"The over-exploitation and mismanagement of fisheries, particularly when combined with other man-made stresses, can lead to the collapse of regional fish faunas. In many countries, aquaculture is rapidly increasing in response to declining natural fisheries, often exacerbating the degradation of inland and coastal ecosystems through habitat alteration, pollution and the introduction of alien species" (Revenga et al., 1998).
The Freshwater Species Population Index measures the average change over time in the populations of some 194 species of freshwater birds, mammals, reptiles, amphibians and fish. Between 1970 and 1999, the Freshwater Species Population Index fell by nearly 50%, which is a very rapid decline in population indices.
The harvest of freshwater fish is likely to increase either through capture fisheries or aquaculture (otherwise known as ’fish-farming’). In many developing countries, freshwater fish provide a significant contribution to the diets of local communities. In Africa and Asia, fish provide 21% and 28% of all animal protein, respectively (Revenga et al., 1998). The figures are more significant in landlocked countries, where data on the fish caught are often not formally recorded, and their importance is not fully known.
In 1999, reported fish production from inland waters totalled 28 million tonnes, with contributions of 8.2 million and 19.8 million tonnes from capture fisheries and aquaculture, respectively. With major under-reporting from subsistence fisheries, these figures could be twice as high (FAO, 2000).
"The introduction of the non-native Nile Perch to Africa’s Lake Victoria in 1954, combined with pollution loading and increased water turbidity resulting from agriculture and industrial development, has greatly reduced indigenous fish populations. Kenya, for example, reported only 0.5% of its commercial fish catch as Nile Perch in 1976. Five years later, the proportion was 68%. Lake Victoria, the second largest lake in the world, has lost an estimated 200 different endemic cichlid species found nowhere else, while the remaining 150 are endangered. Two-thirds of the freshwater species introduced into the tropics worldwide have become established" (Revenga et al., 1998).