his new report provides details of hydro-acoustic surveys in deep pools in the Mekong between Siphandone in the southern Lao PDR and Stung Treng in northern Cambodia. The survey is the first of its type in the Mekong. Hydro-acoustic equipment, which works on similar principles as sonar, can image individual fish and fish shoals living in these special habitats. The results reveal patterns in fish size, numbers and density that vary according to water depth, the location of the pools and the time of year.