Striking personality differences have just been observed in Port Jackson sharks, which are relatively common sharks in the waters off of southern Australia, including near Port Jackson.

The study, published in the Journal of Fish Biology, adds to the growing body of evidence that shark individuals of many, if not all, species are distinct, unique beings just as no two humans are exactly the same.

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"Over the past few decades, personality research has shown that nearly 200 species of animals demonstrate individual personality," lead author Evan Byrnes of Macquarie University said in a press release. "Personality is no longer considered a strictly human characteristic, rather it is a characteristic deeply ingrained in our evolutionary past."

Port Jackson shark face close-up. Credit: Wikimedia Commons

Personality in humans helps to define who we are and how likely we are to respond to certain situations. Some people tend to be bold risk takers, for example, while others are often more wary and careful. Prior research suggests that such inclinations are due to a combination of genetic and environmental factors.

Many aspects of behavior are relatively stable and predictable over time, and it is these general consistencies that define someone's personality.

The researchers designed trials to test the sharks' boldness, which is a measure of the propensity to take risks, but it also influences individual health through its correlation with stress hormones and more. Seventeen juvenile male and female Port Jackson sharks were caught at different locations within their habitat for the study.

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At first the sharks were 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.

For the second test, the researchers held each shark with two hands from underneath for just a minute before release. Byrnes and co-author Culum Brown then noted how quickly the sharks recovered from this bit of stress.

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The scientists found that each shark's behavior was consistent over repeated trials, indicating ingrained behaviors rather than chance reactions. Some sharks were therefore consistently bolder than others, while others were more prone to stress after being handled.

"We are excited about these results because they demonstrate that sharks are not just mindless machines," Brown, also of Macquarie University, said. "Just like humans, each shark is an individual with its unique preferences and behaviors. Our results raise a number of questions about individual variation in the behavior of top predators and the ecological and management implication this may have."

He continued, "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."