[eng] The study of social interactions within species has been a captivating subject in biology. These
interactions dominate over various aspects of an organism’s life and profoundly influence the
ecosystems they inhabit.A particular significance lies in how social animals often engage in cooperative behaviors, such as collective hunting, communal parenting, and group defense, with direct
implications for their survival and reproduction.
While sharks have historically been perceived as solitary predators of the oceans, recent marine
research has challenged this notion, revealing intricate social behaviors in select species. Notably, the
blacktip reef shark (Carcharhinus melanopterus) displays hierarchical social structures influenced
by factors such as sex and size, particularly in the coral reefs of French Polynesia. Similarly, the
grey reef shark (Carcharhinus amblyrhynchos) exhibits dominance-submission dynamics, especially
concerning their habitat.
To investigate these complex social interactions, complex systems theory is employed, exploring
systems with numerous interconnected elements that give rise to collective emergent behaviors. The
research focuses on two shark species, constructing networks to delineate leader-follower dynamics
across multiple observation stations using acoustic data from the Integrated Marine Observing
System (IMOS). Aggregated networks reveal a structure closely resembling a hierarchical Directed
Acyclic Graph (DAG), achieved through the systematic removal of weak interactions. Comparative
analysis against randomized networks highlights the observed networks’ proximity to a perfect
hierarchy.
Results encompass event data analysis, revealing appearance probabilities and circadian patterns,
network inference, including leadership networks, leadership and participation indices, and aggregated leadership networks. The study also investigates directed acyclic graphs (DAGs), strategies
for breaking cycles, and the comparison of observed networks to random configuration networks.
This comprehensive research successfully unveils the hierarchical dynamics within social interactions
among shark species, particularly focusing on the blacktip reef shark and the grey reef shark. The
study not only achieves an understanding of these hierarchies but also lays the groundwork for
further exploration, offering valuable insights into the intricate social behavior of these marine
creatures.