Oyster Aquaculture
Technology Series
AGNR-EM-11-01
Production Systems
“Economy,
Employment,
Environment”
Don Webster and Don Meritt
University of Maryland
This publication was developed
through the “Oyster Aquaculture
Education and Training Program
Project 2A”, funded by the
Maryland Department of Natural
Resources from a grant provided
by the National Oceanic and
Atmospheric Administration.
“Building Our Industry Together”
The University of Maryland is an Equal Opportunity Employer and
offers equal access to all for the programs and services provided
Production Systems
Don Webster and Don Meritt
University of Maryland
Oysters have been cultured for thousands of years and many methods have been
developed to raise them. One of the most important decisions that you will have to
reach as a grower is deciding on the method or methods you will use to grow your
oysters. That choice will affect many of the decisions that will come as you develop
your business.
In the Chesapeake area the principal production method has been bottom culture,
which mimics natural oyster reefs. However, other methods have developed as
growers sought to come up with ways to raise oysters faster so they would not be as
affected by disease or to produce animals with specific traits for the demands of
particular markets. All methods have their
positive and negative points and these should
be carefully considered prior to choosing one
over another. Also, there are methods of raising
oysters have been developed in other areas and
countries that could merit trials here.
This publication provides information on the
principal methods of production currently in use
as well as providing an overview of others used
around the world. This is not meant to advocate
Figure 1 Eastern oyster C. virginica
one particular system over another but rather to
provide you with information about systems that
exist. Our aim is to get you as a grower thinking about what would work best for the
area you are interested in, the markets you are targeting, and the oysters that you will
be raising. Remember, the goal of production aquaculture is to develop a profitable
business.
How should I raise oysters?
The production system you choose for raising oysters will be determined by many
factors. Before determining a method, you should investigate as many as you can.
Growers are often glad to have you observe their operations or there may be some
sites in your area already in production that you are familiar with. Growers are often
comfortable about showing the methods and equipment they use to produce oysters
because they know that expanding production creates benefits for the entire industry.
As one successful grower told us many years ago, “What makes my business
profitable you can’t see by walking around – it’s the marketing and sales that we do.”
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The market you choose to grow for is one of the factors that enter the decision on the
method you will choose. Oysters that are produced specifically for the half-shell or raw
bar trade are often cultchless, or produced by setting larvae on shell chips rather than
with multiple animals on a single shell. These
single oysters are more susceptible to predation
“Consumer preference
and therefore must be protected by placing them
in enclosures. The containers need regular
for oysters is very
cleaning to assure strong growth of the oysters.
subjective and varies
However, it should be noted that bottom cultured
widely across the
oysters have been sold to raw bars for over a
country”
century and should not be dismissed as being
somehow less desirable than others. In fact, in
certain parts of the country, raw bars have
resisted oysters that are “too perfect” because they did not look like the ones local
consumers were used to. Consumer preference for oysters is very subjective and
varies widely across the country. In short, there is no one ‘perfect’ oyster.
The following factors should be considered in choosing culture methods and
equipment for your business:
Local conditions
Laws and regulations
Species being cultured
Material availability and cost
Labor availability and cost
Targeted markets
As a prospective grower you need to do a lot of background work to develop
information for your business. Spending time before you commit to a specific method
or area will pay off in the long run.
Bottom Culture
This traditional method of growing oysters in Maryland was first encouraged by the
legislature as far back as 1830. Changes made to our lease law in 2009 have made
bottom leases available again as well as allowing leasing in areas where it had not
been permitted for decades. Growers are still in production using grounds that have
been leased from the State for many years. Some leases have been passed down in
families for several generations. Our new laws and regulations, however, mandate
that the grounds that are leased must be used in order to remain active and there are
requirements for submitting regular reports and rental payments to maintain that
bottom for your use. A production plan will need to be submitted to outline the method
that you are going to use for your business.
To understand how bottom culture works you should first understand the structure of
a natural oyster reef. These are comprised of shells from previously living oysters that
have died and now have new living oysters attached to them. Oysters tend to spawn
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synchronously (at the same time), with eggs and sperm from female and male oysters
meeting to fertilize in the water column and become larvae. It stands to reason that
they have developed over thousands of years to be in close proximity to each other to
create a high probability that fertilization will occur and provide continued existence
for the animals.
After fertilization occurs, the resulting larvae exist in the water column for a week or
more. During this time they can move using cilia in response to environmental
conditions. When they are ready to set or attach they begin looking for a suitable
location. One of their preferred places to set is on other oyster shells. This is so they
can be near other oysters to complete their life cycle when they in turn are ready to
reproduce in the future. Setting on other oysters also means that the new animals will
be kept from settling into the bottom and
smothering. This ability to be attracted to other
oysters is why many of the productive natural
oyster areas today exist as “lumps” or mounds.
In creating a reef, oysters settle to the bottom and
attach to substrate or suitable surfaces. These
oysters grow by filtering the water that flows past
them, removing the phytoplankton or small algae
particles that provide their food. As the oysters
grow and reproduce, more oysters are hopefully
added to the community building upon each other
until a reef structure is formed. Reefs provide
Figure 2 Oyster larvae ready to
metamorphose and "set"
many benefits for our bays. They are used as
Photo D. Meritt, UM Horn Point Lab
habitat by many small plants and animals, many
of which also help to filter the water. Fish use them to forage for food which exists both
on the reef organisms as well as in the bottom. The key to success is for the oysters to
be kept up in the water column and out of soft sediment in which they could sink and
be destroyed. A successful bottom lease is managed similarly.
In this method the oysters are grown directly on the bottom and without any protection
from artificial cover. It is the most traditional means of raising oysters. In early years,
growers would lease portions of the bottom that were classified as barren or without
significant numbers of natural oysters on them. In most cases these areas had
sediment that consisted mostly of mud or sand. The grower obtained oyster shell from
shucking houses, placing a layer on the lease that would be sufficient to provide a
base thick enough to keep out of the sediment. He or she would wait for a “natural
set” to occur from oysters seeking a place to attach in summer or seed oysters could
be purchased from the James River in Virginia, a Chesapeake Bay location with high
traditional reproductive success. The oysters would grow and be harvested when they
met legal size requirements. Shell could also be obtained from dredge areas in the
upper Bay in locations where fossil shells were taken from long deceased beds. These
shells were generally smaller than shucking house shell but provided a reasonably
priced alternative and were beneficial in stabilizing grounds for planting.
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As the oyster industry declined and shucking plants ceased operations, the availability
of whole shell has constricted greatly. Also, concern by some groups over the dredging
of fossil shell has led to that supply being stopped at this time in Maryland. A recent
permit obtained by the State for reclaiming shell that has previously been planted in
areas around the Bay may offer a way for new growers to stabilize bottom for planting.
Renovating existing shell
The key in stabilizing bottom
culture areas is to make sure that
the seed oysters that are planted,
or the spat that sets naturally, are
kept out of the bottom so that the
animals remain alive and healthy.
In cases where natural spat sets
are desired it will be important to
clean the cultch in early summer
prior to the time when larvae are
searching for places to attach.
Renovating existing shell that has
been in place is a standard
Figure 3 Twelve foot wide drag harrows are used for efficient
management tool for a grower.
ground maintenance in Pacific Northwest states
This has traditionally been done by
Photo: Richard Bohn
towing an oyster dredge, usually with the bag removed, across the lease area. The
action of this “bagless dredging” of the bottom rakes the shell base and re-suspends
sediment and fouling organisms that have collected on the cultch, causing it be
carried away by the tide and
currents. Other equipment, such
as different types of harrows, has
been used for this purpose and
often provides more efficiency
when compared to the standard
dredge due to the increased
width.
The recent changes in lease law
have made it possible for growers
to obtain leases in areas that
were formerly classified as
Natural Oyster Bars. There areas
were considered “off limits” to
Figure 4 Fouled shell at beginning of dredge cleaning
growers. However, many of these
areas have seen the oysters die
and become covered with sediment to the point where they are no longer productive.
However, the key point is that they have shell on them that is capable of being
renovated and used productively for growing oysters. Many of these former bars are
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now classified as Public Shellfish Fishery Areas (PSFA) but can be petitioned for use by
potential growers. Two key factors are used in deciding whether a PSFA can be leased:
a) there must be a record of harvest during the past three years on the area, and b)
there must be a population
of oysters of greater than
1” in size at a rate of 1
animal per square meter
(14.7 bushels per acre). If
those conditions are not
met, the grounds may be
leased for aquaculture
production.
These are that have shell
on them can be renovated
by dredging or towing other
types
of
cleaning
equipment, much like
farmers till fields prior to
planting crops. In cases
Figure 5 Shell after dredge cleaning
where shell does not exist
on the ground or existing
shell has silted over to the point where it would be too expensive to renovate it, new
shell would have to be planted to develop the base required for successful planting.
In considering the addition of new cultch, the following types of material have been
used for creating planting areas:
Shucking house oyster shell
Chesapeake Bay oysters were often shucked or removed from their shells with the
meats being canned and sold for cooking. Traditionally growers would obtain shell
from shucking to build up their bottom leases but with the decline of the industry those
shells have become very scarce. Currently the shell belongs to the shucking houses
that process the oysters. The operators have the option of using the shells on their
own leases, selling them to other leaseholders or
selling them to the State of Maryland, which sets
an annual price that they will pay per bushel.
“Shell is a critical factor
in the development of a
new oyster industry”
Shell coming from shucking houses has been
referred to as “green” shell, shucking house shell
or whole shell since they are mostly unbroken. The
shucking houses will pile the discarded shells
when they are processing them during the public oyster season and they were
traditionally moved in the spring for planting or sale to the State.
5
Most whole shell is now used for setting, or the production of spat for planting. It is a
very important commodity for this purpose since whole shell provides enough space
between the shell when placed in setting tanks for microscopic oyster larvae to
circulate between them while the new animals seek for a location to attach and begin
growing. These remote setting systems are valuable tools in creating the seed oysters
used for planting leases and whole
shell is what makes them work
efficiently.
Oyster shell used for remote setting
must be clean and aged. Using it for
this purpose has been the principal
use of it in recent years and as
aquaculture production increase it
will become more important to
conserve and use if for that
purpose. Having shucking house
shell sit for at least a year will
Figure 6 Aged shell from shucking plants provides the best cultch generally provide the type of clean
for remote setting operations but is now hard to obtain.
shell needed for setting systems to
ensure that there is no organic
matter such as meat or muscle tissue, or other organisms such as barnacles or
mussels that can provide degrading meat.
In addition to local shucking plants, whole shell has been obtained from other states
although the cost of transporting it to the leaseholder’s desired site will often be very
high since it is quite expensive to move shell in bulk. The most cost effective methods
are those that move the largest amounts at a time, such as by barge or train.
Dredged shell
There are deposits of fossil shells in locations around the Bay that are the result of
thousands of years of oysters living and dying. Most of these deposits are in the upper
Chesapeake Bay and were used throughout
1960-90 for public oyster bars replenishment.
Recently, the practice was discontinued due to
“Dredged shell is
opposition from some public groups but the
useful for bottom
legislature has directed the State to reapply for
stabilization but not for
a permit to dredge on a specific location.
use in setting”
Dredged shell, if available, is very useful as a
base for bottom culture. The shells are
generally smaller than whole or shucking house shell. The small size of the shells
means that they are not useful in current setting systems since they pack together too
tightly to allow larvae to circulate. It could be possible to redesign a setting system to
use them but their current value would be to build a base on bottom culture areas to
plant over.
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Maryland has obtained a permit
to reclaim shell that was
emplaced over the years and
some of that would likely be
dredged shell that was moved
for the public fishery. If the use
becomes allowed, it would be
best to reclaim areas, clean
them and place the shell on a
lease as a base for planting set
spat or for providing a suitable
place for natural spat to set.
The price of dredged shell in Figure 7 Dredged shell was historically used to manage public oyster
prior years was based on moving
reefs and build up bottom for successful leases.
large volumes by barge. One of
the problems with using it was the cost of transporting it from the upper Bay dredging
sites to leases that were often many miles away. Also the barges used were frequently
of too deep a draft to be able to successfully plant on shallow leases of less than six
feet water depth.
Ocean clam shell
Large populations of ocean clams (surf clam and ocean quahog) are harvested along
the Atlantic coast. These are processed to create many products with the shells often
sold for road beds and other purposes. The clams are large and more brittle than
oyster shell but offer an alternative for building a base on a lease.
Clam shells are available at area plants from
Virginia to New Jersey. Because of the distance
between plants and leases they must be trucked
from the source and deposited on shore near
where the grower wants to place them. The fact
that they must be trucked makes them expensive
so that even when shells cost little, transportation moving them to a shoreline site,
and then to a boat or barge for planting makes them costly, especially since trucks
have to backhaul empty.
“Ocean clam shells can
be used but cost may
be a factor”
Ocean clam shells are most useful in stabilizing bottom. They are fragile and fracture
easily which may make the pieces too small to use in a setting tank for seed
production. However, they have been used on leases for years and are known to
provide suitable cultch for wild larvae to become spat. Because of the larger and less
dense nature they can move in a strong current. The key to using ocean clam shells is
to accurately calculate the final cost of emplacing them on a lease and weigh them
against other choices of cultch that may be available to get a true cost of using them.
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Alternative cultch
With the depletion of natural shell from shucking plants and the lack of dredged shell
available, many other alternatives have been tried. In most cases these have not
proven to be cost-effective due to their high cost. Experiments during the past few
decades have evaluated everything from stabilized fly ash blocks from power plants to
broken up plumbing fixtures. We wish to state here that we are not in favor of
promoting the use of our bays as dumping grounds in the name of environmental
restoration or for commercial purposes in the production of oysters.
From a cost standpoint, alternative materials have proven very costly. Restoration
sites constructed of gravel or crushed construction materials have proven very
expensive and are usually justified because of their claimed environmental benefits,
definitely not from an economic analysis where profit is required as a success metric.
Construction materials
Stone and gravel as well as ground up material from former roads, dams and bridges
have been used for constructing oyster grounds. The cost of this material is generally
very high due to the expense in
crushing construction rubble and
removing
metal
and
other
undesirable items from it. The cost
of moving it is likewise very high
since it is heavy and requires
expensive equipment.
Figure 8 Geotextiles are used for many construction projects.
Photo Capital Signal LLC (permission requested)
Crushed construction material also
frequently runs in sizes that would
make it more difficult to dredge
oysters for harvest. While it may be
stated that it passes screens of no
more than 4”, the final material will
include larger pieces that will be
harder to operate harvesting
equipment properly.
Stone and gravel are heavy to move as well and, when business calculations are
made, rarely makes good sense to consider.
Geotextiles
The use of these manufactured fabrics for use in shellfish aquaculture has been
investigated but yet not widely used for oyster culture. Clam beds, however, are
covered with plastic mesh nets for predator exclusion and have been extremely
successful. There are many products that fall under the category of geotextiles, from
woven material used as sediment barriers surrounding construction projects to heavy
mat-like materials used for road beds, often in marshy or unstable soils. Geotextiles
8
may provide a means of developing smaller areas for oyster culture, although the
expense of the material and environmental effects need to be fully explored.
An experimental project conducted several years ago used geotextile to cover an area
of sand. This type of bottom is not normally successful for growing oysters since the
animals usually sink into it and quickly die. A plot
was laid out on sand using geotextile with a layer
“Geotextiles could be
of oyster shell over it. A control plot consisting
used in certain small
only of shell was emplaced next to it. Both had
areas for culture”
hatchery spat on shell placed on them but in less
than one year the control plot had completely
disappeared while several years afterward the
treatment plot continued to provide habitat which grew and thrived.
Geotextiles can be obtained in large rolls however the process of using them would
require experimentation. Harvest of the crop would also likely have to be carried out by
diver since it would be difficult to use towed equipment on a base using material. The
issuance of permits for constructing areas using geotextiles would likely be delayed
due to the lack of experience with these materials and the number of agencies that
would be involved in the review process.
Off Bottom Culture
Off bottom aquaculture has been
practiced in many parts of the world
and some of these methods have
been adopted by local growers. It
should
be
pointed
out
that
aquaculture often involves innovation
and methods developed by others can
be evaluated to see how they will work
in other areas. However, all growing
conditions are not similar and a
grower who finds new gear or methods
that interest him or her should develop
a carefully designed project to
evaluate them prior to investing
heavily in them. Conditions or markets
may be very different here from where
they are used.
Figure 9 Surface floats are usually similar in design and
offer protection from predation
Surface floats
These are contained culture systems that provide protection for oysters. They are
usually used for “cultchless” or spat that is set on finely ground pieces of oyster shell
rather than the “spat on shell” that is used in bottom culture. Cultchless spat are
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highly susceptible to predation and must
be protected. That is a principal reason for
using containment gear.
Anything placed in bay waters will, over
time, attract fouling organisms. The type
and rate of fouling will depend upon
where the gear is placed. While watermen
using anti-fouling paints on crab pots to
deter fouling, it cannot be used for oyster
floats due to the nature of the chemicals
Figure 10 Ice covering Choptank Rive, winter 1977
that are used to prevent fouling
organisms from colonizing. The floats will
have to be kept clean in order to keep the meshes open as fully as possible so that
maximum water flow can be obtained past the oysters. This helps them to achieve
their best growth rates but the labor to clean them adds to the expense of raising the
oysters. That is why most contained oysters are grown for the higher priced raw bar
markets.
Ice becomes a problem during some Maryland winters and growers should always
bear in mind that it can cause severe damage. The biggest problem with ice is created
when floes begin to break up and move with the wind and tide. These exert
tremendous forces on stationary items that they come in contact with and have been
known to remove docks and piers, aids to navigation and other structures. During the
winter of 1977 when over three-quarters of the Chesapeake Bay froze over the
damage to structures was severe.
Among the variations in surface floats are the following:
Figure 11 The Taylor Float has a cage suspended
from a collar for holding spat on shell
“Taylor float”
Developed in Virginia for oyster gardening,
these units are normally made from 4” I.D.
schedule 40 PVC pipe with 90o PVC elbows
at the corners formed in a large square or
rectangle. The dimension of the units can be
modified to whatever size the grower wants
although 10’ long is the maximum that most
users recommend. This is due to the
increasing
difficulty
of
handling
progressively larger units.
The Taylor float is relatively simple to
construct and the materials are available at home centers and plumbing supply
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houses. The units are glued and the piping must remain watertight for the flotation to
work. Should the flotation collar leak, the entire unit may sink and result in the loss of
the oysters.
There are several variations on the Taylor
float. These come from the method of placing
oysters in them. The first models developed
used a vinyl coated wire basket suspended
from the collar. Bags were placed in the
baskets and periodically the oysters in them
would be removed for cleaning and grading.
Cleaning of these models could become
challenging as the cage became fouled
throughout the growing season requiring that
the unit be removed for maintenance.
Later versions simply placed the culture bags
in the frame and secured them to the sides
using large cable ties or bungee cords. When
fouling became too heavy on the underside of
the bags, the units would be turned over and
the fouling cleaned from the top using stiff
brushes. Some growers developed levers that
would fit over the units and allow a single
person to turn the units over. This was
particularly useful with larger 8 to 10 foot long
versions.
Figure 12 Float with collar and two different
mesh oyster bags to be fastened by cable ties.
Growers using floats are always trying innovative solutions to cut expenses and
minimize labor, which are the two inputs that most greatly affect profitability. One
Maryland grower recently obtained a grant to develop a float with a twin set of baskets.
His float design used a PVC flotation collar with two large vinyl coated wire cages
suspended from them. The difference in this
design is that while one of the units containing
the oyster bags was suspended in water with the
“Using contained gear
animals feeding, the other was raised totally out
raises the business
of the water where biofouling organisms were
input costs of capital
subjected to desiccation from the sun and wind.
and labor”
This was claimed to cut the labor of maintenance
a great deal. It allowed the grower to scrub or
powerwash the units to remove dried biofouling
material. It should be be noted that this design required more investment in material
because of the duplication of the culture containment sections but savings from
decreased labor or increases in production from available labor being able to care for
more units in a time period could offset the expense. It has been noted that the cage
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area on the surface provides a ready place for birds to perch which could cause
bacteria or water quality problems, especially in summer months.
OysterGro®
This system was developed in Canada where it is used in areas where winter ice
annually causes problems with gear. The OysterGro® system consists of a vinyl coated
wire structure that is designed to hold two racks of containment bags. Specially
designed and molded floats are placed underneath the long edges of the unit. When
the unit is placed with the floats on top, the oysters are suspended beneath the float
to feed and grow. When it is time for maintenance and cleaning the float is turned over
so that the cage rides on top of the floats which lift the unit out of the water while the
animals are cleaned and sorted before being replaced and the unit once again turned
for growout to resume.
A unique feature of this system is the removable end caps on the floats. When taken
off, the flotation tubes flood and the entire unit will descend to the bottom for
protection. This is normally done in winter in Canada to protect against ice damage.
When winter passes, the units are raised, the water is removed from the floats, the
end caps are replaced and growing resumes.
These units are sold by suppliers in the Chesapeake area and are being used and
evaluated by some Maryland growers to determine effectiveness in local conditions.
The equipment is worked by placing them on ground lines in strings of multiple units.
The lines are anchored using either traditional anchors or screw anchors with lines
large enough to provide the needed strength in any weather conditions that might be
encountered in the growing areas. The gear can hold a double row of culture bags,
which are sized according to the oysters that are being grown in order to get the
maximum water flow through the meshes to ensure the best growth.
Figure 13 OysterGro® system concept. Courtesy of Bouctouche Bay Industries Ltd.
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Bottom cages
This equipment has become popular in areas of the Mid Atlantic in recent years. The
Chesapeake region has seen growth in their use that developed during experiments
with non-native oysters. Several companies in Maryland and Virginia are using them
and at there are companies fabricating cages for sale locally.
Cages are available in a variety
of sizes depending upon the
equipment
available
for
servicing them. Large cage
designs may be up to six feet in
length and width while others
are four feet. They have legs on
the corners that keep them off
bottom a short distance. The
design allows them to be used
on bottom without a shell base
making bottom preparation less
costly. However, bottom cages
have the same requirements as
Figure 14 Bottom cages are now used by some growers to produce
surface floats and must be
high quality cultchless oysters for raw bars.
regularly tended to keep them
clean and free of biofouling that can cut the amount of food available to the oysters.
They also add a capital cost to the setup of the business.
Cages are usually used to grow cultchless seed. Because these animals are more
prone to predation, the cages offer protection to the animals. Also, aside from losses
due to mortality, growers will
tend to get all the live oysters at
harvest. Cages can be placed
using individual buoys or they
can be placed on lines. The
latter tends to cut the number of
buoys making the growing area
more acceptable to residents
who may be living where they
can see the culture area. It also
makes it easier to find gear if it
is tossed around during a storm
event.
Some growers have developed Figure 15 Specially designed vessel to tend bottom floats. Hooper
boats designed to service lines
Island Oyster Company, Fishing Creek MD
of oyster cages. These may be
equipped with power washing pumps to clean the containers and tables to sort and
cull oysters to place different sized ones together. Some have rotating drums that
13
tumble the animals to break off new shell growth to spur them to develop better shape
for half-shell or raw bar markets.
Rack and bag
A variation on bottom containment is the rack and bag system. This equipment is not
used in Maryland at this time due to the low tidal fluctuation. It is normally found
where high tidal amplitude
causes the racks to be out of
water at low tide so that
growers can tend their gear.
The system consists of metal
racks, generally made out of
steel reinforcing bars that are
placed on growing grounds.
Plastic mesh bags are charged
with oysters and placed on the
racks to grow. The size of the
mesh is determined by the
size of the oysters with the
Figure 16 Rack and bag system used for oyster production on
animals moved up to larger
intertidal flats in France. Photo: S.K. Allen, VIMS
mesh sizes as they get larger
in order to get the best flow
past the shellfish.
Rack and bag systems help to minimize biofouling since the bags are out of the water
during low tide. This lowers labor costs, however it should be noted that the capital
investment for these systems is quite high and they would likely encounter resistance
from nearby property owners in most areas in Maryland. They would also have to be
placed where there is no danger of the animals being exposed to freezing conditions
when out of water in winter or the potential for high mortality will exist. In most areas of
Maryland this would require that the animals be moved to deeper water during winter
months.
Mid-water culture systems
While these culture systems have not been used to any great degree in this region,
they provide a popular way to produce oysters in other areas of the United States and
the world. Mid-water systems take advantage of another dimension in growing by
using all or most of a water column to suspend oysters during growout.
Shell strings
These have been used in areas of the west coast and are often found in Asia.
Generally, oyster shells are drilled or punched placing a hole in them and placed on
rope or wire. These strings are either placed horizontally across posts in the bottom or
suspended from rafts. In most cases they are used to catch natural spat by providing a
place for the larvae to attach. In some instances they are used in setting tanks where
hatchery larvae are placed and allowed to attach to the shells.
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Federal agencies did some experimentation with shell strings in Maryland many years
ago and it was legalized for leaseholders to place shell strings on rafts in seed areas to
collect seed although not apparently done. Some growers did try horizontal shell
strings in shallow areas
near Nanticoke with some
success but the method
was not widely used. After
collecting the seed, it was
removed from the strings
and placed on bottom in
traditional
leases
for
growout.
The principal problems
with using shell strings
includes the acquisition of
suitable amounts of whole
shell, the labor and
equipment required to
Figure 17 Midwater culture systems such as these net tiers can be used place them on the strings,
in deeper waters found in places like New England.
the handling of the gear
after they are strung and
the permits required to legally place them in off bottom locations. Growout to market
with the strings remaining intact would require placement of rafts and require water
depths that are not likely be found in the Chesapeake or coastal bays.
Lantern nets
Nets have several variations depending upon the intended production. Lantern nets
are circular rings covered with mesh netting into which oysters are placed. There are
multiple nets in a vertical line and these are all attached to horizontal growing lines
and placed in water to cultivate oysters. A
variation on the lantern net is the pearl net
“Innovation in oyster
which is generally a smaller version of this mesh
cage. Pearl nets are used to grow a few animals
culture is found around
from which the pearls are extracted at maturity,
the world and has
This oyster species is not native to this region
existing for centuries”
and would be illegal to culture.
Lantern nets can be found in some locations in New England where they are used to
raise oysters for the half shell market. The method normally requires water depths not
readily found in the Chesapeake region. As with other contained culture methods
biofouling would present a problem that would require constant maintenance and
cleaning. Siting an operation of this type locally would be a principal concern.
Stick culture
This method has been used in places such as Asia in intertidal areas having mud
bottoms. As such, their application in this region would likely be minimal but is
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presented because it shows the innovation that exists within growers around the
world. The bottom used for stick culture is generally very muddy and would not readily
support the growth of oysters. Sticks are placed vertically where they may serve as a
location for natural larvae
circulating in the area to attach
and grow. In some instances
the sticks may be dipped in
light lime slurry to provide a
coating
that
would
be
attractive to larvae.
William K. Brooks, in his book
The Oyster, written in late
1800,
described
ancient
Roman culture using bundles
of sticks being tied together
and weighted with rocks to
place them near the bottom Figure 18 Stick culture used in China to raise oysters on mud bottom
where the sticks would float
that would otherwise be unusable. While innovative it would have
and serve as an attractant for
limited use in places like Maryland. Photo:S.K. Allen, VIMS
larvae. These would either be
moved to other growing areas or the oysters allowed to grow in place until the
increasing weight of their shells would cause them to drop to the bottom to grow until
consumed.
Summary
There are many methods for growing oysters. Some have application here in Maryland
while others are doubtful whether one could use them to develop a profitable
business. That is the most important part of a successful aquaculture business. It has
been said that, “You don’t make money raising oysters; you make money selling
them.” All decisions you make as a grower should be based on sound business
practices.
As the industry grows, innovation will take place and perhaps there are methods that
have not yet been developed that someone will try and find useful. As with all
successful aquaculture businesses the grower needs to determine the production
costs and assess potential markets that he or she can rely on to provide income.
Growers wanting to try new ideas should develop well-designed plans to demonstrate
the gear or method on a small scale before investing heavily in the equipment
required. Contact University of Maryland Extension for assistance in developing a
demonstration project and analyzing the results.
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