Bull sharks cavort in the Shark Reef Marine Reserve in Fiji. But the animals don’t meet by chance. Nor do they randomly interact with each other. Because sharks are not strictly solitary creatures. They have complex social lives and even form friendships.
Researchers from the University of Exter and the University of Lancaster spent six years studying the social behavior of bull sharks (Carcharhinus leucas). They observed the animals in the Shark Reef Marine Reserve in hundreds of dives.
“As humans, we have a variety of social relationships – from casual acquaintances to deep friendships, but we also actively avoid certain people – and bull sharks act similarly,” explains lead scientist Natasha D. Marosi.
In order to examine the social behavior of the animals in more detail, the researchers counted rough contacts that occurred when two sharks were no more than one body length apart from each other. They also looked at finer forms of interaction such as participating, leading and following, parallel swimming and turning back.
The researchers also examined the differences in the encounters depending on age and gender. It was noticeable that male sharks usually maintain more social contact with other sharks than female sharks. “Male bull sharks are physically smaller than females, so a potential advantage could be that they are more socially integrated. This protects them from aggressive confrontations with larger individuals,” says Marosi.
In terms of age, it was found that both older bull sharks and immature animals tended to have fewer social contacts. Older individuals, says Marosi, probably have enough experience and therefore need to be less sociable. Younger individuals, on the other hand, often stay in more distant areas, possibly to avoid conflict with adult sharks. Only shortly before they are fully grown do they join the group of adult sharks. “We have a few bolder juveniles in the reservoir that have established social contacts with some adult sharks. These older individuals could act as intermediaries, integrating them into the social network and possibly also providing an avenue for social learning,” reports Marosi. The results were published in the scientific journal Animal Behavior published.