Some species of sharks are solitary, whilst others live permanently in large groups... Some sharks only form schools or aggregations when they need to find a mate. Group-living can aid in "cooperative hunting" or increases a small shark's chances of survival, but sometimes it seems there is more to how groups of sharks form; something more akin to friendship. Human beings are social animals; we have extensive networks of family, friends, colleagues... so we are often interested to understand if animals also share our habit for forming relationships. It fascinates us, because it allows us to empathise with them on a different level; to feel like we can understand them... So we ask, "Do sharks have friends?"
One of the Gang
There are many examples of sharks that live in groups; large and small. From an evolutionary perspective, group living offer protection from predators, improved foraging opportunities and/or better chances of finding a mate. Therefore, it improves their "fitness".
However, is there more to shark groups? Some kind of a social element?
Scientists using tagging technology to study grey reef sharks (Carcharhinus amblyrhynchos) at the Palmyra Atoll, in the Pacific Ocean, have learned that their movements are anything but random... On the contrary, individual grey reef sharks occupy very specific areas of the reef, where they persistently associate with specific individuals repeatedly. These associations are so consistent, that it causes the wider community to be split into five different subgroups of sharks (Papastamatiou et al, 2020). Basically, they have something akin to 'friends' within their different neighbourhoods.
The Social Network
The elaborate community network of grey reef sharks was consistent across several years of sampling - showing their social structure is very stable throughout both space and time. This kind of complexity is as developed as that found in other social animals, like mammals, which are commonly considered more 'intelligent' or 'emotionally advanced' (Papastamatiou et al, 2020).
"Sharks can display a degree of social complexity traditionally associated more with mammals and birds"
- Papastamatiou et al, 2020
The researchers suspect that grouping allows grey reef sharks to have a higher hunting success. They noted that sharks that were lone foragers, had significantly less success finding prey compared to those which spent time in groups (known as "social foragers"). Therefore, it seems that these sharks were using "social information sharing" to find good patches of food - getting recommendations from friends about where to go eat! (Papastamatiou et al, 2020).
Let's Team Up!
Grey reef sharks are not found in groups by chance, but they have maintain complex and stable social structures within their communities. In fact, they are socially advanced and capable of detailed communication. This social information sharing means individuals can acquire more food, have better health and, as a result, have a higher number of offspring throughout the course of their lives (Papastamatiou et al, 2020).
This is not dissimilar to how human beings have evolved; where forming groups made survival easier, until eventually a complicated social construct became crucial to daily life. So, maybe we have more in common with sharks than we have previously thought...
To learn more about shark social relationships, check out The Social Network.
Papastamatiou YP, Bodey TW, Caselle JE, Bradley D, Freeman R, Friedlander AM & Jacoby DMP (2020). Multiyear social stability and social information use in reef sharks with diel fission–fusion dynamics. Proceedings of the Royal Society B: Biological Sciences, 287:1932. Access online.