Somewhere off the southern coast of Fiji’s largest island, a bull shark glides into the warm current at Shark Reef Marine Reserve. Within minutes, another bull shark appears beside it. They swim in parallel, matching speed and direction, then peel off together toward deeper water. This is not a one-time encounter. Researchers who watched this reef for six years say the same pairs of sharks kept finding each other, season after season, in what amounts to the strongest evidence yet that bull sharks form lasting social bonds.
The study, published in the journal Animal Behaviour in early 2026, tracked 184 individually identified bull sharks using photo-identification methods, cataloging each animal by the unique patterns of scars, notches, and pigmentation on its dorsal fin. Over the six-year observation window, the research team recorded which sharks showed up together, how close they swam, and whether their interactions went beyond simply being in the same place at the same time.
The answer upends the textbook image of bull sharks as solitary, indiscriminate predators.
The same sharks kept choosing each other
The research was led by Natasha D. Marosi, alongside co-authors Dr. David Jacoby and Prof. Darren Croft at Lancaster University. Their dataset drew on years of structured dive observations at Shark Reef Marine Reserve, a protected area off Fiji’s Beqa Lagoon that has operated as a managed shark dive site since 2004.
To measure sociality, the team used two scales. At the broad level, they recorded when two sharks remained within one body length of each other, a standard proximity metric in animal social network analysis. At the fine scale, they documented specific coordinated behaviors: lead-follow sequences, where one shark swam ahead and another tracked its path, and parallel swimming, where two animals moved side by side in synchronized motion. These behaviors go well beyond passive co-occurrence. They suggest active coordination between specific individuals.
The patterns held across multiple seasons and years, ruling out the possibility that sharks simply happened to arrive at the same site on the same day. According to the Lancaster University press release summarizing the findings, the researchers concluded that bull sharks have “friends,” a word chosen deliberately to convey that these associations meet the operational criteria used in comparable studies of dolphins, bats, and other species known to maintain long-term social bonds.
“What we found is that the same individuals were associating with each other repeatedly across years, and these were not random encounters,” Marosi said in the Lancaster University press release, framing the repeated dyadic associations and coordinated swimming as evidence of genuine social preference rather than coincidental overlap at a popular feeding ground.
Building on earlier clues from the same reef
The new findings did not emerge from nowhere. An earlier study at the same Fiji site had already pointed in this direction. That work, published in Frontiers in Marine Science, used temporal association modeling of long-run encounter data to show that bull sharks at provisioning locations exhibited non-random association structures. Some individuals acted as preferred companions rather than casual co-feeders.
The two studies used different analytical tools but reached compatible conclusions. When independent methods at the same site converge on the same result, the finding gains credibility even if neither study alone is definitive. The newer research strengthened the case by adding direct behavioral observations and a much larger identification catalog of nearly 200 animals, making it one of the most comprehensive social studies ever conducted on wild sharks.
What the study cannot yet answer
Several important questions remain open, and the researchers themselves acknowledged limitations.
The full individual photo-ID catalog and raw association matrices from the six-year dataset have not been deposited in a public repository. That means independent researchers cannot yet re-analyze the sighting frequencies or test alternative explanations for the observed patterns. Total observation hours and dive effort per year have not been publicly detailed, making it difficult to assess whether some apparent associations reflect uneven sampling rather than true social preference.
The role of provisioning is another unresolved factor. Shark Reef Marine Reserve is a well-known shark feeding site where dive operators provide food to attract sharks for tourism. Critics of provisioning-based research have long argued that food rewards could artificially concentrate animals and inflate apparent sociality. The study authors accounted for this concern in their analytical framework, but direct records of provisioning volumes and schedules have not been made public. Without that information, fully separating social attraction from food-driven aggregation remains difficult.
Genetic data are also absent. If many of the repeatedly associated pairs turn out to be close relatives, the “friendship” framing would need revision. The bonds could reflect kin-based tolerance rather than the kind of voluntary affiliation seen in bottlenose dolphins. Telemetry data tracking where these sharks go when they leave the reserve would help clarify whether pairs that associate at the feeding site also travel together in open water, a much stronger test of genuine social preference.
And then there is the question of time scale. The six-year observation window captures a meaningful slice, but bull sharks can live 20 years or more. Whether the same companions remain associated across life stages, or whether social ties shift as sharks mature and change reproductive status, is something only longer-term tracking can resolve.
Why a shark’s social circle could reshape conservation strategy
For conservation, the practical implications are real but still emerging. If bull sharks maintain stable social networks, then removing specific individuals through fishing or bycatch could disrupt group structure in ways that simple population counts would miss. A shark would not just be a number in a census; it could be a social node whose absence changes the behavior of others. That hypothesis is testable through future research combining photo-ID with satellite tags, biopsy sampling, and stress hormone analysis, but those studies have not yet been carried out.
The evidence also complicates a deeply ingrained cultural narrative. Bull sharks rank among the species most frequently implicated in encounters with humans, and they have long been portrayed as loners driven purely by hunger and aggression. The Fiji data do not transform them into gentle creatures. They are still large, powerful predators that demand respect in the water. But the finding that they return to specific companions year after year, swimming in coordinated patterns that mirror behaviors seen in highly social mammals, suggests a cognitive and social life far richer than the “mindless killer” stereotype allows.
As of June 2026, the Shark Reef Marine Reserve dataset remains one of the longest-running and most detailed records of wild bull shark social behavior anywhere in the world. If the research team continues tracking these 184 sharks and their successors, the next decade of data could reveal whether these friendships, or whatever we ultimately call them, last a lifetime.
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*This article was researched with the help of AI, with human editors creating the final content.
