For centuries, humans have moulded and adapted to try and fit with the conflicting characters of their own people, in an effort to somehow negotiate their way through this grown-up playground that we call society. These combinations of qualities that form an individual’s distinctive personalities were traits we believed to be present in only a handful of species. But a groundbreaking study, led by Dr. Evan Byrnes of Macquarie University in Sydney, Australia, has revealed that members of a certain species of shark have individual personalities.
The shark species in question, Port Jackson sharks (Heterodontus portusjacksoni) – unknowing pioneers of the age of shark enlightenment – are common bottom-dwelling sharks of Southern Australia. Sometimes referred to as the “Oyster Crusher”, this unusual-looking species is one of the most well-studied sharks in the world.
“Port Jackson sharks’ small size, hardiness, and large abundance in New South Wales waters made them an ideal shark to bring into captivity and test. Additionally, Port Jackson sharks belong to an ancient order of sharks called Heterodontus, or bullhead sharks, which diverged from other sharks nearly 240 million years ago, making them an ideal model to explore for the evolutionary roots of personality in animals,” Byrnes explains.
The study was conducted in captivity to provide each individual with identical testing conditions for multiple trials. The sharks were first introduced to a wide open inflatable pool and provided with shelter.
“I did one test that looked at individuals’ propensity to take a risk, or boldness, and did another test to look at individuals’ recovery from a stressful situation. To test boldness, I used a test called an emergence test, which looks at how long it takes for an individual to emerge from a dark acclimation box into a novel and potentially dangerous habitat. In reality, the dangerous habitat was just the wide open inflatable pool, but since the sharks had no experience in the pool they did not know if they were emerging from the box into a habitat filled with predators.”
Another test gave Byrnes a more hands-on approach: “To examine stress recovery, I measured sharks’ swimming rate after being handled out of water for one minute and then compared it to their normal swimming rate. Each of these tests were then repeated multiple times to see how consistent individuals’ behaviours were compared to the other sharks.”
But what Byrnes and his team discovered was that each shark’s behaviours consistently differed from one another. Some sharks were consistently bolder than others, and some sharks more easily stressed. It confirmed his earlier suspicion, that members of this species of shark do indeed have contrasting personalities – just like us.
“The most surprising find for me was that not only did sharks differ in the speed they recovered from stress, but there also seemed to be a difference in recovery style. While most of the sharks I tested increased their swimming rate after being handled, I observed two of the my 17 sharks decrease their swimming and sit on the bottom. This was quite surprising because it brings a whole second dimension of stress responses into the consideration when determining individual behaviours: An individual can either be reactive and or proactive, and at the same time be docile or panicky – for lack of a better word.”