When we talk about personality, we often assume it is a solely human trait. However, this is far from true! In fact, “personality” (which is defined as consistent individual differences in behaviour throughout time and in different situations) has been proven to exist in over 200 species of animals - from insects to mammals - including several species of sharks, such as the lemon shark, the Port Jackson shark, the tiger shark, the lesser spotted catshark and the blacktip reef shark... But what does this mean? What does personality look like in a shark?
It's Not Only Human Beings that Have Different Personalities
Animal personality is assessed in terms of five personality traits: 1. activity (an animal which is sluggish versus very active), 2. aggression (whether they are placid or aggressive in social contexts), 3. willingness to explore (exploration versus avoidance), 4. boldness (as opposed to shyness) and 5. sociability (whether they are solitary or prefer a large group) (Finger et al, 2017).
Some Sharks are Bolder than Others
An animal which is more bold, compared to one which is more shy, will be less cautious in a situation perceived as dangerous, like when a predator is present. Bold individuals take more risks. For example, juvenile lemon sharks (Negaprion brevirostris) differ in their boldness when foraging for food within their nursery habitat (Finger et al, 2017).
In a study of Port Jackson sharks (Heterodontus portusjacksoni), researchers used an “emergence test” to assess individual boldness. They placed the shark inside a shelter and then measured how long it took to emerge out from relative safety. Scientists found that individuals consistently differed in the time it took them to emerge, with the more bold individuals popping their heads out more quickly (Byrnes & Brown, 2016).
Some Sharks are More Explorative than Others
An animal which is relatively explorative will make extensive movements to orient itself in a new environment. At the opposite end of the scale, an individual that displays avoidance, will only explore a small area - preferring to stay close to home. Individual lemon sharks differ in their small-scale explorativeness (Finger et al, 2017).
Differences in explorativeness can also have implications in movements on a larger scale. Tiger sharks (Galeocerdo cuvier) studied in Hawaii have been shown to have individual differences in how explorative they are, which affects whether they migrated long-distance. This means that some individual tiger sharks were residents of a specific area, where others were only transient (Meyer et al, 2010).
Some Sharks are More Sociable than Others
Sociability as a personality trait refers to an animal’s reaction to other individuals of the same species (aka “conspecifics”). Asocial individuals will avoid conspecifics and favour smaller social groups, where social individuals display an attraction towards conspecifics (Finger et al, 2017).
Lesser spotted catsharks (Scylliorhinus canicula) have been found to have social interactions with specific individuals, which remain consistent even in different habitats; like they have favourite pals. It has also been discovered that the catshark has an organised social structure and each individual’s rank within the hierarchy is consistent (Byrnes & Brown, 2016; Finger et al, 2017).
Blacktip reef sharks and lemon sharks have also been shown to differ in how social they are, with some individuals favouring large groups, where others consistently prefer to spend time in small groups (Finger et al, 2017).
Live Fast, Die Young
Different animal personalities have appeared thanks to evolution because each type has its own benefits. Scientists think boldness has evolved in sharks because it allows these individuals to reach foraging opportunities more rapidly. As a result, bolder lemon sharks are very fast-growing, but being bold and explorative also carries more risks... with a higher chance of becoming food yourself! Bold lemon sharks suffer a higher mortality rate than their more cautious counterparts. It is a trade-off between food and safety (Byrnes & Brown, 2016; Finger et al, 2017).
Scientists think that this is why less bold personalities have also evolved. Whilst the more cautious sharks they may not have be able to exploit all foraging opportunities the bold ones do, they are less exposed to risky situations and therefore have a lower mortality rate (Finger et al, 2017).
Similarly, both explorers and home-bodies are able to coexist because they exploit a different “ecological niche”. The explorative sharks strike out to find new foraging opportunities and leave space for others to utilise food sources closer to home. So both personality types persist (Finger et al, 2017).
Understanding Personality is Vital to Shark Conservation
These studies might seem cute and fun - many people enjoy the idea that animals have personalities - but actually this research is vitally important to conservation!
Think about it... bold and/or explorative individuals may be much more likely to be exposed to fisheries or beach nets because they roam further than counterparts which are more shy. On the other hand, more active and/or more exploitive sharks may be more likely to undergo extensive migrations, which could make them more likely to survive if their normal habitat became degraded (Finger et al, 2017).
These individual differences in behaviour could mean only certain sharks in the population will be able to adapt to environmental shifts, like those associated with climate change for example (Finger et al, 2017).
Whatsmore, in several other types of animals, personality traits actually have a genetic component, which is heritable from parent to offspring. If this is true for sharks, skewed mortality of individuals with a certain personality trait, could reduce the genetic diversity of the species as a whole (Finger et al, 2017).
It is vital that we continue to research shark personality, so that we can design management plans for endangered species of sharks. It's not just about personifying these animals, but about better understanding their behaviour; how they utilise their habitats and occupy their ecological niches, so that we can ensure we protect the sharks which are most at risk of extinction.
To learn more about shark personality, you can check out my articles: To Boldly Go and A Small Shark with a Big Personality.
References
Byrnes EE & Brown C (2016). Individual personality differences in Port Jackson sharks Heterodontus portusjacksoni. Journal of Fish Biology, DOI:10.1111/jfb.12993. Access online.
Finger JS, Dhellemmes F & Guttridge TL (2017). Personality in elasmobranchs with a focus on sharks: early evidence, challenges, and future directions. In: Vonk, J., Weiss, A. & Kaczaj, S.A. (Eds.). Personality in Nonhuman Animals, 129-152. Springer, Berlin.
Finger JS, Guttridge TL, Wilson ADM, Gruber SH, & Krause J (2018). Are some sharks more social than others? Short- and long-term consistencies in the social behaviour of juvenile lemon sharks. Behavioural Ecology and Sociobiology, 72:17, DOI: 10.1007/s00265-017-2431-0.
Meyer CG, Papastamatiou YP & Holland KN (2010). A multiple instrument approach to quantifying the movement patterns and habitat use of tiger (Galeocerdo cuvier) and Galapagos sharks (Carcharhinus galapagensis) at French Frigate Shoals, Hawaii. Marine Biology, 157, 1857–1868. Access online.
By Sophie A. Maycock for SharkSpeak
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