A great range of fishing methods are used on African floodplains and in rivers (Stauch, 1966; FAO, 1969; Welcomme, 1970; Centre Technique Forestier Tropical, 1972; Ratcliffe, 1972). Most of these are, however, general methods which are practised almost universally throughout the continent. The purpose of this chapter is to examine those methods which profit by some morphological feature of the river/floodplain system or from the behaviour patterns of the fish on them. These generally fall into two categories: (i) those methods which use the confinement of fish within limited areas during low water; and (ii) those methods which exploit the migrations of the fish for their capture.
Dry season: During the season when fish are confined to the permanent lagoons, swamps and river channels, there is intense fishing activity. Communal fish drives are common in the floodplain pools and are described from many regions of Africa. Poisoning of pools is also well known and generally such areas are fished out completely at some time during the period. Fishing in the major river channel is usually pursued with a wide variety of nets, traps and long lines. The effectiveness of the fishery in the dry season varies inversely with the amount of water remaining in the system. In periods of extreme drawdown fish are more concentrated and easier to capture. In this way fishing mortality as well as natural mortality increases with increases of HI2.
Period of rising water: Initially fishing activity is intense and is particularly aimed at the capture of fish migrating in the river channel. As the floods increase, the technical difficulties of fishing in the high currents and the dispersion of the fish over wide areas of floodplain make yields low and in most parts of Africa activity is at a minimum during this period. Effectiveness of fishing depends largely on the intensity of the initial stages of flooding. Rapid and high floods disperse the fish more quickly and currents interfere with the efficient working of some types of gear. Thus catches tend to be negatively correlated with HI1 (Muncy, 1973).
Period of falling water: As the waters decrease in area fish become concentrated into depressions of the floodplain and into the main drainage channels. At this time there is once again a very active fishery aimed at the capture of migrating fish, particularly juveniles, and attempts are made to retain fish on the plain by dams or ponds.
Fishing by damming creeks has been described from the Gambia River (Svensson, 1933; Johnels, 1954) where the exit streams from the swamps are blocked by earth dams. Water is then allowed to drain through a hole in the dam where a trap is placed for the capture of the fish. Such weirs prevent the draining of the water at normal speed and the process is thus prolonged. Reed (FAO, 1969) describes a similar experimental method applied to the floodplain of the Niger River, where exit streams from swamps are blocked by earth dams thus retaining more water than usual (Fig. 9). The dams are left in place for several weeks allowing an increased time for the growth of the fish. In the dry season the dam is breached and traps placed in the opening. A doubling of the normal yield of the swamps has been achieved by this method.
Figure 9 Tracing from aerial photographs of the Niger floodplain retention dams, showing the original water area and the area flooded after the closure of the dams (after FAO, 1969) (Key as for Figure 3)
Figure 10 shows the difference in water level over a 12 month period produced in a floodplain lagoon of the Senegal River by the use of such a dam.
Figure 10 Differences in changes of depth and area of a floodplain pool before and after damming of the main access channel. Encircled letters refer to individual illustrations in Figure 7 (after Reizer, 1974)
Fishing in the permanent lagoons and ponds of the floodplain is common and in the Delta floodplain of the Ouémé River the number of such natural features of the floodplain has been considerably augmented by trench-like fish holes “whedos” which have been excavated to a depth of about 1 m in a network all over the plain (Welcomme, 1971). On average, these cover about 3 percent of the dry area of the plain and in some areas reach very dense concentrations (Fig.11). The ponds are fished, after removal of the vegetation covering the water surface, with the aid of fences which are advanced in such a manner as to confine the fish in a small area from which they are removed. Yields from these are discussed in Section 7.
The capture of fish migrating within the channels draining the floodplain has been described from several parts of Africa. This is principally done with barriers or weirs of the type described by Whitehead (1958); however, of these fisheries two can be cited as representative:
The “maalelo” fishery of the Barotse floodplain, which consists of long low earth and grass dams in which conical valve basket traps are placed, has been described by FAO (1968) and FAO/UN (1969; 1970a) and Bell-Cross (1971). This fishery crops mainly juvenile fish on their migration to the river.
Cross channel traps of the El Beid River are described by Durand (1970). Here dams made of enmeshed branches and tree trunks completely block the main river channel diverting the flow over the shallow fringing plain where a series of V-shaped enclosures are constructed. The weir is fished with a type of clapnet designed to seal the space between the enclosures. Weirs are installed in such density as to almost completely bar the passage of the fish migration from the Yaérés floodplain to Lake Chad. The majority of the fish caught are juveniles in their first year.
Figure 11 Portion of the Ouémé floodplain showing the distribution of the “whedo”
floodplain pools
A. Air photograph (by courtesy of I.G.N., Paris)
B. Interpretation: black areas are pools that have already been
fished; white parallel lines indicate vegetation covered
unfished “whedos”
