How to setup the Pearls farm
Pearl farms require only very simple structures, the main purpose of which is to provide some means of holding pearl oysters off the bottom. There are three basic types of farm structures: Tahitian longlines (so-called because they are the most common method used in Tahiti), rafts and underwater trestles. You can also use some combination of these, depending on your needs and location.
1. The Tahitian Longline Method
A Tahitian longline is simply a length of strong line (main line) held in place by anchor lines and kept afloat by buoys. Proper placement of the anchors and buoys keeps the longline at the correct depth (See Figure 7 – longline illustration). The longline can be used to hang chaplets, pocket panels, lantern baskets or spat collectors.
Figure 7. “Tahitian” long line. A mainline is hung from a series of anchor lines kept suspended by floats interspersed along the line. Longlines can be used to hang chaplets, spat collectors or pocket panels. Modified from Gervis and Sims (1992).
This method is favored because the entire farm structure is below water so the farm is hidden and protected from damage from rough weather and boats. Additionally, material costs are low and should the need arise, the lines can be moved more easily than with other types of farm structures. One disadvantage to the longline method is the need to dive to work on the farm. Since the longline method is the most commonly used in the Pacific, only this method will be described in detail. It takes two people working underwater and at least one person in a boat to establish a longline. The line used for the main line should be a minimum of ¾-in (18-mm) polypropylene or nylon line.
To start, a diver ties one end of the main line to a coral or rock pinnacle or other anchoring point no deeper than 9 ft (3 m). Be sure the knot used to tie the main line to the anchoring point is very strong. It is wise to anchor the main line at multiple end points since occasionally the main line may fray where it is attached to the coral or rock pinnacle. Then play out the line in the direction of the next anchoring point. Continue until the end of the main line is reached. When tying the line at the last anchor point, it is important to pull the line as tightly as possible before knotting it securely around the anchor point. Usually two people are needed to do this; one person pulls the line as hard as they can and holds it, while the second person ties the knot. You can also use a boat to pull lines tight.
Once the main line is securely attached at both ends, begin to attach the anchor lines at 66-ft (20-m) intervals. Use at least ½-in (12-mm) polyethylene or nylon rope for the anchor lines. Loop the anchor line over the main line and secure it, using a knot that holds firmly but can be untied easily, since the final adjustments to the anchor lines will be made later. Leave plenty of extra line for making adjustments and tying knots. Tie a weight to the free end of the rope and then drop it straight down. This keeps the anchor line positioned vertically below the main line. When you feel that the weight has hit bottom, one diver follows it down and ties the end of the rope to the bottom. Be sure and tie the rope to a secure point. Divers can take turns doing the deep dives as this makes it safer because of the number of deep dives required.
Depending on the current and location of the line, you may have to add some anchor lines tied at angles to the main line to keep it from drifting to one side. In many cases, you may not be able to use coral heads or rocky pinnacles as anchor points, but will have to use weights as anchors instead. More care is needed in this case, as it is important that several sufficiently heavy weights be used at each end and for each anchor line. The end anchor point should have one anchor line tied directly under the main line, and three additional weighted lines tied at angles to the main line. When using weighted anchors, be sure that each anchor weighs at least 75 lb (34 kg).
You may need to add more anchor weights, depending on how rough the water is. For several months, before adding the pearl oysters check the lines weekly to be sure that the anchors are not shifting and allowing the line to move. Once all the anchor lines are in place, attach one float directly over each anchor line. Use a slipknot, which can be easily untied later but is strong enough to hold the float in place. Once all the floats are attached, go back along the line and begin to pull the main line down to the correct depth by pulling down the anchor lines. The main line should be about 13-16 ft (4-5 m) deep, so when the chaplets are tied on, they will hang at a depth of 19-23 ft (6-7 m). When you have finished doing this, swim back along the line and check the depth at each anchor point. You may have to adjust some of the anchor lines and floats because the line tends to stretch and the weight of the pearl oysters may cause the line to sag. Recheck the depth of the line every week or so; you may have to retie some of the anchor lines or add more floats as the lines stretch.
Maintain the main line at the correct depth.
When pearl oysters are hung on the main line, the added weight will cause the line to sag between the points where the floats are attached. The entire line may also sink. Therefore, you should be prepared to check the depth of the entire line every week or so. Add more floats to points where the lines sag, and add enough floats to keep the line at a depth of 13-16 ft (4-5 m). Keeping the pearl oysters clean will also help reduce the weight on the line. Once the pearl oysters and line become fouled, the line may sink out of sight in just a few days. And a line is very difficult to raise to the surface after it has sunk.
2. Floating rafts.
Floating rafts can be used as bases to hang pearl oysters. Rafts are commonly used in Japan and Indonesia in protected areas and bays. Usually the raft is constructed from lightweight timber or bamboo. The floats can be made from large drums sealed with fiberglass or commercial floats (Figure 8- diagram of raft).
Figure 8. Rafts can be used in calm waters to hang a variety of pearl oyster containers. Modified from Gervis and Sims (1992) by Nakashima. One advantage to this method is that it provides a stable work platform and little diving is needed to tend to the pearl oysters. Floating rafts can only be used in very calm, protected waters and in cases where theft can be prevented. The materials may be expensive, so they should be carefully chosen for the length of their lifetime in seawater. Careful attention must be given to the anchoring to ensure the raft does not break free.
3. Underwater trestles.
Underwater trestles can be built from timber, PVC pipes or steel reinforcing bar. Low trestles are used as a base for trays or cages made out of vinyl-coated wire mesh. Higher trestles can be used to hang chaplets or lantern baskets. Underwater trestles can be used to culture adult oysters or juveniles, depending on which type of container you wish to use (Figure 9-underwater trestle with hanging containers).
Figure 9. Underwater trestles are useful in shallow areas and may be used to support trays, chaplets and other containers. It is important to use materials that are resistant to corrosion. Modified from Gervis and Sims (1992) by Nakashima.
Trestles can be good systems for growing spat if properly constructed, but are expensive to build and maintain. They are best used in fairly shallow water, since diving will be required to tend the pearl oysters. Predation by fishes and carnivorous snails is often a problem. You should check the trays weekly for predators such as snails and crabs, which should be removed and killed.
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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