フィリピンにおけるマングローブ林開発と養殖池の拡大について

抄録

Mangrove forest has rapidly decreased in the last 20 years due to many kinds of human impacts. Therefore, a type of“Marine Desertification”is appearing in tropical and sub-tropical areas, and environmental conditions are worsening, despite a growing awareness of the importance of mangrove forest and ecosystem utilization is more at present. We should make guidelines for of the utilization of mangrove forests.
In this paper, we try to clarify the progress of mangrove habitat in relation to their landform conditions, the actual condition of the destruction of mangrove forest by human impacts, and the diversion of mangrove areas to fishponds in the Philippines.
Results are summarized as follows:
1) In the Philippines, the destruction of mangrove forest has been mainly caused by the construction of fishponds which were enlarged since the late 1960's. Consequently, about half the former area of mangrove forest has been already diverted to it as awhole. That diversion, is remarkable in Luzon Island.
2) Milkfish is mainly produced in the fishponds. However, the productivity of aquaculture is at a within lower level compared with other countries in Southeast Asia. In the Philippines, however it can be said that productivity in regions with a long old history of aquaculture is generally high.
3) Infanta, our study area, is 150 kilometers east of Manila. Mangrove habitat was widely developed in the margin of backmarsh of the Agos River floodplain and in the interchannel basin (lagoon). This habitat has developed since than 2500 year B. P. and has been protected by beach ridges and bars from the wave action.
4) In Infanta, fishponds have been extended rapidly since about 1970. As a result, about 40% mangrove area of total mangrove forest has disappeared. The decrease has had a bad effect on the lives of local people. They say, for example, variety and quantity of fish they catch than before have decreased. Moreover they suffer more damage from flood tides and typhoons.