Environmental context elicits behavioural modification of collective state in schooling fish

Abstract

Pattern formation and collective behaviour in animal aggregations is highly complex and occurs across many scales, over a wide range of environmental conditions. The patterns found in collective behaviour may be modulated by the environmental habitat in which a group is located. Here, we consider whether habitat context influences the collective behaviour of fish schools under threat of predation in a dynamic salt marsh system. By comparing collective responses of wild forage fish prior to and during predator attack across three environmental contexts, we examine whether schooling state is influenced by the habitat that fish schools reside in. Our results indicate that habitat context had a much stronger effect on collective state relative to predation. The habitats studied (both a marsh edge habitat and a higher complexity habitat) induced changes in the behavioural state of fish schools compared to a free-field context, which demonstrates an alteration of the collective behaviours performed by the school. This suggests that other ecological factors, such as the local environment, plays a larger role than predation risk in structuring the spatial and temporal group level patterns found in collective behaviour.