Future developments in fisheries acoustics

This paper is concerned with acoustic systems and techniques of potential benefit to the understanding and management of fisheries. Some of these are briefly mentioned in the introduction; the others are dealt with as follows:

(i) The in situ measurement of fish tilt angles whereby fish orientation can be related to observed target strength is discussed.
(ii) There is a proposal for the use of low-frequency acoustics if the tilt-angle/target- strength measurements indicate that a tilt-angle correction factor for surveys is not feasible. By such means the pattern of backscattering from fish can be made virtually omni-directional. The potential benefits and disadvantages of such a major step are outlined.
(iii) The link between plankton and fish is not well understood but may be improved by more detailed studies of plankton. A description is given of a 21-frequency system for detecting and sizing small organisms between 50 (im and 10 mm which is being used to investigate the distribution and dynamics of zooplankton.