Water for people.pdf - WHO Thailand Digital Repository

P R O T E C T I N G E C O S Y S T E M S F O R P E O P L E A N D P L A N E T / 1 4 1Changes in freshwater biodiversitySerious concern for inland water biodiversity at the global level wasraised in the early 1990s (e.g. Moyle and Leidy, 1992), mainlyreferring to evidence on the conservation status of fish. Most of therelatively few reviews that have attempted a global perspective haveappeared only during the past six years (Revenga et al., 2000;Groombridge and Jenkins, 1998; Revenga et al., 1998; McAllister etal., 1997; Abramovitz, 1996). These still rely heavily on informationrelating to fishes, but draw on many other case studies of groupswhere information is available, e.g. for molluscs in United Stateswaters, and also deal in increasing detail with threat factors andtheir sources.Table 6.6 shows data relating to a sample of the relatively fewcountries where the fish fauna is reasonably well-characterized andassessed. The data of interest relate to the number of species thathave been evaluated under the IUCN categorization system anddetermined to be threatened with extinction, and the percent thatthis represents of the national freshwater fish fauna. In ageographically widespread sample of countries, the proportion is20 percent or greater. At a global level, around 24 percent ofmammals and 12 percent of birds (both of which groups have beenTable 6.6: Numbers of threatened freshwater fish in selected countriesTotal Threatened %species species threatenedUnited States 822 120 15Mexico 384 82 21Australia 216 27 13South Africa 94 24 26Croatia 64 22 34Turkey 174 22 13Greece 98 19 19Madagascar 41 13 32Canada 177 12 7Papua New Guinea 195 11 6Romania 87 11 13Italy 45 11 24Bulgaria 72 11 15Hungary 79 10 13Spain 50 10 20Moldova 82 9 11Portugal 28 9 32Sri Lanka 90 9 10Slovakia 62 9 15Japan 150 9 6The countries listed here have the greatest number of globally threatened freshwater fishspecies, and are ordered by threatened species number. The fish faunas of these twentycountries have been evaluated completely, or nearly so.Source: Groombridge and Jenkins, 2002; total species estimates (all approximate) from UNEP-WCMCdatabase; threatened species data from online Red List http://www.redlist.org (4 March 2002).comprehensively assessed) are in threatened categories (Hilton-Taylor, 2000). Only about 10 percent of the world’s fish have beenassessed, the great majority of these being from inland waters, but30 percent of those are listed as threatened. More than 150 turtlespecies worldwide are restricted to, or occur in, freshwaters, andninety-nine were categorized as threatened in 2000, equivalent toabout 60 percent of all the freshwater forms. Excessive exploitationrather than habitat degradation alone is an important pressure onthis group. Table 6.7 provides concise information on a smallselection of the more than 3,500 vertebrate and invertebrateanimals associated with freshwater habitats that were assessed asCritically Endangered (the category for populations at highest risk ofextinction) in 2000.Some of the most comprehensive national data are from theUnited States, where the Nature Conservancy and Natural HeritageNetwork released an analysis of the conservation status of morethan 20,000 species in 1997. The four groups with the highestproportion of species extinct or at risk – freshwater mussels,crayfish, amphibians and freshwater fish – are all inhabitants of, ordependent on, inland water habitats (Master et al., 1998) (seefigure 6.3). Similarly, in Australia, four (22 percent) of eighteenwaterbird species assessed are listed as threatened, along withtwenty-seven (13 percent) of the frog species and twenty-two(about 10 percent) of freshwater fishes.Many extinctions have taken place in inland waters – at leastthirty-four fish species (six since 1970) and possibly up to eighty,from the late nineteenth century onward – and inland waterecosystems have seen probably the largest known multispeciesextinction episodes of the twentieth century. Lake Victoria, shared byKenya, the United Republic of Tanzania and Uganda, was untilrecently the home of a species population of up to 500haplochromine cichlid fish (not all yet formally described), as well asof a number of other fish species. Following introduction of the Nileperch Lates niloticus – and probably also as a result of heavy fishingpressure, increased sedimentation and oxygen depletion due to theincreased organic and nutrient loading – about half of the nativespecies are now believed extinct or nearly so, with little chance ofrecovery. In the Mobile Bay drainage basin in the United States, damconstruction has had a catastrophic impact on what was probably themost diverse freshwater snail fauna in the world (Bogan et al.,1995). Nine families and about 120 species were known from thedrainage basin. At least thirty-eight species are believed to havebecome extinct in the 1930s and 1940s following extensive damconstruction in the basin: the system now has thirty-three majorhydroelectric dams and many smaller impoundments, as well as locksand flood-control structures. These patterns are likely to have beenrepeated at a smaller scale in many other less well-documented partsof the world.