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Inland fisheries in multiple use of resources.

This technical paper presents three case studies of inland fisheries in the context of a multiple-use of land and water resources in the humid tropics of Asia. Two of the three river basins are situated on islands, i.e. the Agno in the Philippines and the Mahaweli in Sri Lanka; one is on mainland Asia, i.e. the Nam Pong Basin in Thailand. Although the river basins have a number of features in common, such as, for example, their size, forest cover and population density, they differ in a number of other environmental aspects and changes induced by the development taking place in their basins.

Inland fisheries in all three catchments is represented both by capture and culture components with reservoir fisheries gaining in importance. The studies have shown that while the major constraint to the riverine fisheries has been identified as being the high level of transported sediments originating from eroding lands and mine waste discharge (the Agno Basin), in the reservoirs of Nam Pong and Mahaweli basins it has been the high fishing pressure, in one case non-regulated (Nam Pong), which has caused deterioration of fish stocks. Another constraint in force until recently was of a social (religious) character (Mahaweli Basin). The three studies have shown that in most situations inland fisheries can successfully develop under conditions of the multiple use of the resource.

Details are given on the current fish yields, on long-term changes (Nam Pong reservoir), on problems associated with introductions and stocking (Nam Pong and Mahaweli), and on some other aspects of reservoir fisheries and aquaculture developments in these basins. The studies have stressed the need for regular monitoring of fish stocks and fishing effort for successful management. A fishery development sub-model prepared for the Nam Pong reservoir has clearly shown the need for introducing regulatory measures of reservoir fishery, if it is to improve. One of the major constraints for sound fisheries development appears to be the lack of a coordinating river basin authority, both during the planning and design, as well as during the implementation and management phases. Among the recommendations put forward in Chapter 4 “Summary and Future Needs” are the need for improved monitoring of selected limnological, fish and fishery data, for better information on the impact of introductions, for a manual on suitable fish species for stocking the Indo-Pacific reservoirs and lakes, as well as for evaluation guidelines of technical character to advise fisheries planners and managers on measures against constraints imposed on fisheries by other uses and by human induced environmental changes.