Off the southern coast of Fiji’s main island, a group of bull sharks returns to the same reef, week after week, year after year. For a quarter century, divers at the Shark Reef Marine Reserve have watched these animals circle during provisioned dives, close enough to study, predictable enough to learn. What researchers have now documented from six years of that observation is something the popular image of sharks never quite accounted for: these animals are not indifferent to who is nearby. They have preferences. Some individuals they seek out. Others they avoid entirely. The study, published in Animal Behaviour and led by Natasha D. Marosi, a researcher at the University of Exeter and founder of the Fiji Shark Lab, tracked 184 bull sharks across three age groups and found a social structure that looks, in certain ways, like something you might recognize from your own life. “As humans we cultivate a range of social relationships, from casual acquaintances to our best friends, but we also actively avoid certain people,” Marosi said, “and these bull …