Advances in Shallow Water Hydroacoustics

Hydroacoustic sampling is well established for monitoring of fish in the water column.  One of the largest challenges of for fisheries acoustics is to provide reliable data in shallow waters 0-5 m where classical vertical sounding has limitations and many warmwater fish aggregate. Recent tests revealed that the largest difficulties in using scientific echosounders horizontally includes beam bending in stratified layers, ghost echoes mirroring from the surface, reverberation from the surface and the bottom, and the uncertainty of fish aspect.  The latter is particularly problematic in mobile surveys. The presentation will give examples of the biases and suggest ways of correcting them.

A partial solution is to use uplooking transducers and such deployment is beginning to be used in mobile applications with promising results when sufficient water depth is available. Unfortunately, in really shallow habitats, uplooking has the same problems as downlooking. Wider international cooperation is required to overcome inherent problems of horizontal surveying and to standardize this approach for routine monitoring.