Fréon Pierre auteur aut IRD Gerlotto François auteur aut IRD Soria Marc auteur aut IRD text journalArticle eng text/pdf reformatted digital access Pelagic fishes generally dispers at dusk and aggregate in schools at dawn. The dynamics (duration, variation in school number, and characteristics) of these two behavioural processes have been studied during a 26 h survey in a small area of high fish abundance in the Catalan Sea (Spain). The dynamics of aggregation and dispersion were investigated using a dual-beam vertical echo-sounder (BioSonics) connected to a special school integrator software package (INES-MOVIES-B) which estimates school parameters in terms of size, geometry, and density. This study shows that, during the night, fish dispersion is limited and schools can still be observed. They are characterized by a highly skewed distribution of the cross-sectional area (many small schools plus a few medium and large schools), low values of packing density and biomass, and irregular shape, while during the day there are only a few schools which have a lower variability of the area, high values of packing density, and a more regular shape. The dynamics of schooling are different between dawn (fast aggregation) and dusk (slower dispersion). (Résumé d'auteur) specialized POISSON MARIN ESPECE PELAGIQUE COMPORTEMENT SOCIAL RYTHME NYCTHEMERAL SONAR BANC DE POISSONS MEDITERRANEE 034BIOVER01 53 459-464 1996 1054-3139 https://www.documentation.ird.fr/hor/fdi:010008042 10.1006/jmsc.1996.0065 1054-3139 [F B010008042] https://www.documentation.ird.fr/hor/fdi:010008042 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/pleins_textes_6/b_fdi_45-46/010008042.pdf IRD - Base Horizon / Pleins textes 1997-01-22 2006-06-06 fdi:010008042 fre