Acoustic surveys have developed from the estimation of relative abundance of fish to the measurement of their absoluate abundance in recent years. If the results of acoustic surveys are to fall within certain prescribed limits of accuracy necessary to meet their various objectives many factors must be taken into account. In order to ascertain these factors and their relative importance, expertise from the physical, mathematical and biological disciplines is required, plus practical experience with the available equipment and the techniques for its use to survey different fish stocks in many parts of the world.
This manual has been produced because the existing publications deal separately with the many aspects of acoustic surveys. The intention here is to present the whole subject with emphasis on practical application and the problems usually encountered.
It was in Peru during 1980 that the first stage of preparation began in the closing weeks of the project run by the FAO/Norway Regional Acoustics Research Centre in Lima. However, this coincided with the announcement of completely new equipments thus rendering obsolete part of the material collected. Much of the emphasis has been removed and a full revision of the manual has since been supported by the FAO/CIDA Indonesian Fisheries Development Project.
The use of brand names is unavoidable in this kind of document. Information has been included on all brands of commercially available acoustic equipment known to us at the time of preparation.
It will be evident to readers from the list of references and recommended reading, that the authors have drawn on the published work of many people.
Special thanks in acknowledgement of their comments and criticism is due to the following: H. Bodholt, J. Burczynski, R. Brede, D.H. Cushing, J.E. Ehrenberg, K.G. Foote, M. Lamboeuf, O.A. Mathisen, B.J. Robinson and R. Shotton. The authors especially thank S.C. Venema of the Fishery Resources and Environment Division of FAO without whose advice, support and encouragement this manual could not have been completed.
This manual was typed in Lowestoft by Mrs. Doreen Wadland and proof-read by Mrs. P. Mitson. At FAO the references were checked by Ms. Gloria Soave and typed by Ms. Doris Dearing.
Present addresses of the authors:
Indonesian Fisheries Development Project INS/056/CAN
c/o FAO Representative
P.O. Box 2538
Ministry of Agriculture, Fisheries and Food
FAO Fisheries Department
FAO Regional Fisheries Officers
FAO Field Projects
Specialists in Fisheries Acoustics
For bibliographic purposes this document should be cited as follows:
Johannesson, K.A., and R.B. Mitson, 1983 Fisheries acoustics. A practical manual for aquatic biomass estimation. FAO Fish. Tech. Pap., (240):249 p.
The manual begins with a presentation of key physical principles used in fisheries acoustics and continues with a general description of the necessary equipment and its functions. An explanation is given of the acoustic equations followed by the acoustic properties of fish when occurring singly or in schools. Acoustic survey concepts are discussed prior to a description of calibration methods used to determine the electronic and acoustic parameters of the equipment. Use of the equipment in a systematic manner at sea leads on to the sources of error that can arise and explains how these may be removed or minimised. Finally methods are given for the collection and presentation of data in various forms, together with different ways in which to improve results by the use of statistics.