4 research outputs found
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Wetland fish communities above stream regulators with and without fish passage in Lao PDR
We have implemented a multiple lines of evidence approach to assessing the efficacy of fishways in the Houay (small stream) Peung and Houay Souy, Lao PDR. The methods include socio-economic surveys of households, direct observation of fisherman catch, trapping within the fishways, and surveys of fish assemblages in each fishway wetland, along with comparison wetlands that do not have a fishway installed. The in-wetland surveys are designed to be a long-term program and in this presentation I report on the design, monitoring and preliminary results. Whilst there are several differences in the types of fish present in each of the wetlands, there was no statistically significant difference in the CPUE, species richness or the composition of fish assemblages between fishway wetlands and comparison wetlands, regardless of season, during the first two years of our study. This is consistent with previous studies, that found only one or two species are likely to respond in the first few years and it may take 4 or more seasons of operations for major compositional changes in assemblages to be recognised. Our results are consistent with expectations from pre-fishway operations and the monitoring program is well placed to detect changes as the fishways enter full operational mode. We also discuss the implications of high fishing pressure in these wetlands and how this may affect the rate of change and detection of those changes
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Development of a comprehensive fish passage approach for floodplains of the lower mekong basin
Irrigation, flood protection and road development in Lao P.D.R. has led to construction of numerous water regulation structures on the floodplains of the Lower Mekong Basin. Movements of fish (and other aquatic animals) between rivers and floodplains is subsequently restricted, or may be entirely prevented, and this has led to severe declines in fish production in many areas. Developing robust fish passage outcomes requires an integrated and long-term approach. Implementing a strategy that sought to identify the scale of riverine development, develop a widely applicable solution and also capture social and economic benefits was a sound approach that had wider support from government and investment agencies. Subsequent research in Lao P.D.R. demonstrated that fish-passage technology has the potential to enable movement of migratory fish past these low-level (less than 6 m) barriers. Consequently, fisheries agencies were interested in increasing capacity to design manage and operate fish passage facilities on new and existing low-level water control structures in order to ensure the long-term sustainability of fish resources. To raise the importance of the issue with other water users, it was important that barrier mapping had been undertaken at the same time to increase the spatial understanding of existing infrastructure development. This led to active collaboration with engineering and development agencies to include fish passage restoration in ongoing irrigation development projects. Combining this information with an inventory of planned construction would provide a powerful tool for future investment opportunities
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A cautionary tale about the inhibitory effects of gated culverts on fish passage restoration efforts
Connectivity between river-floodplain habitats has been heavily constrained in many large tropical river systems by the construction of regulators, levees and other physical barriers. Fishways are being constructed to ameliorate the effects of these barriers; but it is important that all aspects of fishway design cater for local target species. We investigated the lateral movement patterns of Lower Mekong Basin fish in Laos, through a fishway that incorporated a series of cones, resting pools, and a culvert with a vertical lift gate. Fish needed to negotiate all of these structures to move from the Mekong to an adjacent wetland. We tested the hypothesis that gated culverts may hamper the effectiveness of fishways, by comparing the abundance and species richness of fish at three locations along the path of the fishway and culvert: (1) the fishway entrance; (2) the fishway exit; and (3) the culvert exit (i.e. immediately upstream of the culvert). There were no marked differences in the total abundance and species richness of fish between the fishway entrance and culvert exit while the river remained at levels where the culvert was only partially inundated. Nevertheless, the abundance and species richness of fish were markedly lower at the culvert exit than at the fishway entrance and exit once the headwater levels rose to where the culvert was completely inundated. These findings indicate that fish were able to ascend the fishway but not the culvert once it became completely submerged, and thus support the hypothesis that gated culverts can hamper the effectiveness of fishways in facilitating the lateral movement of fish in large tropical systems. Fish passage at such installations can be enhanced through optimised operating regimes. Ensuring that headwater levels remain below the culvert ceiling is likely to be the best way to maximise fishway effectiveness
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Injury and Mortality of Two Mekong River Species to Turbulent Shear Forces
Global hydropower development is one solution proposed to address an increase in energy needs. However, hydropower-related impacts on riverine ecology systems is not well understood. The Mekong River Basin (MRB) is one of the world’s largest waterways and is presently experiencing significant hydropower expansion. It is also one of the most biodiverse rivers; serving as home to many species that are blocked or hindered by the development of dams. One source of injury and mortality for downstream moving fishes is passage through the turbine environment where fishes may be exposed to a number of physical stressors (e.g., shear forces, rapid decompression, blade strike and turbulence). The current study sought to understand the susceptibility of blue gourami (Trichopodus trichopterus) and iridescent shark (Pangasianodon hypophthalmus) to shear forces. Fishes were exposed to an underwater jet with velocities up to 21.3 m/s (equating to strain rates of up to 1,185 s-1). Fish were assessed for behavioral effects, injuries, and mortality. Overall, it was determined that both species were susceptible to shear forces and the effects were more pronounced at higher strain rates. Gouramis were more susceptible than sharks. To minimize impacts on these species, shear forces within turbines should not exceed critical limits