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. 

Distribution map of Port Jackson shark, highlighted in blue

Distribution map of the Port Jackson shark, highlighted in blue

“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.”

Our own personalities are known to be influenced by both genes and past experiences, and these personalities often adapt and change over the course of our lifetime – due to individual experiences with different stimuli and social situations. With sharks, it’s a similar trend, but more with regard to how they deal with predatory threats and hunting strategies, than job interviews and next door neighbour’s errant barbecues.
 
“Sharks experience different stimuli over their lifetime, such as different predators and social experiences, and the number of times individuals encounter these stimuli and the type of interaction they have will influence how their personality changes. For example, if a bold individual swims up to inspect fishing gear and is captured, it will likely be more shy and cautious of fishing gear in the future.”
 
A diver, face to face with a whale shark. © Krzysztof Odziomek

A diver, face to face with a whale shark. © Krzysztof Odziomek

 
With this finding, the question is whether this individuality is unique to only Port Jackson sharks, or whether it is apparent in the wider underwater world. Byrnes certainly thinks it may be present in other sharks.
 
“The idea to study personality in sharks originated from my experience diving with great hammerhead sharks in Bimini, Bahamas, where I was able to recognise individual sharks based completely off how they behaved rather than off appearance. In fact, individual personality differences have also been demonstrated in catsharks and lemon sharks by researchers from Plymouth, UK and Bimini, Bahamas. Researchers are also beginning to discover that individual sharks of various species have different preferences and specialisations for particular prey or what type of habitat they live and hunt in.”
 
With these newfound personality differences and abilities to adapt their characteristics to suit certain social situations, there is a slim possibility that divers may be able build relationships with individual sharks. Although it is not advised to go out and seek “sociable sharks” to befriend – as this is work best left for shark diving professionals to avoid any injuries to both human and shark – there is that small opportunity to create unique diving environments and better understanding of individual creatures. 
 
“If a bold, non-aggressive shark approaches a human and has a positive experience, it is likely to come back for more human interaction. On the other hand, I would expect that a shyer individual would be less apt to approaching divers and an aggressive shark would have a negative interaction, both leading to less future interaction with divers.”
 
For both divers and non-divers, this study’s conclusions, along with the many groundbreaking findings concerning the species in our oceans, simply reaffirms the reason why we should focus strongly on protecting our vast underwater world.