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Assessing the impact of dam development options on fish migrations and best alternative options in the Mekong Basin

Scenario-based Assessment of the Potential Effects of Alternative Dam Construction Schemes on Freshwater Fish Diversity in the Lower Mekong Basin
Project leader
Eric Baran
1 Sep 2009
28 Feb 2012

The most intensive inland fishery in the world

The Mekong River ranks second in freshwater fish species richness among rivers in the world, with more than 780 species identified. More than 100 of these fish species are long-distance migrants, often travelling over hundreds of kilometers. This basin is also home to the most intensive inland fishery in the world, producing 2.1 million tonnes of fish a year (equivalent to more than three times the total annual inland fish production of West Africa).
With a growing demand for a plentiful and regular supply of electricity, hydropower is developing at a fast pace, and up to 88 dams are planned by 2030. What effect these dams will have on fish migrations and fish productivity is highly uncertain given that there are few ecological studies focusing on Mekong fish migrations. Consequently scientists cannot predict so far how migration patterns will be impacted, where the impacts will occur, or what fish species will be most impacted by dam construction. A report from Nature highlights this issue.

The objectives of this project are two-fold: firstly, to provide updated results about the migration patterns of fish species in the Mekong River, and secondly to assess the impact of planned dams on fish species diversity and fisheries production. The goal is to better inform dam development planning, and to help identify sites for hydropower development that would minimize these risks.

Data gathering and analysis

The project consists of three components. WorldFish is working with the Inland Fisheries Research and Development Institute in Cambodia on component one—data compilation and GIS analyses. Existing data on fish species and their migratory patterns are compiled from FishBase and other data sources.
In component two, led by the Japanese National Institute for Environmental Studies (NIES), analyses of fish catch data and otolith chemistry will help elucidate the migratory patterns of the more commercially important fish species. Otoliths, small calcium carbonate structures in the fish’s inner ear, grow throughout the life of the fish, producing rings similar to the growth rings of trees. The chemical composition of each ring provides clues to the environment as the otoliths store trace elements picked up from river water. This forms a ‘fingerprint’ that can be used to determine when and where the fish travelled through a particular river on its migratory journey.
NIES and Ubon Ratchathani University are working together with WorldFish on component three, using statistical modeling to analyze the implications of various different scenarios. Statistical models will assess the likely loss of species richness and abundance for commercially important migratory fish due to dam development in the Lower Mekong Basin.
Since proposed dam sites can be easily modified within models, associated changes in the predicted loss of species richness can also be simulated. A series of such simulations will be performed to find the best available alternative sites for dam construction where risks to fish diversity, fishery production, and food security would be minimized. This scenario-based approach will enable the team to provide decision makers with a scientifically-based balance of the costs and benefits of hydropower development in the Lower Mekong Basin.

An atlas of fishes

One result of this work will be a science-based atlas of Mekong fishes that visually illustrates the current distribution of the commercially important migratory fish species, the current status of basin development (especially hydropower), future plans for further dam construction, and the potential influence of planned dams on these fish species.