Note 1 to entry: Automatic gain control (AGC) and other nonlinear processing is often employed to enhance images of water-column scatterers such as fish.

Note 2 to entry: The output signal of fisheries echo sounders is generally non-quantitative except for measurement of bathymetry, and hence cannot be used for scientific purposes without altering the device.

Note 3 to entry: Fisheries echo sounders are sometimes used for navigation.