Sharks have been typecast as the short-tempered bullies of the sea, although the truth is that not all of them live up to this hardened reputation. According to new research, sharks actually have distinctive personalities, and contrary to their status as fearless, cold-blooded killers, some are actually considerably shyer and more prone to becoming stressed out than others.
The idea of a flustered shark might sound unlikely, although according to study co-author Evan Byrnes, “sharks are not just mindless machines. Just like humans, each shark is an individual with its unique preferences and behaviors.”
Byrnes and his colleagues came to this conclusion after conducting a series of experiments, using 17 juvenile Port Jackson sharks, designed to gain an insight into the animals’ temperament. The first of these involved placing the sharks in a sheltered “refuge box” inside a tank, and timing how long it took them to pluck up the courage to venture out of their box and explore the open areas of their new environment.
The purpose of this exercise was to measure the sharks’ boldness and willingness to take risks. Interestingly, the researchers discovered that larger sharks tended to be bolder than smaller sharks, taking less time to leave the safety of their box. This would appear to contradict certain pre-existing theories which hold that, among top predators, smaller individuals tend to be bolder and more aggressive, as they generally have to be more competitive in order to survive.
One of the Port Jackson sharks used in the experiment. Evan Byrne
Next, the study authors conducted a stress test, in which sharks were removed from their enclosures and physically held by the hands of the researchers for one minute, before being returned to their tank. By measuring how long it took each shark to recover from this stressful episode and return to their normal level of activity.
Results – which appear in the Journal of Fish Biology – showed that the sharks that were the least bold in the first test also turned out to be the biggest stress-heads in this second experiment, taking notably longer to shake off the experience. Importantly, the behavior of each individual shark was consistently replicated when the tests were repeated, indicating that their conduct was the result of ingrained personality traits rather than just a one-off.
According to Byrnes, this finding could have major implications for shark conservation efforts. “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,” he said in the statement.