A Brief History of Acoustics
Fisheries acoustics has its roots in the development of echo sounders to measure water depth. Several usable instruments were constructed between 1915 and 1920 and used in the first large-scale bathymetric investigation of the ocean floor (the German Meteor expedition in 1925-27 described in Wille 2005). The potential for using this equipment for studying the distribution of fish schools at sea was suggested in the 1920s, and the first experimental validation of the detection of fish with acoustics came from freshwater fish ponds in Japan (Kimura 1929). At sea, acoustics scattering layers observed in midwater were attributed to fish by comparisons with trawl catches (Sund 1935, Balls 1948) and echo sounders were used to map herring schools and follow their movements. The Second World War led to further advances in underwater acoustics as part of submarine warfare, and after the war, fishermen and scientists started to use this technology for fish detection and studies of fish behavior. Echo sounders used for fisheries in the 1960s and 1970s were analog instruments that used paper echograms and oscilloscopes to visualize the data and analog integrating circuitry to analyze the data (Forbes and Nakken 1972). With the rise of digital computing technology in the 1980s, analysis of echo data became more sophisticated and various post processing analyses could be conducted using shipboard computers or in the laboratory using data recorded on magnetic tapes. Much of the development was spearheaded by the International Council for the Exploration of the Sea (ICES) and many useful reports on specific topics have been published by that organization (Foote et al. 1987, Simmonds et al. 1992, Mitson 1995, Ona 1999, Reid 2000). Today (2008) most scientific echo sounders digitize the analog signal early in the signal processing phase and record data directly to computers in the field. Storing large amounts of digital data is no longer a problem and analysis of these data can be made on standard personal computers. Analysis software is available that incorporates filters for identifying and tracking single fish targets, GPS based location information, combination of various data sources comparable to multiple data layers in GIS, school detection and classification algorithms, and three-dimensional imaging (Reid 2000, Balk and Lindem 2000, SonarData 2004). Innovations in hardware and software are ongoing, including acoustic “cameras”, scanning and multibeam sonars, and broadband applications. We predict continued rapid technological and analytical advances and consequently continued expansion of applications of hydroacoustics in fisheries. It is an exciting time to learn fisheries acoustics.