Shallow water fisheries sonar: a personal view

This is the second international conference on the topic of fisheries sonar in shallow waters. One may ask, "Why have a conference on this specialised topic? What problems are characteristic of this field that necessitate a separate conference?" In these introductory comments to this conference, I shall mention several characteristics that may help focus attention on problems that are either unique to shallow water acoustics, or are more difficult to treat in this environment. First, a definition of shallow water sonar will be helpful. Contrary to expectations, shallow water sonar need not be confined to shallow water. The critical feature is measurement of fish near a boundary. Thus, deep water sonar studies of fish near the bottom or near the surface share many of the characteristic problems of shallow water acoustics. The same will be true for fish near any natural or manmade boundary, such as a vertical precipice or a dam. The proximity to boundaries is the central factor. It is a much easier task to observe fish acoustically in mid water than it is near a boundary. Most of the effort in fisheries sonar over the past few decades has been spent on studies and surveys of mid-water fish. It is only relatively recently, with the advent of stable, sophisticated sonar equipment, that a growing effort has been placed on observations of fish near boundaries. The sonar equipment typically used in most shallow water studies includes single-, dual- or split-beam echosounders. More recently, multi-beam, scanning and long range sonar systems have been used to help overcome some of the limitations imposed by the shallow environment. As the integration of software and hardware continues to increase, the spectrum of equipment useful for this type of work will no doubt broaden.