Freshwater Biodiversity: Importance, Threats, Status and Conservation Challenges

Biol. Rev. (2006), 81, pp. 163–182. f 2005 Cambridge PhilosophicalSociety 163 doi:10.1017/S1464793105006950 Printedin the UnitedKingdom Freshwater biodiversity: importance, threats, status and conservation challenges

David Dudgeon1*, Angela H. Arthington2, Mark O. Gessner3, Zen-Ichiro Kawabata4, Duncan J. Knowler5, Christian Le´veˆque6, Robert J. Naiman7, Anne-He´le`ne Prieur-Richard8, Doris Soto9, Melanie L. J. Stiassny10 and Caroline A. Sullivan11 1 DepartmentofEcology &Biodiversity, The University ofHong Kong, HongKong SAR, China 2 Centre for Riverine Landscapes andCooperative Research Centre for RainforestEcology andManagement, Faculty ofEnvironmentalSciences, Griffith University, Nathan, Brisbane, Queensland4111, Australia 3 DepartmentofLimnology, Swiss FederalInstitute ofAquatic Science andTechnology (Eawag/ETH), 6047 Kastanienbaum, Switzerland 4 Research Institute for Humanity andNature,335 Takashima-cho, Marutamachi-dori, Kawaramachi nishi-iru, Kamigyo-ku, Kyoto, 602-0878, Japan 5 SchoolofResource andEnvironmentalManagement, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada V5A 1S6 6 Institutde Recherches pour le Développement,1 rue de Marnes, 92410 Ville d’Avray, France 7 SchoolofAquatic &Fishery Sciences, University ofWashington–355020, Seattle, WA 98195, USA 8 DIVERSITAS,51 bdMontmorency, 75016 Paris, France 9 Instituto de Acuicultura, UniversidadAustralde Chile, Nućleo Milenio FORECOS, Casilla 1327, Puerto Montt, Chile 10 DepartmentofIchthyology, American Museum ofNaturalHistory, New York, NY10024, USA 11 Centre for Ecology andHydrology, WallingfordOX10 8BB, UK

(Received18 April2005; revised30 September 2005; accepted17 October 2005)

ABSTRACT

Freshwater biodiversity is the over-riding conservation priority during the International Decade for Action–‘Water for Life’– 2005 to 2015. Fresh water makes up only 0.01% of the World’s water and approximately 0.8% ofthe Earth’s surface, yet this tiny fraction ofglobal water supports at least 100000 species out ofapproximately 1.8 million– almost 6% ofall described species. Inland waters and freshwater biodiversity constitute a valuable natural resource, in economic, cultural, aesthetic, scientific and educational terms. Their conservation and management are critical to the interests of all humans, nations and governments. Yet this precious heritage is in crisis. Fresh waters are experiencing declines in biodiversity far greater than those in the most affected terrestrial ecosystems, and if trends in human demands for water remain unaltered and species losses continue at current rates, the opportunity to conserve much ofthe remaining biodiversity in fresh water will vanish before the‘Water for Life’ decade ends in 2015. Why is this so, and what is being done about it? This article explores the special features of freshwater habitats and the biodiversity they support that makes them especially vulnerable to human activities. We document threats to global freshwater biodiversity under five headings: overexploitation; water pollution;flow modification; destruction or degradation ofhabitat; and invasion by exotic species. Their combined and interacting influences have resulted in population declines and range reduction of freshwater biodiversity worldwide. Conservation of biodiversity is complicated by the landscape position of rivers and wetlands as‘receivers’ of land-use effluents, and the problems posed by endemism and thus non-substitutability. In addition, in many parts ofthe world, fresh water is subject to severe competition among multiple human stakeholders. Protection offreshwater biodiversity is perhaps the ultimate conservation challenge because it is influenced by the upstream drainage network, the surrounding land, the riparian zone, and– in the case of migrating aquatic fauna– downstream reaches. Such prerequisites are hardly ever met. Immediate action is needed where opportunities exist to set aside intact lake and river

* Address for correspondence (E-mail:[email protected]). 164 D. Dudgeon and others

ecosystems within large protected areas. For most ofthe global land surface, trade-oﬀs between conservation of freshwater biodiversity and human use ofecosystem goods and services are necessary. We advocate continuing attempts to checkspecies loss but, in manysituations, urge adoption ofa compromise position ofmanagement for biodiversity conservation, ecosystem functioning and resilience, and human livelihoods in order to provide a viable long-term basis for freshwater conservation. Recognition of this need will require adoption of a new paradigm for biodiversity protection and freshwater ecosystem management– one that has been appropriately termed‘reconciliation ecology’.

Key words: pollution,ﬁsheries, overexploitation, dams, rivers, lakes, endangered species.

CONTENTS

I. Introduction ...... 164 II. Freshwater riches ...... 164 III. Major threats to freshwater biodiversity ...... 165 IV. Freshwater biodiversity in crisis ...... 166 V. The information gap ...... 167 VI. Conservation challenges ...... 167 VII. Are terrestrial conservation strategies appropriate for freshwater biodiversity? ...... 169 VIII. The importance ofEnvironmental Water Allocations ...... 169 IX. The value offreshwater biodiversity ...... 172 X. Conservation offreshwater biodiversity in the real world ...... 174 XI. Conclusions ...... 176 XII. Acknowledgements ...... 177 XIII. References ...... 177

I. INTRODUCTION unaltered and species losses continue at current rates, the opportunity to conserve much ofthe remaining biodiversity In December 2003, the United Nations General Assembly in fresh water will vanish before the‘Water for Life’ decade adopted resolution 58/217 proclaiming 2005 to 2015 as ends. Such opportunity costs will be magnified by a signifi- an International Decade for Action–‘Water for Life’. cant loss in option values ofspecies yet unknown for human The resolution calls for a greater focus on water issues and use. In addition, these vital ecological and potentialfinancial development efforts, and recommits countries to achieving losses may well be irreversible. Importantly, effective con- the water-related goals ofthe 2000 Millennium Declaration servation action will require a major change in attitude and of Agenda 21: in particular, to halve by 2015 the toward freshwater biodiversity and ecosystem management, proportion of people lacking access to safe drinking water including general recognition ofthe catchment as the focal and basic sanitation. These are vitally important matters, management unit, and greater acceptance ofthe trade-offs yet their importance should not obscure the fact that the between species conservation, overall ecosystem integrity, ‘Water for Life’ resolution comes at a time when the bio- and the provision ofgoods and services to humans. At the diversity and biological resources ofinland waters are facing same time, it is incumbent upon scientists to communicate unprecedented and growing threats from human activities. effectively that freshwater biodiversity is the over-riding The general nature ofthese threats is known, and they are conservation priority during the‘Water for Life’ decade manifest in all non-polar regions ofthe Earth, although their and beyond; after all, water is the fundamental resource relative magnitude varies significantly from place to place. on which our life-support system depends ( Jackson et al., Identifying threats has done little, however, to mitigate or 2001; Postel & Richter, 2003; Clark & King, 2004). alleviate them. This article explores why the transfer of knowledge to conservation action has, in the case of freshwater bio- II. FRESHWATER RICHES diversity, been largely unsuccessful. The failure is related to the special features of freshwater habitats– and the Freshwater ecosystems may well be the most endangered biodiversity they support– that makes them especially vul- ecosystems in the world. Declines in biodiversity are far nerable to human activities. We start by elucidating why greater in fresh waters than in the most affected terrestrial freshwater biodiversity is ofoutstanding global importance, ecosystems (Sala et al., 2000). What makes freshwater and briefly describe instances where humans have caused habitats and the biodiversity that they support especially rapid and significant declines in freshwater species and vulnerable to human activities and environmental change? habitats. If trends in human demands for water remain The main reason is the disproportionate richness ofinland Freshwater biodiversity 165 waters as a habitat for plants and animals. Over 10000fish species live in fresh water (Lundberg et al., 2000); approxi- Over- Water mately 40% of globalfish diversity and one quarter of exploitation pollution global vertebrate diversity. When amphibians, aquatic reptiles (crocodiles, turtles) and mammals (otters, river dolphins, platypus) are added to this freshwater-fish total, it becomes clear that as much as one third of all vertebrate species are confined to fresh water. Yet surface freshwater habitats contain only around 0.01% ofthe world’s water and cover only about 0.8% of the Earth’s surface (Gleick, 1996). Flow Habitat Another way of looking at this is to ask: how many of the modification degradation species described by scientists live in fresh water? The answer is around 100000 out ofapproximately 1.75 million (Hawksworth & Kalin-Arroyo, 1995): almost 6%, and an additional 50000 to 100000 species may live in ground Species water (Gibert & Deharveng, 2002). Given the rate at which invasion humans are degrading fresh waters, it is literally true that, with regard to biodiversity loss and conservation,‘… the medium is the message’ (Stiassny, 1999). Knowledge of the total diversity of fresh waters is Fig. 1. Thefive major threat categories and their established woefully incomplete– particularly among invertebrates and or potential interactive impacts on freshwater biodiversity. microbes, and especially in tropical latitudes that support Environmental changes occurring at the global scale, such as most of the world’s species. Even vertebrates are incom- nitrogen deposition, warming, and shifts in precipitation and pletely known, including well-studied taxa such asfishes runoffpatterns, are superimposed upon all ofthese threat cate- (Stiassny, 2002). Between 1976 and 1994, an average of309 gories. newfish species, approximately 1% of knownfishes, were formally described or resurrected from synonymy each year (Stiassny, 1999) and this trend has continued (Lundberg combination of approaches show that numerous protists et al., 2000). Among amphibians, almost 35% ofthe global (ciliates) may have restricted geographic distributions total of 5778 species has been described during the last (Foissner etal., 2003), implying they could be more speciose decade (AmphibiaWeb, 2005). Regional discovery rates of than supposed by researchers who assume they have cosmo- new freshwater species vary: for example, Rainboth (1996) politan biogeographies (e.g. Finlay, 2002). It is likely that estimates that the Mekong drainage may support as many the richness of freshwater fungi and microalgae has been as 1000fish species, more than twice the total given by likewise underestimated (Johns & Maggs, 1997; Gessner & earlier researchers, placing it third in the global ranking of Van Ryckegem, 2003). rivers according tofish species richness. A more recent figure puts Mekongfish richness in the order of1700 species (Sverdrup-Jensen, 2002). Clearly, the Mekong is one of a number ofglobal‘hotspots’ for riverfish biodiversity (others III. MAJOR THREATS TO FRESHWATER include the Congo and Amazon) but, in general, freshwater BIODIVERSITY hotspots receive less attention than their terrestrial counter- parts (e.g. Myers etal., 2000; see also Section V). The threats to global freshwater biodiversitycan be grouped Adequate data on the diversity of most invertebrate underfive interacting categories (Fig. 1): overexploitation; groups in tropical fresh waters do not exist, but high levels of water pollution;flow modification; destruction or degra- local endemism and species richness seem typical ofseveral dation ofhabitat; and invasion by exotic species (e.g. Allan major groups, including decapod crustaceans, molluscs and & Flecker, 1993, Naiman et al., 1995; Naiman & Turner, aquatic insects such as caddisflies and mayflies (Dudgeon, 2000; Jackson et al., 2001; Malmqvist & Rundle, 2002; 1999, 2000c; Benstead etal., 2003; Strayer etal., 2004). For Rahel, 2002; Postel & Richter, 2003; Revenga etal., 2005). instance, although it is incompletely known, the Mekong Environmental changes occurring at the global scale, such River fauna includes species-flocks of over 100 endemic as nitrogen deposition, warming, and shifts in precipitation molluscs, and a similar radiation has occurred in the and runoff patterns (e.g. Poff, Brinson & Day, 2002, Yangtze (Dudgeon, 1999, and references therein). Infor- Galloway et al., 2004), are superimposed upon all of mation on microbial biodiversity is fragmentary too, not- these threat categories. Overexploitation primarily affects withstanding the crucial role of microbes in driving the vertebrates, mainlyfishes, reptiles and some amphibians, biogeochemical cycles of the Earth. Most prokaryote whereas the other four threat categories have consequences taxonomic diversity remains unexplored (Torsvik, Øvrea˚s for all freshwater biodiversity from microbes to megafauna. & Thingstad, 2002; Curtis & Sloan, 2004). Recent genomic Pollution problems are pandemic, and although some indus- analyses (e.g. Zwart et al., 2003) suggest that aquatic trialized countries have made considerable progress in microbial biodiversity is considerably higher than inferred reducing water pollution from domestic and industrial from classical, non-molecular evidence. Studies using a point sources, threats from excessive nutrient enrichment 166 D. Dudgeon and others

(e.g. Smith, 2003) and other chemicals such as endocrine- The extent of most freshwater systems is not confined to disrupters are growing (e.g. Colburn, Dumanoski & Myers, the wetted perimeter, but includes the catchment from 1996). Habitat degradation is brought about by an array of which water and material are drawn (Hynes, 1975; see also interacting factors. It may involve direct effects on the Naiman & Latterell, 2005). Their position in the landscape aquatic environment (such as excavation of river sand) or (almost always in valley bottoms) makes lakes and rivers indirect impacts that result from changes within the drain- ‘receivers’ of wastes, sediments and pollutants in runoff. age basin. For example, forest clearance is usuallyassociated This is also true ofseas and oceans, but inland water bodies with changes in surface runoffand increased river sediment typically lack the volume of open marine waters, limiting loads that can lead to habitat alterations such as shoreline their capacity to dilute contaminants or mitigate other erosion, smothering of littoral habitats, clogging of river impacts. bottoms orfloodplain aggradation. In addition, in many parts of the world fresh water Flow modifications are ubiquitous in running waters is subject to severe competition among multiple human (e.g. Dynesius & Nilsson, 1994; Vo¨ro¨smarty et al., 2000; stakeholders, to the point that armed conflicts can arise Nilsson et al., 2005). They vary in severity and type, but when water supplies are limiting and rivers traverse political tend to be most aggressive in regions with highly variable boundaries (Poff et al., 2003). There are 263 international flow regimes. This is because humans in these places have rivers, draining 45% ofthe Earth’s land surface. That this the greatest need forflood protection or water storage. That area supports more than 40% of the global human popu- existing dams retain approximately 10000 km3 ofwater, the lation is an indication of the scope of the issue (Bernauer, equivalent offive times the volume ofall the world’s rivers 2002; Postel & Richter, 2003; Clark & King, 2004). In the (Nilsson & Berggren, 2000), illustrates the global extent of vast majority ofdisagreements over multiple uses ofwater, human alteration of riverflow. Water impoundment by whether they are international or on a local scale, allocation dams in the Northern Hemisphere is now so great that it of water to maintain aquatic biodiversity is largely dis- has caused measurable geodynamic changes in the Earth’s regarded (Poff et al., 2003). In China and India, where rotation and gravitationalfield (Chao, 1995). Even some of approximately 55% ofthe world’s large dams are situated the world’s largest rivers now run dry for part of the year (W. C. D., 2000), hardly any consideration has been given or are likely to do so as a result of large-scale water to the downstream allocation ofwater for biodiversity (Poff abstraction (Postel & Richter, 2003). Flow modifications are etal., 2003; Tharme, 2003). likely to be exacerbated by global climate change because greater frequency offloods and droughts, and consequent increased water-engineering responses, can be anticipated (Vo¨ro¨smarty et al., 2000). Although this matter will not be IV. FRESHWATER BIODIVERSITY IN CRISIS explored herein, impacts on river biota (fishes, for example) are likely to be severe (e.g. Dudgeon, 2000a; Xenopoulos The combined and interacting influences ofthefive major etal., 2005). threat categories (Fig. 1) have resulted in population declines Widespread invasion and deliberate introduction of and range reduction of freshwater biodiversity worldwide. exotic species adds to the physical and chemical impacts Qualitative data suggest reductions in numerous wetland of humans on fresh waters, in part because exotics are and water margin vertebrates (19 mammals, 92 birds, 72 most likely to successfully invade fresh waters already reptiles and 44fish species), while population trends indicate modified or degraded by humans (e.g. Bunn & Arthington, declines averaging 54% among freshwater vertebrates 2002; Koehn, 2004). There are many examples of large- (mainly waterfowl), with a tendency toward higher values scale and dramatic effects of exotics on indigenous species in tropical latitudes (Groombridge & Jenkins, 2000; Loh, (e.g. Nile perch, Lates niloticus, in Lake Victoria, the crayfish 2000). Furthermore, 32% ofthe world’s amphibian species plague in Europe, salmonids in Southern Hemisphere lakes now are threatened with extinction, a much higher pro- and streams: see Rahel, 2002), and impacts are projected portion than threatened birds (12%) or mammals (23%), to increase further (Sala et al., 2000). Indirect impacts can and 168 species may already be extinct (AmphibiaWeb, arise from exotic terrestrial plants such as Tamarix spp. 2005). The well-known global decline ofamphibians started (Tamaricaceae), which alter the water regime of riparian during the 1950s and 1960s and has continued at the soils and affect streamflows in Australia and North America current rate of approximately 2% per year, with more (Tickner etal., 2001). pronounced decreases in tropical streams (Houlahan et al., The particular vulnerability of freshwater biodiversity 2000; Stuart et al., 2004). This is close to the estimate of also reflects the fact that fresh water is a resource for 2.4% for declines in populations of freshwater vertebrates humans that may be extracted, diverted, contained or con- over the period 1970–1999 (Balmford et al., 2002). These taminated in ways that compromise its value as a habitat estimates are extremely alarming. Extinction rates offresh- for organisms. In some instances, impacts have been sus- water animals in North America, based on combined data tained over centuries and, in the case ofmany ofthe major sets for unionid mussels, crayfishes,fishes and amphibians, rivers of China, they have persisted for more than 4000 may even be as much as 4% per decade–five times higher years (Dudgeon, 2000a). Indeed, some authors now believe than species losses calculated from any terrestrial habitat it unlikely that there remain a substantial number ofwater (Ricciardi & Rasmussen, 1999). One third of the species bodies that have not been irreversibly altered from their in what was once the most diverse freshwater mollusc original state by human activities (Le´veˆque & Balian, 2005). assemblage in the world (the Mobile Bay Basin in the Freshwater biodiversity 167

Table 1. IUCN Red List classifications for non-marine turtles however, there has been no comprehensive global analysis in tropical Asia (including New Guinea). Around 90 species of freshwater biodiversity comparable to those recently ofnon-marine turtles occur in this region. Classifications as completed for terrestrial systems (Myers et al., 2000; Olson Critically Endangered (CR), Endangered (EN) and et al., 2001). Existing data on the population status or Vulnerable (VU) reflect a dramatic increase in threats due to extinction rates of freshwater biota are biased in terms of overexploitation ofturtles for food and the traditional Chinese geography, habitat types and taxonomy; most populations medicine trade, with the consequence that over 80% ofthe and habitats in some regions have not been monitored at all. regional fauna is now threatened. Species classified as Data Even a basic global mapping ofinland waters, classified by Deficient (DD) are poorly known but perceived to be under broad geomorphic categories, is lacking– and there are threat also (Van Dijk, 2000). no global estimates ofchanges in the extent oflakes, rivers or wetlands (Balmford etal., 2002). IUCN Classification Conservation efforts for freshwater biodiversity are constrained by the fact that most of the species in diverse Year CE EN VU Total % DD communities are rare (e.g. Sheldon, 1988) and thus their 1996 5 9 23 37 41 18 natural histories tend to be poorly known. This means that 2000 18 27 21 66 73 6 even when reductions in overall species numbers are 2003 19 31 23 73 81 6 predictable, forecasting the identities ofthe affected taxa is not possible. Furthermore, the unreliability of estimates of species richness in individual river basins (e.g. the Mekong: see above) makes it virtually certain that regional national south-eastern USA) have been driven to extinction byflow inventories, museum collections and taxonomic knowledge regulation and habitat alteration (Groombridge & Jenkins, in many parts of the tropics are inadequate to document 1998; see also Lydeard & Mayden, 1995); unionids are extinctions, and thus widespread undetected extinctions of now regarded as the most imperilled of all organisms in inconspicuous species have already taken place (Harrison & North America (Strayer et al., 2004). These limited data on Stiassny, 1999; Stiassny, 2002). The problem of species extinction rates from one continent are believed to be being misidentified, or not represented in collections, or indicative ofa global freshwater‘biodiversity crisis’ (Abell, listed incorrectly on protected species lists adds to the 2002; see also Dudgeon, 1992; Kottelat & Whitten, 1996). uncertainty (Kottelat & Whitten, 1996). One important Rates ofspecies loss from fresh waters in non-temperate implication of these various constraints is that, with the latitudes are not known with any degree ofcertainty. They exception ofa few well-known taxa in a limited number of are likely to be high because species richness of many countries (e.g. Ricciardi & Rasmussen, 1999; Strayer et al., freshwater taxa (e.g.fishes, macrophytes, decapod crusta- 2004), it is not possible to estimate or accurately project ceans) increases toward the tropics. The drainage basins of extinction rates of freshwater biodiversity using the many large tropical and subtropical rivers (e.g. the Ganges approaches applied to terrestrial biota (Dirzo, 2001; Dirzo and Yangtze) are densely populated– with large dams, & Raven, 2003). alteredflow patterns and gross pollution from a variety of Globally, awareness of the need to conserve freshwater sources beingthe inevitable outcomes (e.g. Dudgeon, 2000a, biodiversity seems limited. Between 1997 and 2001, only 2002). For larger species in these rivers, the situation 7% ofpapers in the leading journal in thefield, Conservation is parlous: the Yangtze dolphin (Lipotes vexillifer Miller) is Biology, was concerned with freshwater species or habitats probably the most endangered mammal on Earth (now (Abell, 2002). Most reported studies from northern temper- numbering fewer than 100 individuals; Dudgeon, 2005), ate latitudes. This negligence is particularly acute in regions and the Ganges dolphin (Platanista gangetica (Roxburgh)) is where biodiversity is both rich and highly threatened. A ‘Endangered’ (IUCN, 2003). The crocodilian fauna ofthe mere 0.6% ofpapers in the conservation biology literature Ganges and Yangtze likewise consists entirely ofthreatened between 1992 and 2001 dealt with freshwater biodiversity or highly endangered species. Many other species ofwater- in Asia (Dudgeon, 2003b), although this continent supports associated reptiles– a primarily tropical group– are gravely over halfofthe global human population, with consequent threatened (Gibbons et al., 2000; Van Dijk, 2000), most pressures on inland waters, and a very significant part of particularly turtles (Table 1), as are large freshwaterfishes in the world’s biodiversity. Indonesia alone supports about most rivers (e.g. Baird et al., 2001; Carolsfeld et al., 2004; 15% of the word’s species, and has more amphibians and Hogan et al., 2004; see Table 2), and many freshwaterfish dragonflies than any other country (Braatz etal., 1992). The stocks are over-fished to the point of population collapse manifest knowledge impediment in Asia and elsewhere in (e.g. FAO, 2000; Dudgeon, 2002). the tropics limits both attempts to quantify the freshwater biodiversity crisis and the ability to alleviate it. V. THE INFORMATION GAP

Populations of large vertebrates may not be accurate VI. CONSERVATION CHALLENGES indicators ofthe status ofall offreshwater taxa, but there are grounds for grave concern if their status were reﬂected A signiﬁcant challenge to freshwater biodiversity conser- in even 5% of the total species complement. To date, vation results from the complexity imposed on fresh 168 D. Dudgeon and others

Table 2. Riverﬁshes in Asia: threats and conservation status. All species listed are large, long-lived and/or migratory species that seem particularly susceptible to human impacts– especially overﬁshing.

Species (maximum IUCN weight or length) classiﬁcation Range Threats Remarks References

Chinese paddlefish Critically Yangtze Mainly overfishing; also Breeding migrations Wei etal. (1997, 2004) Psephurus gladius endangered endemic pollution. blocked by Gezhouba (Martens) (y300 kg, Dam (1981) following possibly 500 kg; up population collapse; close to 3 m) to extinction Chinese sturgeon Endangered Yangtze and Overfishing, pollution, Population collapse Wei etal. (1997, 2004); Acipenser sinensis Gray Pearl spawning site degraded caused genetic bottleneck; Zhang etal. (2003) (up to 500 kg) by Gezhouba Dam, artificial propagation and habitat fragmentation release ofjuveniles since 1983 Yangtze sturgeon Critically Yangtze Mainly overfishing; also Declining genetic diversity Wei etal. (1997, 2004); Acipenser dabryanus endangered endemic pollution; Gezhouba ofwild populations Wan etal. (2003) Dume´ril (over 16 kg; Dam blocked breeding between 1958 and 1999; at least 1.3 m) migrations large-scale artificial propagation not yet practiced; close to extinction Giant barb Not listed Mekong and Overfishing; few Protected by law in Rainboth (1996); Catlocarpio siamensis Chao Phraya juveniles reach maturity Cambodia Hogan etal. (2001) Boulenger (y150 kg; may reach 300 kg) Mekong giant catfish Critically Mekong Overfishing; navigation Protected by law in Kottelat & Whitten Pangasianodon gigas endangered endemic project in upper Mekong Cambodia; artificial (1996); Hogan etal. (Chevey) (exceeds threatens spawning sites propagation and stocking (2001, 2004) 300 kg) in Thailand since 1985 depleting population and eroding genetic diversity Isok barb Probarbus Endangered Mekong; Overfishing in Mekong; Populations ofProbarbus Rainboth (1996); jullieni Sauvage (over formerly also elsewhere dam construc- labeamajor Roberts and Dudgeon (1999) 70 kg; up to 1 m) rivers in tion and habitat P. labeaminor Roberts, Thailand and degradation endemic to the Mekong, Malaysia are also declining Freshwater whipray Vulnerable Mekong, Overfishing; pollution Unconfirmed records Rainboth (1996); Himantura chaophraya Chao and habitat degradation suggest this stingray may Hogan etal. (2004) Monkolprasit & Phraya, Fly in Chao Phraya be one ofworld’s largest Roberts (possibly andMahakam freshwaterfish; a very up to 600 kg) poorly known species waters by catchment divides and saltwater barriers. As Telmatherinidae on Sulawesi, and Balitoridae in China a result, low geneflow and local radiation lead– in the (Kornfield & Carpenter, 1984; Kottelat & Chu, 1988; absence of human disturbance– to considerable inter- Kottelat & Whitten, 1996). Virtually all ofthese radiations drainage variation in biodiversity and high levels of are severely endangered, as the examples from Africa endemism (Table 3). This is especially notable among illustrate (Table 3). At smaller geographic scales there is assemblages that evolved in isolated lakes on islands or substantial species turnover (i.e. b-diversity) among drainage mountains and inland plateaux such as the karstic regions basins and water bodies, and many freshwater species ofBurma and southwest China (Kottelat & Whitten, 1996). have restricted ranges (e.g. Sheldon, 1988; Pusey & These and similar tropical uplands are poorly represented Kennard, 1996; Strayer et al., 2004). These attributes in existing protected-area networks (Rodrigues et al., 2004). combine with endemism to produce a lack of‘substitut- Ancient lakes such as Lake Baikal in Siberia and those in ability’ among freshwater habitat units. This means that the East African Rift Valley support well-known species protection ofone or a few water bodies cannot preserve all flocks of endemic crustaceans andfishes, but there are freshwater biodiversity within a region, or even a significant important radiations of cichlids, cyprinids, catfishes and proportion ofit. otherfishes, as well as frogs, crustaceans and molluscs, In addition to conflicts arising from the multiple use of elsewhere in Africa (Table 3) and the world. For example, water, conservation of freshwater biodiversity is compli- speciesflocks occur among Cyprinidae in the Philippines, cated by their landscape position as‘receivers’ and the Freshwater biodiversity 169 problems posed by high levels of endemism– and thus The catchment scale is generally appropriate for all types non-substitutability. Other features intrinsic to freshwater of freshwater management of freshwater habitats (e.g. environments, especially rivers, also make them vulnerable Pollard & Huxham, 1998; Moss, 2000), and it helps resolve to human impacts. Rivers are open, directional systems, and the small-scale but damaging conflicts of interest among elements oftheir biota range widely using different parts of competing human demands. However, this approach can be the habitat at various times during their lives. Fishes and problematic in practice, as relativelylarge areas ofland need other animals (from shrimps to river dolphins) use different to be managed in order to protect relatively small water habitats at different times, and longitudinal migrations bodies. A promising approach could involve ecological may be an obligatory component oflife histories especially management that integrates the requirements of terrestrial if– as in many species– migration is associated with breed- and freshwater environments. This will complicate the ing (Welcomme, 1979). Longitudinal migrations may occur process of establishing appropriate boundaries for pro- within the river, or from river to sea or lake and back, or tected areas. However, from the freshwater perspective, it from sea or lake to river and back. Such movements put would have the added advantage ofbroadening the historic animals at risk from stresses in various parts oftheir habitat management approach that has been focused mainly on at different times; long-lived species with low reproductive biodiversity and habitats within river channels, with depen- rates are likely to be the most vulnerable (Carolsfeld et al., dentfloodplains and their inhabitants receiving relatively 2004). Dams in tropical regions are generally constructed little attention (Kingsford, 2000; Ward et al., 2002). Large without appropriatefishways orfish passes, or based upon animals such as bear, swamp deer, rhinos, and elephants designs that are suitable only for salmonids, and thus they make seasonal use of riparian areas andfloodplains for obstructfish migrations (Roberts, 2001). Adam on the lower feeding or breeding (see Naiman & Dećamps, 1997; course ofa river prevents migratoryfishes with an obligate Dudgeon, 2000b; Naiman, Dećamps & McClain, 2005). marine phase in their life cycle from moving to and from Maintaining proximity to water is essential for many large the sea, creating the potential for activities in downstream animals during the tropical dry season, which can be a reaches to impact upstream portions of the river by way period of severe ecological stress for herbivores. Effective of, for example, the nutrient transmission that occurs preservation of biodiversity associated with freshwater during spawning migrations of salmon (e.g. Naiman et al., habitats must therefore take account of the year-round 2002a; see also Pringle, 2001). Lateral migrations, between habitat use and movements by terrestrial, riparian and inundatedfloodplains or swamp forest and the main river amphibiotic fauna (e.g. frogs, water dragons and snakes, channel, represent another axis of connectivity important platypus, otters, and many water birds), as well as the needs for feeding and breeding in manyfishes and other animals ofthe strictlyaquatic biota. Maintenance ofsome semblance (Welcomme, 1979; Ward etal., 2002; Carolsfeld etal., 2004; of the naturalflow variability and theflood/drought cycle Arthington et al., 2005) that is dramatically altered by ofrivers and theirfloodplains, vernal pools, and water-level human activities. fluctuations in wetlands and along lakeshores, also will be essential.

VII. ARE TERRESTRIAL CONSERVATION STRATEGIES APPROPRIATE FOR VIII. THE IMPORTANCE OF ENVIRONMENTAL FRESHWATER BIODIVERSITY? WATER ALLOCATIONS

Terrestrial conservation strategies tend to emphasize areas There is growing awareness that maintenance of natural ofhigh habitat quality that can be bounded and protected. variability inflows and water levels is essential to underpin This‘fortress conservation’ is likely to fail for fresh waters conservation strategies for freshwater or water-associated (Boon, 2000) and may even be counterproductive (Moss, biodiversity and their habitats (Poff et al., 1997; Richter 2000; Dunn, 2003) for river segments or lakes embedded et al., 1997, 2003; Pollard & Huxham, 1998; Arthington & in unprotected drainage basins unless the boundaries are Pusey, 2003). The most straightforward water-engineering drawn at a catchment scale, which is virtually never the response is to provide a water regime (i.e. Environmental case (Naiman & Lattrell, 2005). This problem ofboundary Water Allocations: EWA) that mimics natural variability definition impedes sensible local management offreshwater and includes a range offlows– not just a minimum level biodiversity (but see Baird etal., 2001) because protection of (Fig. 2). Instead of being directed toward preservation of a particular component of river biota (and often habitat) single species (such as salmon or trout), an EWA provides requires control over the upstream drainage network, the theflows required to sustain the entire riverine ecosystem surrounding land, the riparian zone, and– in the case of including surface-groundwater systems (Arthington, 1998; migrating aquatic fauna– downstream reaches (Pringle, Naiman et al., 2002b). Mimicking the naturalflow regime 2001; Pusey & Arthington, 2003). Conservation action at is important because it influences aquatic biodiversity via the catchment scale, involving interconnected landscape several, inter-related mechanisms that operate over different units, is needed also for certain terrestrial taxa that under- spatial and temporal scales (Bunn & Arthington, 2002: see take seasonal migrations, but the shortcomings inherent in Fig. 2). The relationship between biodiversity and the fortress conservation are particularly acute for freshwater physical nature ofthe aquatic habitat is likely to be driven biodiversity. primarily by large events that influence channel form and 1 7 0

Table 3. African lakes as an example ofbiodiversity threats and conservation status offresh waters. Principal drivers ofbiodiversity decline throughout the region are assorted impacts arising from human population pressure as well as climate changes. Data are from Thieme etal. (2005), unless otherwise indicated.

Lake system (location) Biodiversity features Main threats Remarks

Southern Eastern Rift soda lakes Endemic radiation ofphytophagous tilapiine Numerous: soda mining; Soda mining in Lake Magadi extracts 0.5r 106 t (including Nakuru, Magadi, Natron, fishes (Oreochromis spp.); globally important deforestation; agricultural and NaCO3/year with effects on water quality and Manyara and Eyadi) (Gregory Rift numbers oflesserflamingo (Phoenicopterus minor); urban pollution; introduced phytoplankton that impactflamingo andfish ofKenya and Tanzania) primary production (dominated by Spirulina species; climate change. populations. platensis) comparable to highest measured for any terrestrial plant community. Lake Tana (Northern Highlands of Rich endemicfish fauna, including a globally Overfishing; water diversion. Use ofmotorized boats opened access to deeper Ethiopia) outstanding speciesflockofpiscivorous cyprinids waters formerly free fromfishing pressure; (Labeobarbus spp.) and the only known African growing human populations resulted in heavy river loach (Nemacheilus abyssinicus); 15 planorbid exploitation offishes during spawning runs snail species and an endemic sponge (Makedia which, combined with use offish poisons, appears tanasesis); exceptional regional diversity of unsustainable; stocks in the southern Lake Tana resident wetland birds and Palearctic migrants. declining. Western Equatorial crater lakes Around 20 endemic tilapiine cichlids resulting in Deforestation and siltation; The small size ofthe Cameroonian crater lakes (including Barombi Mbo, Bermin, a per-area index offish endemicityin these small agricultural and urban pollution; renders them particularly vulnerable to siltation Ejagham and Kotto) (Cameroon) lakes that is globally unrivalled; almost 60 frog water extraction; overfishing. due to land-use change or water extraction species, y20 endemic to the lakes region; for agriculture and domestic use; lake level invertebrate diversity poorly known, but fluctuations in Lake Barombi Mbo have impacted endemic sponge (Corvospongilla thysi) and atyid fish breeding sites. shrimp in Lake Barombi Mbo. Bangwelo and Mweru Lakes system Extremely rich fauna: over 100fish species Overfishing; agricultural Cichlid (mainly tilapiine) stocks greatly depleted (D. R. Congo and Zambia) (y34 endemics); 37 mollucs (7 speceis endemic pollution. in Lake Bangwelu by overfishing; drainage-basin to Lake Mweru and lower Luapula River); degradation due to growing human populations, 4 near-endemic frogs; 2 near-endemic deforestation and land-use change; community- dragonflies (Aciagrion rarum and Monardithemis based co-management offisheries and sustainable D .

ﬂava) ofconservation concern. resource use being promoted in attempts to D

maintain productivity and ecosystem integrity. u d

Lake Upemba and upper Lualaba Aquatic faunapoorlyknown:atleast14endemic Mining; deforestation; Most ofthe human population is concentrated g e

River system (D. R. Congo) ﬁsh species, 47 frog species (6 endemics); habitat agricultural pollution; in the mining belt south ofLake Upemba, where o also for the slender-snouted crocodile (Crocodylus overﬁshing. mining, settlement, slash and burn agriculture, n a

cataphractus) and several wetland birds of and overﬁshing have degraded aquatic systems; n

conservation concern (e.g. the wattled crane, civil conﬂict plaguing D. R. Congo since 1996 has d Grus carunculatus, and the black-faced waxbill, devastated human welfare and livelihoods; most o t Estrilda nigriloris). conservation and research eﬀorts have ceased. h e r s F

Lake Malawi (Malawi and Globally outstandingﬁsh diversity including Localized overﬁshing; Extreme habitat specialization ofmany inshore r e s

Mozambique) 400–800 cichlid species (99% endemic), a deforestation and siltation; cichlids makes them highly susceptible to over- h radiation of17 deep-water clariid catfishes eutrophication. fishing withfine-meshed nets; changes infish w a t

(Bathyclarias spp.) and many other endemic communities are particularly obvious in along e r

species; at least 30 mollusc species; richness in the densely-settled southern shores; spawning b i

other taxa is likely also. aggregations oflarge, endemic potamodromous o d i

cyprinids are heavily over-exploited. v e

y r Lake Rukwa (Tanzania) About 60fish species (20 endemics), including Land-use change; introduced Two introduced tilapias (Oreochromis esculentus and s i t two small endemic radiations ofhaplochromine species; overfishing. Tilapia rendalli) compete with the native tilapia y cichlids and sucker-mouth (Chiloglanis) catfishes); (O. rukwaensis), but potential long-term impacts are large colonies ofgreat white pelicans (Pelecanus as yet unstudied; decliningfish stocks probably onocrotalus) and white-winged terns (Chlidonias reflect increasedfishing pressures from displaced leucopterus), as well as large numbers of immigrantfishers (many from Rwanda and non-breeding wetland birds. Burundi); gold mining in the region poses the threat ofmercury contamination oflake Rukwa. Lake Tanganyika (Burundi, D. R. Globally outstanding diversity including y470 Sedimentation; localized urban Only one third ofthe lake shore has been Congo, Zambia and Tanzania) fish species, including endemic radiations of and agricultural pollution; thoroughly-sampled forfishes and many cichlids, mastacembelid spiny eels, claroteid overfishing; climate change. deep-water habitats are virtually unknown, so and sucker-mouth catfishes, and latid perches, as current species numbers offish and especially well as a deep-waterfish assemblage capable other taxa certainly underestimate total diversity. oftolerating periodic anoxia; invertebrate O’Reilly etal. (2003) present compelling evidence diversity is also quite exceptional with 74 that climate change (warming) has diminished endemic Ostracoda, 33 endemic Copepoda, productivity in the lake and contributed to and 17 genera and one family ofendemic decreasingfish yields. prosobrach snails. Lake Turkana (Ethiopia and Kenya) Around y50fish species with 11 endemics; Drought (climate change?). Decliningfish catches attributed to falling lake 3 endemic frogs and 2 threatened turtles (at least levels and drying ofthe mainfishery grounds; oil 1 endemic: Pelusios broadleyi); important site for exploration ongoing in Rift Valleylakes, including 84 waterbird species, including 34 Palearctic Lake Turkana, since the 1980s; oil leakage or migrants. spills could have catastrophic effects. Lake Victoria region (including Globally outstanding aquatic diversity includes Causation complex and not fully Concerns about declines in endemic cichlids Victoria, Kivu, Edward and George) y600 endemicfish species in Lake Victoria, understood: overfishing, in- in Lake Victoria raised in the 1980s following 60 endemics in Lakes Edward and George, and troduced species, land-use increases ofintroduced predatoryNile perch (Lates 28 endemics (19 cichlids) in Lake Kivu; over change and siltation; pollution niloticus); losses appear serious although actual 60 frog species (15 endemics), 5 turtles, and two from a variety ofsources. number ofextinctions has yet to be determined aquatic snakes are known from the region; (Harrison & Stiassny, 1999); visually-mediated 54 mollusc species (6 endemics). sexual selection for male breeding coloration drives reproductive isolation in manylake cichlids, but increasing turbidity disrupts mate recognition by inshore species (Seehausen etal., 1997). 1 7 1 172 D. Dudgeon and others

Fig. 2. Graphical representation ofthe naturalflow regime ofa river showing how it influences aquatic biodiversity via several, inter-related mechanisms (Principles 1–4) that operate over different spatial and temporal scales (redrawn from Bunn & Arthington, 2002). For further explanation, see text.

shape (Principle 1 in Fig. 2). However, droughts and low- data are relatively scant or resources are too limited to flow events also play a role by limiting overall habitat allow detailedfield investigations, with the results used to availability and quality. Many features of theflow regime inform and improve subsequent EWA practices (Poffet al., influence life-history patterns, especially the seasonality and 2003). A new approach to water management– termed predictability of the overall pattern, but also the timing of Integrated Water Resources Management (IWRM)– is now particularflow events (Principle 2). Someflow events trigger evolving into a process to reconcile the needs ofhumans and longitudinal dispersal of migratory aquatic organisms and ecosystems through the development of holistic resource other large events allow access to otherwise disconnected management (Wallace, Acreman & Sullivan, 2003). IWRM floodplain habitats (Principle 3). The native biota of rivers stresses the requirement for EWA to sustain the ecological has evolved in response to the localflow regime. Catchment integrity offresh waters, and the biodiversity they support, land-use change and associated water resource development while recognising and managing the trade-offs that will inevitably lead to changes in one or more aspects of the inevitably be generated as a result. flow regime resulting in declines in aquatic biodiversity via these mechanisms. Invasions by introduced or exotic species are more likely to succeed at the expense of native biota if the former happen to be adapted to the modifiedflow IX. THE VALUE OF FRESHWATER regime (Principle 4). BIODIVERSITY There are over 200 methods for assessing EWA (Tharme, 2003). The challenge is therefore to evaluate their relative Freshwater biodiversity provides a broad variety ofvaluable merits and provide regionally relevant, hydro-ecological goods and services for human societies– some of which models (Benetti, Lanna & Cobalchini, 2004; Scatena, 2004). are irreplaceable (Covich et al., 2004a). The value of this The main features of some of the more widely used biodiversity has several components: its direct contribution approaches are given in Table 4. Because simplistic‘rules to economic productivity (e.g. fisheries); its‘insurance’ of thumb’ about when and how much water should be value in light ofunexpected events; its value as a storehouse allocated are confounded by the range of relationships of genetic information; and its value in supporting the between ecosystem integrity andflow characteristics, meth- provision ofecosystem services (e.g. cleaning water) (Pearce, odologies have been developed in Australia and southern 1998; Heal, 2000; Covich et al., 2004b). Estimates of the Africa that are based on explicit links between these par- full value of biodiversity need to account for each ofthese ameters (e.g. Arthington & Pusey, 2003; Arthington et al., four components; to date, this has not been done. Anumber 2003; King, Brown & Sabet, 2003). This integrative offundamental questions still have to be answered (Loreau approach to EWA has been used primarily for evaluating et al., 2001), but substantial progress has been made in alternative water allocations within drainage basins where understanding the effects ofbiodiversity on the functioning Freshwater biodiversity 173

Table 4. Comparison ofthe four main types ofenvironmentalﬂow methods used worldwide to estimate environmental water allocations (EWA: adapted from King etal., 1999; Tharme, 2003). Riverine ecosystem components, data requirements (or resource intensity) and levels ofapplication are indicated for each method.

Type Riverine ecosystem components Data requirements Levels ofapplication

Hydrological Whole ecosystem, non-specific, Primarily desktop; virgin/ Reconnaissance level ofwater- or some components (e.g.fish: naturalised historicalflowrecords; some resource developments, or as a tool Tennant, 1976). use historical ecological data. within habitat simulation or holistic methodologies. Used widely. Hydraulic Instream habitat for target biota Desktop, limitedfield data; historical Water resource developments where rating (e.g. Stalnaker & Arnette, 1976). flow records. Discharge linked to little or no negotiation is involved, hydraulic variables– typically single or as a tool within habitat simulation river cross section. Hydraulic variables or holistic methodologies. Used (e.g. wetted perimeter) used as surrogate widely. for habitat-flow needs oftarget biota. Habitat Models instream habitat for target Desktop andfield data; historical Water resource developments, often simulation biota (e.g. PHABSIM: Bovee, 1982; flow records. Many hydraulic large-scale, involving rivers ofhigh Stalnaker etal., 1995). May include variables– multiple cross sections. conservation and/or strategic channel form, sediment transport, Physical habitat suitability or preference importance, and/or with complex, water quality, riparian vegetation, data for target species. trade-offs among users, or as method wildlife, recreation and aesthetics. within holistic approaches. Primarily used in developed countries. Holistic Whole river ecosystem; may also Desktop andfield data, plus historical Water resource developments, consider ground water, wetlands, flow and/or rainfall records; requires typically large-scale, involving floodplains, estuaries and coastal multidisciplinary teams ofriver rivers ofhigh conservation and/or waters. Social dependence on scientists. Many hydraulic variables strategic importance, and/or with ecosystems and related economic assessed at multiple cross sections. complex user trade-offs. Simpler factors may be assessed (e.g. Biological data onflow- and habitat- approaches (e.g. expert panels) DRIFT: King etal., 2003; related requirements ofall biota and often used where there are limited Benchmarking: Arthington, 1998). some/all ecological components; exotic trade-offs among users, and/or time species may be included in assessments constraints. Used in developing and ofbiodiversity implications (e.g. developed countries. Arthington, 1998; Arthington etal., 2004). Hydro-ecological relationships and models increasingly used within holistic frameworks.

of terrestrial ecosystems (Hooper et al., 2005). However, to a level whereby they become so scarce that their eco- the precise impacts of biodiversity change will vary with logical roles are degraded to an extent that they might as ecosystem type and the processes and properties considered well be extinct. Such functional extinctions, and associated (Giller et al., 2004; Hooper et al., 2005). Although much reductions in ecosystem services, have been projected for a less is known about fresh waters than terrestrial eco- variety of land birds (Sekercioglu, Daily & Ehrlich, 2004) systems, there is evidence that ecosystem processes can be and may have already taken place in some freshwater impacted by changes in biodiversity (Covich et al., 2004a). ecosystems. Invertebrates, for example, play multiple roles in the Appreciating the value of freshwater biodiversity is functioning of rivers (Wallace & Webster, 1996), and the essential to ensure its well-being. It is certain that ifscientists presence of key species (Dangles et al., 2004), magnitude are unwilling or unable to place a value on‘free’ ecosystem of species richness (Cardinale, Palmer & Collins, 2002; goods and services, then politicians and policy-makers Jonsson & Malmqvist, 2003), and other attributes of com- will interpret this as‘zero value’. The resources apt to be munities (e.g. Dangles & Malmqvist, 2004) can affect rates protected are those that are appreciated. Water must no of ecosystem processes. In addition, variability of process longer be a free or cheap resource– as it is still treated rates is likely to be increased when species are lost, even in in most countries (Kingsford, 2000; Clark & King, 2004). situations where average rates remain unchanged (Dang, Realistic economic valuations of water as a habitat for Chauvet & Gessner, 2005). In some cases it is possible to freshwater biodiversity, and the services that such bio- predict how different anthropogenic stresses will affect diversity provides, will be an essential driver ofany change ecosystem functioning (Jonsson et al., 2002), but in most in societal attitudes (Postel & Carpenter, 1997; Holmlund instances insufficient information is available to make in- & Hammer, 1999; Postel & Richter, 2003; Clark & King, formed predictions. Ofparticular concern is the decline in 2004). Thefirst estimate of the global values of ecosystem populations oflarge freshwater vertebrates (see Section IV) goods (e.g. food in the form offishes), ecosystem services 174 D. Dudgeon and others

(e.g. waste assimilation), biodiversity, and cultural consider- stakeholders in environmental valuations and the develop- ations yielded a value ofUS$6579r 109/year for all inland ment ofeffective conservation policies (Opschoor, 1998). waters (Constanza et al., 1997). It exceeded the worth of Freshwater biodiversity is also ofimmense direct import- all other non-marine ecosystems combined (US$5740r ance to human health. Although many formerly devastating 109/year), despite the far smaller extent of inland waters. infections related to water (e.g. cholera, typhoid fever) are To provide an economic benchmark, the gross domestic now largely in check, other water-borne diseases continue product of the United States is US$9000r 109/year. Of to be widely responsible for societal burdens and human course, all valuation estimates are subject to controversy misery. This is especially true in the tropics where water- (Pearce, 1998; Toman, 1998; Balmford et al., 2002), but borne diseases contribute to around 80% of all illnesses. other approaches to assess values offreshwater systems (e.g. Thefigures for parasitic infections, which are expressed in Barbier, Acreman & Knowler, 1997; Wilson & Carpenter, terms of years of life lost to death or disability annually 1999, Woodward & Wui, 2001; Patterson, 2002) convey (DALY), speak for themselves (W.H.O., 2004): 46.5 million the same general message: inland waters have immense DALY due to malaria (although recent estimates ofmalarial economic importance. incidence are more than 50% higher: Snow et al., 2005); The value of inland waters is bound to increase as 5.8 million due to lymphaticfilariasis, 1.7 million due to ecosystems become more stressed and their goods and schistosomiasis (bilharzia), and 0.5 million due to oncho- services scarcer. However, there is a paucity of empirical cerciasis (river blindness). The last of these has declined data showing how the yield of goods and services derived substantially as a result of research that allowed targeted by retaining habitats in a relatively undisturbed condition control of the river-dwelling blackfly (Simuliidae) larvae compares with that obtained when they are converted for that are obligatory hosts of this parasite (Le´veˆque et al., human use (Balmford et al., 2002; but see Hooper et al., 2003). Nevertheless, outbreaks of water-borne diseases 2005). One of the few good examples assessed the value continue to occur and can be greatly exacerbated by human of pristine freshwater habitat of coho salmon (Oncorhynchus alteration of hydrological regimes, as well as increases kisutch (Walbaum)) on the West Coast ofCanada in relation in the extent of irrigation ditches and channels and hence to various alternative states of degradation (Knowler et al., the availability of habitats for disease organisms and their 2003). Even when only this single species was considered, vectors (e.g. de Moor, 1994). Habitat degradation, creation retaining spawning and rearing streams in a pristine state of‘ruderal’ freshwater habitats, and simplification ofnatu- produced annual values ofUS$940 to US$4980 per stream ral species assemblages may foster mass proliferation of km, as measured by increased profits in the commercial insect and mollusc vectors for infectious human diseases. If fishery situated downstream. Whilefish conservation cannot so, maintenance of natural freshwater communities and be used as the sole index for assessing the relative value of overall system integrity may contribute substantially to the different catchment management strategies, information alleviation ofconditions for disease transmission. ofthis type can help communicate the extent ofthe loss of It maybe possible to meet human needs for water without benefit that accompanies degradation of freshwater eco- loss of most inland-water species but, this will require systems. For instance, income derived from the global sports implementation of environmental water allocations that fishing community provided an incentive to preserve the mimic natural patterns offlow variability and include a spawning habitat ofmarble trout (Salmo marmoratus Cuvier) range offlows– not just a minimum level (Poffet al., 1997; in the Soca River, Slovenia, thereby generating an econ- Bunn & Arthington, 2002; see Fig. 2). For most freshwater omic benefit of US$2.9r 106/year– equivalent to 44% of systems and taxa, scientists can– at present– neither esti- all tourist revenues in the upper Soca region (Sullivan etal., mate the quantities of water that can be extracted nor 2003). Likewise, sportfishing (albeit for exotic salmonids) in the temporal changes in flow that can be tolerated. Lake Taupo, New Zealand, generates almost 10% of the Maintenance of biodiversity is a critical test of whether activity in the local economy, which is based largely on water use or ecosystem modifications are sustainable, and tourism and forestry (Anon, 2003). Freshwater biodiversity this assumption underlies all use of freshwater organisms has particular importance for indigenous people in many as biomonitors or indicators of habitat condition (e.g. parts of the world, who depend upon aquatic products Rosenberg & Resh, 1993; Karr & Chu, 1999). Preservation and the seasonalflux of wetland conditions to support of all elements of freshwater biodiversity would guarantee livelihoods. Examples include the Mesopotamian‘Marsh that water use for humans is sustainable, and the magnitude Arabs’, who have been profoundly influenced by draining ofthe threat to and loss ofbiodiversity is probably a reliable and ongoing restoration of riverine wetlands in Iraq indicator of the extent to which current practices are (e.g. Richardson et al., 2005), as well as societies on African unsustainable. Riverfloodplains (e.g. the Dinka, Lozi and Tonga peoples: Tockner & Stanford, 2002), and communities in the Lower Mekong Basin (Choowaew, Chandrachai &Petersen, 1994). X. CONSERVATION OF FRESHWATER Amerindian communities inflooded forest (varzea) along the Amazon also use many products for handicrafts, BIODIVERSITY IN THE REAL WORLD medicines and food (Neves, 1995). Theseflooded forests have been calculated to generate a level of household Inland waters constitute a valuable natural resource, in income equivalent to US$2330/year (Sullivan, 2002), which economic, cultural, aesthetic, scientific and educational highlights the importance of considering a wide range of terms. Their conservation and management are critical to Freshwater biodiversity 175 the interests of all nations and governments. Immediate depends upon effective communication and engagement conservation action is needed in some instances where among scientists, politicians, non-government organisations opportunities exist to set aside‘pristine’ lake and river and local communities (Poff et al., 2003). Pragmatic systems in large protected areas. Realistically, it must be approaches will be needed to ensure that attempts at recognised that there are significant portions ofthe Earth’s communication between freshwater scientists and water- surface where it is almost inconceivable that any freshwater resource managers, as well as other stakeholders, contribute resource could be dedicated to the sole purpose of bio- to planning and problem solving (Richter et al., 2003; diversity conservation, with humans denied access or their Bernhardt et al., 2005) and do not become a dialogue of use ofthe resource substantiallylimited. Even well-protected the deaf. This is a significant challenge as motivations conservation areas can become focal points for tourism and of the broader community may be neither open nor fair. recreational activities that may reduce habitat quality and Conservation typically operates in a world where many biodiversity (Hadwen, Arthington & Mosisch, 2003). Thus, players are characterized by dishonesty, self-interest, and for most of the global land surface, trade-offs between hostility to nature, and where corporate interests often conservation of freshwater biodiversity and human use of assume disproportionate importance (Stearns & Stearns, ecosystem goods and services are necessary. 1999; Meffe, 2001). Ifscience is to be deployed in a manner that will secure Emphatically, the importance of freshwater biodiversity commitment to the conservation of freshwater biodiversity to society must be communicated successfully to all. The from politicians and decision-makers, scientists will have to threats to freshwater biodiversity are becoming sufficiently make some adjustments in attitude (e.g. Le´veˆque & Balian, known among scientists, but are insufficiently incorporated 2005). In particular, reconsideration of what is regarded within water development. Those making policy and as acceptable forms of ecosystem management for bio- management decisions affecting freshwater biodiversity and diversity conservation will be required in the wider context water resources need to apply the relevant scientific infor- of national development policies. We do not advocate mation, as far as this is available, and employ robust abandoning attempts to check species loss but, in many risk-assessment procedures, monitoring, and adaptive situations, a compromise position of management for bio- management (see Richter etal., 2003; Revenga etal., 2005). diversity conservation, ecosystem functioning and resilience, Ecologically-sustainable water management will only be and human livelihoods will provide the most successful achievable if concerns about ecology and biodiversity are long-term basis for freshwater conservation (Moss, 2000). treated with the same importance as other goals (such as Furthermore, this approach is more likely to be achievable engineering considerations) when water-resource develop- than idealistic prospects of‘win–win’ situations between ments are planned (Richter et al., 2003). This will be a economic development and ecological management prac- significant advance on the prevailing approach wherein tices within which all species can be saved (Redford & ecological criteria are treated as compliance factors to be Sanderson, 1992), or the alternative and discouraging view evaluated after a water-resource development plan has been that conservation of biodiversity is fundamentally incom- completed. Afirst step in this process would be stipulation patible with economic development (Terborgh, 1999). An of ecosystemflow requirements (which inform EWA) so apparent lack of common ground between organisations that water-resource managers can take account of these committed to sustaining livelihoods and those concerned throughout the planning process. with biodiversity conservation might arise from different While preservation of intact freshwater bodies and their starting points and prioritisation ofgoals; ifso, such differ- biodiversity remains a priority, it is important to recognize ences must be recognised but they need not imply that the potential that partly degraded habitats may have to attempts to combine the goals ofconservation and meeting support significant portions of their original biodiversity. human needs should be regarded as futile (Adams et al., Rich aquatic communities can persist in some human- 2004). dominated landscapes (e.g. densely-populated Hong Kong: Data are insufficient to estimate accurately loss rates Dudgeon, 2003a), although certainly not in all situations of freshwater biodiversity in many regions. An immediate, (e.g. Singapore: Brook, Sodhi & Ng, 2003). Strategies are coordinated effort to assess global freshwater biodiversity, needed for managing and rehabilitating degraded eco- including identification ofmajor hotspots, is mandated, and systems– even if they contain exotic species– in order to should involve partnerships among major non-government maximize the persistence of native biodiversity. In Chile, organisations, the United Nations, research institutions, for example, freshwater management is mainly directed and scientific societies. However, the current impediment towards habitat protection for exotic salmonids. However, of insufficient data should not be used as justification for this approach contributes to the maintenance ofecosystem preventing further losses. Nor does the broader community functioning and a good deal of indigenous biodiversity, have to wait until all possible information is in hand before although some nativefishes are confined to places where taking action. As the current trends in turtles,fishes and salmonids do not do well (Soto & Stockner, 1995; Soto & other taxa indicate, there are sufficient reliable data to show Arismendi, 2005). There would certainly be strong oppo- that the global crisis of freshwater biodiversity is now a sition to removing salmonids from Chilean streams because calamity. Developing effective conservation and manage- most stakeholders view them as ecosystem goods of high ment strategies for freshwater biodiversity requires docu- value. In New Zealand also, the desire to preserve valuable menting declines and extinctions and understanding the fisheries based on exotic salmonids (see Section IX) has underlying causes. Implementation of such strategies led to the development of habitat management plans 176 D. Dudgeon and others

(e.g. Anon, 2003) that incidentally protect elements of (4) Inventories offreshwater biodiversity are incomplete native biodiversity. Elsewhere, many important fresh- and in many parts ofthe world, especially the tropics, and rates brackish-water wetlands are largely man-made or human- ofspecies loss may be higher than currently estimated. An dominated environments. Some– such as certain import- immediate, coordinated effort to assess global freshwater ant Ramsar sites– host globally significant numbers of biodiversity, including major hotspots, should be launched endangered water birds, thereby demonstrating that human in partnership with major non-government organisations, alteration of ecosystems is not always incompatible with the United Nations, research institutions and scientific biodiversity conservation. In an attempt to move towards societies. This exercise should take place in parallel with such ‘win–win’ solutions, Rosenzweig (2003) advocates the ongoing development ofstrategies for the conservation an approach to enhancing species richness in human- and management offreshwater biodiversity. dominated landscapes termed‘reconciliation ecology’. It is (5) Fresh water is subject to severe competition among to such strategies that freshwater scientists should consider multiple human stakeholders, in many regions, and serious turning, where appropriate, rather than persisting only in conflicts can arise when water supplies are limiting or attempts to preserve intact ecosystems in the face of traverse political boundaries. Conservation of biodiversity burgeoning human pressure. Given the multiple and grow- is complicated further by the landscape position of rivers ing demands upon fresh waters, it can be anticipated that and wetlands as‘receivers’ of land use effluents, and the whatever principles emerge from reconciliation ecology problems posed by endemism, limited geographic ranges will have direct relevance for conservation of freshwater and non-substitutability. biodiversity. While scientists may not yet have all the tools (6) Protection of freshwater biodiversity is perhaps to ensure that biodiversity conservation and human use of the ultimate conservation challenge because, to be fully fresh waters can be reconciled, Charles Elton, the‘father effective, it requires control over the upstream drainage of animal ecology’, was prescient when he wrote that we network, the surrounding land, the riparian zone, and– in should be‘… looking for some wise principle ofco-existence the case ofmigrating aquatic fauna– downstream reaches. between man and nature, even if it has to be a modified Such prerequisites are hardly ever met, and will necessitate kind of man and a modified kind of nature. This is what development of inclusive management partnerships at I understand by conservation’ (Elton, 1958; p. 145). appropriate (drainage-basin) scales. The complicated issues associated with protected-areas design and management for fresh waters require energetic and imaginative attention from researchers. XI. CONCLUSIONS (7) Water regimes influence aquatic biodiversity via several, inter-related mechanisms operating over a range of (1) Fresh water makes up only 0.01% of the World’s spatial and temporal scales. The maintenance of natural water and covers only 0.8% of the Earth’s surface, yet variability inflows and water levels is therefore essential to this tiny fraction of global water supports at least 100000 underpin conservation strategies for freshwater biodiversity species out ofapproximately 1.75 million– almost 6%. Not and habitats. This requires establishing a hydrological surprisingly, considering their landscape position and value regime that mimics natural variability inflows and water as a natural resource, fresh waters are experiencing declines levels rather than focusing on minimum levels only. For in biodiversity far greater than those in the most affected most freshwater systems and taxa, scientists can– at terrestrial ecosystems. These declines seem to be especially present– neither estimate the quantities of water that can serious in some tropical latitudes, and particularly affect be extracted nor the temporal changes inflow that can be largefishes and other vertebrates. tolerated. Research on this matter of environmental water (2) Freshwater biodiversity is the over-riding conser- allocations is needed urgently. Furthermore, it is essential vation priority during the International‘Water for Life’ that provision offlows needed to preserve biodiversity be Decade for Action (2005 to 2015) and beyond. Assuming treated with the same importance as engineering concerns trends in human demands for water remain unaltered and and other goals when water-resource developments are species losses continue at current rates, the opportunity planned. to conserve significant proportions of the remaining bio- (8) Freshwater biodiversity provides a broad variety diversity in fresh water will vanish before the‘Water for of valuable goods and services for human societies. Some Life’ decade ends. are irreplaceable. Notwithstanding, there is a paucity of (3) Threats to global freshwater biodiversity fall into empirical data showing how the value ofgoods and services five categories: overexploitation; water pollution; flow derived by retaining habitats in relatively natural conditions modification; destruction or degradation of habitat; and compares with that obtained when they are converted invasion by exotic species. Their combined and inter- for human use. The uses of fresh water, including non- acting influences on biodiversity are now worldwide, and consumptive use, underscore the importance ofconsidering are exacerbated further by global-scale environmental the perspectives ofa wide range ofstakeholders in environ- changes such as nitrogen deposition and climate change. mental valuation and in the development of effective Knowledge of these threats is increasing among scientists conservation policies. but is insufficiently incorporated within water-resource (9) Maintenance of biodiversity is a critical test of development, and thus requires wider dissemination and whether water use and ecosystem modifications are sus- emphasis. tainable. Conservation strategies protecting all elements of Freshwater biodiversity 177 freshwater biodiversity would guarantee that water use for ARTHINGTON,A.H.&PUSEY, B. J. (2003). Flow restoration and humans is sustainable while, in contrast, the magnitude of protection in Australian rivers. River Research and Applications 19, the threat to and loss of biodiversity is an indicator of the 377–395. extent to which current practices are unsustainable. ARTHINGTON, A. H., RALL, J. L., KENNARD,M.J.&PUSEY,B.J. (10) A mixture of strategies will be essential to preserve (2003). Environmentalflow requirements offish in Lesotho freshwater biodiversity in the long term. It must include Rivers using the DRIFT methodology. River Research and reserves that protect key, biodiversity-rich water-bodies Applications 19, 641–666. (especially those with important species radiations) and ARTHINGTON, A. H., THARME, R., BRIZGA, S. O., PUSEY,B.J. their catchments, as well as species- or habitat-centred &KENNARD, M. J. (2004). Environmental flow assessment plans that reconcile the protection of biodiversity and with emphasis on holistic methodologies. In Proceedings of the societal use of water resources in the context human- Second International Symposium on the Management ofLarge Rivers for Fisheries, Vol. II (eds. R. Welcomme and T. Petr), pp. 37–56. modified ecosystems. In parallel, scientists must more FAO Regional Office for Asia and the Pacific, Bangkok, effectively communicate the importance and value of Thailand. freshwater biodiversity to stakeholders and policy makers, BAIRD, I. G., PHYLAVANH, B., VONGSENESOUK, B. & so as to make certain that all available information on XAIYAMANIVONG, K. (2001). The ecology and conservation of freshwater biodiversity is applied effectively to ensure its the smallscale croaker Boesemania microlepis (Bleeker 1858–59) in conservation. the mainstream Mekong River, southern Laos. Natural History Bulletin ofthe Siam Society 49, 161–176. BALMFORD, A., BRUNER, A., COOPER, P., CONSTANZA, R., FARBER, XII. ACKNOWLEDGEMENTS S., GREEN, R. E., JENKINS, M., JEFFERISS, P., JESSAMY, V., MADDEN, J., MUNRO, K., MYERS, N., NAEEM, S., PAAVOLA, J., The International Programme on Biodiversity Science, RAYMENT, M., ROSENDO, S., ROUGHGARDEN, J., TRUMOER,K.& DIVERSITAS, made collaboration on this paper possible through TURNER, R. K. (2002). Economic reasons for conserving wild funding provided for international meetings on freshwater bio- nature. Science 297, 950–953. diversity held in Paris, France. The DIVERSITAS network BARBIER, E., ACREMAN,M.&KNOWLER, D. (1997). Economic (www.diversitas.org/freshwater) offers support to scientists dedi- Valuation of Wetlands–A Guide for Policy Makers. Ramsar Con- cated to the discovery, conservation and management of fresh- vention Bureau/IUCN, Gand, Switzerland. http://www. water biodiversity, and will also champion the relevance of biodiversityeconomics.org/valuation/topics-02-00.htm (ac- their work to stewardship of the biosphere. The authors thank cessed 7 April, 2005). J. D. 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