Sharks of the same species can have different personalities, indicates a new study published in the Journal of Fish Biology.

The study, led by Dr. Evan Byrnes of Macquarie University in North Ryde, Australia, examined interindividual personality differences between Port Jackson sharks (Heterodontus portusjacksoni).

Trials were designed to test the sharks’ boldness, which is a measure of their propensity to take risks, but also an influencer of individual health through its correlation with stress hormones and associated physiological profiles.

Port Jackson sharks were first introduced to a tank where they were provided with shelter, and timed to see how long it took for each shark to emerge from their refuge box into a new environment.

The second behavior test exposed each shark to handling stress, similar to handling by a fisherman, before releasing them again and observing how quickly they recovered.

The results demonstrated that each shark’s behavior was consistent over repeated trials, indicating ingrained behaviors rather than chance reactions.

That is, some sharks were consistently bolder than others, and the sharks that were the most reactive to handling stress in the first trial were also the most reactive in a second trial.

“This work shows that we cannot think of all sharks as the same,” Dr. Byrnes said.

“Each has its own preferences and behaviors, and it is likely that these differences influence how individuals interact with their habitat and other species.”

“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 co-author Dr. Culum Brown, also from Macquarie University.

“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 influences variation in shark behavior – such as prey choice, habitat use and activity levels – is critical to better managing these top predators that play important ecological roles in marine ecosystems.”

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E.E. Byrnes & C. Brown. Individual personality differences in Port Jackson sharks Heterodontus portusjacksoni. Journal of Fish Biology, published online May 26, 2016; doi: 10.1111/jfb.12993