Sharks have personalities, too. A group of researchers at Australia's Macquarie University department of biological sciences found that the behavior of Heterodontus portusjacksoni sharks, which they observed in Port Jackson, Australia, revealed differences in personalities. When exposed to stress or an unfamiliar environment, while some shark responses were consistent with one another, others were unique to the individual.
The group tested sharks' boldness and risk-taking characteristics by initially putting them in a tank with a shelterbox and fish (as their food), and timed how long it took each shark to emerge from the shelter and explore the new surroundings.
Certain sharks also seemed to become more stressed than others when they were held out of water. Researchers found a correlation between boldness and more active stress responses, while juvenile sharks seemed to be bolder over all.
"The strong link between boldness and stress response commonly found in teleosts was also evident in this study, providing evidence of proactive-reactive coping styles in H. portusjacksoni [the Port Jackson shark]," the study says. "These results demonstrate the presence of individual personality differences in sharks for the first time."
The study shows that not all sharks can be thought of as the same, said Evan Byrnes, lead author of the study, which appeared in the Journal of Fish Biology. "Each has its own preferences and behaviors, and it is likely that these differences influence how individuals interact with their habitat and other species," he said. "Understanding how individual sharks vary in behaviors such as foraging and habitat use may have large ecological implications and it is important to managing these species."
Because each shark's behavior was consistent over repeated trials, the researchers were able to conclude that the sharks were exhibiting regular behavior rather than one-time reactions. Some sharks were consistently bolder in personality, and others consistently exhibited acute reactions to stress. Personality is not only a strictly human characteristic, said Byrnes, but part of evolutionary history.
"We are excited about these results because they demonstrate that sharks are not just mindless machines. Just like humans, each shark is an individual with its unique preferences and behaviors," said Culum Brown, associate professor at Macquarie University and assistant editor of the Journal of Fish Biology. "Our results raise a number of questions about individual variation in the behavior of top predators and the ecological and management implications this may have. If each shark is an individual and doing its own thing, then clearly managing shark populations is much more complicated than we previously thought."
Understanding how personality differences influence shark behavior, such as prey choice, habitat use, and activity levels, added Professor Brown, "is critical to better managing these top predators that play important ecological roles in marine ecosystems."