For decades people have been scared of sharks, with films like Jaws and Megladon perpetuating the mindset that these beautiful creatures are mindless killing machines. However, studies have shown that sharks actually have personalities: some are social, some are loners and some are just a little bit curious- but why?
In 2014 researchers from the University of Exeter and the Marine Biological Association (MBA) showed that sharks exhibit repeatable behavior in different contexts. Or, in lamens terms: they have personalities!
Whilst the personalities of primates and other social animals is well-known, this was the first study of its kind in sharks. To test for personality, researchers exposed groups of 10 small spotted catsharks (Scyliorhinus canicula) to three different habitat types with varying levels of structural complexity. They found that sharks had different social preferences: although group size changed, social individuals remained well-connected regardless of habitat and loner sharks remained isolated. In other words, their social network positions were repeated through time and across different habitats (Jacoby et al., 2014).
Above: small spotted catshark (Scyliorhinus canicula). IUCN red list status: least concern.
The different personalities of catsharks are thought to be driven by two main factors: social drivers and environmental context. Environmentally, variations in social behavior could reflect different strategies for avoiding predators. Some individuals in the study were more solitary and used the gravel substrate as an opportunity to become individually inconspicuous whilst out in the open. By contrast, other individuals appeared more gregarious, using the stone structures to hide in and around as a group. Although the percieved risk of predation in sharks was not tested directly in this study, predation risk has been shown to influence aggregation behaviour in juvenile lemon sharks (Negaprion brevirostris; Guttridge et al., 2012).
Above: lemon shark (Negaprion brevirostris). IUCN red list status: near threatened.
In addition to predation, an individuals’ preference for group size has been known to fluctuate depending on a range of environmental factors from parasite load to background colour (Krause & Ruxton 2002). However, the researchers detail that further research is required in order to distinguish between these environmental factors and social influences on personalities in catsharks (Jacoby et al., 2014).
But what about all those curious sharks? The ones you hear about in the news that approach divers and make friends?
Well, although the evolutionary mechanisms behind curiosity in sharks have not been directly tested, Richard Byrne, a neuroscientist at the University of St Andrews, had this to say about its evolution across the animal kingdom:
‘Once you think of animal behaviour in information-processing terms, the need for something like curiosity becomes obvious: whether learning is ‘latent’ or not no longer matters. The point is that, barring animals with the very simplest of lives (limpets?), information is power. Information-gathering is worth doing, even if there are no obvious payoffs at the time, as long as getting it is not unduly costly or risky. Storing information in memory is cheap, and you never know when a little knowledge may come in handy: such as when a psychologist suddenly deprives you of food, and puts you back in that maze where you’d happened to notice some cheese….’
‘it’s not far wrong [to say curiosity is a sign of intelligence]. What information can be extracted from any given situation depends on how that situation is perceived. With more advanced perceptual and brain processes, there’s more to discover; with more advanced motor abilities of brain and effectors, more can be done. Inevitably those species with limited perception, small brains, and restricted ability to affect the environment are not going to show much signs of curiosity; so what animals are curious about, and how long their curiosity lasts, may be revealing of their information-processing abilities.‘
So, curiosity results in information learning, which can benefit an animal in the long run. So, next time you see a shark, instead of seeing them as a man-eating monster, think: that could be one smart, social cookie.
Byrne, Richard. (2013). Animal curiosity. Current biology : CB. 23. R469-70. 10.1016/j.cub.2013.02.058.
Guttridge et al. (2012) Deep danger: intra-specific predation risk influences habitat use and aggregation formation of juvenile lemon sharks Negaprion brevirostris. Mar Ecol Prog Ser 445:279–291
Jacoby, et al. (2014). Behav Ecol Sociobiol. 68: 1995. https://doi.org/10.1007/s00265-014-1805-9
Krause J & Ruxton GD (2002). Living in groups. Oxford University Press, Oxford