Do sharks have friends?
Show notes
Welcome to another episode of The Whole Tooth, a shark podcast that asks YOUR questions to shark and ocean science experts! This week, we are asking SOSF project leader and Science and Policy advisor for Saving the Blue, Dr Bryan Keller, all about shark social behaviour. Are sharks the lone wolves they’re made out to be? Why do we sometimes see sharks in groups? And do they have preferences for who they hang out with?
Before finding out the answers to those questions, we first talk about Bryan’s life and career. He has not one but two most memorable experiences – both unexpected encounters with sawfish [04.30]. One even involves some sawfish midwifery, a Whole Tooth first [07.01]! We then go back to the beginning, to Bryan’s upbringing in the Arizona desert, where he developed an obsession for sharks on family holidays to the beach and the aquarium [09.52]. This led to learning to dive and an internship at an aquarium in Baltimore. From there, he interned at the Bimini Biological Field Station, working with the likes of Tristan Guttridge and Dean Grubbs and gaining experience in the field [11.19]. He then did his master’s project on the social behaviour of juvenile lemon sharks in the area, a PhD, and now has a job with Saving the Blue [14.00].
We then move on to our central topic: shark social behaviour! We start with the basics: the difference between aggregations and social groupings [16.44]. As Bryan explains, it has to do with the structure within those groups, and the preferences of the individuals within that group. Aggregations are any gathering of animals that can occur due to requirements for basic needs like food or shelter [19.09]. Social grouping refers to some level of social structure that relates to the preferences of the individuals – in other words, it’s not random. There is a reason behind the group’s formation and the way it is structured.
An example would be certain sharks choosing to associate with the females in the group or hanging out with individuals they know as opposed to ‘strangers’. Social groupings can occur within aggregations, too [21.00]. Almost like going to your favourite restaurant, bumping into a group of friends, and choosing to sit with them!
This brings us to Bryan’s master’s research, which examined familiarity and partner preference in juvenile lemon sharks. Previous research on lemons had shown that the same individuals often showed up to the same refuge sites together – and Bryan wanted to understand why. He placed pairs of juvenile lemon sharks in sea pens, where they stayed for two weeks. The assumption was that these sharks were complete strangers at first – although some may have been related or associated before, likely, they had never met. Once they were allowed to mingle again, Bryan and his team looked at their swim patterns. They found that sharks were more likely to swim with their ‘pen-mates’ than the other sharks they didn’t know, meaning that they showed a preference for familiar individuals [27.40]. In other words, they chose to swim with friends!
This may seem a bit weird, but there is a good reason for this [28.03]. Essentially, we find comfort in what we know – for example, a toddler at pre-school is more likely to hang out with other toddlers they’ve known before. It provides a sense of comfort and safety – you know what you’re getting with that familiar face, and it can make us more confident. Bryan and his team also found that this partner preference for familiars strengthened as the experiment continued over two months [29.48]. These findings suggest that these partnerships are developing, and sharks can possibly grow a stronger affinity for each other. This can happen between brothers and sisters, but not always – meaning that sharks are capable of complex social behaviours. This concept is challenging to study in the wild, as not all species are as accessible as lemons [32.57]. But similar findings have been observed in small-spotted catsharks.
We then talk about the importance of understanding why and where sharks aggregate and form social groupings for fisheries management and policy, in which Bryan is heavily involved [36.17]. He now looks at aggregations of silky sharks around fish aggregating devices (FADs) to understand how they overlap with fishing pressure. There is a higher risk of being captured around these FADs, making silky sharks vulnerable to overfishing. Bryan is working to reduce by-catch underneath FADs to help protect silky aggregations. We also discuss some advice for early career marine scientists on how to translate their research into policy and management actions and impact their research [40.43]. The good news? We’re discovering more about shark social behaviour all the time, and the more we know, the more tools and management measures we can develop to help protect sharks from intense fishing pressure [48.39].
About our guest
Dr Bryan Keller
Bryan researches the spatial and temporal ecology and social behaviour of elasmobranchs. He holds a doctorate in Biological Oceanography from Florida State University; his dissertation was focused on the spatial ecology and seasonal migrations of bonnethead sharks, and his M.Sc. on the social behaviour of juvenile lemon sharks. Bryan is currently a Science and Policy advisor for Saving the Blue and contributes to research on species including great hammerheads, silky sharks, and smalltooth sawfish.
Bryan’s Instagram: @bryankeller
Save Our Seas Foundation Project page
Saving the Blue Instagram: @savingtheblue
