Data and code for: Collective motion diminishes, but variation between groups emerges, through time in fish shoals

Despite extensive interest in the dynamic interactions between individuals
that drive collective motion in animal groups, the dynamics of collective
motion over longer time frames are understudied. Using three-spined
sticklebacks, Gasterosteus aculeatus, randomly assigned to twelve shoals
of eight fish, we tested how six key traits of collective motion changed
over shorter (within trials) and longer (between days) timescales under
controlled laboratory conditions. Over both timescales, groups became less
social with reduced cohesion, polarisation, group speed and information
transfer. There was consistent inter-group variation (i.e. collective
personality variation) for all collective motion parameters, but groups
also differed in how their collective motion changed over days in their
cohesion, polarisation, group speed and information transfer. This
magnified differences between groups, suggesting that over time the
‘typical’ collective motion cannot be easily characterised. Future studies
are needed to understand whether such between-group differences in changes
over time are adaptive and represent improvements in group performance or
are suboptimal but represent a compromise between individuals in their
preferences for the characteristics of collective behaviour.