Fish and Fisheries in the Sesan River Basin

Baseline survey.The present component of the project focussing on i) the Sesan Basin and ii) fisheries will: ‐ establish a fisheries baseline for the Sesan catchment, focussing on fish biodiversity, fish production, fisheries zoning, resource use and the fisheries sector; ‐ Identify ecological flows suitable for fish in the Sesan catchment (how much flow should be left for downstream fish production); ‐ contribute to the identification of a set of ecological sustainability principles which will guide multiple uses of water resources and riverine systems; ‐ assess the impacts of dam development on the fisheries sector (how much capture fish will be lost due to dam construction, how this loss can be mitigated, and how much fish can be produced from reservoirs)

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

Cambodian Freshwater Fish Assemblage Structure and Distribution Patterns: Using a Large-Scale Monitoring Network to Understand the Dynamics and Management Implications of Species Clusters in a Global Biodiversity Hotspot

Mekong River Basin is one of the world’s fish biodiversity hotspots. Fisheries of the Cambodian Mekong are characterized by high diversity and productivity. However, few studies have focused on broad scale patterns and fish assemblage structure of this important system at a national level. Here, we describe spatial and seasonal variation in fish assemblages by analyzing one year of daily fish catch data sampled at 32 sites covering Cambodia’s main inland water bodies. We recorded 125 fish species. Four clusters were distinguished based on assemblage composition similarity, and 95 indicator species were identified to characterize each of the identified assemblage clusters. High diversity fish assemblages were associated with the upper Mekong system and Mekong/Bassac/Tonle Sap Rivers in Kandal Province and southern Tonle Sap Lake while lower diversity assemblages were observed in the Mekong River in Kratie and the northern area of the Tonle Sap Lake. We find significant variation in the assemblage composition between wet and dry seasons, indicating strong seasonal species turnover within clusters. Length–weight relationship analysis indicated a negative allometric growth among a majority of indicator species, reflecting suboptimal conditions for growth. Our study establishes contemporary structure and diversity patterns in the Lower Mekong River system of Cambodia, which can be used to map fish biodiversity hotspots and assess key indicative fish stocks’ statuses for conservation and management