Abstract
Since 1969, the authors have been involved in over 200 hydroacoustic surveys of fish populations in more than 25 lakes. These studies have included a variety of different species assemblages and objectives, although most, such as Lakes Washington and Ozette in Washington and Tustumena in Alaska, are sockeye salmon nursery lakes. The objectives of these studies have included fisheries management, evaluation of lake enhancement programs, or environmental impact. During the 14 years of these investigations, both the equipment and procedures have evolved and improved considerably. Earlier techniques were very limited in their ability to detect fish near surface or in shallow water and had very limited capabilty for size discrimination. Current technology has solved most of these problems. These developments and their capabilities are presented along with the results of surveys on lakes with a variety of biological and physical characteristics. The results include a considerable amount of "ground truth" data from other assessment techniques. In many cases these data are obtained from various net sampling techniques. However, some comparisons have revealed considerable biases with net sampling techniques which are associated with changes in light intensity, turbidity, or fish behavior.