Data from: Local interactions and global properties of free-ranging stickleback shoals

Collective motion describes the global properties of moving groups of animals and the self-organised, co-ordinated patterns of individual behaviour that produce them. We examined the group-level patterns and local interactions between individuals in free-ranging shoals of threespine sticklebacks, Gasterosteus aculeatus. Our data reveal that the highest frequencies of near neighbour encounters occur at between one and two body lengths from a focal fish, with the peak frequency alongside a focal individual. Fish also show the highest alignment with these laterally placed individuals, and generally with animals in front of themselves. Furthermore, fish are more closely matched in size, speed and orientation to their near neighbours than to more distant neighbours, indicating local organisation within groups. Among the group-level properties reported here, we find that polarisation is strongly influenced by group speed, but also the variation in speed among individuals and their nearest neighbour distances of group-members. While we find no relationship between group order and group size, we do find that larger groups, faster groups and those exhibiting lower variance in speed tend to be more densely packed, which in turn may be important in maintaining group order.