Humans have more in common with sharks than meets the eye. Sharks, like people, have varied personalities. They can be introverted or extroverted.

This study, titled "Shark personalities? Repeatability of social network traits in a widely distributed predatory fish", was published today in the journal Behavioral Ecology and Sociobiology.

Researchers from the University of Exeter studied ten groups of small spotted catsharks to observe their social characteristics. The sharks were placed in three different situations, ranging from a complex territory to a simple tank with nothing but sand. The researchers found that each shark had a unique personality, consistently opting either to stick in groups or go out on its own to find shelter. This was consistent for each shark even when the group moved to a new area.

"The results were driven by different social preferences, that appeared to reflect different strategies for staying safe. Well-connected individuals formed conspicuous groups, while less social individuals tended to camouflage alone, matching their skin colour with the colour of the gravel in the bottom of the tank," said Dr. David Jacoby, lead author of the study. Jacoby studies animal behavior at the Institute of Zoology in London.

Professor William Hughes, one of the other researchers involved in the study, compared the groups of sharks to groups of ten co-workers, each placed in a bar, then a nightclub, then an office setting. Hughes said that, like the sharks, the people would tend to stick to the same groups no matter what setting they were placed in.

"It's a very nice piece of work. It provides some pretty reasonable evidence that sharks show a form of social personality," Hughes said.

This is the first research study that shows individual personalities and social groupings in sharks. Other studies have shown animals have personalities, but they mostly focused on traits such as aggressiveness. Hughes said that probably all animals show some signs of individual personality in terms of extroversion or introversion.

Another animal behavioral researcher, Jean-Sebastien Finger, said that the results of this study weren't unexpected to him, since almost every species of animal displays some kind of personality.

The authors of this study believe that, although this study consisted of captive sharks, results would be repeatable if the sharks were studied in the wild. Jacoby also said that he believed other species of sharks would have similar traits if studied.