Abstract
An Acoustic Doppler Current Profiler, ADCP, can detect the presence of fish in water using the backscatter intensity. The Doppler profiler does not, however, make a point measurement; rather, measurement is made by averaging multiple beams and assuming that the current velocity is uniform between the distinct sample locations. As a result, individual fish speed cannot be measured. However, data are presented that demonstrate that the ADCP can measure the swimming speed of large fish schools. Fish speed and direction were measured for Norwegian spring herring. Observed speeds were 0–40 cm sec−1. Diel vertical migrations were observed with Norwegian herring ascending to the surface at dusk, and descending to greater depth at dawn. The accuracy and precision of an ADCP is a complex function of many variables (i.e., frequency, pulse length, transducer characteristics, backscatter strength, type and distribution of scatters). The other problems to be considered are sampling criteria and calibration. These sampling problems are explored for the case of ADCP measurements of fish movement.