| Stage | Other uses | Fish Community | Fisheries | Research Priorities | Development and Management |
|---|---|---|---|---|---|
| Unmodified Rhithron and potamon zones show most characteristic natural features. Flow regimes unaltered by direct human intervention but indirect effects of activities elsewhere in the basin may be apparent. | In wild state banks and floodplains forested and support game. Later used for grazing cattle. Vegetation modified by burning. Seasonal occupation by nomadic fishermen, hun- ters and pastoralists. | Fish stocks in original condition of abundance and diversity but size structure may be modified by fishing. Baseline productivity. | Moderate to heavy fishery throughout system. Area available to fisheries - whole river and accompanying plains. | “Quick and dirty” estimates of potential. Exploratory fishing for description of fish stocks. Identification of major resources. Studies on biology of individual species and their geographical and seasonal distribution. on. | Frame surveys and catch assessment surveys to define fishery. Studies in local fishing methods and introduction of appropriate additional techniques. Simple regulatory measures for protection of major stocks Introduce and improve access, living space and marketing networks. |
| INTRODUCTION OF SYSTEMATIC AGRICULTURE | |||||
| Slightly modified Smaller streams unmodified although removal of forest cover. On floodplains some drainage channels for more rapid removal of flood waters. Smaller depressions and oxbows filled or regularized. Flow regime still largely unaltered for timing although irregularity in discharge may be detected especially in low order streams | River banks and floodplains largely cleared of forest. Extensive agriculture on areas adjacent to streams and drawdown agriculture on floodplains. Beginning of floating rice culture in suitable depressions. Cattle grazing widespread on water meadows and floodplains. Zonation of floodplain for different uses highly developed. Settlement on river banks, levees and higher grounds or on artificial islands and stilt villages. | Large individuals of bigger species becoming rare. Size structure heavily biased toward smaller individuals. Overall productivity sometimes altered, reduced or even slightly increased. | Heavy fishing throughout system. On floodplains some depressions may be dammed as holding ponds. Area available to fisheries - whole river. | Population dynamics of major element of the community to give refined estimates of potential yield. Deeper studies on biology of important species to identify possible sub-populations and to describe ecological interactions between species. | Frame surveys and catch assessment surveys to define fishery. Monitoring to detect potential overfishing of major stocks. Intensification of regulatory measures to protect fish stock from bad fishing practices. Investigation of simple forms of extensive aquaculture. Improvement of fish landing and preservation techniques. |
| INTRODUCTION OF FLOW CONTROL | |||||
| Extensively modified Smaller rivers beginning to be regularized with water extraction. Drainage and irrigation common. Floodplain depression lakes usually filled or regularized. Flow regimes often extensively modified in timing and duration with some flood control structures. | Intensive dry season agriculture and wet (rice) culture with attendant use of fertilizer and pesticides. Moderately extensive occupation of the dryer areas of the plain for habitation, beginning of urbanization. Much of plain still liable to flooding. Mining, gravel and sand extraction from beds of low order rivers. | Disappearance of larger species and modification of fish community as habitats required by certain species are modified. Overall productivity somewhat reduced. | Commercial capture fisheries very intense in main river channel. Some new fisheries in flood control reservoirs. Drain-in ponds and some intensive fish culture in regularized depressions. Emergence of recreational fisheries as important competition to commercial fisheries. River area available for fisheries restricted. | Examination of general dynamics of fish community to judge reaction to various types of stress. Pre-impoundment studies to predict potential effects on fish and fisheries and to help plan fisheries in new water bodies. Investigations to establish minimum flows in rivers. | Intensification of monitoring of fisheries with increased control of catching methods by licensing and legislation. Examine impacts of other activities in river basin on fishery and endeavour to ensure that suitable conditions are maintained. Planning strategies to minimize effects of dams and other alterations of the environment. Investigation of intensive aquaculture. Develop reservoir·fisheries and seek alternative employment to reduce fishing pressure on main river. |
| CONSTRUCTION OF MAJOR DAMS | |||||
| Completely modified Smaller rivers channelized and often completely enclosed. Main channel sometimes channelized. Floodplain largely dry but still subject to occasional catastrophic floods. Flow control nearly complete with large upstream dams and levees. River sometimes reduced to a chain of reservoirs. | Urbanization. Intensive use of plain for agriculture, industry and habitation. | Fish community extensively changed by loss of species through pollution, or channelization and other environmental modification. New elements of fish fauna by introduction of exotic species. Overall productivity considerably lowered. | Commercial fisheries mostly disappeared. Sport fisheries in small streams, main channel and in few remaining flood lakes. Some intensive aquaculture in specially constructed ponds. Area for fisheries small as little of original area remains. However, new reservoirs, may be developed for fisheries. | Investigation of pollution and other management impacts to establish criteria for maintenance of fish stock. | Regularization of discharge and effluent quality according to criteria established. Contemplate introduction of new elements of fish community to both river and reservoir or stocking to support threatened species or fill vacant niches. Study access problems to river and reservoir fisheries to resolve conflicting demands by sport and commercialfisheries. Intensify development of aquaculture and reservoir fisheries. |
