VNMC Mekong Dam Study: Fisheries Impact Assessment

Study of the Impacts of Mainstream Hydropower on the Mekong Delta

Greater Mekong Forum on Water, Food and Energy:

Phnom Penh, Cambodia,

21 October 2015

Fisheries Impact Assessment

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Study of the Impacts of Mainstream Hydropower on the Mekong River

Outline • Background

• Assessment Objectives

• Indicators

• Impact Assessment Strategy

– Historical data

– Research study

– Data issues (limitations and challenges)

• Results

– Scenario 1 – 11 mainstream dams


Fisheries of the lower Mekong Basin

Total first-sale value is US$7.0

billion per year

• Per capita consumption average is

about 46 kg/person/year

200+ species; 30+ of high

commercial importance

More than 50% of total fish catch

in the lower Mekong basin (about

1.3 million tonnes worth US$2.5

billion) dependent on migratory fish

Fish migrate all seasons of year


Links between fisheries and hydrological cycle regimes

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m3/s

)

Day-month

High flow nursing and feedingin the floodplain

Minimum flow refuge in dry season habitat (deep pool)

Medium flow moving from mainstream to tributary

Extreme flow spawning in the floodplain

Medium flow migrating from floodplain to mainstream for dry season refuge


White fish: undertake long distance migrations, in particularly between lower floodplains and the Mekong mainstream and its major tributaries.

Characteristics of the main fish groups

Grey fish: ecologically intermediate between other groups - fishes that spend dry season in floodplain ponds, and do not undertake long distance migrations.

Black fish: Floodplain resident fish, with limited lateral migrations from the river onto floodplains and no longitudinal migrations.


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s)

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acu

lture

pro

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(t x

10

00) Fish

Shrimp

Other aquatic species

Fisheries and aquaculture - status and trends

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nd p

roducti

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tons)

Cà Mau

Bạc Liêu

Sóc Trăng

Hậu Giang

Cần Thơ

Kiên Giang

An Giang

Đồng Tháp

Vĩnh Long

Trà Vinh

Bến Tre

Tiền Giang

Long An

Inland capture

Aquaculture

Declining inland capture fisheries : Possible cause - disconnection of floodplain for rice – see later Growing aquaculture sector – based on intensification


Overview – cause effect of dams on fisheries

Mainstream Hydropower

Projects

Changes in River Flows,

Sediment Transport, and

Water Quality

Changes in Fish Habitat

Quality, Quantity, &

Productivity

Obstructions in Fish

Migration Routes &

Habitat Connectivity

Fish Abundance and

Community Composition

Yield and Consumption

Social & Economic Impacts

Other exogenous factors


Overview - questions

Review designed to answer the following key questions:

• How will changes in water flow regime, water quality, and connectivity of the Mekong River affect the species composition of catch and size of high economic value fish species?

• What fish species will be affected significantly and how?

• How much will capture and aquaculture fisheries production change and where?

Assessment Scenario 1: 11 mainstream dams


Fisheries Impact Assessment Methodology


Assessment Indicators – linked to fish guilds

Indicator Unit Comments

Impact on capture fisheries

Loss of fish catch yield tonnes, % Relate to hydrological and sediment

variables and barrier effect. Loss of OAAs yield tonnes, %

Loss of yield of economically

important fish species tonnes

Relate changes in exploitation

patterns to hydrological change

Species at risk species Determine number of species at risk

Impact on aquaculture

Change in extent of aquaculture

area per species group ha

Relate change in aquaculture

production patterns to hydrological

change and saline intrusion Change in production per

aquaculture species group tonnes


Primary impact assessment –fisheries and OAAs

Assessment methodologies

• Alteration of habitat availability impacts

• Hydrology/flow modification impacts on fish productivity

• Sediment/nutrient loss on fisheries yield

• Disruption to longitudinal connectivity (barrier and reservoir) impacts on fish migration and production

• Changes in fish catch biodiversity

• Impact of changes in water flow regime and water quality on aquaculture

• Baseline fisheries and OAA yield based on Hortle 2007 consumption study


Impact assessment –fisheries data sources • Dai Fishery Monitoring Programme (DFMP), Tonle Sap, Cambodia

(1994–2013);

• Lee trap and Gill net Monitoring Programme Lao PDR (1994-2013)

– outside impact assessment area

• Vietnam fisher catch database-2005-Feb 2013 –good spatial and

temporal coverage of catch composition and CPUE

• GSO/MARD fish and aquaculture production data – 1990-2013 -

• DoF fisheries and aquaculture production maps – prediction for

future production areas

• Fish Abundance and Diversity Monitoring Programme (FADMP) at

up to 40 sites across the LMB (2003–2013) - provides spatial and

temporal catch composition and CPUE per habitat and gear

• Fish Larvae Density Monitoring Programme (FLDMP), Cambodia

and Viet Nam (1999–2013) provides temporal fluctuations in catch

composition and CPUE .

• MDS fisheries surveys (2014) - provides catch composition and

CPUE per habitat and gear.


Data Issues • Much of the available data

– are fragmented and of varying quality and completeness

– original purpose of data was not for focused impact assessment analyses.

– Fish and fishery production vary substantially between years in response to varying climatic and hydrological conditions and not collected by standardised methods

• GSO (VN) and FiD (Cam) known to underestimate fisheries harvest and lack cross validation.

• Data generated by the MDS RIA2 study intended for use in impact assessment, but are collected over less than one year

• Data constraining factors may influence robustness of the impact analyses and the interpretation of the tangible outputs



Alteration of habitat availability

impacts

• Areas of different habitats in

impact area determined.

• Fisheries productivity of

different habitat types

determined from literature and

RIA2 study

• Changes in wetted areas of

different habitat types under

scenario 1 determined using

MDS hydrology model output.

• Change in fisheries productivity

calculated



Alteration of habitat impacts

Yield-per-unit

area (kg ha-1 yr-1)

Guild Proportions

Habitat category OAA Blackfish Whitefish Greyfish

River-floodplain 250 0.11 0.39 0.43 0.18

Rainfed wetlands 100 0.11 0.95 0.00 0.05

Large water bodies

outside flood zone

200 0.11 0.40 0.00 0.60

Inland capture fishery yield estimates for each major aquatic

habitat category (Based on Halls 2014 and Hortle & Bamrungrach 2013



Flow modification impacts

• Models of fish production

versus hydrological variable

developed for

• VN freshwater provinces

• Cambodian floodplain

area

• Dai fishery

• Shifts in fisheries productivity

due to changes in hydrological

patterns predicted

y = 47575x - 15010 R² = 0.5366

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mean annual

Delta fishery

Tonle Sap



Flow modification impacts

• SC1: No detectable change in

flow level = no loss of fish

production

• Possible impact of onset and

offset and duration of flood

pulse on fisheries with other

scenarios

• Problem with external factors

disrupting flow fisheries

relationship, e.g. rice

production

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Prek Kdam_SC1



Alteration of habitat impacts

Distribution of fisheries production (capture and culture) in the Mekong delta in Viet Nam

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Vietnam Delta

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Cambodian floodplain

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1206 t loss of fish production





Assess potential impact of reduced sediment loading of

fisheries yield on capture fisheries yield.

• Tabulate potential changes in extent of fisheries yield per

zone for each hydropower development scenario.

• Evaluate potential impact of reduced sediment loading of

fisheries yield


Fisheries Impact Assessment - - sediment

Predicted loss of sediment and associated nutrients at Kratie and Tân Châu + Châu Đốc

Scenario Total sediment (million tons/ per year)

Kratie Tân Châu + Châu Đốc

Baseline 54.6 32.1 Scenario 1 (11 dams) 22.4 13.9

Nutrient (remaining) Total nutrient (1000 tons/ per year)


P Baseline 19.1 11.6

Scenario 1 (11 dams) 10.1 6.3

N Baseline 48.7 29.6

Scenario 1 (11 dams) 13.8 8.6


Estimated loss in bioavailable phosphorus and equivalent loss in fish (adjusted for double accounting for loss of white fish by barrier effect) and OAA yield in the Mekong Delta and Cambodian floodplain

bioavailable P (t x 1000)

bioavailable P (t x 1000)

Yield (t) Yield (t) loss in aquatic

production t

Loss in aquatic

production t

Capture fisheries


Cambodia floodplain

and Tonle Sap

Viet Nam Delta

Cambodia floodplain

and Tonle Sap

Viet Nam Delta

Baseline level (t x 1000/yr

19.1 11.6 481,537 692,118

Scenario 1 (11 dams)

10.1 6.3 [378,662] [585,120] 63931 64905

Fisheries Impact Assessment - sediment

OAAs Baseline level (t x 1000/yr

19.1 11.6 105,467 160,705

Scenario 1 (11 dams)

10.1 6.3 82.935 135,861 22532 24844



Impact of loss of connectivity in Mekong by mainstream dams

on fisheries

Dam creates barrier

• Interrupts migratory pathways – mitigate with fish passage facilities

• Disruption of downstream passage – adults, eggs and larval stages

• Reduction in species diversity and abundance

Problems due to: • Loss of species migrating to spawning habitats

• Impoundment floods spawning and nursery areas

• Disruption of downstream flows

• Limited passage over dams, especially

for larval stages

• Reduced flow through reservoirs -Impoundment

acts as egg and larval sink

• Passage through turbines



Impact of loss of connectivity in Mekong by mainstream dams

on fisheries (Following procedures of Halls 2014)

• Estimate loss of yield of whitefish caused by loss of migration

potential caused by barrier

• Fish species allocated to guilds

• Estimate proportion of catch of white-long distance

migrators, white –short distance migrators

• Based on fisheries monitoring of catches – RIA2, MRC

and national surveys

• Change in fish production

• ΔY = loss of white fish production

• No account for replacement by grey + short distance

whitefish



Disruption to longitudinal connectivity

Contribution of fish species guilds to catches

40.02

17.44

10.27

17.08

13.06

2.10

whitefish

grey fish

black fish

marine/estuarine

exotics

OAAs

Vietnam Cambodia 40 % whitefish [33 species] in Vietnam highly vulnerable/at risk based on RIA2 study

37.20

33.40

28.90

0.20

whitefish

grey fish

black fish

marine/estuarine



Disruption to longitudinal connectivity

Fish production (t)

SC0 -VN SC0-Cam SC1 -VN SC1-Cam Δ -VN Δ-Cam

White fish loss

Consumption (Hortle 2007) 692,118 481,537 415,271 303,368 -

276,847 -

178,169



Impact of changes in water flow regime and water quality on

aquaculture.

• Changes in water level for average, wet, and dry years

determined from MDS model.

• GIS modelling to determine extent of aquaculture

production for key species and how it relates to flooding

cycle.

• GIS modelling of change in aquaculture production area

caused by change in flood regime



Distribution of aquaculture production areas) in the Mekong delta in Viet Nam

Shrimp culture Extensive pond and flood forest areas

Pangasius culture Intensive pond and cage production



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(t x

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Sóc Trăng

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Cần Thơ

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Đồng Tháp

Vĩnh Long

Trà Vinh

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Long An

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Aquacu

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Shrimp

Other aquatic species

Pangasius - pond

Pangasius - cage

Shrimp - pond

Province

Species group



• Changes in extent of aquaculture production of Pangasius negligible although expansion to coastal provinces may be affected

by saline intrusion. • Negligible loss of mangrove area for shrimp culture under scenario 1 • May be indirect effects of ‘trash’ fish used for aquaculture feeds


Fisheries Impact Assessment – losses SC1

Indicator/Sub-indicator Vietnam Cambodia Baseline Fisheries yield1 (t) 692,118 481,537

Baseline OAA yield1 (t) 160,705 105,467

Loss of fish due to reduced habitat flooding (t) 721 1,650

Loss of OAAs due to reduced habitat flooding (t) 227 473

Loss due barrier effects of dams (t) [primarily white fish]

276,847 178,169

Loss of fish due to reduction in sediment loading and nutrients

63,931 64,605

Loss of OAAs due to reduction in sediment loading and nutrients

24,844 22,532

Cumulative loss of fish adjusting for whitefish loss due to barrier effects (t) 341,499 244,425

Cumulative loss of OAAs (t) 25,701 23,004

Total loss of capture fishery and OAA yield 366,570 267,428


Questions?

Prepared by: Fisheries Team Leader: Prof. Ian Cowx Director, Hull International Fisheries Institute

VNMC Mekong Dam Study: Fisheries Impact Assessment

Science

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