Kainji Lake is characterised by a relatively low pelagic photosynthetic activity.
The water temperature and hydrogen ion concentration do not limit the primary production.
Low nutrient content and restricted transparency of the water caused by inorganic turbidity are believed to be the main factors limiting primary production.
The lake has reached a dynamic equilibrium as regards the primary production level. Future development depends on the utilisation of the land resources in the drainage area and the transport potential of the Niger River.
Introduction of plant nutrients in the lake through intensified use of fertilizers in the drainage area may cause a higher level of primary production which will cause an excess of organic matter. Decomposition of this excess may lead to oxygen deficiency with an effect on fish production.
Commercial transport through the lake has to be regarded as a threat to fisheries production, unless controlled by regulations.
Urban development upstream of the lake is at present not believed to cause sufficient pollution to affect the lake ecosystem, partly because of the distances involved.
The work on the primary production in Kainji Lake came to an end when the expert completed his assignment, because there was no counterpart to continue the activities. It is, however, essential to monitor production at the primary level, as any changes in the aquatic environment will first be reflected here. The relationship between photosynthetic activity and the environment should be studied in more detail, as should the energy flow through the ecosystem, which is little known for tropical systems. It is recommended that measurements should be concentrated at station 14 in the main basin since this station shows the lowest variation in production. A minimum of four measurements a year is expected to be sufficient. The observations should be spaced so that the periods of peak transmission, peak turbidity and each period of transition are covered.
In general it seems clear that the plankton production of the lake is low for a tropical system and the opportunities for increasing this are few since the lake is too large for artificial modifications. The opportunities for substantially increasing the total production of fish beyond the apparent limits are more likely to be found in better utilisation of allochtonous organic material or improved littoral production than in better use of pelagic production. Possible areas which should be considered include artificial support (e.g. stocking) of detritus feeders (Citharinus), or future development in agriculture in the drawdown area.
Following the production studies, it is essential that the economic value of the lake fisheries be assessed and their role in the economy of the region determined, as they are already competing with other interests in the utilisation of water resources.
