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

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

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

On-farm feed resources for catfish (Clarias gariepinus) production in Laos

The aim of the thesis was to collected information African catfish (Clarias gariepinus) production systems, and the chemical composition and nutritive value of potentially available feedstuffs. Moreover, the apparent digestibility (AD) of nutrient and amino acids (AA) in raw, sun-dried and ensiled Golden Apple snails (GAS) was evaluated, as well as the potential of GAS to replace fish meal in the diet for growing African catfish fingerlings. The farmers used traditional feedstuffs such as maize, broken rice, cassava root meal, rice bran, soybean, soy waste, dried fish and fish meal. In addition, some more unconventional feedstuffs such as leucaena meal, earthworms, termites and GAS were used. The fish diets were low (150-220 g kg-1 dry matter (DM)) in crude protein and had to low protein to energy (P/E) ratio. Catfish pond areas per farm ranged from 100 to 5,000 m2 with a fish yield that ranged from 1.7 to 3.0 tons ha-1 6 months-1. The average AD of crude protein (CP), crude fat, total carbohydrates and energy in potentially available feedstuffs was 90.6 % (SD 2.4), 87.0 %, (SD 3.4), 77.7 % (SD 3.7) and 84.5 % (SD 2.3), respectively. Only a few of the currently available and used feedstuffs have the potential to provide optimum P/E ratios in the diet for growing African catfish (25-30 g CP/MJ digestible energy (DE)). The content of DE ranged from 13.2 MJ kg DM-1 for rice bran to 18.1 MJ kg DM-1 for frogs. The AD of CP, AA and energy was highest in sun-dried, followed by raw and ensiled GAS. The CP to DE ratio that ranged from 17.8 g MJ-1 in raw GAS to 24.8 MJ-1 in ensiled GAS. It was concluded that sun-drying, rather than ensiling should be the preferred preservation method of GAS. High addition of sugar cane molasses (>15 % in DM) was needed to maintain an acceptable quality of GAS ensiled for 28 days. Finally, it was shown that protein from GAS can completely replace fish meal in diets for growing African catfish fingerlings without negative effects on growth performance and feed utilization

Finding the best ‘ways’ with fish passes around dams

The Lower Mekong Basin provides habitat for more than 480 species and 40 families of fish, many of which are endemic. The catchment provides 2% of the worlds commercial fish catch, with 2.2 million tonnes per annum extracted. Movement of fish through the Basin is vital to maintain fish populations, especially for migratory species. However, thousands of barriers have been installed throughout the Lower Mekong Basin hindering fish passage. Work is being undertaken to establish the best responses to the increasing number of barriers throughout the Lower Mekong Basin. Engineered structures are being designed to account for specific ecological objectives, hydrology and fish species within a site. This endeavour is not without challenges, and one size does not fit all. The Pak Peung Wetland Research site is located about 100 km to the north-east of Vientiane, the capital of Laos. The ACIAR-supported project started in 2008 and a fully commissioned cone fishway was installed in 2014. Monitoring has been an essential part of the project; to learn about the success of the fishway so similar projects can be successfully rolled out across the Basin. This talk discusses an example of an engineered fishway at Pak Peung, Laos, and some of the successes and challenges of fish passage design