conserving Asian riverine biodiversity in a warmer world

David DUDGEON

Going with the flow: conserving Asian riverine

biodiversity in a warmer world

Division of Ecology & BiodiversitySchool of Biological SciencesThe University of Hong Kong

[email protected]

(Photo by Zeb Hogan)

http://www.hku.hk/

Photos: CAS

Yangtze dolphin (baiji): Lipotidae

4 species of river dolphins occur only in Asia: IUCN Red List status = CR or EN

Endangered riverine megafauna

December, 2006

Threats to Asian river turtles

.

(Photos by W.P. McCord http:// nytts.org/asianturtlecrisis.html)

Asia is the richest part of the world for freshwater turtles; most species are riverine

Endangerment of Asian river turtles~ 90 spp.: IUCN ‘Red List’ classifications

1996 2000 2002 CR 5 18 19 EN 9 27 31 VU 23 21 23 Total 37 (41%) 66 (73%) 73 (81%)DD 18 6 6

Subsequent changes minor only; most DD species too rare to evaluate

Endangerment of Asian river turtles90 spp.: IUCN ‘Red List’ classifications

1996 2000 2002 CR 5 18 19 EN 9 27 31 VU 23 21 23 Total 37 (41%) 66 (73%) 73 (81%)DD 18 6 6

Subsequent changes minor only; most DD species too rare to evaluate

In 2002-03, 72 threatened species (CR + EN + VU) were traded in markets in HK & Guangdong1

(1Cheung & Dudgeon 2006)

Rivers face multiple threats globally1

• Pollution from many sources

• Loss of habitat & drainage-basin degradation (land-use change, deforestation)

• Over-exploitation (fishes, reptiles & amphibians)

• Flow modification, regulation & consumption; water transfers & dams

• Invasive exotic species

(1Dudgeon et al. 2006)

Interactions with ongoing global climate change

Monsoons drive natural seasonal flow cycles

Discharge seasonality of Yangtze: 30-yr average up to 2000

Effects of warming on river flow patterns

Effects of warming on river flow

• Scenarios for monsoons vary; increased flood peaks & lower dry-season rainfall probable (= more extremes)1

• Warmer dry seasons will cause greater evaporation & transpiration reducing soil-water inputs to rivers & streams

• Streams that formerly flowed year-round may become intermittent

• Flow patterns to which biota are adapted will change adding to thermal stress

(1Labat et al. 2004)

Effects of warming on river flow

• Scenarios for monsoons vary; increased flood peaks & lower dry-season rainfall probable (= more extremes)1

• Warmer dry seasons will cause greater evaporation & transpiration reducing soil-water inputs to rivers & streams

• Streams that formerly flowed year-round may become intermittent

• Flow patterns to which biota are adapted will change adding to thermal stress

(1Labat et al. 2004)

Glacial melting will increase flow unpredictability: consequences for ~2 billion people living around rivers originating in the Himalaya

What is the scope for thermal adjustment?1

• Shift altitudinal range upward (~500 m)– Suitable sites upstream are not vacant– Sites upstream may not provide suitable habitat– Access may be limited by natural barriers or dams– Potential for upward extension depends on local

topography

Fully-aquatic species have 2 options:

1Assuming 3oC rise in mean temperature (Leung et al. 2004)

What is the scope for thermal adjustment?1

• Shift altitudinal range upward (~500 m)– Suitable sites upstream are not vacant– Sites upstream may not provide suitable habitat– Access may be limited by natural barriers or dams– Potential for upward extension depends on local

topography• Shift habitat occupancy northward (~300 km)

– Possible if rivers flow north-south– Not possible if rivers flow east-west– Not possible if river is dammed

Fully-aquatic species have 2 options:

1Assuming 3oC rise in mean temperature (Leung et al. 2004)

The human dimension: dams

• Climate change causing more floods & droughts will stimulate dam-building for– Flood protection– Water storage for people & agriculture– Hydropower as an alternative to fossil fuel

• River flows further altered from pre-warming patterns• Migrations & movement of biota blocked; populations

fragmented• Disrupt lateral & longitudinal connectivity of rivers that

is mediated by seasonal flows

Threats to Asian rivers are already acute

• Monsoonal Asia is most densely populated region on Earth: >50% humans in 13% global land area1

• Much of landscape is disturbed, degraded & polluted1,2 & >60% of it is human-dominated2,3; high rates of urbanization

• Fastest rates of land-use change, deforestation & logging on Earth with frequent forest fires4,5

• Asia (esp. China) has ~55% of world’s large dams6

(1ADB 1997; 2Hannah et al. 1994; 3Taylor et al. 1999; 4Laurance 1999; 5Achard et al. 2002; 6WCD 2000)

Global ranking of Asian rivers (out of a total of 107 major world rivers) based on fish biodiversity

(1Kottelat & Whitten 1996; Rainboth 1996; Groombridge & Jenkins 1998; MRC 2003)

River Species total

Rank by species

Rank by area

Mekong 1800 3 25Ganges 350 4 16Yangtze 320 5 11Cauvery 265 7 98Kapuas 250 8 88Chao Phraya 222 10 69

Why does the intensity of threat matter? River fish biodiversity in Asia



Rank by species


River Species total

Rank by area




Rank by species

Rank by area


River Species total


1971 1972 1973 1974 1975 1976 1977 1978 1979 1980

Qua

ntity

of f

ish

fish

sold

(t)

0

20

40

60

80

100

Total market sales

Mystus spp. (Bagridae)

Wallago attu (Siluridae)

Wild-caught river fishes(Perak State, Malaysia)

Over-exploitation of fishes

Raw data from I. Baird, Aquatic Conservation (2006)

Annual biomass of catches (kg) of surveyed fishers in Hang Khone, Lao PDR

1993 1994 1995 1996 1997 1998

Cat

ches

(kg)

0

100

200

300

400

500

600

Probarbus labeamajor Probarbus jullieni

Probarbus jullieni (EN)

Threats to fishes: river pollution in China

• Yangtze received 26 billion t waste water in 2005 (17 billion t in 2004); 40% of China’s total – 80% of it untreated1

• 40% of 740 river sites surveyed in 2003 & 20042

were “heavily polluted”• ~80% of the 50,000 km of major rivers in China

are too polluted to sustain commercial fisheries3

• Fish kills frequent during dry season; fish entirely eliminated from >5% of total river length3

(1Lu Jianjian, East China Normal University; 2SEPA 2003, 2004; 3FAO 1999)


• Yangtze received 25.6 billion t waste water in 2005 (16.8 billion t in 2004); 40% of China’s total – 80% of it untreated1

• 40% of 740 river sites surveyed in 2003 & 20042

were “heavily polluted”• Fish kills frequent during dry season; fish entirely

eliminated from >5% of total river length3

• ~80% of the 50,000 km of major rivers in China are too polluted to sustain commercial fisheries3

(1Lu Jianjian, East China Normal University; 2SEPA 2003, 2004; 3FAO 1999)


Yangtze River: formerly 70% of China's inland catch (~500,000 t/yr); yields fell by 50% from 1954-19703.

Continued overfishing, large dams & pollution → further declines; now only ~100,000 t/yr

Under 11th 5-year plan, in 2006-2010 China intends to spend 1.6% of GDP

cleaning up pollution


Under 11th 5-year plan, in 2006-2010 China intends to spend 1.6% of GDP

cleaning up pollution

Since 2003, Fishery Dept of the Agriculture Ministry has imposed an annual

fishing moratorium along large parts of the Yangtze


Threatened migratory fishes in

the Yangtze

Chinese paddlefish (CR)

Yangtze sturgeon (CR)

Chinese sturgeon (EN)

All affected by interactions of overfishing, pollution & dams blocking migrations

The Three-Gorges Dam: the world’s largest engineering project (dam completed May 2006)

Mekong giant catfish Pangasianodon gigas (CR)

Large river fishes in Asia - especially long-lived migratory species adapted to seasonal flows - very vulnerable to human impacts in different places at different times

Undertake longitudinal migrations

Undertake lateral migrations

Maintenance of connectivity is essential

Inter-governmental Mekong River Commission (MRC) includes 4 nations

Mekong-Lancang Jiang

Mandate1 to facilitate cooperation in “…all fields of sustainable development, management and conservation of water related resources of the Mekong Basin”

(1MRC 2002)

Tonlé Sap Lake

Planned Mekong River dam array

Planned Mekong River dam arrayProjects abandoned

by MRC in 2002

Inter-governmental Mekong River Commission (MRC) includes 4 nations -but not China

China’s new dams on the Lancang Jiang (Mekong)

Tonlé Sap Lake (Cambodia): dry season

Image courtesy of Jesse Allen, Modis Rapid Response Team, NASA GSFC

Tonlé Sap Lake: wet season (Oct 2002)

Image courtesy of Jesse Allen, Modis Rapid Response Team, NASA GSFC

Upstream dams impact Tonlé Sap Lake1

(1Campbell et al. 2006; 2Coates et al. 2004)

Fisheries (149 spp.) based on seasonal flow cycle -causes 8 m water-level changes that stimulate breeding by (mainly) blackfishes in this floodplain lake1,2

Effect of 2 dams already completed on Lancang Jiang is reduced amplitude of flow seasonality & one prediction is an 11% decrease in inundated area around lake (by ~1500 km2) due to construction of remaining dams1

(1Campbell et al. 2006; 2Coates et al. 2004)

Fisheries (149 spp.) based on seasonal inundation cycle causing 8m water-level changes that stimulate breeding by (mainly) blackfishes in this floodplain lake1,2

Effect of 2 dams already completed on Lancang Jiang is reduced amplitude of flow seasonality & one prediction is an 11% decrease in inundated area around lake (by ~1500 km2) due to construction of remaining dams1

Important: Lower Mekong Basin fishery estimated at >2 m t/yr (~2% of global SW+FW fishery)

Fish consumption around Tonlé Sap region is 70 kg/person/yr (80% of protein) 1,2

Upstream dams impact Tonlé Sap Lake1

China’s planned dams on the Nu Jiang (Salween)

Planned new dams on the Yangtze

Damming Asia’s great rivers

Synergistic effects of change

• Increased dam-building will change temperature regimes in rivers altered by global warming

• Greater fragmentation of populations by dams may limit genetic responses & adaptation to warming

• Altered flow regimes may be too unpredictable to permit biological adaptation (NB: glacier melt)

• Increased water extraction/storage will affect pollution burdens in rivers

• Riverine species may be unable able to shift ranges northward fast or far enough to offset warming

(What will happen to species at high altitudes?)

What do we need to know?

• What are thermal tolerances of the Asian river biota? Which will be most vulnerable to warming?

• How does ecosystem function (+ goods & services for humans) change with rising temperature?

• What are priorities for intervention? Is translocation of riverine species feasible or desirable?

• E-flows are relatively new in Asia1 & largely untested. What aspects of the natural flow are critical for riverine biodiversity in monsoonal Asia?

(1Tharme, 2003)

What do we need to know?

• What are thermal tolerances of the Asian river biota? Which will be most vulnerable to warming?

• How does ecosystem function (+ goods & services for humans) change with rising temperature?

• What are priorities for intervention? Is translocation of riverine species feasible or desirable?

• E-flows are relatively new in Asia1 & largely untested. What aspects of the natural flow are critical for riverine biodiversity in monsoonal Asia?

Can we reproduce them in the human-dominated rivers of a warmer world?

(1Tharme, 2003)

“20 million years & farewell; thanks for all the fish”

Photo courtesy of baiji.org

http://www.hku.hk/

conserving Asian riverine biodiversity in a warmer world

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