The Surprising Social Lives of Bull Sharks
Recent evidence describes the social nature of bull sharks after an
extensive study of their habits in the Shark Reef Reserve in Fiji.
Credit: CC-BY-2.0
Bull sharks have some of the highest levels of testosterone in the animal
kingdom and a reputation for being among the most aggressive of all
sharks. Until recently, scientists also thought they lived fairly solitary lives.
In reality, though, bull sharks aren’t loners at all. They have surprisingly
complex social networks, including “friends” they prefer and other sharks
they avoid.
Researchers spent six years tracking 184 bull sharks in the Shark Reef Marine Reserve in Fiji, observing them for more than 136 hours during hundreds of dives. The sharks fell into three age groups: nearly-adults who were not yet sexually mature, sexually mature adults, and older adults who were past their reproductive age. The scientists considered sharks to be “associating” if they stayed within one body length of each other, and they identified several behaviors indicating different relationships. Some sharks swam side by side while others led or followed another shark or yielded to a passing shark. For example, two male sharks, named Big Poppa and Sharkbite, sometimes swam parallel to one another or engaged in a lead-follow behavior.
Middle-aged adult sharks were the most socially connected, and they spent more time with sharks around the same size as they were. Older sharks generally got less social as they aged. Male and female sharks both spent more time with other females, yet males had slightly more overall social connections than females did. Much like humans, some bull sharks were social butterflies, while others had far fewer associations. Also like humans, some bull sharks intentionally avoided certain individuals. Since Fiji’s shark reserve is an ecotourism site, it’s unclear how much this social networking reflects bull shark behavior elsewhere or why it occurs. What is clear is that bull sharks have far more elaborate social lives than scientists ever realized.
Researchers spent six years tracking 184 bull sharks in the Shark Reef Marine Reserve in Fiji, observing them for more than 136 hours during hundreds of dives. The sharks fell into three age groups: nearly-adults who were not yet sexually mature, sexually mature adults, and older adults who were past their reproductive age. The scientists considered sharks to be “associating” if they stayed within one body length of each other, and they identified several behaviors indicating different relationships. Some sharks swam side by side while others led or followed another shark or yielded to a passing shark. For example, two male sharks, named Big Poppa and Sharkbite, sometimes swam parallel to one another or engaged in a lead-follow behavior.
Middle-aged adult sharks were the most socially connected, and they spent more time with sharks around the same size as they were. Older sharks generally got less social as they aged. Male and female sharks both spent more time with other females, yet males had slightly more overall social connections than females did. Much like humans, some bull sharks were social butterflies, while others had far fewer associations. Also like humans, some bull sharks intentionally avoided certain individuals. Since Fiji’s shark reserve is an ecotourism site, it’s unclear how much this social networking reflects bull shark behavior elsewhere or why it occurs. What is clear is that bull sharks have far more elaborate social lives than scientists ever realized.
