Random patterns in fish schooling enhance alertness: A hydrodynamic perspective

¹ School of Mathematics, Cardiff University - Cardiff, CF24 4AG, UK
² Department of Mathematics, Massachusetts Institute of Technology - Cambridge, MA 02139, USA
³ Institute of Biology, University of Stuttgart - Pfaffenwaldring 57, 70569 Stuttgart, Germany
⁴ Faculty of Agricultural Sciences, Institute of Plant Breeding, Seed Science and Population Genetics, University of Hohenheim - Stuttgart, Germany

Received: 7 May 2016
Accepted: 24 November 2016

Abstract

One of the most highly debated questions in the field of animal swarming and social behaviour is the collective random patterns and chaotic behaviour formed by some animal species, in particular if there is a danger. Is such a behaviour beneficial or unfavourable for survival? Here we report on one of the most remarkable forms of animal swarming and social behaviour —fish schooling— from a hydrodynamic point of view. We found that some fish species do not have preferred orientation and they swarm in a random pattern mode, despite the excess of energy consumed. Our analyses, which include calculations of the hydrodynamic forces between slender bodies, show that such a behaviour may enhance the transfer of hydrodynamic information, and thus the survivability of the school could improve. These findings support the general hypothesis that a disordered and nontrivial collective behaviour of individuals within a nonlinear dynamical system is essential for optimising transfer of information —an optimisation that might be crucial for survival.