Acoustical Estimation of Zooplankton Populations

Acoustical estimates of zooplankton abundance can be made rigorously if the scattering behavior as a function of size and frequency for the zooplankters is known. Measurements of scattering at a single frequency can be used to estimate abundance if the mean zooplankter size is known. Measurements at two frequencies can be used to estimate the dominant size as well as abundance if a single size zooplankter dominates the acoustical scattering. Measurements at several frequencies can be used to estimate size distributions and abundances. In a field experiment, acoustical scattering was measured at three frequencies for zooplankton layers composed largely of euphausiids (for which an approximate scattering model is known). These data are analyzed by each method and estimates of numerical abundance given.