Environmental Context Elicits Behavioral Modification of Collective State in Schooling Fish

Pattern formation and collective behavior in animal aggregations is highly complex and occurs across many scales, over a wide range of environmental conditions. The patterns found in collective behavior arise from the many local interactions between individuals within the group and the underlying mechanisms that govern these interactions may be modulated by the environmental habitat the group is located in. Here, we consider whether habitat context influences the mechanisms that govern the behavioral schooling state 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 (and its underlying interaction rules) is influenced by the habitat fish schools reside in. Our results indicate that both a marsh edge habitat and a higher complexity habitat induce changes in the behavioral state of fish schools compared to a free-field context, which demonstrates an alteration of the individual interaction mechanisms that dictate the complex behaviors performed by the school. This suggests that the local environment containing animal aggregations plays a role in structuring the spatial and temporal group-level patterns found in collective behavior.