A new study reveals that bull sharks form social relationships with specific “friends”, challenging the long-held idea that these predators live mostly alone lives.
The study, conducted at Fiji’s Shark Reef Marine Reserve, found that bull sharks are not simply mixed together at random. Instead, they display “active social preferences,” choosing certain individuals to spend time with and avoiding others.
The study involved researchers from Exeter University, Lancaster University, Fiji Shark Lab and Benka Adventure Divers.
“As humans, we cultivate a range of social relationships, from casual acquaintances to best friends, but we actively avoid certain people, and these bull sharks do the same thing,” said lead author Natasha D. Marosi, an Exeter researcher and founder of the Fiji Shark Lab.
Long-term study on social networks of bull sharks
The findings are based on six years of tracking of 184 bull sharks across three age groups: subadults (not yet sexually mature), adults, and late adults (post-reproductive age).
The scientists analyzed both broad association patterns, defined by sharks staying within the same 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 other sharks of similar size.
Professor Darren Croft, from the Exeter Center for Animal Behavior Research, said: “Contrary to common perceptions about sharks, our research shows that sharks have relatively rich and complex social lives.”
“We’re just beginning to really understand the social lives of many shark species. Like other animals, they may benefit from being social. This could include learning new skills or finding food or potential mates while avoiding conflict.”
Women’s preferences and men’s social dominance
The researchers found that both male and female bull sharks tended to socialize more frequently with females. At the same time, men had more social connections overall.
“Male bull sharks are physically smaller than females, so one potential advantage they may have is that they are more socially integrated, buffered from aggressive confrontations with larger individuals,” Marosi said.
Although adult sharks formed the central “nucleus” of the network, senior adult and subadult sharks typically had fewer social connections.
How age shapes sharks’ social lives
Dr David Jacoby, from Lancaster University’s Lancaster Environment Center, said: “This study draws on data and knowledge from one of the world’s longest-operating shark ecotourism dive sites. It provided a unique opportunity to closely observe shark shark growth, development and management of social relationships over many years.”
Marosi added: “Shark Reef Marine Sanctuary is a sanctuary that attracts large numbers of sharks year-round, allowing us to study individual sharks repeatedly over long periods of time.
“Our results show that older sharks tend to be less sociable.
“These older adults have years of experience honing skill sets such as hunting and mating, and sociability may not be as essential to survival as it is for prime-age individuals.
“Subadult bull sharks rarely visit sanctuaries. Subadult bull sharks typically occupy habitats near the coast, but juvenile bull sharks can be found in Fiji’s rivers and estuarine systems.”
“During these early stages of life, they must avoid predation, including the threat of adult bull sharks.
“There are also some brave subadults in the reserve, who have formed social bonds with some of the adult sharks. These older adults may act as facilitators for participation in social networks, and may also provide an avenue for social learning.”
Why shark social behavior is important for conservation
Marosi emphasized that understanding how sharks interact socially can play an important role in conservation planning and management strategies. The Fiji Shark Lab is already working with the Fiji Ministry of Fisheries to apply these insights to ongoing conservation efforts.
This research was funded by the Fiji Shark Lab, the High Stiften Shark Foundation, and the Waite Foundation.
The study was published in the journal Animal Behavior under the title “Rolling into the Deep: Social Preferences and the Drivers of Social Interaction within a Population of Fiji’s Bull Sharks.”
