INTRODUCTION

Remote setting is a techniquefor producing oyster seed fromlarvae. It consists of two phases: (1) setting, in which larvae attach to “cultch,” a setting material suchas shell; and (2) a nursery periodwhere newly set oysters (calledseed) are placed in protected areasuntil they are ready for planting.Oyster growers often use remotesetting when natural seed suppliesare not consistently available ormust be purchased. By using yourown cultch, labor and equipment,you can reduce the cost of seed, amajor factor in oyster farming; withpractice and planning, you canproduce a consistent supply tomeet your own needs.

Adult oysters are spawned at ahatchery where they producemillions of tiny larvae. These freeswimming larvae are reared forapproximately two weeks or untilthey develop a structure commonlyreferred to as an “eye-spot.” It is atthis time that the “eyed larvae” areready to attach to a surface andundergo metamorphosis intojuvenile oysters. In remote setting,hatcheries ship eyed larvae tooyster growers for setting at theirsites. Shipping a small package

PRODUCING OYSTER SEED BY REMOTE SETTINGRichard E. Bohn, Donald W. Webster and Donald W. Meritt

Maryland Sea Grant Extension Program

containing millions of larvae issignificantly less expensive thanmoving seed already attached toheavy cultch.

Oyster shells are the mostcommon cultch, but growers useother materials as well. While theremote setting process normally isused to produce seed for bottomculture, you can also produce seed for other growing methods.Setting systems can often beadapted to using different types of suitable cultch.

Growers usually set oystersduring the warm summer months,though heaters in the tank can be

Free-swimming eyed larva.

Contents

Introduction

Selection of setting and

nursery sites

Cultch selection and

preparation

Cultch containers

Setting equipment

Water delivery

Preparing the setting tank

Adding larvae to the tank

Feeding oyster larvae

Record keeping

Cleaning the tank

Nursery area

Planting in production beds

Summary

AquacultureCenter

Northeastern Regional

University of Massachusetts DartmouthNorth DartmouthMassachusetts 20747

A capsule of one million eyed larvae.

NRAC Bulletin No. 220

Cooperative Extension ServiceUniversity of Maryland at College ParkUniversity of Maryland Eastern Shore

Maryland Sea Grant Extension ProgramOyster Aquaculture FactsheetUM-SG-MAP-95-03

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used to begin earlier. In the settingphase, containers filled withcultch are placed in a tank of saltwater that is equipped withaeration. Cultch is often soakedfor 24 hours before the larvae areadded. In two to three days, thelarvae attach to the cultch in apermanent bond. Growersmaintain these new seed, alsocalled spat, in the tank for a few days, and then transfer them to a nursery area. Producinglarge amounts of seed for bottomplanting is simplified whenmachinery is used to handle the cultch.

In the nursery phase,containers of seed are placed in aprotected area, usually shallowwater. This practice will allow foreasy retrieval when the oystersgrow large enough for planting.Protecting tiny oysters againstpredation and siltation during thenursery period results insignificantly better survival rates.While many types of containerscan be used, they must permitwidespread circulation of water,thus bringing food and oxygen tothe growing oysters. Despite beingcrowded, spat will grow toplanting size — usually about 3/4inch — in a few summer months.

SELECTION OF SETTING ANDNURSERY SITES

Proper sites for setting andnursery phases are critical forsuccess in remote setting. Chooselocations that will minimize yourlabor and lead to high survivaland rapid growth of young oysters.While the choice of good sitesmay be limited, an importantconsideration should be lack ofpollutants in the water. Oysterlarvae are very sensitive tonoxious compounds. Water frompoorly flushed harbors, forexample, can contain anti-foulingchemicals from boat paints,

bilge cleaners, oil, grease, or otherpollutants.

Survey surrounding lands todetermine if herbicides andpesticides could enter the waterafter a rainfall. Runoff containingtoo much organic matter, forexample, leaves, can also beharmfully acidic: decaying leavesproduce tannic acid and whenviewed from the surface, the waterwill have the appearance of darktea. If you are unfamiliar with anarea, investigate its history. Forexample, if oysters are growing innearby locations, it is an indica-tion that water conditions arefavorable. If in doubt about anarea, proceed cautiously and beprepared to move to anotherlocation if there is a problem withoyster survival rates.

Salinity fluctuations in thesetting and nursery areas also canaffect survival of seed. Settingsuccess decreases below 10 ppt,although adult oysters can toleratesalinities at or below 5 ppt.Nursery areas should not normally have salinities below 7ppt. In the setting tank, salinitycan be increased by adding salt;however, this option is not alwayspractical and becomes tooexpensive to use for long periods.You should know the salinity thatlarvae were raised at in thehatchery: they should not besubjected to extreme salinitychanges between the hatchery and the setting location. A changeof more than 15 ppt betweensystems can be harmful. Ifvariation exists between sites, it is safer to go from lower to higher salinity.

Much of the labor in remotesetting involves moving cultch, sochoose a site which will minimizehandling. Look for simple methodsof loading tanks and movingcontainers to the nursery. Cranes,winches, forklifts, or front-endloaders can be adapted for use.

In addition, a shorter distancebetween your water source andyour tank will lower pumping and equipment costs. Electricity is an important consideration inorder to supply aeration, runpumps, and possibly provide heat. Use three-phase power if it is available.

Holding newly set oysters in anursery area will enhance theirsurvival and growth to plantingsize. In selecting a nursery site,simplicity in placing andretrieving seeded cultch is alsoimportant. Water quality andbottom characteristics arecritical: they can affect seedsurvival in many ways. Manygood areas are intertidal witheasy access at low tide.

Submerged nurseries areeffective but may presentproblems in seed retrieval andmonitoring. In intertidal areas,seed must be placed below meanhigh water. Higher placementoften results in slow growthbecause oysters are out of thewater too long and therefore notfeeding. Prolonged exposure todrying winds, particularly insummer, may reduce survival. Asa rule, the useful tidal range isbelow the height at which largebarnacles are found.

The nursery area should have a firm bottom so that seedwill not sink. Waters which carry large amounts of suspendedmaterials, particularly areaswhere sand is shifting, can cause problems. The cultch slowsthe current movement and allows suspended particlesto settle. Sediment can thenaccumulate and smother the tiny oysters.

Make sure that containers ofseed do not present a hazard toboating traffic. Marking the edgesof the nursery with a hedge ofstakes extending above the watercan prevent both injuries to

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boaters and inadvertent damage tovaluable oyster seed. Suchmarkings are required by law.Check local and state regulationsbefore using a nursery site. Finally,theft of oysters is a potentialproblem and should be aconsideration when you arechoosing nursery sites.

CULTCH SELECTION ANDPREPARATION

The cultch material and type ofcontainer you select for remotesetting are critical decisions indesigning a setting system. Suitablecultch can improve setting success,and should be appropriate forgrowout later on. Growers prefercontainers which are simple to filland empty, and which minimizehandling throughout the remotesetting process, because they maydirectly affect profitability.

Oyster shell is one of the bestcultch materials. The irregularshells provide spaces which allowwater flow to distribute the settinglarvae and to deliver nutrients andoxygen. Other small, brittle, orcrushed shells that tend to packtogether collapse open spaces andreduce the surface area for larvaeto set on. Remote setting is lessproductive if a large amount ofcultch remains unseeded. You mayhave to modify your setting systemif you use cultch other than oystershell.

The cultch with new oystersmust be suitable for use in your growout area. For bottomplanting, the cultch must provideenough weight to keep the seedanchored in the currents, yet offer a broad surface area to keep fromsinking into the bottom. Wholeoyster shells have excellentcharacteristics that serve thesepurposes well.

Artificial cultch materials havebeen examined for suitability inremote setting. For bottom

planting, the requirements abovestill apply. In addition, artificialcultch must not leach toxicmaterials while being held in thesetting tanks. Even small amountsof toxins can seriously affectsetting success and reduceprofitability. A trademarkedpolyvinyl chloride (PVC) product,commonly shaped in pipe formand called “French tubes,” hasbeen used successfully. Growersuse tubes in suspended orintertidal culture systems. Othermaterials are being examined, butoyster shells are still often thecultch of choice.

Before shell cultch can be usedin the setting tank, it must beconditioned. This means thatorganic matter such as foulingorganisms attached to shells oroyster meats must be allowed todecay. Toxins which may bepresent in the manufacture ofartificial cultch should be allowedto leach out before use. If not,such toxins and harmful bacteriamay accumulate during setting andresult in poor survival of seed.Therefore, shell cultch must first beaged, or dried out, for a minimumof one year after meats areshucked; artificial cultch mayrequire at least as long. To speedup the process, you can placecultch in water for several monthsfollowed by air-drying for a month;however, this process adds tohandling costs. Efforts to chlorinateor steam-clean cultch have not

proven economical. As a result,you should estimate the quantities of cultch you will need for thefollowing one or two years andobtain it in advance.

CULTCH CONTAINERS

Important considerations inchoosing cultch containers are thatthey be nontoxic and sturdy andthat they allow for good water flowto oyster larvae. The kind ofcontainer and its size mayinfluence the type of setting tankyou use; most importantly, it willdetermine your labor and equip-ment needs in filling, transportingand planting, factors that all affectprofitability. A container withcultch weighing 30 pounds willweigh approximately 40 poundswhen retrieved from the nurseryarea; this increased weight is theresult of oyster seed, sediments,and fouling. The added weightmust be considered in whether youuse machinery or hand labor.Handling small containers may

Baskets of shell cultch stacked in asetting tank.

Oyster netting is a common shellbagmaterial.

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seem easier, but they require moretime and labor. When possible, sizeyour cultch containers to takeadvantage of available equipmentto reduce handling effort.

Commonly used containersinclude plastic milk carriers, bushelbaskets, or tubular plastic webbing,often called “oyster netting,” whichis used for making shell bags. Bagscan be cut from rolls, which areseveral hundred feet long. A 4-footlength of oyster netting will holdsome 30 pounds of shell, or about1/2 bushel. Shell bags can be usedindividually, or stacked, bound, andhandled in units as your equipmentallows. Growers normally cut bagsopen for planting seed in growoutareas and then properly dispose ofthem on shore. Larger containersare often custom-made accordingto the handling equipmentavailable.

Another consideration to keep in mind when using largecontainers or stacked and boundunits is the depth of the nurseryarea: it needs to be sufficient toprevent overexposure to dessicationof the upper layers of oyster seedby tides. Water flow must besufficient to deliver nutrients to theseed. Finally, your equipment mustbe able to raise the weight of thecultch at planting time.

In preparing your containers for the tank, make sure you removedebris and small chips of cultch:they can attract some oyster settingthat will be lost during handling.Rinsing cultch or containers with alarge volume of water shouldremove most debris; also effective is dipping the filled containers in awater bath several times before use.

SETTING EQUIPMENT

TanksMany sizes and types of remote

setting tanks have been usedsuccessfully. Large tanks willminimize the number of settings

you need to produce sizeablequantities of seed. Tanks mustpermit easy container handling,and are often sized to match thecontainers. If the cultch providesproper spacing, the containers canbe packed tightly in the tank.

Tank materials are often amatter of availability or cost. Wood,con-crete, fiberglass and metalshave been used successfully,though there are a number ofconstruction factors you’ll want toconsider. You must make sure thatwhatever the material, surfacesexposed to water must be non-toxicto oyster larvae.

Wood is frequently used in tank construction, either as marinegrade plywood or treated lumber.Joints must be sealed and water-proofed; internal surfaces should becoated with fiberglass. If the tankheight exceeds three feet, extrasupports may be required at the sides and joints.

Concrete, poured at least fourinches thick and reinforced at sides and bottom, has also provedeffective and allows a variety ofdesigns. New, pre-cast concreteseptic tanks have been used with

success, but there are indications that some concrete mixes canleach harmful compounds intosalt water. Coating internalsurfaces with epoxy paint may beadvisable.

Fiberglass and metals have alsobeen used successfully. Metals maycorrode with expo-sure to saltwater; consequently, internalsurfaces must be coated withfiberglass or epoxy paint to prevent harmful compoundsfrom leaching into the water.Fiberglass tanks should be filled carefully when usingmachinery in order to avoidcracking the units.

All new tanks should be filled with sea water and allowedto stand overnight. The water should then be changedseveral times before initial use; thisprocess allows residues remainingafter construction to leach out before coming in contact with oyster larvae.

Because of their weight when full, tanks should be wellsupported. Be cautious if youconsider locating your tank on adock. In time, settling may occur

Large fiberglass cylindrical tank for holding cultch containers — in this example,containers are bags of shell.

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and result in the tank warping orcracking. It is safest to set tanksdirectly on flat, compacted surfaceswhenever possible.

Tanks need to be drained easily:slightly tilting the tank (about oneinch over its length) toward thedrain will allow easier emptyingand cleaning after setting. Drainscan be plugged from inside oroutside the tank, or a removablestand pipe can be cut to the properwater level. A screened drain covermay be necessary to keep objectsfrom lodging in the opening.

Aeration SystemsGood circulation of water

within the tank is essential;consequently, setting tanks requireaeration, which helps to ensuresufficient flow. Aeration alsodistributes the free-swimminglarvae and then brings nutrients tothe settled oysters.

To provide aeration, an airpump is commonly connected to a3/4 to 1-1/2 inch PVC pipe gridwhich fits the bottom of the tank.The pipes are spaced 12 to 16inches apart. A large number ofsmall air outlets are needed tocirculate water uniformly, so 1/8-or 1/16-inch holes are drilled atleast every 12 to 16 inches alongthe pipes for air to escape.

An air lift system can also beused to circulate water. It consistsof a wide tube placed vertically inthe tank, with an air outlet installed1/3 of the distance from the bottomof the pipe for greatest efficiency.The rising air lifts water and candirect it using an elbow at the topof the tube. Airlifts at the cornersand the center of the tank, withcultch packed around them, canprovide adequate and inexpensivewater circulation for the system.

Air pumps should produce largevolumes rather than high pressure.Growers should avoid compressorsbecause they can leak oil, which istoxic to larvae. Blowers are sizedaccording to the depth of water in

the tank and the number ofoutlets. Consult a knowledgeablesource when purchasing a blower.

Homemade blowers can alsobe constructed from vacuumblowers, or from automobilepollution control pumps.Normally, about 1/4 to 1/2 hp isrequired per tank. Use a valve tobleed off excess air since onlygentle bubbling is needed.Multiple tanks can share acommon blower, but controls forindividual tanks are necessary. Theblower should be located abovewater level in the setting tanks toprevent water from siphoningback in case of a power failure.

Heating SystemsOyster larvae set most

successfully between 80° and 90°Fahrenheit. Below 75°F, settingproceeds very slowly, if at all. Forthis reason, most remote settingsystems are used in the summermonths, when optimal tempera-tures are easily maintained.However, if the system is operatedduring cooler periods, a heatingsystem becomes necessary.

A heating system can also helpyou produce oyster seed earlierthan you would normally be ableto; this seed can then benefit froma longer growing season and mayresult in an earlier harvest. Settinglarvae at near-optimal tempera-tures results in a quicker turnoverof tanks and allows the system tobe used more efficiently and moreoften. For these reasons, heatingsystems are in common use inremote setting operations.

Use energy-efficient heaters —remember that available powerand equipment costs areconsiderations, so consult heatingexperts before purchasing asystem. A heater needs to increasewater temperatures in a reason-able amount of time, usually overseveral hours. Use gentle aerationwhile heating water to prevent the

formation of hot spots in the tank.A setting tank, once heated, willmaintain temperature quite well;thus, heating requirements aresporadic. If heating is used regular-ly, additional foam insulation willreduce heat lost by the tanks.Covering the tanks will also reducethe greatest loss of heat.

The most common units areelectric heating elements placeddirectly in the tank. However, many metals can leach toxiccompounds — make sure that your unit employs only nontoxicmaterials. Even some grades of stainless steel can adverselyaffect larvae. So far, titanium orIncoloy™ compounds have proven safe for use.

Electrical power outlets mustcontain ground fault circuitinterrupters (GFCI). In somesystems, blowing air heated bypropane or wood along tubesrunning through the tank has alsoproven feasible. In general, seekthe most inexpensive and depend-able energy source available.

WATER DELIVERY

Water in the setting tank willneed to be replaced regularly.Because oyster seed should not dry out between draining andfilling, pumps should be capable of refilling the tank in 15 to 20minutes. Filter intake water —a 1/2-inch or greater mesh willprevent small fish or other water-borne materials from being pulled into the pump anddamaging the impeller. You mayalso find it necessary to filter the water to remove smallpredators, sediment, and organic debris which can coat the cultch and reduce theavailable setting surfaces. A sand filter with large grains, orreusable polypropylene bag filtersof about 25 micron mesh, willremove most of this debris without removing natural algae

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or restricting water flow.Make sure that all materials

which come in contact with waterare nontoxic. Use pumps withplastic impellers and PVC pipes tocarry water to the tanks. Flexiblehoses may be used in someapplications. The water system itselfcan be permanently installed orportable.

Not all larvae will settle whenfirst placed in the tank. Some maystill be swimming a few days later.Rather than lose these larvae, drainwater from the tank through a finesieve. You can return larvae to thetank after refilling and give themanother chance to set. U-shapedsiphons can be constructed from

1-1/2 or 2-inch diameter PVC pipe,readily available in hardware stores.You can make a sieve from finenylon screening of 165 microns orless. Nylon screening is available from aquaculturesupply houses and can be glued to a section of wide plastic pipe.You can also use a clean, fivegallon plastic bucket with a lockinglid by removing the bottom andcutting a large hole in the lid:stretch the screen across the topand snap the lid back on. The sieve should be supported onblocks or legs to allow water toflow easily and prevent damage to the fine screening.

Monitoring water quality is

essential for managing your systemproperly. To monitor salt content ofthe water, it is useful to have asalinity meter, refractometer or testkit. For temperature, a simplethermometer will do. To help keeptrack of larval activity as well assetting success and growth of theoyster seed, you can use a 40X orgreater magnifier.

PREPARING THE SETTING TANK

A successful remote settingsystem should allow free swimminglarval oysters to attach to thecultch, complete their metamor-phosis to become spat and recoverfrom this strenuous period beforebeing transported to a nursery area.Each step occurs more quickly anduniformly at 80° to 90° F.

In filling the tanks with thefiltered sea water, allow the tank tooverflow — this will help removefloating debris. The water should beclear, or have a green tint causedby natural algae. All of the cultchmust be submerged. If a heatingelement is used, apply gentleaeration to distribute the waterthroughout the tank. This helpsavoid hot spots which may damagethe tank.

Larvae ready to set may receivea beneficial “cue” from cultch thathas a thin surface coating ofbacteria: this coating will formnaturally on the setting surfaces byfilling the tank with the cultch andwarm water a day before addinglarvae. In early spring, fewerbacteria may be present, so anextra day of soaking could provehelpful. However, good sets dooccur without this aging processand if time doesn’t permit, it maybe possible to skip this process.Experience with your setting systemwill allow you to determine if thisstep is necessary for your system.

If the larvae are ready to setwhen they arrive from the hatchery,they may attach to the cultchwithin a few hours. Normally, most

Estimating Eyed Larval Needs from the Hatchery

The number of eyed larvae you order from the hatchery willdepend on the size of your remote setting tank, the number ofcultch containers it will hold, and the count of spat per shell youwould like to have for planting.* In addition, your estimate musttake into account eyed larvae survival from the hatchery (assume50%) and survival from eyed larvae to spat in the remote settingtank (assume 10%). These percentages could well differdepending on your operation.

Sample calculation: for cultch containers (e.g., shell bags) thathold 200 shells/containers and a setting tank that holds 100 ofthese containers, the tank will hold:

200 shells/container x 100 containers = 20,000 shells

To achieve a count of 10 spat/shell at planting, you multiply 10eyed larvae/shell x 20,000 shells = 200,000 eyed larvae. Ifsurvival from the hatchery is assumed to be 50% and survival inthe setting tank is assumed to be 10%, you will need to multiplyspat/shell needs by 2 and 10, respectively:

200,000 eyed larvae x 2 x 10 = 4,000,000 eyed larvae

Keep track of spat survival from planting through harvest to gain abetter understanding of optimal seed counts for each oyster bed.

*Counts above 25 spat/shell are often too crowded, and counts much below 5 spat/shell may result in large numbers of blank shells.

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settlement occurs during the firstday. Metamorphosis of settledlarvae to spat takes about anotherday. Most larval energy reserveshave been drained during thisprocess. Thus, allowing the youngoysters to recover for a few daysin the tank will improve theirchances of survival during thestress of being moved to a nurseryarea.

ADDING LARVAE TO THE TANK

Larvae are shipped in contain-ers from the hatchery — they areextremely fragile and should be handled carefully. If aerationin the tank can be adjusted,strong bubbling should be appliedto the tank. Place the larvae in abucket of water that has beentaken from your tank. Havingbeen cooled during shipment,larvae will take a few minutes torevive and start swimming. Beforethis occurs, mix the water in thebucket, then scoop water from thebucket with a small plastic

container and spread across thesurface of the setting tank: thisaction will distribute the larvaebefore they begin swimming.

Many growers cover settingtanks with tarps, black plasticsheeting or thin plywood to tryand improve oyster settingdistribution. This is becauselarvae tend to orient themselvesto the light: in an uncovered tank in bright sunlight, larvaemight set in the upper layers ofcultch. By darkening the tank,larvae are likely to spread moreevenly throughout the cultch.After covering the tank, adjustaeration to promote good waterflow.

One to two days after thelarvae have settled, change thewater in the tank. This step isimportant because toxic wasteproducts from the larvae willaccumulate otherwise; inaddition, new water alsoprovides food for the small spat.The more often water is ex-

changed, the better your waterquality will be.

Water needs to be changedquickly to avoid stressing theyoung oysters. You may find iteasier to change part of the waterdaily, rather than completelychanging it every few days. Thisnew water should also be filtered.As the oysters increase in size,filtering becomes less critical.During setting and metamor-phosis, usually during the first 48 hours, maintain optimaltemperatures. When water isdrained from the tank, siphon it through the screen — knowinghow much water you drain, you can estimate the number of larvae still swimming. If a large number are swimming,maintaining temperatures of 80° to 90°F may help speed larvalsetting. Observing oysters setting on the cultch isdifficult, though, with practice, it gives the best indication ofsetting success.

You can lower temperatures after setting and metamorphosis: this reduces the need to reheatwater. Several days after setting,oyster seed should be ready formoving to the nursery. If watertemperature in the nursery area is cooler than tank water, anaccepted management practice is to reduce the tank temperature5°F per day to reach the nurserytemperature. This procedure also allows the oysters to gain aslightly larger size before movingthem to the nursery area. Near theend of the holding period,unfiltered water can be flushedthrough the tank as well.

With practice, you willbecome familiar with theseoperations and should be able to adjust your management strate-gies to improve the settingsuccess, spat distribution, and survival.

Oyster larvae are distributed by spreading them across the surface of the tank.

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FEEDING OYSTER LARVAE

While natural water suppliessome algae, the young oysters willbenefit from supplemental feedingduring setting. This is because thenumber of oysters in the tankexceeds densities in nature.Though newly-settled oysters donot feed during their metamor-phosis, they are ravenous feedersonce the process is completed. Youcan observe this feeding after awater change: if setting has beensuccessful, the green tint of algaewill be removed within a fewhours. At this point, no furthernutrition is available for spat.Increasing the frequency of waterchanges can supply additionalalgae, but it is simpler to addconcentrated algae, available fromhatcheries or specialty firms.

Daily feedings of supplementalalgae are sufficient for the first fewdays, but should be increased afterthat. The changing tint of the waterwill indicate when more food isnecessary. Feeding large amounts of algae at one time, however,should not replace more frequentfeedings; in fact, overfeeding maycause feeding to cease. Whileoysters will consume many typesof available algae, they may simplypass much of the food throughtheir systems without digesting itcompletely. This is a waste of food,and it will increase yourproduction costs. An amount ofalgae which can be cleared byoysters in four to six hours isusually sufficient. Check withsuppliers for effective amounts and methods of feeding.

RECORD KEEPING

It is essential that you recordwater quality data (i.e., tempera-ture, pH, salinity) and otherobservations during the settingprocess and that you keep track of different batches of the seed you produce. There are variations

achieve more evenly-distributedsetting and to prevent blankcultch. It is especially important toverify an even distribution of spatearly in the use of a setting system.

CLEANING THE TANK

Clean your setting tank afterevery use. A few oysters willinevitably settle on the tank itself; if the tank is used often, they may be able to survive andgrow. These oysters compete with the smaller oysters for food,and produce waste products in the tank. Consequently, it isimportant to remove them. Scrub the sides and bottom with a stiff brush. Sponging off theaeration system and rinsing theunit thoroughly is all that isnecessary — it is easiest to do thisafter you’ve emptied the tank andit is still wet. It is also goodpractice to allow the tank to dry inthe sunlight before being usedagain. Scrubbing with a dilutedbleach solution may preventpersistent growth on the tank, butrinse thoroughly and use bleachonly in a well ventilated area.

in setting success and survivalbetween batches — havingaccurate data can enable you toassess differences in survival andsetting efficiencies. Good recordsare critical to the success andprofitability of your operation.

The percentage of oysters thatsuccessfully set is difficult toassess accurately until seed hasgrown for a few weeks; however,oysters on cultch should increasevisibly in size in the setting tanks.The larval shells are stillsomewhat transparent at thisstage, and the spat may bedifficult to see until they beginfeeding. By removing about 25pieces of cultch from severallocations in the tank duringunloading and suspending thembelow the tidal range for a fewweeks, you can get an accuratecount. Count spat as soon as theyare all visible to prevent loss bycrowding or predation.

It is important to sampledifferent levels and locations inyour tank during the first sets toensure that setting has beenoccurring throughout. You mayfind it necessary, for example, tomodify the aeration system to

Pallets can provide a foundation for stacking cultch containers on bottom grounds.

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NURSERY AREA

When the oyster seed is ready,you should move it to the nurseryarea as quickly as possible. Onhot or windy days, sprinkle saltwater or fresh water on the oystersduring transport. The evaporatingliquid will cool the oysters andreduce the stress that results frombeing out of water. Handlecontainers with the least possibledisturbance since the oysters arefragile and can be easily crushedor scraped off the cultch.

In the nursery, place cultchcontainers where they areprotected and can be easilyretrieved. Unless the bottom isvery hard the containers will tendto sink into the sediment,smothering lower layers of seedand making retrieval difficult.Wooden poles or inexpensivepallets can be laid down and thecontainers stacked on top of eachother. Supports may be mired inthe sediment when the seed ispicked up, but will provide abetter foundation for the nextcrop. Hard bottom is important if the pallet and cultch containersare moved and retrieved as a unit.

Containers can be deeplystacked and still provide goodoyster growth. Seed is small andrequires little water flow for foodand oxygen: currents and tides can provide adequate flow,especially if it is less than two orthree feet to an outside edge fromany point in the stack. Stackingreduces the impact of being on anoutside edge, such as heavierfouling or exposure to dryingwinds, by protecting seed fromthese effects.

While stacking protects seed from exposure and improvessurvival, it increases the need tomonitor the nursery. Sedimentscarried by water may settle outamong the cultch, smothering thesmall seed. Be on the lookout for

smothering, especially afterstorms.

Seed should be monitored forsigns of predators: in many cases,predation is not a concern at firstbut can result in escalating lossesjust before planting. Mostpredators leave obvious signs oftheir presence by how theyopened the spat. Examine emptyshells closely since predatorsleave clean shells behind, whilesmothering causes shells toblacken. Large predators likestarfish are easily observed andremoved in intertidal sites.

Nurseries should be free ofoyster drills, not only because oftheir predatory habits butbecause movement of seed frominfested grounds is restricted bymany states. Invasive species,including crabs and flatworms,may actually seek shelter ormultiply among the cultchcontainers, resulting in anexploding number of hungrypredators. In these cases, plantingthe seed and exposing thepredators to their natural enemiesmay be the simplest approach.

Predation losses in the nurserymust be balanced against extralosses in handling and the risk of siltation affecting the smalloysters planted.

Keep track of seed growthand survival. Differences within anursery from tidal or seasonaleffects may mean that you have to adopt other methods to improve survival. Examineinner layers of seed, whichrepresent the bulk of the cultchand often appear different thanoutside layers.

Seed is ready for planting togrow-out areas or productionbeds when oysters reach a lengthof 1/2 to 3/4 inch. Often, theseed will begin growing awayfrom cultch, seeking more food.They can be held in the nurseryindefinitely although their growthwill slow down. But they shouldnot be kept in the nursery untilthey begin to grow through theholes in their containers: thismakes removal of the seed forfinal planting difficult and willresult in higher labor costs andincreased seed mortality.

Planting oysters in a protected area.

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PLANTING IN PRODUCTION BEDS

Growers often plant seed inearly fall or spring. Overwinteringin a nursery should be avoided ifthere can be excessive exposure tocold air, ice, or silt.

Handle the seed carefully whenplanting to avoid damage, althoughsome losses should be expected.Planting rates differ greatly due to anumber of factors, but should bebased on accurate seed counts.Counting will reveal the survivalrate, the ultimate goal forimprovement. Take care to obtainsamples from several locationswithin containers. Blank shellssuggest poor distribution of larvaein the setting tank or sedimentsaccumulating in the nursery.

SUMMARY

Many factors must beconsidered in a successful remotesetting system. Reducing labor andeffort in handling cultch is critical.Pollutants and toxic materials mustbe avoided, and providingfavorable conditions will improvethe survival of oysters andprofitability of a system. With goodrecords, frequent monitoring andsome luck, you can achieve astable source of oyster seed forplanting or sales.

ACKNOWLEDGMENTS

This publication was supportedby the Northeastern RegionalAquaculture Center through a grantnumber 91-38500-5908 from theCooperative State Research Service,U.S. Department of Agriculture.Publication No. K-320501-1-93NJAES and Contribution No. 93-13at the Institute of Marine andCoastal Sciences, RutgersUniversity. Any opinions, findings,or recommendations expressed inthis publication are those of theauthors and do not necessarilyreflect the views of the U.S.Department of Agriculture.

Publication of this fact sheetwas also supported in part by theUniversity of Maryland CooperativeExtension Service, the Center forEnvironmental and EstuarineStudies and through grantNA86AA-D-SG-006 awarded bythe National Oceanic andAtmospheric Administration to theUniversity of Maryland Sea GrantCollege Program.

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FOR FURTHER INFORMATION:

Maryland Sea Grant ExtensionCooperative Extension ServiceWye Research and Education

CenterQueenstown, Maryland 21658Telephone: (410) 827-8056

Maryland Sea Grant ExtensionHorn Point Environmental

LaboratoryUniversity of Maryland SystemP.O. Box 775Cambridge, Maryland 21613Telephone: (410) 221-8475

Maryland Sea Grant ExtensionChesapeake Biological

LaboratoryUniversity of Maryland SystemP.O. Box 38Solomons, MD 20688Telephone: (410) 326-7356

Maryland Sea Grant Collegewww.mdsg.umd.edu

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Publication NumberUM-SG-MAP-95-03 –––––––––––––––––––––––––––––––

Issued in furtherance of CooperativeExtension work, acts of May 8 and June30, 1914, in cooperation with the U. S.Department of Agriculture, Universityof Maryland at College Park, and localgovernments. Nick Place, AssociateDean and Associate Director ofCooperative Extension Service,University of Maryland at College Park.

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The University of Maryland is equalopportunity. The University’s policies,programs, and activities are in conformancewith pertinent Federal and State laws andregulations on nondiscrimination regardingrace, color, religion, age, national origin, sexand disability. Inquiries regardingcompliance with Title VI of the Civil RightsAct of 1964, as amended; Title IX of theeducational Amendments; Section 504 of theRehabilitation Act of 1973; and theAmericans With Disabilities Act of 1990; orrelated legal requirements should bedirected to the Director of Personal/HumanRelations, Office of the Dean, College ofAgriculture and Natural Resources, SymonsHall, College Park, MD 20742._______________________________