A Small Shark With a Big Personality
Updated: Jan 6
"Personality" is no longer a trait which is only assigned to human beings. In fact, personality (defined as individual differences in behaviour which are consistent across both time and contexts) has been proven in over 200 species! Including mammals, amphibians, molluscs, birds, fishes and even insects!
When psychologists discuss human personality, we are defined based on 'the big 5' behavioural axes, named 1. Openness to experience, 2. Extraversion, 3. Conscientiousness, 4. Agreeableness and 5. Neuroticism (If you want to learn ore about your personality type, you can take a Myers-Briggs test at: https://www.16personalities.com). However, in animals behaviours are defined differently. Generally, animal personalities are explored based upon individual differences in: 1. Activity (how active they are and how much they move), 2. Aggression (how aggressive they are in social contexts), 3. Boldness (how shy or bold they are), 4. Explorativeness (how likely they are to explore novel experiences or to avoid them) and 5. Sociability (whether they are particularly gregarious and interact with many other individuals) (Conrad et al, 2011).
Researching personality in animals is a relatively new field, but becoming increasingly popular amongst scientists. So now, we have started to see studies of shark personality!
For example, a recent study proved that personality in terms of individual differences in sociability, is present in the small spotted catshark (Scyliorhinus canicula). They considered both the size of the group and each individual shark's position within the network to assess sociability, and also investigated whether sociability was consistent in different habitats (Jacoby et al, 2014).
They tested sociability in the laboratory by determining which individual sharks preferred to rest together on the "substrate" by tagging each shark, so it could be tracked accurately in the aquarium. Sharks were considered to be associating with each other when they rested within one body length of another individual. They then used some fancy statistics called a Simple Ratio Index (SRI) to give interactions between two individuals a weight, based on how often they hung out together. What they found was that individual catsharks differed in their social interactions; preferring to associate with certain, familiar individuals... Basically they had pals they preferred to be around (Jacoby et al, 2014).
The researchers hypothesised that having consistent social partners might allow the catsharks social stability and social cohesion. This is particularly important in prey species, like the catshark, because grouping together can increase their chances of survival (Jacoby et al, 2014).
The researchers also investigated whether this sociability was consistent in different contexts, by looking at the size of groups the catsharks rested in when they were in a different kind of habitat. They found that in simple, gravelly areas the sharks formed a small number of large groups, but in more three-dimensionally complex structures, like coral reefs, the sharks generally formed many, small groups. This suggests that's, whilst individual sharks differed in their sociability, the environment also had an impact on their behaviour. This is called "plasticity"; meaning that an animal is able to adapt based on the context to ensure its behaviour is not sub-optimal in different situations (Jacoby et al, 2014).
Imagine how lively you are in different situations. In a social situation, with lots of friends you know, you might be very active, loud and laugh a lot, but if you were in a situation where you and the same friends were sitting in an exam hall taking a test, your behaviour would be very different. This does not mean your personality has actually changed, but that the context you find yourself in affects how you behave.
The catsharks adapt their behaviour in this way because, in a more complex habitat, they are less vulnerable to predators, but in a simpler habit, they are much more exposed. In this situation, they form large groups for safety via the "predator confusion effect". Their spotted skin provides them camouflage when they are in a group because it is more difficult for a predator to pick out an individual within the school. In a habit with more structure, which already offers them some camouflage, the catsharks were able to relax in their favoured small cliques (Jacoby et al, 2014).
Conrad JL, Weinersmith KL, Brodin T, Saltz JB & Sih A (2011). Behavioural syndromes in fishes: a review with implications for ecology and fisheries management. Journal of Fish Biology, 78, 395-435.
Jacoby DMP, Fear LN, Sims DW & Croft DP (2014). Shark personalities? Repeatability of social network traits in a widely distributed predatory fish. Behavioral Ecology and Sociobiology, 12:68, 1995-2003. Access online.