A small sonic tag for measurement of locomotor behaviour in fish

Abstract

A technique for measuring the patterns and levels of swimming activity of unrestrained fish in their natural environment during a period of 24 h is described. The fish were marked with small tags which emitted continuous ultrasonic signals by which they could be located and tracked using submerged, remotely controlled, directional hydrophones. Preliminary results obtained from 2 brown trout ( Sahno trutta ) showed a pronounced diurnal activity pattern and remarkably low swimming activity levels.