Abstract: Areal population density and detailed behavior of fish schools and their interaction are continuously monitored over continental-shelf-scale areas spanning thousands of square kilometers by ocean acoustic-waveguide remote sensing. In some embodiments, the capacity of certain geophysical environments, such as continental shelves, islands, etc. to behave as acoustic waveguides is utilized; sound propagates over long ranges via trapped modes that suffer only cylindrical spreading loss, rather than the spherical loss suffered in conventional sonar approaches.