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FACTS ABOUT BIODIVERSITY

Although freshwater ecosystems such as rivers, lakes and wetlands occupy less than 2% of the Earth's total land surface, they provide a wide range of habitats for a significant proportion of the world's plant and animal species: the number of known freshwater species worldwide is estimated at between 9,000 and 25,000, but this number is rapidly decreasing due to human interference.

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 around the world. Between 1970 and 1999, the Freshwater Species Population Index fell by nearly 50%, which constitutes a very rapid decline in population indices.

At a global level, around 24% of mammals and 12% of birds are in threatened categories. Only about 10% of the world’s fish have been assessed, the great majority of these being from inland waters, but 30% of those are listed as threatened.

More than 150 turtle species worldwide are restricted to, or occur in, freshwaters, and 99 were categorized as threatened in 2000, equivalent to about 60% of all the freshwater forms.

Lake Malawi (southern Africa) is an aquatic system that was originally endowed with a great deal of fish as well as freshwater snail biodiversity. However, loss in fish biodiversity has resulted in the favouring of certain snail species that play a role in the transmission of schistosomiasis. The increased health risk has greatly affected the tourist industry of Malawi and the whole economy has declined.

An estimated 30 million people depend on Lake Victoria, a lake whose natural resources are under increasing stress. The population on the shore has grown fast over the past century with corresponding increases in the demand for fish and agricultural products. Following the introduction of gill nets by European settlers at the beginning of the 20th century, populations of indigenous fish species declined. Many were specially adapted to eat algae, decaying plant material, and snails that host the larvae of schistosomes. The lake started to eutrophicate and people became more vulnerable to disease.

As fish catches declined, non-native species were introduced, causing further stress to indigenous fish. The greatest impact resulted from the introduction of nile perch (Lates niloticus) in the 1960s, as the basis of commercial freshwater fisheries. This had repercussions on the local fishing economy and distribution of wealth. Local people who previously met most of their protein requirements from the lake began to suffer from malnutrition and protein deficiency. Although 20.000 tonnes of fish are exported annually to European and Asian markets, local people can afford only fish heads and bones from which the flesh has been removed.

Information from:
World Water Development Report 'Water for People, Water for Life',
website Vital Water Graphics: problems related to freshwater resources,
webpage GEO: Global Environment Outlook 3: Vulnerable places

Source: UNESCO Water Portal, May 2005