REMOTE ACOUSTIC DETECTION OF ZOOPLANKTON RESPONSE TO FLUID PROCESSES, OCEANOGRAPHIC INSTRUMENTATION, AND PREDATORS

A narrow-beam multifrequency acoustic backscattering system operating at discrete frequencies in the 10-600-kHz band was used to detect predator-prey interaction, the passive response of zooplankton to fluid processes such as internal waves, lee waves, hydraulic jumps and the response of organisms to the presence of an oceanographic instrument in the water column. The acoustic flow visualization data illustrate the extent of the vertical and horizontal displacements and mixing of organisms by fluid processes. Fluid processes may strongly influence predator-prey distribution in the continental shelf and sound regimes and that the interpretation of biological field data should include the influence of small-scale fluid motion on the vertical and horizontal distribution of organisms and nutrients. The predator-prey interaction data indicate that small organisms will move 7-20 m in the vertical to avoid larger organisms. Organisms appear to be able to detect the presence of oceanographic instruments to ranges of .simeq. 15 m. It is unknown whether the organism detection range is related to the optical properties of the water column or other physical parameters.