Pearls Farming : Spat collection
Spat collection is the best means of supplying a farm with young pearl oysters of the right age for grafting. If spat collection is biologically possible in your area, it is the preferred means of obtaining spat. Collecting adult, wild oysters can threaten the wild populations and most of these animals are too old to produce high quality pearls. Hatchery-produced spat are a good option if available and reasonably priced, but there are very few Black-Lip pearl oyster hatcheries.
What is spat collection?

The pearl oyster has several different life stages (Figure 5-life cycle). During the first 2-3 weeks of life, the pearl oyster larva can swim freely. It then begins to look for a place to which it can attach itself, such as a reef or the shell of another pearl oyster, to spend its adult life. The transition from free swimming larva to settled juvenile is called metamorphosis. Metamorphosis lasts 2-3 days and major changes occur in the anatomy and behavior of the pearl oyster during this time. Metamorphosis is also call “setting” or “settling” because attachment of the juvenile to a substrate is one of the main changes that occurs throughout a pearl oyster’s life cycle. The small, juvenile pearl oyster that has passed through metamorphosis and attached itself is called a “spat.”
Important things to remember in spat collection Choose materials that increase the probability of spat set. Spat collectors are designed to offer a protected area where spat can settle and grow safely. Pearl oyster larvae generally prefer to attach to dark materials that offer shelter from predators. Many types of materials have been used with success. These include pearl oyster shells, nursery shade cloth (55% shade), black plastic strips (polyethylene sheeting), coconut husks, bundles of brushy twigs such as “miki-miki” (Pemphis acidulus) or commercial spat collection material. Plastic materials, especially nursery shade cloth, work best because these are lightweight and can easily be reused. Other materials will collect spat, but tend to be so heavy that extra care is needed to ensure the spat collector lines do not sink.

Correct placement of the spat collectors will improve the likelihood of good spat set.
Selecting a good area to place spat collectors can be difficult the first time spat collection is attempted. Generally, protected areas such as lagoons or bays are best since it is assumed that larvae are retained in these areas long enough to mature and set on the collectors. Lagoons with high rates of water exchange or open-ocean areas are usually less likely to produce good spat set because larvae produced in these areas may be flushed out by tides and currents. Areas within a lagoon where large numbers of pearl oysters are found are also likely to produce good spat collection. Look also for areas where there are gyres or eddies in the current, which may help retain spat in the location. Areas where there are a
number of coral pinnacles near the surface may also be good, since currents may slow near the pinnacles, especially on the leeward sides.
Keep spat collectors as near the surface as possible.
Materials hung near the surface of the water appear to collect the most spat. Keep collectors within 3-5 ft (1-2 m) of the surface by hanging collectors on very shallow main lines. Do not attempt to use the farm lines to hang spat collectors since these are too deep. Add floats at frequent intervals on the line to prevent sagging. Collectors that sink below 5 ft (2 m) rarely collect Black-Lip oyster spat, although they may collect other types of animals and plants.
Locating spat collectors in calm areas prevents loss of spat. Young spat are capable of detaching their byssal threads and moving if environmental conditions are not suitable. This may happen if the spat collectors are in rough areas. Once you have seen spat set, you can lower the lines so they experience less movement.
Making the collectors

Using shade cloth or plastic materials The spat collectors should be about 3 ft (1 m) in length if using shade cloth or other plastic materials. The material is first cut into strips that measure 3-5 in (7-8 cm) in width. Thread these onto a length of 1/8-in (4-mm) polypropylene rope in accordion fashion (See Figure 13-shade cloth spat collector). The material should be packed onto the rope firmly, but not tightly. Snugly packing the material onto the line creates a collector with a large amount of surface area and protected areas where spat are safe from predators. Tie knots at the top and bottom of the collector to keep the material from slipping off the rope. You may wish to tie a knot in the middle of the collector line to keep the material from sliding down and bunching at the bottom once it becomes
heavy with fouling.
Figure 13. Making a spat collector out of shade cloth. Shade cloth is cut in strips and thread onto a line. The shade cloth is then compressed to form a bushy mass of shade cloth to provide shelter for young spat. Leave about 13 in (30 cm) of rope free at the end of the collector so it can be tied onto the spat collector main line using a slipknot (see Figure 14-knot for tying spat collectors or chaplets onto the main line).
Figure 14. Collectors should be tied on to the mainline using a knot that can be easily tied and untied using one hand, such as the knot shown here. This knot can be easily broken loose even when fouling organisms have covered the line.
Using plant materials or shells: If using miki-miki or some other brushy material, leave the small leaves and twigs in place and cut the branches in lengths of about 22 in (50 cm). Then tie them together with rope or monofilament. Leave enough extra line to tie the bundle onto the main line. If using coconut husks (the inner, brown husk), make a hole in the end of each coconut half. Shred the coconut husk so that a furry mass is created.
Using a piece of 1/8-in (14-mm) polypropylene rope, tie a knot at one end, then thread on a coconut husk. Tie another knot about 8 in (20 cm) above this and add another coconut half. Repeat this until 5 or 6 coconut halves are on the collector and then hang it on the main line.
The same can be done using pearl oyster shells. This is a good use for old or broken shells. Drill a hole through the center of the shells and thread them on the collector line, using knots to keep the shells from touching each other. Shells that have been aged in the sun will work best. When using any of the heavier materials, the spat collector line will need more floats and will have to be checked more often to be sure it does not sink.
Setting the collectors in the lagoon
Collectors should be set on main lines as close to the surface as possible. Locating and maintaining collectors within 3 ft (1 m) from the surface of the water is ideal. It may be necessary to set the collectors a bit lower if boats pass through the area, but do not set the collectors deeper than 6 ft (2 m). When tying the collectors to the main line, use a slipknot that holds firmly, but that can be tied and untied using one hand (Figure 15-slip knot for tying spat collectors onto main line).
Space the collectors about 8 in (20 cm) apart to prevent them from getting tangled up with each other. If your main line sags more than 6.5 ft (2 m) between floats, try using empty plastic drink bottles to serve as “mini-floats” along the sagging part of the line to keep the collectors high in the water. A second method for deploying spat collectors is to tie them onto a line on land, which is then attached to the main line. This method has the advantage of allowing most of the work to be done on land, rather than in the water. When the time comes to harvest the spat, the collectors and the line they are attached to are removed from the water. The main line is left in place.
Spat bags may help protect the spat from predators.
Spat bags are fine-mesh bags that are used to enclose the collectors in order to protect them from predators. These have been used with mixed results. Spat bags are best used when the main cause of predation is fish picking off the small spat. They may also be useful in areas that are often rough, since spat falling off the collectors will be retained inside the bag. However, if predation by snails or crabs is a problem, spat bags may only worsen the problem by retaining the predators near the collectors. Also, once the mesh of the spat bag is fouled, there will be little spat set. It is recommended that the effectiveness of spat bags be tested along with unenclosed collectors the first time spat collection is done in a new area.
Keep collectors at least 160 ft (50 m) from reef areas to prevent predation. Reefs shelter fish and other animals that eat spat. Keeping the collectors as far away as possible from these areas will help prevent losses due to predation. When to set out spat collectors Spat set will be heaviest about 1 month after the high annual water temperatures occur.
Pearl oysters spawn (produce eggs and sperm) when water temperatures are highest, although they will usually spawn at lower levels during the entire year. Setting out collectors about 1 month before the peak spawning season will improve your chances of capturing large numbers of spat.
In the southern hemisphere, peak spawning seasons are in October and November, with a smaller peak in March and April. Pearl farmers there set out spat collectors in late September and October. In the northern hemisphere, very little spat collection has been done, so the peak spawning time is unknown. In many areas, the highest water temperatures occur in July and August, so these may be the best times to set out spat collectors. It is recommended that in areas where spat collection has not been previously done, the pearl farmer set out some collectors every month during the first year and keep a record of the times when the best settlement of spat occurs. Keeping a weekly record of water temperatures may also help provide information that suggests best times to deploy spat collectors.
Maintaining the spat collection line

The most important part of maintaining the spat collection line is keeping it high in the water. As spat, other animals and plants begin to settle on the collectors and main line, they begin to weigh down the line. If the line sinks below 6 ft (2 m), very few spat will set on the collectors. You should check the spat collector line at least every week. Keep the main line high in the water by cleaning the line often and adding more floats as needed. Inspect the collectors to see if any spat have settled. Be sure to look at the center of the collector for small, hidden spat since they tend to seek protection there. Keep monthly records of the number of spat settling on collectors. This will allow you to determine which time of year is best for setting out spat collectors.
Identifying Black-Lip pearl oyster spat
Generally Black-Lip pearl oyster spat can be easily identified when they reach a size of 1/2 in (1 cm). Spat reach this size about 2 months after setting. Very small spat can sometimes be confused with other species of oysters (Pinctada radiata or Pinctada maculata), which look very similar to small spat. Small Black-Lip pearl oyster spat are distinguished by being entirely or partially green, particularly in the area near the umbo. The predominant green color is most obvious when the spat are smaller than approximately 1/2 in (1 cm). As the spat grows, there may only be a hint of green near the umbo, while
the rest of the spat is brown or brownish-green. Other species tend to be entirely brown, orange or yellow.
Black-Lip pearl oyster spat also tend to have fewer streaks of white in their shells and when they do occur the streaks usually do not reach back to the umbo area, but are confined to the middle or edge of the shell. The smallest spat (less than approximately 1 in or 2 cm) tend to be smooth. Later small growth process (spines) appears. The small spines on Black-Lip pearl oysters are wider and flatter than the spines on similar species, and may be broader at the tips than the base. The spines on Black-Lip pearl oysters also tend to be more rounded on the ends and crowded together. If in doubt, keep the spat until they are large enough to positively identify their species. Consulting with an experienced farmer or extension agent may also be helpful.
When spat appear on collectors
When spat are large enough to be identified, you have two choices of what to do next.
- Cut (never pull) the spat off the collectors and keep them in lantern baskets. The lantern baskets have the advantage of protecting the spat from predators and fewer spat will be lost due to falling off the spat collectors. This option is more costly and requires more maintenance. The lantern baskets should be cleaned and inspected weekly for the presence of predators such as snails and
crabs. - Leave the spat on the collectors until they are large enough to drill and hang on chaplets. Spat are large enough to be drilled when they reach a size of 4 inches (8-10 cm), or are large enough to put in panels. If you wait to remove them from the collectors until after the spat are larger, be prepared to add more floats to the spat collector lines since they will become very heavy and sink. In addition, you may lose some spat to predators this way to predators or they may fall off the collector. However, if spat settlement is heavy, this option is less expensive and more efficient.
- After removing the spat, the collectors can be dried for a few weeks, cleaned and reused. Caring for the spat Spat are like all young animals; they are weak and easy to damage. Spat should be handled gently at all times, and never more than necessary. Most importantly, never pull the byssal threads out of a spat, as this will kill them. Always gently cut the byssal threads.

Spat are very sensitive to heat and drying out.
If you must handle them, do not leave them out of the water for more than a few minutes. When out of the water, keep them cool and shaded. Give spat plenty of room to grow. When spat are kept in lantern baskets, they tend to attach themselves to each other. You should check the lantern baskets at least once a week and gently cut the spat apart if they are attached. Make sure that each spat has at least 4 in (10 cm) between it and other spat, whether they are kept in lantern baskets or panels.
Protect the spat from predators.
Carefully inspect lantern baskets at least once a week for predators like snails and crabs and exterminate them. If spat are kept on the collectors or in some type of container that is not enclosed, be sure to keep these at least 165 ft (50 m) from reef areas to lower the risk of predation from fish and octopus. Once spat are removed from the collectors they can be kept at a depth of 19-23 ft (6-7m).
Hang lantern baskets or panels containing spat at a depth of 19-23 ft (6-7 m). If keeping spat on the collectors until they are large, the main line holding these collectors can be allowed to sink slightly. What to do if the spat collectors do not collect any spat In some areas, it may be difficult to collect many spat. You should expect to collect at least 1 or 2 spat on each collector, although more is ideal. If the collectors do not yield this number of spat after 6-8 months in the water, see if any of the following tips help:
- The collectors may be too deep. If you see spat setting on the ropes and floats, but not the collectors, this may be a sign that the collectors are too low in the water. Make sure all collectors are no deeper than 6 ft (2 m). Add more floats at any part of the line that sags below 6 ft (2 m).
- The collectors may be too shallow. In some cases, you may observe that a large number of other bivalves are settling on the collectors. If you see Black-Lip spat anywhere on the anchor lines lower than the collectors, you may need to lower the collectors to the same depth.
Be sure the water currents are not too strong near the main line.
Try to put the lines in fairly calm water or spat may fall off the line. Try other locations in the lagoon. Spat settlement will be uneven throughout a lagoon. The best areas are those where the water is calm or where eddies form, because spat will spend more time in these areas. Also try locations on the down current side of small patch reefs, since eddies may occur here. Try putting collectors out each month to determine which time is best. The best times of year to collect spat are still unknown in many regions. Periodic deployments throughout the year may be necessary to detect the best times.
Collectors lose their effectiveness if fouled with other organisms.
If collectors are set out more than 2-3 months before the peak spawning season, other organisms will colonize the collectors first and possibly prevent pearl oyster spat from settling. If the collectors are becoming colonized with other animals, the collectors should be removed from the water, cleaned and deployed again. Try different types of materials for making the collectors. If a first attempt using materials other than shade cloth or other plastic materials specifically made for spat collection has failed, you may have to switch materials. Materials such as shells, coconut husks or miki-miki may not work if they have sunk too deep.

Article source: The Basic Methods of Pearl Farming, Author: A Layman’s ManualMaria Haws, Ph.D. (Director, Pearl Research and Training Program, Pacific Aquaculture and Coastal Resources Center, University of Hawaii at Hilo, Hilo, HI 96720 USA, Center for Tropical and Subtropical Aquaculture, Publication No. 127, March 2002)
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- Twitter : @abdurrachim
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