Echosounders are used to measure acoustic backscatter as a proxy for detecting zooplankton, fish, bubbles or other particles in the water-column. An echosounder has one or more transducers which emit acoustic pulses at a particular frequency. When the pulses strike animals or other objects in the water, echoes are produced, which can be detected and converted by the transducers back into electrical signals. Software is then used to determine distances, sizes, concentrations and movements of organisms and other objects in the water. A public forum (www.fisheriesacoustics.com) is available to connect researchers around the world working in hydroacoustic data analysis and research.