Scientists just discovered bull sharks have friends

The study -- conducted at the Shark Reef Marine Reserve in Fiji -- found that bull sharks do not simply mix randomly. Instead, they display "active social preferences," choosing certain individuals to spend time with while avoiding others.

The work involved researchers from the University of Exeter, University of Lancaster, Fiji Shark Lab, and Beqa Adventure Divers.

"As humans we cultivate a range of social relationships -- from casual acquaintances to our best friends, but we also actively avoid certain people -- and these bull sharks are doing similar things," said lead author Natasha D. Marosi, an Exeter researcher and founder of Fiji Shark Lab.

Long-Term Study of Bull Shark Social Networks

The findings are based on six years of tracking 184 bull sharks across three age groups: sub-adult (not yet sexually mature), adult and advanced-adult (post-reproductive age).

Scientists analyzed both broad patterns of association -- defined by sharks staying within one body length of each other -- and more detailed interactions such as "lead-follow" behavior and parallel swimming.

Adult sharks were the most socially connected, frequently forming bonds with others of similar size.

"Contrary to commonly held perceptions of sharks, our study shows they have relatively rich and complex social lives," said Professor Darren Croft, from Exeter's Centre for Research in Animal Behaviour.

"We are only just beginning to really understand the social lives of many shark species. Just like other animals, they likely gain benefits from being social -- this may include learning new skills, finding food and potential mates while avoiding confrontations."

Female Preference and Male Social Advantage

Researchers found that both male and female bull sharks tended to associate more often with females. At the same time, males generally had a greater number of social connections overall.

"Male bull sharks are physically smaller than females, thus one potential benefit they may gain is by being more socially integrated; they are buffered from aggressive confrontations with larger individuals," said Marosi.

Adult sharks formed the central "core" of the network, while advanced adult and sub-adult sharks were typically less socially connected.

How Age Shapes Shark Social Life

"This study capitalizes on data and knowledge from one of the longest running shark ecotourism dive sites in the world. This offered a unique opportunity to observe the detailed behavior of these individuals over many years, as they grow, develop and manage their social relationships," said Dr. David Jacoby, from Lancaster University's Lancaster Environment Centre.

Marosi added: "The Shark Reef Marine Reserve is a protected area where large numbers of sharks gather year round, giving us the ability to study individual sharks repeatedly over time.

"Our results show that older sharks tend to be less social.

"These older individuals have many years of experience honing their skill sets, hunting and mating, and sociality may not be as integral to their survival as it is for an individual in their prime.

"Sub-adult bull sharks rarely visit the Reserve. Sub-adults usually occupy near-shore habitats, while juvenile bull sharks can be found in Fiji's river and estuarine systems.

"During these early life stages, there is a need to avoid predation -- including the threat posed by adult bull sharks.

"We do have some bolder sub-adults at the Reserve, and they have established social ties with some of the adult sharks. These older individuals may act as facilitators for inclusion within the social network, and also possibly provide pathways for social learning."

Why Shark Social Behavior Matters for Conservation

Marosi emphasized that understanding how sharks interact socially could play an important role in conservation planning and management strategies. Fiji Shark Lab is already collaborating with Fiji's Ministry of Fisheries to apply these insights to ongoing protection efforts.

The research was funded by Fiji Shark Lab, Hai Stiftung Shark Foundation and the Waitt Foundation.

The study appears in the journal Animal Behaviour under the title: "Rolling in the deep: drivers of social preferences and social interactions within a bull shark aggregation in Fiji."