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Tests show some sharks are bolder than others

Screen Shot 2016 06 02 at 15.31Professor Culum Brown with a Port Jackson shark. Photo: Quentin Jones

An Australian University study suggests that sharks have distinct personalities - some are bolder than others, while others get stressed out more easily.

Evolutionary biologists argue that animals exhibit personality traits - that is they exhibit predictable behaviour in given circumstances.

In humans, our behaviour tends to demonstrate repetition over time or in similar situations - that predictability is what is thought to define personality.

‘Over the past few decades, personality research has shown that nearly 200 species of animals demonstrate individual personality. Personality is no longer considered a strictly human characteristic, rather it is a characteristic deeply engrained in our evolutionary past,’ says lead author of the research, Evan Byrnes of Macquarie University’s Department of Biological Sciences.

The study looked at Port Jackson sharks - a species common on the east coast of Australia which grows to 1.5m and feeds off crustaceans. Published in the Journal of Fish Biology, the results show smaller sharks tend to be much more shy, probably because they are more vulnerable to predators, Associate Professor Culum Brown said.

However, unexpectedly, there was no personality difference noted between the sexes.

Screen Shot 2016 06 02 at 15.32Port Jackson shark. Photo: Julianna Kadar

‘Males tend to be bolder than females in just about every animal that has ever been looked at,’ Professor Brown said. ‘So this was unexpected. But it could be due to the small sample size.’

The trials were designed to test the sharks' boldness.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. The second behaviour 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 behaviour was consistent over repeated trials, indicating ingrained behaviours 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.

‘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 behaviours,’ said Professor Brown.

‘Our results raise a number of questions about individual variation in the behaviour 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 behaviour – 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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