Signatures of criticality in turning avalanches of schooling fish

TL;DR

This study demonstrates that schooling fish exhibit scale-free, power-law distributed turning avalanches indicative of criticality, which are linked to collective decision-making and influenced by boundary effects.

Contribution

It provides the first detailed analysis of criticality signatures in fish schools using avalanche metrics and physics tools, revealing scale-free behavior and boundary influences.

Findings

Turning avalanches follow power-law distributions.

Fish schools exhibit scale-free, critical dynamics.

Boundary effects and clustering influence avalanche behavior.

Abstract

Moving animal groups transmit information through propagating waves or behavioral cascades, exhibiting characteristics akin to systems near a critical point from statistical physics. Using data from freely swimming schooling fish in an experimental tank, we investigate spontaneous behavioral cascades involving turning avalanches, where large directional shifts propagate across the group. We analyze several avalanche metrics and provide a detailed picture of the dynamics associated to turning avalanches, employing tools from avalanche behavior in condensed matter physics and seismology. Our results identify power-law distributions and robust scale-free behaviour through data collapses and scaling relationships, confirming a necessary condition for criticality in fish schools. We explore the biological function of turning avalanches and link them to collective decision-making processes in selecting a new movement direction for the school. We report relevant boundary effects arising from interactions with the tank walls and influential roles of boundary individuals. Finally, spatial and temporal correlations in avalanches are explored using the concept of aftershocks from seismology, revealing clustering of avalanche events below a designated timescale and an Omori law with a faster decay rate than observed in earthquakes.