Processes affecting size of fish schools in agent‐based model

Fish school size varies with several factors, such as environmental conditions, individual size, time of day, and variations between individuals. In this study, we investigate the mean size of fish schools formed in a simple agent-based model, wherein each individual swims at a fixed speed with the direction modified by interactions with the neighbors. If alignment (tendency to swim in their neighbors' direction) is stronger than cohesion (tendency to swim toward the neighbors), then “ marches ” are formed, in which individuals swim in the same direction. If alignment is weaker than cohesion, then “ circles ” are formed, in which individuals chase one another and the entire group moves minimally. We analyzed various processes that control the shape and mean size of the schools. The school's shape is primarily affected by the magnitude of alignment, cohesion, and individual noises. In contrast, the mean size of the group is affected by several factors, including the spatial interaction range, initial configuration, individual differences in swimming speed, and sudden encounters with predators.