PHILIPPINES

Current status

Various species of oysters are found in almost the entire coastal areas of the country and they are particularly abundant in bays and estuaries that have some runoff from the land. Four species of oysters are cultured in the Philippines, the slipper-shaped oyster Crassostrea iredalei, the subtrigonal oyster C. malabonensis and the curly or palm rooted oysters C. palmipes and Saccostrea cucullata. The species receiving particular attention in terms of culture are C. iredalei, which are usually 6–9 cm long when marketed and the moderately sized C. malabonensis, which are usually 4–5 cm long. The above species are particularly abundant in Bacoor Bay and extend to the entire Manila Bay from Tarnate, Cavite to Mariveles, Bataan, along the coast of Northern Luzon, Lingayen Gulf, Tayabas and Sorsogon; and to some extent in Batangas Bay, Banate Bay in Iloilo, Binalbagan, Hinigaran and Himamaylan, Negros Occidental, and in areas around Catbalogan, Western Samar, Northern Leyte and Palawan. Commercial farming however tends to concentrate along the coast of various provinces largely in Bulacan, Capiz, Cavite, Pangasinan, Sorsogon and Negros Occidental (Table 8 and Fig. 16). Oyster production figures from 1980 to 1986 are shown in Figure 17. The highest output during this period occurred in 1982 with a production of 19,017 MT, whereas the production dropped to 11,469 MT the following year (Fig. 17). From 1983 to 1986 there was an annual growth rate of about 36 %. The total area of oyster farms in operation in 1986 was 467 hectares in contrast to the 707 hectares the previous year (Malig and Edra, 1987). Such decline was attributed to the rising production costs and slack demand due mainly to the poor sanitary quality of the product.

Culture practices

Four methods of oyster culture are practised in the Philippines; broadcast (sabong), stake (tulos), lattice and hanging (bitin, sampayan, horizontal, and tray) methods.

Broadcast method. The broadcast method is the most simple and primitive method and it is adopted in areas with firm enough bottoms to support the collectors. Empty oyster shells, stones, logs and tin cans are scattered over the selected area where natural setting occurs. Oyster spats are grown to the commercial size on the collectors.
The advantage of the method is the low investment required, whereas the major disadvantages are that it can be used only in coastal areas with firm bottoms and shallow waters, high mortalities due to silt and predation, and difficulty in harvesting.

Stake method. The stake method is usually used in areas with relatively shallow waters and soft muddy bottoms. The main material used in this culture system is bamboo poles (5–9 cm in diameter), however other rigid poles such as split coconut trunks and tree branches are often used. The stakes are driven into the bottom in rows and spaced 0.5 m apart (Fig. 18). The tip of the stake extends to the high water level, due to the fact that oysters can survive and grow in the intertidal zone (Plate 4 and Plate 5).
The bamboo poles provide a clear surface to which the oyster larvae settle after their pelagic phase. Culturists often increase the attachment surface by adding horizontal bamboo sections or by clipping empty oyster shells or other hard materials to the stakes.
This culture method is commonly used in Binakayan in Cavite, Binloc in Dagupan, Binmaley in Pangasinan and in Abucay in Bataan.
The main advantage of this method compared to the broadcast one is that spat mortality is greatly reduced, and growth rate and production per unit area are increased. The disadvantages are that predators such as crabs, starfish, and burrowing snails can easily crawl up the stake and reach the oysters, the high cost of bamboo poles if not locally available and the relatively short life-span of the poles (1–2 years).

Lattice method. In this method bamboo splits are used to construct a lattice which is held together with galvanized wire or monofilament nylon twine. The splits are spaced about 15–30 cm apart and usually one lattice unit comprises 10–16 splits, which can be easily handled by one operator. This structure can be positioned in a great variety of ways, either horizontally or vertically. In the fence style the lattice is stuck on the bottom or supported by bamboo poles. It can also be mounted on rocks or suspended in the water column when mounted on long bamboos or empty drums.
The above method is popular due to a number of advantages: the lattice can be used alone or in groups; collection and fattening of oysters occur efficiently, and harvesting is simple.

Hanging method. Another effective and practical practice is the hanging method. Empty oyster shells or coconut shells are used as collectors. These are strung together on a synthetic rope and held 10 cm apart by spacers, such as bamboo tubes or knots made on the twine. Often collector shells are not spaced during the spatting season but are restrung with spacers during the grow-out phase. Usually each collector measures from 1–2 m depending upon the depth of the water.
Variations of the hanging method are being used in the Philippines. In the bitin or inhitin variation the collectors are fastened on a bamboo platform or fence with bamboo posts attached horizontally near the high-tide level (Fig. 19). The collectors are spaced at regular intervals of 25–30 cm. In the sampayan or long-line variation four or more parallel lines, approximately 20 m long and 20 cm apart, are strung between two bamboo poles. The cultches are fixed at regular intervals on the above lines. In the tray method, bamboo trays are used to hold the collectors. Rafts made of 5–6 bamboo poles are also employed. The rafts are moored to the four corner posts with enough slack to allow the raft to float at different water levels. The hanging collectors are fastened 30–60 cm apart. During the harvesting process, the collectors are merely untied from the bamboo poles and hauled to a raft or small boat.
The advantages of the hanging method are many, such as the high productivity per unit area and no mortality from silt and crawling predators. Disadvantages include the cost of materials (rope, bamboo, etc.), and the requirement of floats, anchors and anchor lines if the raft system is used.

Problems and constraints

Poor sanitary quality and limited demand are probably the major reasons for the failure of oyster farming to expand rapidly. Due to the former constraint the Philippine oyster export market is practically non existent.
Other problems in this culture system range from fouling organisms (eg. ascidians and algae) to siltation. However, these constraints can be avoided by correct management and by the adoption of the suitable culture technique for a given area.

Future plans

The shellfish industry in the Philippines is facing the problems of direct displacement of farming areas by housing and industrial estates and of environmental deterioration. There is a strong concern for the need to develop adequate sanitation standards and methods. Considerable work on bivalve depuration has been recently carried out by the Department of Fish Processing Technology of the University of the Philippines in the Visayas, in cooperation with the German Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) (Barile, Pers. comm., 1987). A simple purification unit has been successfully tested, however, the installation of such a system by single farmers would not be economically feasible due to the present low price of oysters.

Table 8. Distribution and main culture areas of commercially important oyster species in the Philippines.

Figure 16: Major oyster farming areas in the Philippines.

Figure 17: Oyster production data in the Philippines from 1980 to 1986. (Source: Malig and Edra, 1987).

Figure 18: Oyster stake culture system as practised in the Philippines.

Figure 19: Oyster hanging (bitin) culture system as practised in the Philippines.

Plate 6: Oyster culture by the stake method in Cavite Bay, Philippines.

Plate 7: Oyster stake culture during low tide, Cavite Bay, Philippines. Small guard-house built on stilts is visible on the background.