marine fisheries in Southeast Asia
Industrial push netting developed from traditional, small hand-operated push-nets and small boat-operated nets (dugouts, rafts and sailing boats) in the region. Fishing with traditional push-nets involves scooping or seining, usually along the bottom or just off the bottom in relatively shallow waters in estuarine areas, mangrove creeks, shallow bays and littoral areas. A bag net connected to poles is pushed forward through the water by hand to catch coastal marine animals such as shrimp, crabs and fish. Traditional push-net fishing operations of different scales are reported from Indonesia, Malaysia, Myanmar, the Philippines, Singapore and Thailand. The most visible push-net fisheries in the region are those off the Gulf of Thailand covering the Thai and the northern Malaysia (Terengganu) coastlines.
In the wake of fishery industrialization, some push-net fisheries have developed beyond the non-motorized or hand-held operations and, since 1970, the efficiency of this traditional equipment has increased by using motors rather than manpower (in the Manila Bay, Philippines [Silvestre et al., 1987] and Gulf of Thailand [Nagalaksana, 1987]). This change allowed for push-net fishing farther from the shore and a larger sized net. Push nets are non-selective and it is believed that motorized push-net fishing boats are causing the deterioration of marine animal resources and the coastal ecology in shallow, near-shore areas.
In Thailand, the Department of Fisheries imposed a 3 km near-shore fishery limit to exclude trawling and push netting but the number of push-net boats has increased and there have been warnings from many local communities regarding push-net fishing boats operating illegally within the 3 km near-shore limit. The rapid development of the commercial trawling and purse seining fleet resulted in economic hardships for small-scale, coastal fishers who became less competitive, forcing them into these illegal fishing activities, which is particularly damaging to the resource because of the high percentage of juvenile shrimp and fish species captured with this gear (Nagalaksana, 1987). Controlling push-net activities in the near-shore zone has proven difficult (Suvapepun, 1996). The use of artificial reefs in these shallow waters has been recommended as a means to deter both push-net fishing and trawling (Pramokchutima and Vadhanakul, 1987).
In Thailand, a total of 354 push-net fishing boats were registered in 1970, the first year of registration. In 1974 there were 740 registered push netters with a length of between 14 and 18 m (out of a total fleet of 3241 vessels, representing 22 percent of fishing vessels) operating mainly on the Gulf of Thailand seaboard (Everett, 1974). In 1984, a total number of 16006 fishing boats were registered to the Department of Fisheries of which 960 were push netters. (Pramokchutima and Vadhanakul, 1987). By 1989, the number of boats had increased to 1907. A census of marine fishing in 1995 counted about 4000 push-net boats, of which 1142 were large boats, and noted a trend toward even more such boats. Large boat push-net poles are about 28 to 44 m long with a net mesh size of between 0.5 and 1.5 cm. The push-net poles of small push-net boats are 6 to 15 m long, with approximately the same size of net mesh as large push-net boats. Push-net boats are still operating in many areas such as Prachuapkhirikhan, Chumpon, Suratthani and Pattani provinces and in some extreme cases the legs of the push-net have been extended to allow push netting in deeper waters beyond the near-shore zone up to depths of around 30 m.
Push-net boats harvest both large and small marine animals. In Thailand, those with economic importance such as shrimp make up about 40 to 45 percent of the total catch; the balance, some 60 percent which are classified together as trash fish, include juveniles of economic marine animals such as sardines, spider crabs and drum fish. These juvenile economic fish constitute some 65 to 70 percent of the trash fish total. The remaining 30 to 35 percent are true trash fish. It has been estimated that in one year the total push-net harvest from boats of all sizes is 26289 tonnes, of which 15–16 percent are large shrimp, 8–9 percent are spider crabs, 7 percent are fish, 4–5 percent are squid/cuttlefish, and the balance a mixture of other species.