Le Fur Jean auteur aut IRD Simon P. auteur aut IRD text journalArticle eng text/pdf born digital access Coastal populations of small pelagic fish display nested aggregation levels. Above the level of the school structure, clusters are observed the nature of which has not been definitively determined. We hypothesized that these clusters corresponded to a materialisation of the microcohorts originating from successive spawnings of fish populations in their vital domain. A candidate individual-based model was developed to investigate this hypothesis. This model is based on pattern-oriented modelling of a concrete documented case: the dynamics of the round sardinella (Sardinella aunita) population living off the West African coasts and subject to environmental fluctuations caused by seasonal upwelling. The simulated agents were round sardinella microcohorts situated and moving in a discretised physical environment. The combined effects of environmental forcing (temperature, wind, retention) and inner biological dynamics (reproduction, growth and mortality, competition) condition the dynamics of this population. The modelled behaviour generated realistic dynamic patterns (population distribution, spawning zones, periods and plasticity, biomass fluctuations), which were obtained simultaneously and successfully compared with observations. The steady-state number of microcohorts obtained after simulation convergence was similar to the number of clusters observed in situ in this area for this population. The realism and diversity of the patterns simultaneously simulated suggested the cluster-microcohort equivalence hypothesis as a candidate framework accounting for the origin of the clusters observed in situ. Within this preliminary exploration, we discuss the consistency of the hypothesis and the accuracy of the model. If the correspondence between clusters and microcohorts proves to be real, it may be transient and progressively modified by other environmental factors. If stable over time, as simulated in the model, the number of observed clusters should be related to the number of spawning events in the species' lifetime. specialized Individual-based model Observed patterns Upwelling Small pelagic fishes Sardinella aurita West Africa Microcohort Cluster Aggregation 040 220 9-10 1291-1304 2009 0304-3800 https://www.documentation.ird.fr/hor/fdi:010046034 10.1016/j.ecolmodel.2009.02.012 0304-3800 [F B010046034] https://www.documentation.ird.fr/hor/fdi:010046034 https://www.documentation.ird.fr/intranet/publi/2009/05/010046034.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2009-06-08 2017-08-23 fdi:010046034 fre