Gerlotto François auteur aut IRD Jones E. auteur aut IRD Bez Nicolas auteur aut IRD Reid D. G. auteur aut IRD text journalArticle eng text/pdf born digital access Converging results in different scientific fields (behavioural ecology, fisheries biology, acoustic tagging, fisheries acoustics, behavioural modelling) suggest the existence of "micro-groups" inside fish schools. These would comprise a few (5-10) fish maintaining contact during a period long enough to allow individuals to recognise each other. It is hypothesised that they would prefer to share the space with familiar rather than anonymous conspecifics. To evaluate whether acoustic methods could be used to recognise "micro-structures" inside fish schools and help test the "micro-group" hypothesis we analysed acoustic data from anchovy schools off Peru, and gadoids in the North Sea. Data collection used a multibeam sonar (Reson SeaBat 6012). In the Peruvian case study, the sonar was mounted set horizontally on a drifting research vessel and the internal structure of the schools of anchovies was analysed, although individual fish could not be discriminated. In the North Sea case study, the sonar was orientated vertically above a demersal trawl to allow observation of individual fish entering the trawl. Geostatistical analyses were used to evaluate the existence of small spatial structures in anchovy schools. In these schools, "micro-structures" with a scale as small as 0.5 m were observed acoustically. For the gadoids nearest neighbour distance (NDD) measurements were carried out, suggesting that the fish aggregated in small groups (2 to 25 individuals, with an average of 3.7 fish per group) in the trawl catches. The perspectives and limitations of these results are discussed. specialized Anchovy Behaviour Geostatistics Multibeam sonar Fish school Spatial structure Micro-group 040 23 2 143-151 2010 0990-7440 https://www.documentation.ird.fr/hor/fdi:010049692 10.1051/alr/2010017 0990-7440 [F B010049692] https://www.documentation.ird.fr/hor/fdi:010049692 https://www.documentation.ird.fr/intranet/publi/2010/08/010049692.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2010-09-03 2017-08-23 fdi:010049692 fre