Sharks have greatest mates and go swimming collectively, analysis finds
New research has found that sharks have a friendlier side to them than stereotypes of the species would have us believe.
A study conducted at the Shark Reef Marine Reserve in Fiji has discovered that bull sharks do not swim together at random – but actually form consistent relationships with particular individuals, forming what we would term ‘friendships’.
Thus the ‘lone shark’ image in popular culture may be wrong for many of the sea dwellers, since the research has proven that sharks have complex social lives.
The study, published in the scientific journal Animal Behaviour, used data from an observation of 184 bull sharks conducted over six years.
The breed of sharks are among the largest and most adaptable within the species, measuring up to 3.5metres in length and weighing up to 230kg. They lurk in warm waters around the world and are rare in their ability to tolerate fresh water, so can be found swimming in rivers and estuaries too.
They are also one of the most threatening species for humans, being in the top three sharks for biting humans alongside great whites and tiger sharks – although these incidents remain extremely rare.
The study looked at two types of interaction – the first involving sharks staying within one body length of each other, and the second including more deliberate behaviour.
The more intentional patterns fascinatingly included sharks swimming alongside each other and ‘lead-follow’ movements, whereby one shark appeared to be guiding another.
The research observed 184 bull sharks in Fiji over the course of six years
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The results revealed that their movements were not random – in fact, sharks repeatedly paired up, often swimming in parallel or tracking one another through the water.
They also did not mix equally with every neighbour – suggesting a preference for some companions and the deliberate avoidance of others.
Natasha Marosi, the lead author of the study and founder of the Fiji Shark Lab, told the Times: ‘As humans we cultivate a range of social relationships, from casual acquaintances to our best friends, but we also actively avoid certain people.
‘These bull sharks are doing similar things.’
The reason behind the social behaviours of the bull sharks could be strategic, the research suggested.
Adult sharks of reproductive age formed the core of the social network and maintained the most consistent relationships.
Size mattered in the shark world too – both male and female sharks appeared to prefer interacting with females, but males tended to have a greater number of social connections overall.
Since male bull sharks are typically significantly smaller than females, their greater sociability could have a strategic purpose in providing a social buffer from aggressive confrontations with larger individuals.
Professor Darren Croft of the University of Exeter’s Centre for Research in Animal Behaviour said it is only the beginning of understanding how sharks socialise.
Professor Croft said: ‘Contrary to commonly held perceptions of sharks, our study shows they have relatively rich and complex social lives. We are only just beginning to really understand the social lives of many shark species.’
