When you think of a shark, you might picture a fish roaming the ocean all alone. But scientists have found that bull sharks often hang out with other bull sharks. And sometimes, they even have friends.

Scientists at the Shark Reef Marine Reserve in Fiji studied 184 bull sharks over a period of six years. They observed how the bull sharks interacted, or acted toward one another. They found that the sharks chose certain other sharks to be near, as if they had favorites, or “friends.” These shark friends sometimes swam side by side. Other times, sharks would swim closely behind another shark, as if following a friend.

Scientists also noted that sharks would avoid certain sharks as if they didn’t want to hang out with them.

Within the group, male sharks were more likely to have friends. This could be because male bull sharks are smaller than females and may feel more protected from larger sharks when they’re with their friendly peers.

Older sharks were less likely than younger sharks to have friends. Scientists believe this may be because they’re experienced hunters that feel safe being alone. 

“As humans, we [have] a range of social relationships—from casual acquaintances to our best friends,” researcher Natasha D. Marosi said. “But we also actively avoid certain people—and these bull sharks are doing similar things.”