50 September 2009 on foot. Other types are the cast-nets, beach seines, lift nets and mosquito nets. But there are also traps in the form of pots among other types of gear. Many catching operations are performed without any type of boat; others use simple vessels such as rowboats or sailboats in Bangladesh (Rahman 2001). In that country five types of gillnets are used. In addition, trammel nets and beach seines are used. Various types of bagnets are also used. Specialized nets are used for collecting shrimp postlarvae that are used for growout by aquaculturists. Fine-mesh push nets, fixed bagnets and dragnets are used along the coastline for harvesting postlarval Penaeus mondon. The Industrial shrimp trawl fishery The industrial fishery is carried out in offshore waters and involves various types of trawlers, which use one, two or four nets. The nets are usually 10-30 m long and made of polyethylene or polyprophylene in Nigeria (Ogbonna 2001). The mesh size in all trawl sections are, except for the cod end, between 51 and 55 mm. The legal mesh size in the cod end of the shrimp trawl net is 44-mm stretched net. The average engine power is 450-800 hp. The vessels are furnished with a refrigerated fish hold and with a freezer. The vessels can operate day and night. The double-rigged/outrigger refrigerated vessels operate day and night pulling either two or four otter trawl nets. The towing speed is 2.5-3.0 knots. Many vessels are furnished with turtle excluder devices. In various developing countries, the detrimental effect of shrimp trawling on natural resources is recognized. It is obvious that the trawling methods may impoverish the living resources if the fishery is not regulated. This is especially true for shallow nursery grounds along the coast. Too many shrimp juveniles are taken and killed before they mature and can contribute to the fishery. Another problem is that benthic fauna and seagrass beds are being destroyed by trawling activities. In some areas, the situation is alarming and the natural habitats for shrimp and other invertebrates are destroyed, which can lead to decreased production. Another serious effect of shrimp trawling is the amount of bycatch. In some areas the bycatch is very large. It may be 80 percent or more of the catch. This is also the case when fishing for juveniles where often more than 90 percent of the catch consist of non-desirable species. The Catch of Small or Medium Sized Shrimp in the Atlantic and the Pacific Except for the large tropical shrimp species, there are four species of great importance in the Atlantic and Pacific. In the northern Atlantic, the northern prawn (Pandalus borealis) is of economic interest. The total catch in 2004 was 450,000 t. Common shrimp (Crangon crangon) was also of economic interest. The catches are around 40,000 t per year. In the northwest Pacific, two species are of great importance: southern rough shrimp (Trachypenaeus curvirostris) and Akami paste shrimp (Acetes japonicus). The catches were 300,000 t and 680,000 t. The northern prawn is a coldwater species that is distribFig. 2. Catches of Northern prawn ( Pandalus borealis) on the northwestern (NW) and northeastern (NE) sides of the Atlantic between 1993 and 2004. Figures from FAO. Fig. 3. The catches of Common shrimp ( Crangon crangon) in the North Sea and adjacent areas. (Figures from FAO). Fishing Technology in Tropical Areas Artisanal fishery The large tropical shrimps are caught with rather primitive methods in the artisanal fishery and usually with advanced methods in the industrial fishery. The artisanal fishery for shrimp is extremely important in many developing countries. In Bangladesh, for instance, 4-5 more shrimp are taken in this type of fishery than in the industrial fishery (Rahman 2001). It is, therefore, likely that many catches are never registered in that type of fishery, which means that the reported catches, in general, are underestimated by many countries. In many tropical countries, the dugout canoe is the most common craft in use in small scale fisheries, such as in Tanzania (Haule 2001). It is propelled by oars and poles or occasionally with sails when operating in open waters. Planked boats equipped with sails and/or outboard engines are employed. Various types of seines are the predominant gears. There are nets and seines made of nylon yarn with mesh sizes ranging from 2.5 to 5 cm and 0.16 to 1.3 cm. There are two types of nets usually operated from dugout canoes drifting with one end attached. The length of that net is 103 m, while a longer one of 344 m is set across channels within the intertidal zone. Nets held between two mangrove poles are frequently towed by two persons operating (Continued from page 48)
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