Séminaire de Mécanique d'Orsay

Le Jeudi 8 juin 2023 à 14h00 - Salle des séminaires FAST-LPTMS (Bât. 530, salle C.120, 1er)

Collective motion of fish in complex environments

Aurélie Dupont
LiPHy

Crowd movements can be observed across species and scales: from insects to mammals but also in non-cognitive systems such as eukaryotic cells. But, what happens when gregarious animals have to momentarily adopt an individual behaviour? To challenge the balance between herd and individual behaviours, a school of Neons (Paracheirodon innesi) was forced to cross a constriction. This experiment is reminiscent of panic crowd escaping through a narrow door. Using statistical analysis developed for granular matter and applied to crowd evacuation, our results clearly show that contrarily to human crowds or herds of sheep, no clogging is formed at the bottleneck. Fish don’t collide and wait by respecting their social distance and a minimum waiting time between two successive exits. When the constriction starts to be comparable to or smaller than their social distance, the individual domains fixed by this cognitive distance must deform and the fish density is increased. We show that the current of escaping fish indeed behaves as a set of deformable 2D-bubbles, their 2D domain, through a constriction and obeys the same law. The complex environment has also been addressed with an assembly of obstacles, preliminary results on this second experiment will also be presented.

Accès Salle des séminaires FAST-LPTMS (Bât. 530, salle C.120, 1er)