While state-of-the-art technologies for fish passage at hydropower dams for small and medium-sized rivers or for single species such as salmon are available nowadays, solutions for large rivers with multi-species such as the Mekong River are widely missing. Objective of this review is to elucidate migratory particularities of large rivers inhabiting multi-species fish assemblages, analyse advantages and disadvantages of existing fish pass solutions, discuss the potential applicability to the Mekong River and identify research gaps. Large warm-water rivers inhabit a wide range of different species encompassing migratory fish ranging from 20 to >200 cm, migration distances >1000 km and iteroparous life histories. Migrations may take place throughout the year due to species-specific spawning seasons and other migratory needs. A key challenge for fish pass solutions at large rivers is to attract fish to fish pass entries. As a solution, multiple fish passes and/or entries are recommended including options for bottom, surface and open water orientated species. Large fish and large number of fish during migration peaks require dimensions of fish passes going far beyond the size of conventional fish passes. A further challenge is that solutions or even experiences for downstream migration in large, multi-species rivers are widely lacking.

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Challenges for Fish Pass Solutions
in the Mekong River
Stefan Schmutz
Carina Mielach
Institute of Hydrobiology and Aquatic Ecosystem Management
Department of Water, Atmosphere and Environment
BOKU - University of Natural Resources and Life Sciences, Vienna,
AUSTRIA
AFS Annual Meeting Portland
Tuesday, August 18, 2015: 1:20 PM, B-118 (Oregon Convention Center)

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Fish fauna of the Mekong River

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• World‘s 10th longest river (4,909 km)
• 6 countries
• >800 fish species (biodiversity hotspot)
• exact number is unknown
• 2nd highest species richness in the world (after Amazon)
• Diversity increases from headwaters to lower sections
• Highest inland fish productivity
Fish fauna

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Fish fauna
Giant pangasius
(Pangasius sanitwongsei – CR)
Mekong giant catfish
(Pangasianodon gigas – CR)
Giant barb
(Catlocarpio siamensis – CR)
Giant Sheatfish
(Wallago attu – NT)
Goonch
(Bagarius yarrelli – NT)
Seven-striped barb
(Probarbus jullieni – EN)
Thicklip barb
(Probarbus labeamajor – EN)
Striped catfish
(Pangasianodon hypophthalmus – EN)
Highest number of giant freshwater fish
FAO

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Fish fauna
0 50 100 150 200 250 300
Henicorhynchus ornatipinnis
Labiobarbus lineatus
Henicorhynchus cryptopogon
Henicorhynchus lineatus
Henicorhynchus lobatus
Lobocheilos cryptopogon
Paralaubuca barroni
Paralaubuca typus
Amblyrhynchichthys micracanthus
Henicorhynchus siamensis
Yasuhikotakia modesta
Labiobarbus leptocheilus
Lycothrissa crocodilus
Pangasius macronema
Puntioplites proctozystron
Tenualosa thibaudeaui
Osteochilus hasseltii
Osteochilus vittatus
Hampala dispar
Pangasius pleurotaenia
Puntioplites falcifer
Mekongina erythrospila
Poropuntius malcolmi
Bangana behri
Hemibagrus filamentus
Notopterus notopterus
Phalacronotus bleekeri
Cirrhinus microlepis
Hemibagrus nemurus
Hampala macrolepidota
Cyclocheilichthys enoplus
Helicophagus waandersii
Hemisilurus mekongensis
Labeo chrysophekadion
Boesemania microlepis
Chitala ornata
Cosmochilus harmandi
Pangasius elongatus
Pangasius bocourti
Pangasius conchophilus
Pangasius krempfi
Micronema apogon
Pangasius larnaudii
Phalacronotus apogon
Pangasianodon hypophthalmus
Probarbus labeamajor
Probarbus jullieni
Bagarius yarrelli
Wallago attu
Catlocarpio siamensis
Pangasianodon gigas
Pangasius sanitwongsei
< 25 cm
25 to < 50 cm
50 to < 100 cm
≥ 100 cm
< 25 cm
25 to < 50 cm
50 to < 100 cm
≥ 100 cm
not conisdered in
this report
100 200 300 cm
Maximum length of
commercially
important species
Data sources: Poulsen et al. (2004), Baran et al.
(2005), Halls et al. (2013) and fishbase.org
Halls et al. (2013):
16 species comprise
50% of the total catch
Halls et al. (2013)

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Fish fauna – migration triggers
Flora & fauna evolved in accordance to distinct hydrological cycle and highly
depend on timing (seasonality), duration and magnitude of flows
• 4 distinct seasons
limited habitat
availability, water
quality alteration
determines
productivity
Transition seasons  trigger migrations (e.g. spawning)

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Fish fauna – migration guilds
Migratory (white) and non-migratory (black) species with intermediate (grey) guild
(Baran 2006, 2010, Welcomme 2001, Poulsen et al. 2002, Ferguson et al. 2011)
More detailed classification (MRC 2009)
(1) Rithron resident;
(2) Migratory main channel (& tributaries) resident guild;
(3) Migratory main channel (& tributaries) spawner guild;
(4) Migratory channel refuge seeker guild;
(5) Generalist guild;
(6) Floodplain resident guild;
(7) Estuarine resident guild;
(8) Semi-anadromous guild;
(9) Catadromous guild;
(10) Marine guild (enters estuaries opportunistically)

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Fish fauna – migration systems
(Poulsen et al. 2002, Baran 2006)

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Facilities for upstream migration
Facilities for downstream migration

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Fish pass types
Large scale
bypass systems
Bypass channels &
rock ramps
Nature-like Technical
Upstream Downstream
Vertical slot
fish passes
Fish protection Fish passage
Screens Bypasses
Spill flowFish-friendly turbines

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2. Facilities for upstream migration

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Upstream fish pass
 functionality
• Attraction/perceptibility
• where migrating fish search for a way up-
/downstream
• close to the - barrier
- migration corridor
- main current
• Passage (for all species)
• hydraulic conditions (swimming capabilities)
• spatial conditions (large species, high biomass)
• Post-passage effects
• reservoir (no orientation or suitable habitat)
At least during spawning periods but preferably all year long

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Upstream fish pass
 perceptibility – several entries
Wide barriers (at least two, one at each side)
Variable water levels
Multiple entrances required
• close to banks and mid-stream
• bottom, mid-water, surface
• high flow, low flow

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Upstream fish pass
 perceptibility
Attraction flow
• Has to be actively recognised and tracked by fish (0.7-1.5 m/s)
• Low turbulence (<30° to main current)
• No interruption of the current towards the entry (connected migration corridor)
• High impulse of the flow  Velocity: restricited to swimming capabiliteis
 Volume: 1 – 10% (>in large rivers, depending on the location)
• Additional flow can be introduced at downstream part  Attraction flow turbines
 Water coming from the tailrace

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Upstream fish pass
 passability – spatial dimensions
H = 66
L = 300
slot depth (ds)
2 to 2.5 * H = 132 to 165 cm
pool width (Wp)
2 * L = 600 cm
slot width (ws)
3 * W = 123 cm
(for nature-like FP by a factor of 1.25-1.5 larger)
Estimation for Mekong giant catfish
pool length (Lp)
3 * L = 900 cm
hydr. depth (Dmin)
2.5 * H = 165 cm

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Vertical slot fish pass
Example: Geesthacht, Elbe River, Germany
• FP length 550 m
• Weir head 4 m
• 45 pools 9 x 16 m
• 2 slots/ pool 1.6 m
• Max. discharge 15 m³/s (2% of MQ)
• Passage of
• 43 species
• 300.000 ind./year
• Also large individuals of Atlantic salmon,
sander, European catfish and 3 m long
sturgeon

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3. Facilities for downstream
migration

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Downstream fish pass
• Fish protection (to prevent migration through turbines)
• Behavioural barriers
• Physical barriers
• Construction of suitable downstream fish pass systems
• Fish-compatible turbines
• Bypass systems
• Spillway passage
• Trap & truck
• Widely lacking for large, multi-species rivers
• Solutions for passive downstream drift of fish larvae through reservoirs?

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6. Conclusion and
future research priorities

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Innovation: Hydroconnect
Up- & downstream fish pass
Downstream
passage
Upstream
passage
28/08/2015

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Integrative fish pass solutions
Jungwith et al.2005
Fish ladder
Integrated mitigation solutions

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Mekong fish passes
Remaining challenges and research
• Most fish passes for small-medium sized-dams (15m height)
• Mainly for upstream migration
• Large migrating species
• Migration peaks with high biomass
• High diversity of species (with different requirements)
• Limited knowledge of all migratory species (e.g. Mekong)
• High discharge variations
• Fish passage efficiencies (multiple dams!)
Worldwatch Institute
292 m high Xiaowan Dam. Mekong, China

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Thank you for your attention!
Stefan Schmutz
University of Natural Resources and Life Sciences Vienna
Institute of Hydrobiology and Aquatic Ecosystem Management
Max Emanuel-Straße 17, A-1180 Wien
Tel.: +43 1 47654-5202, Fax: +43 1 47654-5217
stefan.schmutz@boku.ac.at
www.boku.ac.at
For more information see
Mekong River Commission report