To Boldly Go
Updated: Jul 12, 2021
When we talk about personality, we often assume it is solely a 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 fish to chimps! Personality has been proven to exist in several different shark species from very diverse evolutionary lines, which suggests it is likely present in many other sharks that we are yet to study.
Scientists look at specific behaviours to determine if animals have certain personality traits. For example, we can measure how far a shark swims in a day to determine how active it is. Or we could measure the distance they travel to assess how explorative an individual is.
Recently, scientists studying the Port Jackson shark (Heterodontus portjusacksoni) tested how bold individuals were using "open field emergence trials". This method involved placing the shark into a shelter within a new enclosure and allowing it to become used to the situation (known as "habituation"), before opening a side of shelter so it could explore the whole tank. Measuring the time it took for the shark to emerge suggested how bold it was compared to other individuals.
The researchers found that individual Port Jackson sharks were consistently different in how long it took them to emerge from a shelter, suggesting some were more bold than others. "Shy" individuals are generally more cautious in potentially dangerous situations, whereas "Bold" individuals take more risks; like a live-fast-die-young strategy (Byrnes & Brown, 2016).
They also assessed how sensitive each individual was to stress. This species tends to swim rapidly and erratically when they are under stress and therefore, slow, relaxed swimming, or resting on the floor, suggests that the shark has habituated. The researchers mildly stressed the sharks by handling them and exposing them to open air for several seconds, before returning them to the water (It is important to note that this does not cause injury to the sharks and no sharks were hurt or died during the study- in fact, they were all rereleased into their natural habitat). They then counted how many times the shark beat its tail within a 30 second period (known as "tail beat frequency"). They found that individual sharks had consistent high or low tail beat frequencies, suggesting that each individual differed in how rapidly they habituated when stressed (Byrnes & Brown, 2016).
The study in Port Jackson sharks found that individuals which were fast to habituate to stress were also more bold, whereas individuals which were more shy also experienced stress very acutely (Byrnes & Brown, 2016).
When we see certain behaviours are commonly displayed in cohort with other features, we call this a "behavioural syndrome"(also known as a "coping style"). For example, an animal which is often aggressive might also be commonly active, whereas an individual which is particularly bold might also be very explorative.
As these researchers proved that behavioural syndromes exist in these sharks, we now know that, not only do sharks have personalities, but these personalities are complex and multi-faceted.
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.
By Sophie A. Maycock for SharkSpeak.