To date DIFRA has data sets of 910 African inland waters: 316 lakes (including 20 international lakes), 279 reservoirs (including 2 international reservoirs), 135 rivers of which 64 are international waters, 30 large floodplains (including 5 international floodplains), 9 swamps and 141 coastal lagoons.
The individual data sets differ considerably. A small number of water bodies (e.g. Lake Victoria and Lake Tanganyika) have relatively large data sets with a wide range of morphometric and limnological data and catch statistics over more than 10 years but others have only their name given.
Previous models for estimating potential fish yields relate morphometric and edaphic factors like area, length, mean depth and MEI and fishing effort (in numbers of fishermen per km2) to catch (in tonnes per year) or yield (in kg per ha).
Analysis of the data sets of DIFRA clearly revealed the lack of data on the above mentioned factors for most African inland waters.
For lakes and reservoirs surface area is the most common morphometric characteristic. However, DIFRA contains information on surface area and catch statistics for one or more years for only 87 lakes and 37 reservoirs. Most of the 470 lakes and reservoirs for which no information is available on catch have a surface area less than 100 km2. Other morphometric and limnological information on lakes and reservoirs is even more restricted.
Only 37 rivers could be selected from DIFRA which had data on length, drainage area and catch statistics. SIFRA did not provide information on the floodplains additional to that given by Welcomme (1985), nor on other floodplains.
Coastal lagoons also have a very restricted data set. Most of the data on coastal lagoons were tabulated by Kapetsky (1984). An important feature of coastal lagoons is eutrophication due to domestic and agricultural waste inflows. In some of the African lagoons eutrophication has significantly contributed to fishery productivity (Kapetsky, 1984). This resulted in a wide range of yields which was too diverse to develop into a reliable yield model.
Finally, only 2 of the 9 swamps given in SIFRA have information on catches. Therefore updating of existing models was confined to models for lakes and reservoirs, and models on rivers and floodplains were recalculated for African waters only.
