Risk for fisheries in small waterbodies in relation to annual precipitation
Broadly speaking, small waterbodies include reservoirs and lakes with an area of less than 10 km2, small ponds, canals, irrigation canals, swamps and small, seasonal, inland floodplains. They may be permanent or temporary and can be separated into natural waters or constructed ones.
The world distribution of small water bodies, in terms of risks for fisheries (drying out or losing significant volume that would negatively impact fish production) shows that about 60 percent of the global land mass is too dry for perennial small waterbodies, or volumes would fluctuate widely (see image). About 11 percent could support small waterbodies with cost-adding modifications (moderately high risk), in about 6 percent water would be sufficient with little or no cost-adding modifications (low risk), and some 23 percent would have ample water (very low risk).
Comparing across continents
Examining continents, Europe possesses the largest relative amount of territory favouring small waterbodies, about 40 percent, while Africa, South and North America share a similar capacity with 18 to 20 percent. The Commonwealth of Independent States and the Baltic States (former USSR) as well as Oceania have less of this capacity.
There are uncounted millions of multipurpose small waterbodies around the globe that could contribute more importantly to food production if they were managed appropriately and in a way that is compatible with their other uses. More than 11 000 small waterbodies have been inventoried in Zimbabwe and the larger ones have been mapped and characterized, with the total for southern Africa estimated at anything between 50 000 and 100 000.
Management of small waterbodies
Fisheries in small waterbodies complement those in large inland waters or the sea, but are as opposed to larger waterbodies mainly fished by part-time fishers including women and children. They provide an opportunity to increase food production in local areas, but are usually also used for other purposes. Management therefore requires a multidisciplinary problem-solving approach.
Occurrence of small waterbodies by continent in relation to annual rainfall
In southern Africa, the potential fish yield from small waterbodies and reservoirs is estimated to be between 1 to 3 million tonnes per year. A comparative study of small waterbodies and reservoirs in seven countries in three continents shows extreme variations in the contribution of small and medium-sized waterbodies to national fish production.
As a large number of small waterbodies already exists, no capital expenditure is required to build them. They are located in rural, often semi-arid areas, and are potentially highly productive. This means that they are a possible source of protein and employment in places where both are in short supply. Small waterbodies are relatively easy to manage as fishers can operate over most of the area of a small waterbody. This is especially significant because it increases the possibility of effective management, as compared to large waterbodies with open access character.
Small waterbodies are well-suited to being managed by local communities, and this may be the best way of realizing their productive potential. The current interest in them derives mainly from their use for fisheries enhancement, which involves guidance on stocking, exploitation and species management, in order to obtain optimum yield on a sustainable basis. Small waterbodies are well-suited to being managed by local communities, and this may be the best way of realizing their productive potential. However, conflicts often arise where people who traditionally have fished the waterbodies no longer have access due to new management regulations.