FISHERIES IMPACT ASSESSMENT · Mekong fisheries produce 0.75 - 2.6 million tonnes each year; this represents 7 to 22% of the world’s freshwater fisheries LMB countries consume the

FISHERIESIMPACT ASSESSMENT

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To what extent can mainstream dams alter fish biodiversity, fish migration patterns and fish catches in the Mekong aquatic systems?

Key strategic question

1- Baseline situation (reminder)Main featuresFuture trends without LMB mainstream dams

2- Impact assessment (future trends with LMB mainstream dams)MethodologyPreliminary findingsGeneric findingsFindings by zone

Outline

ICEM | MRC SEA of mainstream hydropower | Impacts Assessment Workshop 19-20 May 2010

3

Baseline


Black fishes: migrate between floodplains and ponds

White fishes: migrate between floodplains and remote tributaries

Grey fishes: migrate between floodplains and local tributaries

4


Even in absence of mainstream dams a number of sub-basins will be blocked to migrations

5

Nam Chi

Nam Mun

BDP definite future scenario

Dams existingDams under construction


6


20

40

60

80

100

2000 2005 2010 2015 2020 2025

Rel

ativ

e su

stai

nabi

lity

(no

unit,

leve

l 100

in y

ear 2

000)

7

Capture fish production is expected to decline in the future even in the absence of mainstream dams


8

Aquaculture will plateau soon in Vietnam, within 15 years in Thailand, and will remain low in Laos and Cambodia


9

Mekong fisheries produce 0.75 - 2.6 million tonnes each year; this represents 7 to 22% of the world’s freshwater fisheries

LMB countries consume the most freshwater fish in the worldFreshwater fish supply is critical for food security in the basin, particularly in Cambodia.

The Mekong River has the second highest fish biodiversity in the world

The migratory fish resource at risk from mainstream dam development ranges between 0.7 and 1.6 million tonnes per year

Aquaculture cannot replace capture fish production

Capture fish production is huge and not yet declining, but will not increase in the future

Summary


Planned damsPresent dams

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Impact assessment

Ban Koum

Latsua

Middle cluster

Don SahongStung Treng

SamborDownstream cluster

Gongguoqiao

Nuozhadu

GanlanbaMengsong

Xiaowan Manwan

Dachaoshan

Jinghong

Upstream clusterPak Beng

Luang Prabang

Xayaburi

SanakhamPak Lay

Pak Chom

METHODOLOGY


Fraction of the river network blocked by dams

Heart of the migratory system = downstream floodplains

Use of BDP2 development scenarios

Km2 of watershed upstream not accessible to migrations upstream of a given dam

Assessment of cumulative surface area of watershed obstructed by dams

Methodology

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16 47 77 83 86 88Number of dams:ICEM | MRC SEA of mainstream hydropower | Impacts Assessment Workshop 19-20 May 2010

Wetlands, floodplains and fish productivity

Wetlands(= floodplains + rice fields + permanent water

bodies + aquaculture + swamps)

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Floodplains


Methodology

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Rice fields = floodplain rice fields (high fish productivity) + rainfed rice fields (RRF, lower fish productivity)

LMB wetlands = 184,900 km2

LMB floodplains = 50,152 km2

Floodplain productivity: low=50kg/ha/year, average= 119± 25 kg/ha/year, high=200 kg/ha/year


Fish production of dam reservoirs

Review of reservoir production figures in the Mekong and in Asia

Methodology

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Calculation of i) surface area of each mainstream

reservoirii) average and cumulated surface

area of reservoirs in tributaries

Analysis of the best predictor of reservoir fish production → area


Proportion of white and black fish basinwide

Method 1: mainstream catch monitoring (MRC 2003-2004)

Method 2: surveying experts

Method 3: catch statistics in Cambodia

Method 4: update integrating black fish production in non-floodplain rice fields

Methodology

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Long-distance migrants and fish production

i) Use assessment of dominant species in catches basinwide (Halls and Kshatriya in press)

ii) Use all migration maps from MFD2003

iii) Combine all ecological information in FishBase and MFD 2003

→ migration patterns and contribution to catches of 43 long-distance migrants representing 30% of the total catch

Methodology

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Impact assessment

I. PRELIMINARY FINDINGS


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Hydrological changes (i)2015: Dry season Q: +41-45%; wet season WL: - 50 to 60 cm

2030 no MD: Dry season Q: +53-65%; wet season WL: - 0 to 50 cm

2030, 6 MD: Dry season Q: +54-58%; wet season WL: -50 to 70 cm

2030, 9 MD: Dry season Q: +55-60%

2030, 11 MD: Dry season Q: +55-60%; wet season WL: -50 to 70 cm

2015: Dry season Q: +32%; wet season WL: - 30 cm

2030, 9 MD: Dry season Q: +33%

2030, 11 MD: Dry season Q: +33%; wet season WL: - 50 cm

2030, no MD: Dry season Q: +31%; wet season WL: - 40 cm

2030, 6 MD: Dry season Q: +32%; wet season WL: - 50 cm

2015: Dry season Q: +13-22%; wet season WL: - 30 cm, Floodplains: -251,000 ha

2030 no MD: Dry season Q: +13-25%; wet season WL: -20 to 60cm

2030, 6 MD: Dry season Q: +14-26%; wet season WL: -20 cm

2030, 11 MD: Dry season Q: +15-28%; wet season WL: -20 to 60 cm, Floodplains: -309,000 ha

2030, 9 MD: Dry season Q: +14-27%


Floodplain after the dam

Floodplain before the dam Dry season water level

Wet season water level

Losses in floodplains should be computed as the surface area that will not be flooded any more in the wet season plus the surface area that will be permanently flooded in the dry season.

Area not flooded any more in the wet season

New area permanently flooded in the dry season

Areas characterized by loss of flood pulse= loss of productivity

Hydrological changes (ii)20


Hydrological changes detailed by BDP2 are seasonal; these changes are minimal compared to daily variability in downstream water levels following peak operation.

Problem already experienced with the Yali Falls dam in Vietnam.

This daily variability is expected to have major effects on fish resources and on the environment in general and cannot be ignored in future analyses.

Seasonal variation from baseline (cm) in nearest hydrological monitoring site

Daily variation in the

reservoir (cm)

Mode of operation

Louang Prabang

Wet season: ‐68Dry season: +149

200 Peak load 12‐15 h/day

Xayaburi Wet season: ‐68Dry season: +149

0 NA

Pak Lay Wet season: ‐68Dry season: +149

100‐200 Peak load 8‐10 hours/day

Pakchom Wet season: ‐53Dry season: +145

200 Continuous

Latsua Wet season: ‐47Dry season: +51

200 Peak load >16 hours/day

Stung Treng

Wet season: ‐47Dry season: +51

200 Continuous

Sambor Wet season: ‐61Dry season: +85

small NA

Hydrological changes (iii)

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→ between 35% and 70% of the fish production basinwide is made of long-distance migratory species vulnerable to mainstream dam development

→ the current level of knowledge does not allow a lower uncertainty range.

35%

70%

Proportion of white and black fish basinwide

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→ for mainstream dams, the surface area alone is the best single predictor of reservoir productivity

→ productivity ranges between 20 kg/ha/year and 200 kg/ha/year

→ largely unpredictable nature of reservoir fish production


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Impact assessment

II. GENERIC FINDINGS

In 2000, 20.6% of the Lower Mekong Basin was already barred by 16 dams In 2015, 23.6% of the LMB will be barred to fish migrations due to 47 dams on tributariesIn 2030:

if no mainstream dams are built, 37.3% of the LMB will be inaccessible to long distance migrant fish because of 77 dams ontributariesif mainstream dam development is limited to the 6 dams of the upstream cluster, then 68.7% of the basin will be barred if 9 mainstream dams are built (but none in Cambodia) then 78.8% of the basin will not be accessible to long distance migrant fish.if 11 mainstream dams are constructed, then 81.3% of the watershed will be obstructed and fish migrating from floodplainsfish will not be able to migrate further than Kratie (Sambor dam)

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Fraction of the river network blocked by dams

100,000

200,000

300,000

400,000

500,000

600,000

700,000

Pakbe

ngLu

angp

raban

g

Xayab

ulyPak

laySan

akha

mPak

chom

Ban K

umLa

tsua

Don S

ahon

g

Stung T

reng

Sambo

r

Pak Beng

Luang Prabang

Xayaburi

Sanakham

Pak Lay

Pak Chom

Ban Koum

Latsua

Don Sahong

Stung Treng

Sambor Km

2of

wat

ersh

ed u

pstr

eam

of t

he d

am26

Fraction of the mainstream turned into a reservoir

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DamReservoir length

(km)

Total length of reservoirs

(km)River length (km)

% of mainstream turned into a reservoir

Upstream cluster

Pak Beng 180

715 790 90

Luang Prabang 150

Xayaburi 100

Pak Lay 110

Xanakham 90

Pak Chom 85

Middle clusterBan Koum 155

165 713 23Lat Sua 10

Downstream cluster

Don Sahong 5

140 330 42Stung Treng 45

Sambor 90

Total 1020 1833 55

Calculated after dams heights and a digital terrain model

If 11 reservoirs are built, 55% of the mainstream in the LMB will be turned into a dam reservoir. If 6 dams are built between Chiang Saen and Vientiane, then 90% of the Mekong mainstream between these two points will be turnedinto a reservoir ecosystem.

Fraction of the mainstream turned into a reservoir

If Cambodian dams are not built but 9 other mainstream dams are, then 48% of the mainstream in the LMB would be turned into a reservoir.

Stung Treng + Sambor reservoirs = 1/3 of Tonle Sap surface area

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Predict fisheries production in reservoirs

Range of productivity based on previous cases (20 to 200 kg/ha/year)

Most important characteristic is surface area (less important is depth)


Combination of surface areas of reservoirs created by mainstreamdams (150,000 ha) and fish productivity of reservoirs (20 to 200kg/ha/year depending on reservoir characteristics):

→ the highest fish production to be expected from reservoir fisheries in mainstream dams amounts to 30,000 tonnes basinwide.

→ in fact the most likely production represents about 10,000 tonnes.

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>43 species>28% of total catch

>28 species

>27 species

>41 species

>15 species

Kratie

3SKhone Falls

Mun/Chi

>25 species

Vientiane

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Long-distance migrants and fish production

43 white fish species, 30% of the catch of the fish catch basinwide:

→ 95% of them (= 28.5% of the catch basinwide) migrate through Khone Falls;

→ 2/3 undertake a migration between Khone Falls and upstream


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Impact assessment

III. FINDINGS BY ZONE


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Upstream cluster

The migration barrier effect would apply to 40 sub-basins

Hydrologically, the area is dominated by the influence of Chinese dams

A drop in the recruitment of local species is expected even in absence of mainstream dams. The contribution of these upstream species to the fish biodiversity of the basin is very important (in particular Balitoridae)

90% of the river in this section will be converted to reservoirs if 6 mainstream dams are built


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Upstream cluster

41 species are specifically at risk, including the Giant Mekong catfish (at risk of extinction if dams completed)

The risk of fish production losses in case the 6 upstream mainstream dams are built amounts to 130,000 – 270,000 tonnes.

Reservoir fish production would range between 2,000 and 20,000 tonnes of fish, the most likely estimate being around 7,000 tonnes


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Middle cluster

The migration barrier effect would apply to 40+40 = 80 sub-basins

The Latsua dam would have much more negative impact on fish migrations than the Ban Kum dam because it would block access to the Mun/Chi system (70,000 km2). The Latsua dam would have the same impact than the Pak Mun dam on Mun-dependent fish species, plus additional impact on species migrating up the mainstream.

Latsua

Ban Koum

Mun River

Mekong River

LAOS

THAILAND

Ban Kum

Latsua

Bord

er

Pak Mun


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Middle cluster

The Ban Koum and Latsua mainstream dams would result in some 78% of the Basin being blocked to migrating fish

These dams would create 147 km2 of reservoir, i.e. 23% of the mainstream between Pakse and Vientiane would be turned into a reservoir.

These reservoirs can be expected to produce between 300 and 3,000 tonnes of reservoir fish, the most likely estimate being 330 tonnes

The risk of capture fish production losses in case the 2 mainstream dams of the middle cluster are built amounts to 210,000 – 420,000 tonnes


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Downstream cluster

The migration barrier effect would apply to 40+40+6 = 86 sub-basins, including the Sekong-Sesan-Srepok system (second largest in Mekong)

Overall, these dams would be those blocking most migration routes and thus would have the biggest impact on fish resources.


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Downstream cluster

The risk of fish production losses in case the 2 mainstream dams of the downstream cluster are built amounts to 220,000 – 440,000 tonnes

The loss of floodplains inherent to these dams corresponds to 3,000 to 12,000 tonnes of fish only

The Stung Treng and Sambor mainstream dams would create 950 km2 of reservoir. This area can be expected to produce between 2000 and19,000 tonnes of reservoir fish, the most likely estimate being 8,000 tonnes


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IV. CONCLUSIONS


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The 11 dams, if built as planned, would result in a loss of fish production ranging between 700,000 and 1.4 million tonnes

In the same conditions, the recent BDP2 report on fisheries impact predicts a loss of 600,000 tonnes

The most conservative estimate common to all studies and reports is a loss of 600,000 tonnes of annual fish production in case of hydropower development. This corresponds to the whole freshwater fish production in West Africa (15 countries)

Reservoir fisheries from mainstream dams will not compensate for losses in capture fisheries, since they will produce at most 30,000 tonnes per year


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The planned dams will not be uniformly damaging to fisheries, certain dams having more impact than others:

• Latsua blocking the large Mun/Chi system• Stung Treng/Don Sahong blocking Khone Falls• Sambor largest dam blocking 78.8% of the Mekong system

If all 11 dams are built, then 55% of the Lower Mekong mainstream will be turned into a reservoir


Several additional aspects relating to fisheries remain to be addressed:• Impact of sediment retention on water and fish production• Effect of changes in species composition on nutritional value• Effect of changes in species composition on market value of

fisheries products• Effect of changes in fish and fisheries on socio-economics of

various social groups

The present study is an initial attempt to assess the impact of investments worth USD 18,847 million on a resource worth USD 2,100 –3,800 million.

The magnitude of possible impacts calls for major investment in view of assessing in detail the impacts of hydropower development on food security and livelihoods in the Mekong Basin.

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Thank you!


Documents

FISHERIES IMPACT ASSESSMENT · Mekong fisheries produce 0.75 - 2.6 million tonnes each year; this represents 7 to 22% of the world’s freshwater fisheries LMB countries consume the