Lessons from damming in the Mekong tributaries:Effects on riverine fish community and biology

Tuantong Jutagate, Michio FukushimaPisit Phomikong and Wachira Kwangkhang

Rationales• Ziv et al. (2012) reported that fish biomass in the Mekong basin would

decrease by about 0.3% (ca. 1700 t/yr) for each additional terawatt hour per year produced by hydropower dams in tributaries and that about six species will become endangered for every 1% of lost biomass.

• Few Mekong’s migratory fishes are known to complete their life cycle in reservoirs (Baran, 2006).

• Thus, in this presentation, we demonstrate

(a) the fish assemblages in the dammed tributaries with different degrees of regulation

(b) the performances of the Mekong’s migratory fishes that can live in the new lentic (or semi-lentic) environment

Baran, E. 2006. Fish migration triggers in the Lower Mekong Basin and other tropical freshwater systems. MRC Technical Paper No. 14, Vientiane, Lao PDR, Mekong River Commission.

Ziv, G., Baran, E., Rodríguez-Iturbe, I., and Levin, S.A. 2012. Trading-off Fish Biodiversity, Food Security and Hydropower in the Mekong River Basin. Proceedings of the National Academy of Sciences 109 (15): 5609-5614.

The Songkhram River (intact tributary)

The Gam River (cascaded tributary with 5 low-head dams)

The Mun River (blockage by the large hydropower dam)

Fish diversity and assemblages among the three rivers

• Previous studies showed similar fish species composition among the three rivers, with more than 90% of common species (Srisatit et al., 1981; Duangswasdi and Chookajorn, 1991; Boonyaratpalin et al., 2002)

Temporal changes in cumulative species richness in each studied tributary

SongkhramGamMun

Case: The Songkhram River

The Migratory guilds of fishes in the Mekong River

Grey Fishes

White Fishes

Black Fishes

Temporal changes in cumulative species richness in each studied tributary

SongkhramGamMun

The effectiveness of the measure has beenstudies by using the “presence / absence” offish monitoring data of the Mun River from1967 to 2007 and analyzing probability ofoccurrence of individual species

Probability of occurrence

X1960s X1980s DC Impound X2001 Implement

020

4060

80

Example of the species that benefit from the measurement I:

Jutagate et al. (2007; 2008)

Henicorhynchus siamensis

Bangana behri

Henicorhynchus lobatus

Mekongina erythrospila Scaphonathops spp.

Sikukia gudgeri

There were 32 species (with 8 specieshad been reported on ascending thefish ladder)

X1960s X1980s DurCon After X2001 Impleme

020

4060

8010

0 Probability of occurrence

Jutagate et al. (2007; 2008)

Cosmocheilus harmandi Luciosoma bleekeri

Helicophagus leptorhynchus Pangasius micronema

Pangasius bocourti Micronema spp.

Example of the species that benefit from the measurement II:

There were 55 species (with 8 specieshad been reported on ascending thefish ladder)

Benefit to spawning migration

Similarity of fish assemblage patterns among the three selected rivers

Fish diversity and assemblages among the three rivers

Fish diversity and assemblages among the three rivers

Larval fish diversity and assemblages among the three rivers

Assemblage I: Songkhram (August and December) and Mun (October)

Nineteen (19) larval species had the average %OP more than 40% in this assemblage. They were mostly grey fish (11 species) such as Rasbora dusonensis, Rasboraborapetensis, Clupeichthys aesarnensis, and Crossocheilus atrilimes.

Rasbora dusonensis

Clupeichthys aesarnensis

Rasbora borapetensis

Assemblage II: Songkhram (February, April and June)

The assemblage II was dominated by 6 grey fishes e.g. C. aesarnensis , Hampala dispar, R. borapetensis) and 3 white fishes, i.e. Mystacoleucus ectypus , Henicorhynchussiamensis and Barbonymus gonionotus.

Barbonymus gonionotus

Hampala dispar

Henicorhynchus siamensis

Assemblage III: Gam (All sampling months)

The average %OP of white fishes, in this assemblage, was significantly lower than the other guilds. Only five larval species were dominant.

Parambassis siamensis

Trichopsis pumila

Assemblage IV: Songkhram (October)

Assemblage IV formed a unique characteristic, which no black fish larvaesinvolved among the 30 highest %OP species . Fifteen dominant white fishes included Sikukia gudgeri, Setipinna melanochir, Pangasius macronema

Notopterus notopterus

Sundasalanx mekongensis

Assemblage V: Mun (February, April, June, August and Decemebr)

The %OP grey fish larvae were significantly higher than the other two guilds in assemblage V but only 2 species, i.e. R. borapetensis and C. aesarnensis were dominated.

Clupeichthys aesarnensis

Rasbora borapetensis

Table I Average ±SD of total length (mm) of commonly observed fish species (N > 150) collected in the three rivers.

Fish species N P River

Mun Songkhram Gam

Barbonymus gonionotus 335 0.179 130.5 ± 47.1 144.9 ± 86.5 126.3 ± 40.9

Barbonymus altus 156 < 0.001 75.5 ± 25.5b 94.6 ± 44.3a 86.9 ± 43.5ab

Henicorhynchus siamensis 450 < 0.001 130.5 ± 49.3a 134.0 ± 21.1a 87.8 ± 36.1b

Cyclocheilichthysa rmatus 162 < 0.001 87.1 ± 24.5a 100.4 ± 15.6a 81.2 ± 20.5b

Puntioplites proctozysron 712 < 0.001 86.3 ± 35.8b 142.0 ± 34.7a 145.1 ± 42.1a

Osteocheilus vittatus 1,175 < 0.001 123.8 ± 29.9b 123.8 ± 34.9b 135.8 ± 38.5a

Labiobarbus lineatus 776 < 0.001 99.0 ± 27.4b 117.9 ± 22.2a 112.5 ± 36.7a

Hemibagrus nemurus 165 < 0.001 64.5 ± 41.6c 203.5 ± 27.6a 174.1 ± 54.8b

Size variations of the adults of commonly found species

Changes in life history traits

(Jutagate et al., 2004; Suvarnaraksha et al, 2011)

• The riverine species, such as H. siamensis and Labeo chryophekadion can establish populations in a lentic system but the production was too low, compared to those in lotic condition.

• The reservoir residents showed slow growth rate and delay in age (size) at maturity, compared to those lived in the rivers.

• The spawning ground is located in the upstream of reservoir, i.e. the inlet area, and highly related to the hydrological cycle and related to flow.

Changes in life history traits