7. IMPLICATIONS FOR FISHERIES OF NEW RESERVOIRS IN AFRICA

Presently, the some 41 000 km² of existing African reservoirs (up to 1982) provide about 10 percent of the total 1.4 million ton fish harvest from Africa's inland waters. Recent yields from Africa's largest reservoirs with developed fisheries have ranged from 27 to 65 kg/ha/year with a median yield of 55 kg/ha/year.

The projected increases in reservoir surface area have the potential to make a substantial addition to Africa's inland fishery output. At a conservatively estimated harvest rate of 3.5 t/km²/year (35 kg/ha/year) the additional 24 000 km² of reservoir area projected for the 1980s could provide 84 000 t, and the 32 000 km² of new reservoir area projected for the 1990s could add a further 112 000 t by 2000. However, the net increase in fishery yield will be less because of improvement caused losses to downstream river and floodplain fisheries.

These new reservoirs could be made to yield even larger quantities of fish than indicated above; however, to do so will require efficient and early (pre-impoundment) planning for new reservoir fisheries, timely fishery development as reservoir area expands, and well-conceived management of the fisheries as resources come under increasingly heavier exploitation.

Planning

Much useful information has been gained from observations on existing Africa reservoir fisheries, including the results of pre- and post-impoundment applied fishery research, and from management and development activities as the reservoirs have aged (Kapetsky and Petr, 1984). While each new reservoir is unique from an ecological and economic point of view, it is clear that it is generally possible to design and operate hydropower dams to benefit fisheries with little or no economic sacrifice to the efficiency of electricity generation nor inconvenience to other user interests.

Broad guidelines to enable the incorporation of special characteristics in overall dam design favouring both downstream and reservoir fisheries, are now available (e.g., Bernaczek, 1984). However, if such design features are to be adopted, it is necessary for fishery officials to intervene in the planning process at its earliest stages when fundamental dam designs are first conceived.

Similarly, at a later planning stage, once the basic physical characteristics of the future reservoir have been established (e.g., area and depth) along with the geochemistry of the watershed and knowledge of riverine fish fauna, fishery yield potential and general reservoir ecology can be predicted (e.g., Marshall, in press). These predictions can be made with accuracy sufficient for planning for such basic fishery development parameters as numbers of fishermen which the resources can support, quantities and kinds of fishing equipment required, and needs for government services such as health, transportation and education.

With the same basic information, losses to downstream fisheries can be gauged. Again, it is incumbent on fishery officials to ensure that these predictions are generated at the earliest possible moment. Such preliminary predictions can be made well in advance of dam construction (see Marshall, in press, for example), and ideally they should accompany the “system studies” referred to in Section 5.

The broad implications of new reservoirs for national and intra-national fishery organizations are that needs for trained fishery personnel at all levels have to be anticipated and acted upon at once, if the full fishery potential of new reservoirs is to be realized. Just as there are long lags between the planning for hydropower development and bringing it “on stream” so there are similar lags in providing personnel sufficiently trained and experienced to manage and develop reservoir fisheries, whether of administrators, field biologists, or extension workers. One way to ensure that adequately prepared fishery personnel are available when required is to include their training as one of the costs of the hydro-development “package”. Ample justification for such expenditure, from a purely investment point of view, is available from the economic performance of existing African reservoir fisheries as providers of income and employment in fishing, processing, transporting and marketing the catch as well as in boatbuilding, engine maintenance, sales of fishing gears, and other activities economically tied to the fishing industry.

Table 1
Details of known dams and reservoirs to be constructed in 1980–90

^a With Rwanda and Zaire
m - millions

Table 2
Projected hydro supply in MW installed capacity 1980–2000

Table 3
Ratio of installed capacity to reservoir area at some existing sites

Table 4
Most likely hydro projects to year 2000

Figure 1. Reservoir Area in Africa to the Year 2000