the oysters and it’s to grow faster. Of course, for oyster
easier to remove them when they are culturists market demands will place size
small. limits on practical harvest size for oysters.
Mammals - The principal mammalian
threats to cultured oysters are river otters, Health Concerns
raccoons and humans. The first two are Oysters filter large volumes of water
generally excluded with securely fastened and thus have the capacity to concentrate
lids, fending off the latter often requires both toxins and human pathogens. Tidal
greater vigilance. waters in Virginia are classified open,
We are currently preparing a fuller seasonally restricted or closed to shellfish
description of organisms associated with harvest by the Virginia Department of
cultured oysters, including a pictorial Health. It is important to know the desig-
guide, as part of a more detailed handbook nation of your growing waters and to take
on oyster cultivation which should be care in consuming shellfish (especially
published in 2000.25 This book will also raw) from waters of unknown designation.
incorporate more details of predator and Contact the local office of the Shellfish
fouling control mechanisms. Sanitation Program within the Virginia
Department of Health for more informa-
Harvesting tion about status of water quality in your
Following the procedures outlined growing area.
above some oysters should be ready for It is possible to relay oysters from
harvest within approximately 12 months contaminated waters to clean waters prior
(fall of the second year). Oysters should be to harvest and consumption. However, a
harvested as soon as they are large enough number of specific restrictions apply.
to consume or be marketed. For the Water temperature at the time of the
gardener this is largely a matter of per- relaying must exceed 50oF (10oC) and a
sonal preference since regulations limiting minimum of 15 days in the clean water is
harvest size for wild stocks do not pertain required. Regulations guiding relaying of
to cultured oysters in Virginia (but again shellfish were originally directed towards
18
relocations of wild stocks and the entire other than Virginia before making plans to
procedure required oversight by a marine import oyster seed.
patrol officer of the Virginia Marine As noted above, cultured oysters are
Resources Commission. At the time of this exempted from fisheries management size
writing the Virginia Marine Resources restrictions; however, regulation 4VAC
Commission (VMRC) and the VA Shell- 20-720-90 requires that “any person
fish Sanitation Program are reviewing harvesting or attempting to harvest
their required procedures for relaying oysters...on the seaside of the Eastern
shellfish from contaminated to clean Shore” must first obtain a harvest permit
waters in an attempt to develop procedures from the Virginia Marine Resources
more amenable to aquaculturists. Inter- Commission. The requirement for this
ested growers in Virginia should contact permit includes aquaculture operations.
their regional office of the Shellfish The VMRC has recently developed a
Sanitation Program. general permit (#3) which authorizes the
use of riparian waters for the noncommer-
Regulations cial culture of shellfish. This permit is
intended to facilitate the development of
Most states have regulations on the
noncommercial oyster gardening and is
placement of structures in the water for
much less cumbersome than previous
aquaculture and on the importation of seed
permitting requirements. However, certain
from other states. Restrictions have been
restrictions apply concerning the size and
placed on the importation of hatchery-
location of the structures and impacts to
reared oyster seed into Virginia and Mary-
navigation and submerged aquatic vegeta-
land. In Virginia, Marine Resource Com-
tion. Interested individuals should contact
mission regulation #450-01-0102 requires
the VMRC to receive a copy of the permit
that the hatchery-reared oyster seed (shell
application.
height less than 25 mm) be accompanied
by certification from a shellfish patholo-
gist that the seed are disease free. All Economic Considerations
importation of oyster seed into Maryland It is not our goal in this brochure to pro-
from northern hatcheries is forbidden due vide a detailed economic analysis of oyster
to concerns over juvenile oyster mortality cultivation. However, there are a few
syndrome. Because these regulations are important economic considerations which
subject to change and new ones may be we would like to briefly highlight. We
promulgated, it is wise to check with the begin with a very cursory, “back of the
VMRC or appropriate agency in states envelop” estimate of the cost of produc-
19
tion. Using the ranges of cost values in wild-harvested oysters has varied greatly
Box 7, we compute that the cost of pro- for the past several years, for product
duction currently ranges between 6.5 and delivered to Virginia it has generally been
11¢ per oyster and that does not include in the neighborhood of 8-9¢ an oyster. For
such expenses as maintenance and opera- the noncommercial oyster gardener this
tion of a vessel, leases, licenses, marketing cost of production is usually not an issue.
costs and a variety of other legitimate (After all, those of us with backyard
expenses. In a forthcoming book,26 slated vegetable gardens seldom are concerned
for publication in the spring 2000, we will that it is more expensive than buying our
discuss these estimates in more detail. tomatoes from the grocery store.) For the
Additional discussion of the economics of commercial oyster culturists, however, this
culturing oysters in the mid-Atlantic production cost is a critical issue, making
region are provided in publications by it is necessary to market the oysters as a
Allen & colleagues27 and Lacey & high quality product at a premium price.
Thacker.28 At the present time, this appears to be
working well in Virginia where oyster
Box 7. Rough estimates of production culturists are generally selling oysters
costs for oysters cultured using the between 20 to 45¢ apiece.
methods described here.
2 - There is more marginal gain to be
Cost/Oyster made from marketing than from cutting
Seed 0.5¢ - 2¢ production costs. This follows directly
from the foregoing discussion and our
Materials 3¢ - 4¢
estimates of production costs. Although it
Labor 3¢ - 5¢ is common now to hear commercial oyster
culturists in Virginia proclaim “we’ve got
to cut our costs so that we can get our
In this publication we wish to make production up,” we believe that this misses
three points about the economics of cultur- two critical points. First, if our production
ing oysters using the methods which we cost estimates, which include labor at $8-
have described. 10/hr, are reasonable, then the solution to
1 - It is not cheap! With a production the labor-intensiveness of the approach is
cost which is probably around 10¢ an to hire more labor. The profit margin
oyster, it costs more to produce an oyster would seem to support this contention.
by this means than the wholesale price for The second point is that, while improve-
wild-harvested oysters from the Atlantic ments to the cost of production are surely
and Gulf coasts. Though the price for possible (perhaps they could be reduced by
20
a nickel per oyster), far greater range for provide a single set of guidelines as to
improving profit margins exist in the sales what constitutes an oyster which is too
price. After all, current variation in sales small to retain. That will vary to some
price is at least 25¢ an oyster. degree between different culture sites and
3 - Seed oysters are cheaper than other each grower must learn from experience.
production costs. This is an important Generally, we find that oysters smaller
point for both commercial and noncom- than the lower curve in Box 3 have limited
mercial oyster culturists. Since it costs chance of reaching harvest size before
more in materials and labor to grow an succumbing to disease.
oyster to harvestable size than the price of Much still remains to be done in
seed, it is a waste of money to retain improving the economics of oyster cultiva-
oysters too small to reach harvestable tion and the marketing of cultured eastern
size. In other words, buy more seed oysters. At the present time we cannot be
oysters than you need and be liberal in absolutely certain of the economic viabil-
throwing away slow growers during the ity of the approach described here. How-
cultivation cycle. We often hear growers ever, we believe that the fundamentals of
say of their runts “it doesn’t cost me the approach are sound and that it is either
anything to keep them.” Not true! In economically profitable or on the verge of
addition to labor and materials costs being so. Continued improvements in
associated with holding them, they com- culture practices and marketing techniques
pete for food with your other oysters and should improve the current economic
slow the growth of all oysters in the outlook for the practice.
system. Unfortunately, it is not possible to
21
References
1 Hargis, W.J., Jr. 1999. The evolution of the American Fisheries Society Symposium
Chesapeake oyster reef system during the 22:438-454.
Holocene Epoch. pp. 5-23, in: M.W. 7 Coen, L.D. & M.W. Luckenbach. 2000.
Luckenbach, R. Mann & J.A. Wesson Developing success criteria and goals for
(eds.), Oyster Reef Habitat Restoration: A evaluating shellfish habitat restoration:
Synopsis and Synthesis of Approaches. ecological function or resource exploita-
Virginia Institute of Marine Science Press, tion? Ecological Engineering (in press).
Gloucester Point, VA. 8 Breitburg, D.L. 1999. Are three-dimen-
2 Kennedy, V.S. & L.P. Sanford. 1999. sional structure and healthy oyster popula-
Characteristics of relatively unexploited tions the keys to an ecologically interesting
beds of Eastern Oyster, Crassosstrea and important fish community? pp. 239-
virginica, and early restoration programs. 250, in: M.W. Luckenbach, R. Mann &
pp. 25-46, in: M.W. Luckenbach, R. Mann J.A. Wesson (eds.), Oyster Reef Habitat
& J.A. Wesson (eds.), Oyster Reef Habitat Restoration: A Synopsis and Synthesis of
Restoration: A Synopsis and Synthesis of Approaches.Virginia Institute of Marine
Approaches.Virginia Institute of Marine Science Press, Gloucester Point, VA.
Science Press, Gloucester Point, VA. 9 Posey, M.H., T.D. Aplin, C.M. Powell and
3 Lenihan, H.S., C.H. Peterson & J.M. Allen. E. Townsend. 1999. Oyster reefs as habitat
1996. Does flow speed also have a direct for fish and decapods. pp. 229-237, in:
effect on growth of active suspension M.W. Luckenbach, R. Mann & J.A.
feeders: an experimental test on oysters, Wesson (eds.), Oyster Reef Habitat Resto-
Crassostrea virginica (Gmelin) . Limnol. ration: A Synopsis and Synthesis of
and Oceanogr.41:1359-1366. Approaches.Virginia Institute of Marine
4 Bartol, I., R. Mann & M.W. Luckenbach. Science Press, Gloucester Point, VA.
1999Growth and survival of oysters 10 Cloern, J.E. 1982. Does the benthos control
(Crassostrea virginica) on constructed phytoplankton biomass in South San
reefs: effects of tidal elevation and sub- Francisco Bay? Mar. Ecol. Prog. Ser.
strate depth. J. Exp. Mar. Biol. Ecol. 237: 9:191-202.
157-184. 11 Cohen, R.R.H., P.V. Dresler, E.J.P. Phillips
5 O’Beirn, F. X., M. W. Luckenbach, J. A. & R.L. Cory. 1984. The effect of the
Nestlerode, and G. M. Coates. 2000. Asiatic clam, Corbicula fluminea, on
Towards design criteria in constructed phytoplankton of the Potomac River,
oyster reefs: Oyster recruitment as a Maryland. Limnol. and Oceanogr. 29:170-
function of substrate type and tidal height. 180.
J. Shellfish Res. (in press). 12 Newell, R.I.E. 1988. Ecological changes in
6 Coen, L.D., M.W. Luckenbach & D.L. Chesapeake Bay: are they the result of
Breitburg. 1999. The role of oyster reefs as overharvesting the American oyster,
essential fish habitat: a review of current Crassostrea virginica? pp. 536-546,
knowledge and some new perspectives. in:M.P. Lynch & E.C. Krome (eds.) Under-
22
standing the Estuary: Advances in Chesa- 20 Haskin, H.H. & S.E. Ford. 1987. Breeding
peake Bay Research. Chesapeake Research for resistance in molluscs. pp. 432-441, in:
Consortium, Publication 129 CB/TRS 24/ Proceedings of the World Symposium on
88, Gloucester Point, VA. Selection, Hybridization, and Genetic
13 Andrews, J.D. 1988. Epizootiology of the Engineering in Aquaculture, Vol. II.
disease caused by the oyster pathogen Henenmann, Berlin.
Perkinsus marinus and its effects on the 21 Burreson, E. M. 1988. Effects of Perkinsus
oyster industry. Am. Fish Soc. Special Pub. marinus infection in the eastern oyster,
18:47-63. Crassostrea virginica (Gmelin, 1791): I.
14 Burreson, E.M & L.M. Ragone Calvo. Susceptibility of native and MSX-resistant
1996. Epizootiology of Perkinsus marinus stocks. J. Shellfish Res. 10:417-424.
disease of oysters in Chesapeake Bay, with 22 Creswell, L., D. Vaughn and L. Strumer.
emphasis on data since 1985. J. Shellfish 1990. Manual for the cultivation of the
Res. 15:17-34. American Oyster, Crassostrea virginica, in
15 Andrews, J.D. & S.M. Ray. 1988. Manage- Florida. Florida Department of Agriculture
ment strategies for control disease caused and Consumer Services, Tallahassee, FL.
by Perkinsus marinus. Am. Fish Soc. 23 Kemp, P.S. 1995. “Oyster Chub Ladder
Special Pub. 18:257-264. System”, NC Sea Grant project reports.
16 Ford, S.E. and H.H. Haskin 1988. Manage- 24 MacKenzie, C. L. and L. W. Shearer. 1961.
mentstrategies for MSX (Haplosporidium The effects of salt solutions of different
nelsoni) Disease in Eastern Oysters. Am. strengths on oyster enemies. Proc. Nat.
Fish Soc. Special Pub. 18:249-256. Shellfish Assoc. 50:97-104.
17 Ford, S.E. 1992. Avoiding the spread of 25 DeBrosse, G. A. and S. K. Allen, Jr. 1993.
disease in commercial culture of molluscs, Control of overset on cultured oysters using
with special reference to Perkinsus marinus brine solutions. J. Shellfish Res. 12:29-33.
(Dermo) and Haplosporidium nelsoni 26 Luckenbach, M.W. & F.X. O’Beirn. (In
(MSX). J. Shellfish Res. 11:539-546. prep) A practical guide to intensive culture
18 Bushek, D. & S.K. Allen, Jr. 1996. Host- of oysters in the mid-Atlantic, with special
parasite interactions among broadly reference to Virginia.
distributed populations of eastern oyster 27 Allen, S.K., Jr., L.G. Anderson & D. Jones.
Crassostrea virginica and the protozoan Guide to shellfish farm spreadsheet and
Perkinsus marinus. Mar. Ecol. Prog. Ser. economic analysis. New Jersey Sea Grant
139:127-141. College Program Special Publication.
19 Brown, B.L., A.J. Butt, S.W. Shelton and 28 Lacey, P.F. & S.G. Thacker. 1995.
K.T. Paynter. 1998. Growth and mortality AquaPlan. Business Planning Software for
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ulture 8:25-39.
23
Appendix I
List of contacts for further information on oyster aquaculture in Virginia and Maryland.
Permits
Virginia Marine Resources Commission (VMRC):
Habitat Management Division, Mr. Robert Neikirk (757) 247-2252, rneikirk@mrc.state.va.us
Conservation and Replenishment, Dr. James Wesson (757) 247-2121, jwesson@mrc.state.va.us
Maryland Department of Natural Resources:
Shellfish Division, Steve Minkkinen (410) 260- 8326
Water Quality
Virginia Department of Health – Division of Shellfish Sanitation (804) 786-7937
Maryland Department of the Environment, (800) 633-6101
Extension Support
Virginia Institute of Marine Science (VIMS) - Sea Grant Advisory Services
Mr. Michael Oesterling, (804) 684-7165, mike@vims.edu
Mr. Tom Gallivan (also VIMS ABC Program), (757) 787-5575, gallivan@vims.edu
University of Maryland, Sea Grant Extension Program
Dr. Don Merritt (also Center for Envir. Studies), (410) 221-847 meritt@hpl.umces.edu
Don Webster, (410) 827-8056, dw16@umail.umd.edu
Jackie Takacs, (410) 326-7356, takacs@cbl.umces.edu
NGOs
Chesapeake Bay Foundation
In Virginia: Rob Brumbaugh, (757)-622-1964, rbrumbaough@savethebay.cbf.org
In Maryland: Bill Goldsborough, bgoldsborough@savethebay.cbf.org
Stew Harris, (410) 268-8816, sharris@savethebay.cbf.org
Maryland Oyster Recovery Partnership, (410) 269-5570
Virginia Shellfish Growers Association c\o VIMS Marine Advisory Service, (804) 684-7173
Oyster Gardening Organizations
Tidewater Oyster Gardeners Associations, Jackie Partin, (804) 694-4407, jpartin@crosslink.net
Northern Neck Oyster Gardeners, Don Beard, (804) 438-6563, donbeard@rivnet.net
Southside Virginia Oyster Gardeners Association, Cliff Love, (757) 481-6449
Assateague Coastal Trust, Ron Pilling, (410) 629-1538
24
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