Grey Reef Shark Study Finds Long-Term Social Bonding
New research has shown that grey reef sharks form long-lasting social bonds, according to a report published in Proceedings of the Royal Society B, Biological Sciences.
Lead author Yannis Papastamatiou and a team of scientists from Florida International University, UC Santa Barbara, the University of Hawaii and the University of Exeter in the UK, followed 41 grey reef sharks (Carcharhinus amblyrhynchos) around the Palmyra Atoll, approximately 1,000 miles south of Hawaii.
The team used a combination of acoustic tags and cameras affixed to the sharks to track 41 animals over a four year period. Grey reefs sharks are known to congregate in the morning, with groups slowly gathering in number during the day until they disperse at night, a dynamic known as 'fission-fusion' grouping. The new study found that not only did the sharks return to the same groups in the same locations, they also consisted of the same individuals.
'Using one part of the reef helps you find your friends,' said Papastamatiou, in an interview with FIU news. 'It can be hard to maintain social bonds when you live in the ocean, but if sharks all routinely return to the same spot on the reef then that will help them maintain their group structure.'
It is not the first time that social networking has been identified in sharks. Previous studies have shown that lemon sharks and blacktip reef sharks, among others, form social groups. The behaviour has also been observed in manta rays.
It is thought that the social grouping assists with hunting and feeding, as group foraging on known hunting grounds is thought to be more successful, and also prohibits competing species from taking resources. Grey reef sharks are known to drive other shark species away from their favourite hunting grounds. Papastamatiou's study suggests that sharks which did not participate in the dynamic social groups - 'loners' - were less healthy than their networking peers.
The most significant finding of the new study, however, is the length of time that sharks retain their 'friends'. While group interactions may benefit feeding and reproductive behaviours, some of the sharks were observed to remain in the same buddy pairs for the entire four-year duration of the study, indicating that longer-term bonding was likely.
'For some time now, we have known that sharks are capable of having distinct social preferences for other groupmates,' said David Jacoby of the Zoological Society of London, who assisted with data analysis from the study. 'We had no idea, though, that these social bonds could last for multiple years or that in the absence of reproduction or parental care that such communities might function as areas to exchange information.'