In this chapter an attempt is made to summarize the present study's major findings. Table 9.1 summarizes the availability of data and information on the various subject matters investigated for the various man-made lakes.
It is interesting to observe that although the present study indicates that the availability of relevant data is limited, some documents surfaced which had not been included in the comprehensive Source Book for the Inland Fishery Resources of Africa by Vanden Bossche and Bernacsek (1990a, 1990b and 1991): for instance the studies carried out by De Kimpe (1980a; 1980b and 1981) in Lagdo and Maga; the report by Khalid on Jebel Aulia (1990); the work done by FULREAC in Zaire; the summary by Bearez (1988) on Kossou; the SWECO reports on Mtera.
It may be obvious that due to the lack of various types of data it will be difficult to compare the different situations in the lakes. If lakes are comparable at all, then the data sets are practically always incomplete. The present study, however, indicates in which fields data are missing. Improved and intensified data collection should be carried out. For all existing artificial lakes it is too late, of course, for a pre-impoundment study, but it is never late to start relevant fisheries data collection. It is regretful for instance that after the extensive pre-impoundment study for the Mtera Reservoir hardly any serious data collection took place during the filling phase and during subsequent phases. As a result the impact of the lake can hardly be assessed.
Data collected on a reservoir fishery are not necessarily comparable with those from another lake. Some examples are given in the following sections.
From Table 9.1 it may be observed that species compositions are known for a number of lakes. However, compositions may be difficult to compare, as was pointed out by Van der Knaap et al. (1991b), who determined different species compositions for different mesh sizes. Ruwet (1961) found various compositions for various different biotopes in one lake. As a result it is difficult to compare different lakes.
Another variable in the lakes is the surface of bush that was cleared before impoundment. SWECO (1976) reported that 141 km2 of bush was cleared before closure of the Mtera dam. Entz (1984) found that 95 km2 of bush was removed before the Kossou Lake was created. In Lake Lagdo a certain unknown surface was cleared near Lagdo village. No fisheries data were ever collected for comparison in this field.
The most utilized reservoir management technique has been the introduction of non-indigenous fish species, most often tilapias. The present study, however, indicates that these species were introduced only into a small number of lakes: Lake Kossou (Kapetsky, 1986; Kouassi, 1979) and recently in Mwadingusha Reservoir (Damas, 1961). In both lakes data collection was of reasonable quality in relatively short periods; however, the results do not allow comparison.
The evolution of the microclupeid fishery was well described in Lake Kossou. If this type of fishery develops well in Lake Lagdo then there may be some possibilities for comparison. As far as the other lakes are concerned, it is unknown whether small clupeids occur (see Table 9.1).
The number of options for management measures is limited. The existing measures are the following:
In Lake Lagdo some gear and techniques are prohibited; in Maga a closed season is imposed and in Kossou an attempt was made to increase the production by introduction of species and cage culture. The management options for Mwadingusha date back to the 1960s; the present situation is unknown.
The present study summarizes data and information available and one of the findings is that the gaps in data availability became apparent. The general shortcoming is the lack of data collection; if data were collected during a survey or a research programme, then the system would collapse or halt after termination of the survey or project.
