|OverviewShrimp driftnet fishing is a unique fishing technique used mainly by small-scale fishery. It is generally a daylight fishing operation starting early morning, which is carried out in several sub-tropical countries where the bottom configuration allows this kind of fishing operation.Species EnvironmentIn Indonesia, the penaeid shrimps consist mainly of Parapenaeopsis spp., Penaeus merguiensis, Metapenaeus brevicornis and Metapenaeus ensis (Anonymous,1976). Other important species are P. indicus, P. monodon , Penaeus semisulcatus, Penaeus latisulcatus, Metapenaeus monoceros and Solenocera crassicornis (Unar and Naamin, 1984). The non-penaeid shrimps consist of small atyids, caridean species and Acetes spp. (Gulland, 1971).|
In the Gulf of Venezuela, there are five shrimps species presently exploited, belonging to the Penaeidae Family: (Farfantepenaeus) Penaeus brasiliensis (pink stained), F. notialis (pink), F. Subtilis (three species which are commercially called as brown shrimps); F. schmitii (White) and Xyphopenaeus kroyerii (shrimp titi). From these species, the most important is (Farfantepenaeus) Penaeus subtilis, which constitute more than 50% of the landings.
In Venezuela, Margarita area, shrimps species are: Farfantepenaeus brasiliensis (pink stained), comprising 98% and F. notialis (pink), which is the last 2% balance. Crab species (2%) are represented commercially by species Calappa (C. sulcata, C. flamea and C. nitida).
In El Salvador, both species appear in the inner Gulf and in the eastern part of the outer gulf, at a maximum depth of 50 m. These are areas with muddy or sandy bottoms. The white shrimp can complete its whole life cycle within the Gulf of Nicoya. Spawning has been observed in the inner gulf.Fishing GearEl Salvador's bottom driftnet for shrimps has the following characteristics: the netting body is made of PA monofilament white or light green color. Twine diameter: 0.33 mm. Meshsize can vary from 63-82 mm stretched meshes. One hanged net size is generally 54 meters x 50 meshes deep. Hanging ratio: E.0.50-0.60. Buoyancy is 30 grams/m. Sinkers is generally 35-40 grams/m. About 300 meters of hanged net were used per small canoe in 1986. Fishing is done by daylight by a maximum depth of 20 metres, with drifts lasting from 15 minutes to two hours.In Venezuela, Margarita/Maracaibo area, fishermen use a bottom driftnet for shrimps, which consists of a single panel of webbing, typically 3-5 m in height and 250-350 m in length. The webbing for such a net is made of PA monofilament twine, with a stretched mesh size about 70 mm.Fishing GearIn Colombia, the bottom gillnets for shrimps are made of PA monofilament netting material of 69-89 mm stretched mesh size netting. Hanged net length per canoe is ranging from 300-580 meters for 6-8 m height.Fishing GearIn India, (Tamil Nadu), drift gillnets used by the kattumaram have stretched mesh size varying from 35-36 mm. Netting is generally made of PA multifilament R50 tex. As per the carrying capacity, a kattumaram can operate with hanged length of 180-300 meters x 1.5-1.6 meters height. Hanging ratio is generally around E.0.50.Fishing GearIn Indonesia, the bottom gillnets are of monofilament nylon with a mesh size of 25-50 mm, and are operated in the intertidal zone in combination with other units, resulting in nets of 25-200 m length which are set parallel to the shore.Fishing GearIn Senegal, in the Casamance river, gillnets for shrimps are used, and fishing operation is done mostly at night. Netting is made of PA multifilament R 165 tex. Stretched mesh size generally used is from 24-32 mm. Hanging ratio is about E.0.40. Canoes operate with a hanged net length ranging from 100-300 meters x 1.3-1.8 meters height. Buoyancy is about 154 gram/force per meter.Vessel OverviewThis fishing technique is operated especially by small open boats or small vessels. Net hauler are often used.Handling ModeCatches are iced on board or not and, normally landed only a few hours later, in very good condition.Fishing OperationsIn a sea fishery the nets may drift independently, accompanied by a vessel, but generally they are fastened to a boat that drift with them; in this way nets are closely watched during the night so that they can be controlled and hauled at any time, without searching for them. The method of operating very long rows of driftnets is particularly important because large areas of water can be covered by the drifting net walls. In this way they are able to filter large volumes of water and so catch even scattered shrimp or fish in sufficient commercial quantities. The net is set either across or with the flow of the current, and if properly rigged, it moves with the current pulling the float line ahead of the lead line. Shrimp, sensing the approach of the lead line or the lower part of the webbing, jump up and are entangled in the "overhang". Fishing is done by day or by night in depths as great as 20 m, with drift lasting from 15 minutes to two hours.Fishery Production SystemsShrimp driftnetting is a fishing technique used mainly by small-scale fisheries. Bottom driftnet, for shrimp as for other species, are effective in places where some current makes the net drifting (up to about three knots) and obviously in large areas whithout obstacle to drifting. In fact, the area swept can be considerable. A driftnet 300 m long, moving at 1.5 knots, could sweep over 400 000 square meters in a half-hour drift. Both bottom drifting gillnets and trammel nets are used for shrimp fishing at sea, in shallow waters areas; they are also, commonly, used, for specific species in backishwater (lagoons, large lakes and rivers) and estuaries. In contrast to sea fisheries, driftnets are not used much in freshwater fishing because the areas are so limited. In places where large areas of clear bottom are not found over rough bottom, or on grounds where currents are not favorable for driftnetting, small-scale fishermen sometimes use bottom set gillnets or trammel nets to catch shrimp.Fishery AreaDriftnetting for shrimp operate in some Latin American countries (El Salvador; Colombia) and in some Asian countries (India; Bangladesh; Indonesia; Malaysia and Japan). On the Casamance river in Senegal, shrimp driftnetting began some ten years ago, and the practice appears to be spreading rapidly.SeasonalityThe driftnets fishing season may change zone by zone according to the target species and its migration patterns.IssuesConflicts By nature, the use of drifting fishing gear, set gear and towed one on the same ground creates conflicts ans, therefore, in areas where there has been expansion of shrimp driftnetting, problems with driftnetters and trawlers or fishermen using fixed gear appeared. It has been said that driftnetters, which generally work in shallow water and sometimes in estuaries, harm breeding populations and contribute overfishing and, on the other side, that trawlers have for years made heavy fishing pressure on some coastal grounds which, in addition, is less selective than fishing with driftnets. According to a 1984 study by IDERENA (Instituto Nacional de los recursos Naturales Renovables y del Ambiente) in Colombia, the Penaeid shrimp caught by driftnets of 61-81 mm mesh size, were mature adults of 146-200 mm total length, which had already spawned at least twice. In contrast, standard shrimp trawls captured smaller specimens (96-180 mm total length). In any case, the rapid expansion of shrimp driftnetting is likely to continue. Although an effective and profitable method, its use is unknown in many countries where conditions may be favorable.