Underwater acoustics in marine fisheries and fisheries research

Underwater acoustics enables the detection and precise location of fish and is therefore a prerequisite for effective fishing methods such as pelagic trawling and purse seining. The application of acoustic instruments to detect fish and monitor gear performance in model commercial fisheries is outlined. The latest developments in obtaining information such as bottom roughness and determining such characteristics of fish detected as size and species are presented. Echo integration is now widely used to estimate the abundance of commercially important fish stocks. The principles of the method are outlined briefly, and special emphasis is put on such effects of fish behaviour as the dramatic influence of fish orientation on its backscattering cross section, the possible effects of vessel avoidance, and the uncertainties connected with spatial variability. The use of acoustic tags, echosounders and sonar to study and quantify fish behaviour and distribution is outlined, with particular attention to new developments that provide detailed information on fish behaviour and distribution in relation to environmental parameters. Future developments and improvements in the application of underwater acoustics to commercial fisheries and fisheries research are suggested.