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."