Jenness (1967) describes a variety of plant poisons used within the Kainji Lake basin. The use of poisoning to harvest fish by local fishermen has been noted by Fishery Biologists F.O. Otobo and E.O. Ita (personal communications). Literally thousands of small Tilapia and many small fish of other species are uselessly destroyed by this procedure, being too small to be collected by the fishermen. While poisoning is illegal and should be vigorously combatted, there is at present no effective agency to control this activity on the lake.
Lelek (FAO, 1972) examined 90 T. galilaea of mixed sex from Kainji Lake and found the smallest mature individual to be a female in the 110–150 mm S.L. group; in the 160–200 mm group, 31.4 percent of the fish were mature; and of fish 210 mm and larger 69.8 percent were mature. He comments that the onset of maturity (fish over 150 mm S.L. in Kainji Lake) corresponds to that in Volta Lake, where Lelek and Wuddah (1968) found 50 percent of the females maturing at about 155 mm S.L. and that first spawning took place in 24 fish at an average size of 155 mm S.L. (range 135–195 mm). Applying these data to Kainji Lake, from Figure 6 and Table 7, it is noted that to allow this species to mature before harvesting would necessitate a gillnet and castnet stretched mesh size larger than 3-inches. This may be unrealistic for the entire lake since it would limit the harvest of several other species of fish which do not reach a size to be taken in nets larger than 3-inch. However, in certain Tilapia-rich areas such as Warra, Yelwa and selected bays young Tilapia might well be protected by such mesh-size regulation. Identification and complete protection of particularly important spawning and nursery areas might also be considered, although the need for this should first be established.
At present the trend in Kainji Lake is to an ever-decreasing mesh size (Bazigos, 1972; Smart and Sagua, 1972) and the use of gillnets and castnets down to 1-inch stretched mesh is common. It will be very difficult to reverse this trend. Indeed, experience in Lake Victoria in enforcing a 5-inch minimum mesh size was found to be impossible, with subsequent illegal decreases in mesh to 21/2-inch and catastrophic results in a population of T. esculenta (Fryer and Iles, 1972 p. 436–43).
At present the fishing industry on Kainji Lake provides a borderline economy for an estimated 6 000 fishermen (Bazigos, 1972). He estimates that even though the price of fish has increased on Kainji Lake between 1970–71 and 1972, the average revenue has decreased by 30 percent due to lower catches. One of the major considerations of fisheries management must be to somehow limit the number of fishermen to enable the development of viable economic units. When the fish populations have reached relative stability and the long-term expected annual production is known, an economic study will be necessary to determine the number of fishermen units the lake will support. Meanwhile relocation of fishermen to other areas or industries should be encouraged.
At present there is no agency concerned primarily with management of the Kainji Lake fishery. The need for activation of such an agency is obviously a priority for fisheries management. Experience in enforcing fishing regulations on Lake Victoria (and other countries) suggests that this agency should be strongly oriented towards fishermen education, but with able police facilities.
