HARVESTING SYSTEMS
The importance of fish as food for human consumption is indisputable and fishing is one of mans’ most ancient occupations. In inland waters fish-culture has intensified to a point which was unthought-of a few years ago and the production of hundreds of tons of fish per hectare has been achieved.
FISH TRAPS
Trapping is a widely used method of catching fish. Traps suitable for use can be constructed in a variety of designs, shapes and materials. Conical, cylindrical or other shaped traps made of reeds or sticks are commonly used by African fishermen. These traps are not very successful because they are dark inside and the fish are reluctant to enter them. Better results are achieved in dams with traps made of wire or plastic netting which do not obstruct the light.
To make a rectangular trap 1 metre long, 60cm high and 60cm wide, the following materials are needed:
- 9 metres 8-gauge galvanised wire
- 5 metres chicken-netting 60cm wide
- 25 – 30 metres 22 – gauge wire
Two frames of 8 gauge wire are required as shown in Figure 1, one for the bottom and one for the top. Cover the frames with chicken netting and sew along the edges. Double both ends of the netting approximately 2cm over the frame to eliminate sharp wire-ends at the corners. Stitch the netting for the sides and entrance to the bottom frame. A trapdoor should be made in a corner of the top frame. The structure will be stronger if wire supports are attached between the top and bottom frames at the entrance and corners.
Figure 1: A Rectangular Trap
A handle fixed on top of the trap makes handling easier. All joints of frames and supports should be brazed or welded together to make an oval trap which is made along the same line as a rectangular trap, two frames are made top and bottom – 100cm long and 60cm wide. Cover them with wire netting. Place the netting roll upright on one of the frames and sew around it, starting from point a and ending at point b so that the entrance opening is in the middle of the trap. Both ends of the entrance opening must be straight and of equal length or the fish may escape.
To strengthen the trap, take a piece of 8 gauge wire 150cm long, bend it into a U-shape as wide as the entrance opening and insert through the entrance-meshes from top to bottom. Bait such as porridge may be used, either hung in small baskets or coarse bags in the centre of large traps, or placed on the bottom of smaller ones.
Figure 2: Oval or Kidney Shaped Traps
FISHING NETS
The adoption of synthetic fibers in the fishing gear industry has brought about a remarkable increase in catching efficiency. The best known of these fibers is nylon, and they are rapidly replacing all natural fibres. Natural or synthetic fibres for fishing nets are called netting twines. The size of netting twine is usually shown by a number based on the mass of single yarn in a given length. Fabric consisting of one twine or systems of yarns which are crossed, knotted or joined so as to form meshes, is known as netting, netting-sheeting or webbing.
Netting used for fishing gear may be knotted, usually made with a reef-knot, sheet-bend or double knot, either by machine or hand braiding. Netting used in the fishing industry at present is mainly machine-made, but knowledge of hand-braiding is useful and necessary for shaping some sections of various types of fishing gear when hanging or repairing the nets.
GILL NETS
Gill nets belong to the type of fishing gear commonly known as passive gear. They are laid out in the water and the fish have to enter the meshes to be caught. They are suitable for fishing in nearly all farm dams and in areas where seine nets cannot be used effectively. Gill nets consist of a sheet of netting fixed between four ropes, a buoyant top-rope, a foot-rope supplied with weights and side-ropes at each end.
Gill nets should be invisible in the water so that the fish get enmeshed easily. The twine should be thin and soft but strong enough to hold the fish and have a degree of elasticity to let fish enter the mesh. Usually the net closes tightly around the fish, fastening on its gill-covers, fins, scales, head-bone and teeth. For most fish species the meshes fasten mainly behind the gill-covers, hence the name, gill net.
The recommended twine for various mesh size gill nets for farm dams are:
| MESH SIZE | TWINE NO |
| 24mm to 90mm | 210/3 or 110/3 |
| 100mm to 125mm | 210/4 or 110/4 |
| Over 125mm | 210/6 or 110/6 |
The hanging of gill nets determines the shape of the meshes and the degree of looseness of netting. This influences the selection of gill nets. The most widely used hanging ratio is mesh hung by a half, this means to 50 % of its stretched length. This shape of mesh should catch most of the varied fish species. This hanging has sufficient looseness to entangle the fish at the same time as it is gilled. The mesh size in gill nets determines the size of fish being caught within a certain range.
To choose a suitable mesh size, one must know the composition of the fish population and the size of species in the water. In farm dams the range of mesh varies from about 60 to 125mm. The top, foot and side ropes should be strong enough to withstand the wear and tear of setting and lifting. Gill nets in most countries have the float braided or woven into the top-rope material, and the foot rope consists of short lengths of lead around a nylon core covered with plastic or woven nylon. For side ropes, hanging twine or strong netting-twine may be used.
To keep the nets in a vertical position in the water, the top rope is supplied with floats and the foot rope with sinkers. The best material for floats is cork, which is strong and buoyant, but plastic or other synthetic materials may be used. Sinking nets are used in waters fairly free of submerged shrubs and other obstacles which damage the nets. They may be set parallel or at right angles to the shoreline, along or between weed patches, singly or joined together to form one ‘fleet’. To turn a sinking net into a floating net, additional floats are attached to the top rope between the existing floats. Floating nets catch fish which are mostly near the surface. They are very effective when insects such as flying ants are present, as these attract the fish to the surface of the water. The length of gill nets may vary but a convenient length for use in farm dams is from 30m to 50m when hung.
Figure 3 and 4: Show a Floating Gill Net and a Sinking Gill Net
SEINE NETS
In commercial fisheries a variety of nets under the name of seines are used, differing widely in their designs and their application. Of these, shore-seine, beach-seine or drag nets may be used effectively in farm dams provided there are suitable areas free of obstructions. Seine nets are pulled through the water, usually against the shore, enclosing the fish in a semi-circle in such a way that they cannot escape. A netting area should have a gently sloping smooth bottom entirely free of rocks, trees and dense vegetation.
Seine nets, like gill nets, consist basically of netting hung with a floated top rope weighted foot rope and with side ropes at the ends as shown in Figure 5 below:
Figure 5: A Seine Net
For farm dams and fish ponds a popular measurement is 34m long, 3m deep in the centre, tapering to 1.2m in the wings. The mesh size of 20 to 24mm in the centre and 25 to 50mm in the wings. In medium sized and large dams, a net 65m to 75m long and 5m deep in the middle, tapering to 2m in the wings is suitable. The mesh sizes should be 25 to 40mm in the centre and 40 to 50mm in the wings.
For seine nets the netting is made of strong twine and small meshes which help to prevent the ‘gilling’ effect of the fish and while this makes the nets heavier and more expensive, it increases their effectiveness and lengthens their life span.
Tapering of seine net wings may be achieved by any of the following methods:
- Hanging the machine-made netting at a varying degree of looseness;
- Cutting the machine-made netting into the required shape; or
- Creasing or bating the number of meshes when hand-braiding.
Twines recommended for nets with 20 to 40mm mesh sizes are No. 210 d/9 and 210 d/12, and for nets over 40mm mesh size, No. 210 d/15 and 210 d/18. For top, foot and side ropes, use nylon sash cord No. 6 or 7 for small nets and for nets over 60 in length No. 8 sash cord or stronger would be advisable. For the side ropes sash cord No. 6 or 7 should be spliced to the top and bottom ropes. The bottom rope should be weighted so that it is heavy enough to follow the depressions on the bottom of the dam, but not too heavy to cut into the mud and make the net impossible to handle.
Figure 6: A Seine Net without a Bag (Top) and a Seine Net with a Bag (Bottom)
Figure 7: Hanging of a Seine Net with various Looseness of Mesh for the Correct Tapering
Bating, is too lessen or decrease
There are other types of fishing gear which are seldom used, but which are useful in some instances.
A TRAMMEL NET
This net consists of three sheets of netting hung on the same top and bottom ropes so that they lie together in one sheet. The two outer nets have large meshes hung so that the bars lie exactly opposite each other. The inner netting has very small meshes, is deeper and hung loosely. When a fish strikes the net, the force carries the loose smaller mesh netting through the larger mesh on the opposite side thus forming a pocket in which the fish becomes entangled.
Since fish are more easily caught when they strike the net at speed, the best catches are achieved by driving them into the net from places where they are concentrated, such as flooded grass areas.
A CAST NET
This net is a conical net with small meshes, usually operated by one man. It is heavily weighted around the perimeter and is provided with a draw cord and a retrieving line which passes through the top portion as shown in Figure 8 below. The net is thrown outspread over the water to cover the fish and is allowed to sink to the bottom. When it is drawn up slowly the fish underneath are caught in the bag formed by pulling the draw cords.
Figure 8: A Cast Net
A FYKE OR HOOP NET
Is a tubular or funnel shaped bag of netting held open with hoops and may be used instead of wire-traps. A fyke net is usually fitted with one or more non-return entrances. Set in shallow water, it is left stationary until the catches decline. The fish caught are removed by regular checks.
Figure 9: A Fyke or Hoop Net
DIP OR LIFT NETS
Used in several African lakes, such as Kariba and Cahora Bassa, for catching small kapenta. The nets are immersed in the water, left for a while and lifted out quickly so as to capture as many as possible of the fish which happen to be above. These nets usually have a metal frame, round or rectangular in shape. Small lift nets are raised by hand, but larger ones need a mechanism operated from the shore or from a boat. A bright light is used to attract the fish into the net at night.
Figure 10: A Dip and Lift Net
LONG LINES WITH HOOKS
The use of long lines is economical mainly when catching predatory fish. For bottom-feeders the hooks are laid on or slightly off the bottom. For fish with mid-water feeding habits, hooks should float in the water. A long-line carries 25 to 50 hooks attached to traces which are tied at intervals of 2 to 4m apart or at least at a distance of three times the length of the traces to ensure that fish caught on adjacent hooks do not become entangled. Very large fish will need stronger twine but a synthetic fibre line with a breaking-strain of 15 to 25kg for the traces is usually adequate. The choice of hooks depends on the size of the fish to be caught, but generally Nos. 1/0 to 5/0 are used. Suitable baits are worms, or pieces of fish or meat.
LONG LINES WITH FLOATING HOOKS
For floating hooks, use a line of synthetic fibre 300m long carrying 25 hooks, with a breaking strain of 20 to 30kg for the line and 5 to 15kg for the traces. Traces 2 to 4 m long are tied 5 to 12m apart on the line and the knots weighted to keep the corks submerged. The corks regulate the distance of the baited hooks from the water’s surface and the free ends of the traces are tied in a loop to which hooks with short wire traces are attached. (Tiger fish will bite through a fibre trace. Small live fish are used as bait.)
Figure 11: Long Lines with Floating Hooks
ADDITIONAL EQUIPMENT
Fishing requires a certain amount of additional equipment apart from the actual fishing gear. This includes boats for setting and hauling in nets as most dams cannot be properly managed from the shore. A necessary item includes a hand-net for lifting fish from the water, wells in which to keep fish alive when caught or to store live-bait and grapples for recovering long-lines or gill-nets and lead-lines for taking soundings. For successful and effective fishing, all fishing gear needs care and timely attention to repairs, which must be carried out speedily. Gill nets should be lifted daily and both gill and seine-nets washed cleaned after fishing, repaired and stored carefully.
