An evaluation of horizontal echo sounding as a method for behavioural studies of 0+fish in field experiments

A 120 kHz echo sounder, with two split-beam transducers, was used horizonta lly to monitor the behaviour of 0+ roach Rutilus rutilis, from June to Augu st, in field enclosures. 0+ roach outside the vegetated area of the enclosu res were registered both as schools and as single swimming fish. Combining echo counting and tracking with direct observation of echograms, an estimat e of relative abundance of 0+ roach in the open water volume was obtained a lso. With this set up, intermediate sized field experiments studying 0+ fis h, may be performed during the whole summer season. (C) 2001 The fisheries Society of the British Isles.