Richard H. Love
Charles H. Thompson
Naval Res. Lab., Stennis Space Center, MS 39529-5004
The Naval Research Laboratory (NRL) has been investigating low- to mid-frequency scattering from dispersed layers of fish for a number of years. Since 1988, NRL has conducted eleven experiments in a variety of regions, over shelf, slope, and deep waters. Scattering measurements have been made on many different fishes, from large commercially important fish, such as salmon, to small mesopelagic fishes that comprise the deep scattering layer. The frequency range of interest in these measurements, approximately 0.5 to 10 kHz, is the frequency range in which the swimbladders of many fish resonate. By employing a swimbladder scattering model in conjunction with the scattering data, information of the biological characteristics of the scatterers can be derived. This technique can provide information on the geographical distribution, depth, size, abundance, and swimbladder characteristics of the scatterers. The technique has been used successfully to provide detailed information on well-known species as well as to identify significant populations of fish in habitats where they were not expected. Examples of results for both well-known and unknown fish from both deep and shallow water are presented.