Session D5: Using a Waterfall System as a Natural Laboratory to Inform the Design of Fish Passes in the Mekong

Abstract: The Mekong Basin features 103 long distance migratory fish species contributing 800,000 tonnes per year to the regional inland fishery. At Khone Falls in southern Laos, the Mekong River splits into multiple channels and flows through numerous waterfalls that constitute a major obstacle to fish migrations across the basin. We present here the approach and methodology of a new research project using the Khone Falls bottleneck as a natural laboratory to inform the design of fish passes in the Mekong. This project is based on systematic gathering of local ecological knowledge, combined with hydrological measurements and river geomorphological characterization in multiple sites. The project will produce a matrix detailing, for the dominant Mekong migratory species, flow conditions and river conditions passable, preferred or not passable to fish. This information will help design fish ladders better adapted to native fish species, thus contributing to improved mitigation of the impact of hydropower dams on food security and fish biodiversity in the Mekong Basin

Thai river sprat : biology and management in Sirinthorn Reservoir, Thailand

The Thai river sprat (Clupeichthys aesarnensis) is a short-lived clupeid, which supports an artisanal fishery in a number of reservoirs in the Lower Mekong Basin. This study presents the C. aesarnensis biology, population dynamics and its fishery in Sirinthorn Reservoir, NE Thailand. C. aesarnensis fishery management schemes are also proposed

Chronicle of marine fisheries in the Gulf of Thailand: variations, trends and patterns

1302-1309A comprehensive picture of marine fisheries in the Gulf of Thailand (GoT), within Thailand’s boundary, has been described by using fish landing data for 26 years, between 1984 and 2009. Thirty-five (35) species/groups of fish landings were used in analysis. Rastrelliger brachysoma showed the lowest long-term variation (CV) in fish landings at 15.53% and the highest CV was observed in Lates calcarifer at 146.16%. The relationship between CV and fish landings showed a negative trend with a high correlation (r = 0.62) and was associated with species life-history strategies. For short-term variations, the means of the relative variation (28%) were higher than the absolute variation (25%), indicating a higher uncertainty when catches are low. Three trends in fish landings were analyzed by Spearman’s rank correlation. Seven (7) and 3 species/groups trended to decrease and increase, respectively, over the studied period. Meanwhile, 15 species/groups showed a trend of inversion, i.e. increased then decreased. The self-organizing map was used to cluster patterns of fish landings, which indicated temporal trends of chronological order, i.e. 1985-1990, 1992-1998, 1999-2007 and 2008-2009

Diversity And Assemblage Patterns Of Juvenile And Small Sized Fishes In The Nearshore Habitats Of The Gulf Of Thailand

Sichum, Surasak, Tantichodok, Pitiwong, Jutagate, Tuantong (2013): Diversity And Assemblage Patterns Of Juvenile And Small Sized Fishes In The Nearshore Habitats Of The Gulf Of Thailand. Raffles Bulletin of Zoology 61 (2): 795-809, DOI: http://doi.org/10.5281/zenodo.535306

Biologies des deux principales espèces de poissons et des modèles assemblage de poissons et d'approches de modélisation dans les régions tropicales des bassins fluviaux (le cas de la rivière Ping bassin, de la Thaïlande)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Growth and competitions of the Australian red-claw crayfish, Cherax quadricarinatus (von Martens, 1868) in Thailand: the experimental approaches

The Australian red-claw crayfish (RCC) Cherax quadricarinatus (von Martens 1868) (Crustacea: Decapoda: Parastacidae) has been introduced and promoted for freshwater aquaculture in many countries including Thailand. This study i) evaluates the growth performance of RCC in near-natural conditions relative to captive conditions and ii) investigates how successfully RCC can compete with a trophically and functionally analogous native species. Growth of RCC was compared among two aquaculture systems (concrete tank and earthen pond) and a treatment with simulated natural conditions. After 12 months of rearing, total length and weight were greatest in the earthen pond and poorest in the near-natural treatment, with significant differences in total length between the near-natural treatment and the two culture systems. Length-weight relationships showed that the RCC had positive allometry in the culture systems but negative allometry in the near-natural treatment. Competition was evaluated by means of a biotic resistance test and an additive–substitutive experiment between RCC and the native freshwater crab Esanthelphusa dugasti (Rathbun, 1902) (Crustacea: Decapoda: Gecarcinucidae). Specific growth rates after 90 days of the experiments suggest that the crab inhibited growth of RCC. This implies that the invasion of RCC in Thai waters could be limited by competition from resident freshwater crabs

Determination of short mackerel Rastrelliger brachysoma (Bleeker, 1851) stocks in the Gulf of Thailand using otolith microchemistry

The short mackerel Rastrelliger brachysoma (Bleeker, 1851) is a commercially important fish in the Gulf of Thailand (GoT). The management strategy for this species in the entire GoT is based on the single-stock approach, which may not be efficient or effective. This study aims to identify the stock structure of short mackerel in the GoT. A total of 55 samples of short mackerel were collected throughout the GoT, sexed, weighed and measured. The pair of sagittal otoliths were removed from individual fish. The left sagittae were used for stock identification via microchemistry elements. The microchemical composition of the otoliths from four locations (Eastern, Upper, Central and Lower GoT) was different (MANOVA, P < 0.01) for both sexes. The linear discriminant function analysis (LDFA) using eight microchemical elements in the edge zone showed high classification accuracy of short mackerel with regard to their sampling location (89 % for males and 79 % for females). The LDFA results also showed high classification accuracy in both sexes (more than 85 %) and indicated that there were four short mackerel stocks in the GoT. The right sagittae, meanwhile, were used for fish ageing. Results showed that the adults had resided in the stock more than 50 % of their life before being captured

Potential effects of hydroelectric dam development in the Mekong River basin on the migration of Siamese mud carp (Henicorhynchus siamensis and H. lobatus) elucidated by otolith microchemistry.

The migration of Siamese mud carp (Henicorhynchus siamensis and H. lobatus), two of the most economically important fish species in the Mekong River, was studied using an otolith microchemistry technique. Fish and river water samples were collected in seven regions throughout the whole basin in Thailand, Laos and Cambodia over a 4 year study period. There was coherence between the elements in the ambient water and on the surface of the otoliths, with strontium (Sr) and barium (Ba) showing the strongest correlation. The partition coefficients were 0.409-0.496 for Sr and 0.055 for Ba. Otolith Sr-Ba profiles indicated extensive synchronized migrations with similar natal origins among individuals within the same region. H. siamensis movement has been severely suppressed in a tributary system where a series of irrigation dams has blocked their migration. H. lobatus collected both below and above the Khone Falls in the mainstream Mekong exhibited statistically different otolith surface elemental signatures but similar core elemental signatures. This result suggests a population originating from a single natal origin but bypassing the waterfalls through a passable side channel where a major hydroelectric dam is planned. The potential effects of damming in the Mekong River are discussed

Variations, trends and patterns of fish landings in large tropical reservoirs

Temporal variations of fish yields in four major reservoirs in Thailand (Ubolratana; Sirindhorn; Srinakarin; Vajiralongkorn) were investigated with the use of long-term fish landing data (≥20years). The long-term variations in fish yield, measured as the coefficient of variation of yearly yield, ranged mostly between 50% and 100%. For short-term variations, the means of the relative variation (85%) were larger than the absolute variation (63%). This finding indicates that short-term variations were inversely related to fish yield and that a higher uncertainty occurs when fish catches are low. The stocked exotic species exhibited higher variations than the indigenous species. The trend analyses indicated some species had sharply declined fish landings, while some species were quite stable (i.e. reservoir-adapted species). Stocked species tended to increase in relatively shallow reservoirs, compared to the deep reservoir. Fish landing data for each reservoir were patternized, using the self-organizing map, indicating temporal trends of chronological order. The differences among clusters in each reservoir were with respect to the weight of each species in the fish landings in each year, and temporal changes in species composition in the reservoirs, which would primarily be attributed to the environmental changes followed by anthropogenic pressures. The mean trophic level (τ) fluctuated, resulting from changes in species composition and weight of fish landing, as well as fish stocking programmes