The Mekong's fisheries are one of the most valuable, productive and diverse inland fisheries in the world. Around 120 species of fish are commercially traded in the region (Coates et al. 2003). As shown above, fisheries play a unique and important role in the basin in terms of livelihoods. The threat that large infrastructure such as dams pose to the Mekong's capture fisheries is widely recognised (Poulsen et al. 2004; ADB and World Bank 2006). The impacts of existing hydropower dams on the lower Mekong's tributaries, including a decline in the abundance of fish, have already been documented (MRC 2003). Proposed lower Mekong mainstream dams pose a particular threat to fisheries because they will block fish migration routes. A large number of Mekong fish species are migratory, migrating and up- downstream to breed and feed. More than 70% of the total fish catch in the Mekong (roughly 1.8 million tonnes) is dependent on long distance fish migration, with the Mekong mainstream acting as a migration corridor (Dugan 2008). Blocking fish migration routes impacts not only on the fish themselves, but on livelihoods. Reducing the amount of fish reduces the availability of food for people, reduces food security and has an economic impact on poor people and their livelihoods (Interview Mekong Fisheries Scientist 0608). That hydropower dams generally, and the proposed lower mainstream dams specifically, will impact fish migration is widely accepted amongst Mekong actors including civil society and organisations such as the MRC.