Guillard J. auteur aut IRD Balay P. auteur aut IRD Colon M. auteur aut IRD Brehmer Patrice auteur aut IRD text journalArticle eng text/pdf born digital access Hydroacoustic methods are widely employed by fish scientists for assessing fish stocks. The method most often used is echosounding, beaming vertically. Nowadays the multibeam sonar, and therefore the 3-D presentation of fish schools, has yielded better knowledge of school morphology. Using the data collected simultaneously by both sonar and echosounding in a lake, we have identified boat-induced behavioural changes in small pelagic fish schools. Using high resolution sonar data, we showed that the fish schools detected under the boat have a significantly larger volume than those alongside the boat. This finding is explained according to behavioural response due to the theoretical characteristics of the boat diagram sound pressure, and the existence of a strong thermocline. Then we compared two descriptors, the height of the fish school and the backscatter energy. We found significant differences, which reveal vertical fish school compression occurring simultaneously with the horizontal and sidelong escape behaviour. specialized fish school behaviour avoidance multibeam sonar echosounder lake 040 19 3 373-380 2010 0906-6691 https://www.documentation.ird.fr/hor/fdi:010049727 10.1111/j.1600-0633.2010.00419.x 0906-6691 [F B010049727] https://www.documentation.ird.fr/hor/fdi:010049727 https://www.documentation.ird.fr/intranet/publi/2010/09/010049727.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2010-10-01 2024-01-08 fdi:010049727 fre