CROWDS OF METRE-LONG sharks lie motionless on the seafloor within gutters etched into the rocky reef. Some are piled up under overhangs, while others are isolated and out in the open.
Beneath a waving frond of kelp, a shark raises its head and pivots upward on a pair of pectoral fins. With a few beats of its club-like tail it propels itself forward to reveal a pencil-sized cylindrical device attached to its flank.
A diver motions forward to grab the shark. He catches it by placing one hand on the back of its head, and the other around the tail. It struggles and bucks back and forth, before finally admitting defeat and allowing the diver to swim it up to the small canoe waiting above.
“Yes, this is the recapture we’re after!” says Nathan Bass, a PhD candidate with Macquarie University, which is studying the social networks of Port Jackson sharks.
He passes the shark up to the team in the canoe. They work methodically to gather as much data as possible during each short encounter with this species.
Like all sharks of the primitive order Heterodomtiformes (horn sharks), the Port Jackson has a blunt head and spines on the leading edge of the two dorsal fins.
Yet its unique colour pattern is distinguishing and intricate. Dark harness-like markings cover the eyes, run along the back and cross over along the side of the body.
The team measures the shark from the tip of the snout to the upper lobe of its dorsal fin before placing it in a bag and hoisting it into the air to confirm the weight. The average size of a male Port Jackson is 95cm (6kg), while a female is slightly larger at 1.2m (14kg).
A tissue sample is then collected for DNA analysis, and a unique identification number is read from an orange tag attached to the shark’s tail (which is used to identify individuals during diver surveys). Finally, the receiving device that drew Nathan to this particular Port Jackson is removed, before the shark is released back into the sea.
“Each proximity receiver we find adds another piece to the puzzle,” says Nathan. “It’s just a matter of locating the sharks again so that we can download the data.”

THIS LATEST MARVEL in acoustic technology records and stores information about encounters with other acoustically tagged sharks. By recording the date, time and an identifying number, the research can take place without human interference over a continuous period of time.
For this relatively small and slow-moving species the recording distance is set at four body lengths (4m), but the distance can be adjusted to suit larger and more mobile species.
“We’re trying to demonstrate how the sharks interact,” says Nathan. “The social structure of a population is closely connected to their behaviour, ecology, and evolution.”
By combining the proximity receiver data with other tried-and-tested acoustic technology – including continuous acoustic tags and receiving stations strategically placed around the survey sites – Nathan aims to demonstrate that the sharks form social relationships, and then to determine the functions of these relationships.
It’s his second winter studying the sharks, which are endemic to southern Australia. They gather in numbers off New South Wales (NSW) between June and September, during which time Nathan divides his time between two study locations in Jervis Bay and off Sydney.
The sharks are popular with the avid groups of divers drawn to the same temperate reefs along the southern NSW coastal fringe. Peppering the reefs throughout their distribution, some of the key locations for encountering this species include Forster and Seal Rocks, Fingal Island off Port Stephens, Bare Island off Sydney and throughout Jervis Bay.
The diving in Jervis Bay has been rated among the best in Australia. Shallow seagrass meadows provide a haven for a diverse suite of colourful characters such as weedy seadragons and pyjama squid, while the kelp-dominated shallow rocky reef gives way to boulder fields encrusted in sea tulips, sponges and ascidians.
Large blue grouper, schools of old wives and inquisitive giant cuttlefish are regulars, while red Indian and blue devilfish are among the hidden gems to be found in the Port Jacksons’ domain.
Diving conditions vary by the day, with water temperatures fluctuating from 16-22°C. Vis can also change with the tide, wind and prevailing weather conditions, and varies from 40m to within arm’s reach. Fortunately for Nathan and his team, the sharks are common at the study sites, and most conditions are workable.
The gentle Port Jackson is the perfect model species to study the application of the proximity receivers. “There are plenty of them and they’re easy to handle – you can just reach right out and pick them up,” says Nathan.
The team works within the constraints of strict animal care and ethics guidelines to ensure minimal impact on the shark during the encounter.
Each step of the scientific process is calculated and performed by researchers with a passion for shark conservation.

EAGER TO ASSIST are enthusiastic volunteers hoping to get hands-on with wild sharks. Many of them have their own marine postgraduate research projects.
Once trained, the volunteers can participate in all aspects of the fieldwork, and it’s the perfect project for budding marine scientists to hone diving and field skills that can then be applied to their own projects.
Up to four dives are undertaken daily at the study sites, and sometimes further afield during exploratory excursions, so there is plenty of time in the water.
On one exploratory dive Nathan recalls the discovery of a huge aggregation of Port Jackson sharks off the southern side of Jervis Bay. “There were so many sharks there it was unbelievable, hundreds on
the seafloor in small groups – it was a remarkable encounter for our team.”
“It’s just an amazing experience all round,” says Jo Wiszniewski, Research & Conservation Co-ordinator for the Taronga Conservation Society Australia and co-supervisor of this project. “All the sharks have different personalities – some come quietly to the surface, while others can be feisty and whip around.”
Jo’s own PhD examined the social networks of dolphins. “These two projects are quite similar – they’re both asking questions about the social relationships within a population and the factors that influence those relationships,” she says.
To document the social interactions of dolphins along the NSW coast, Jo used photo-identification and a biopsy pole to obtain muscle samples.
She identified separate populations to show that dolphins living in bays such as Yamba and Port Stephens were genetically distinct from those living offshore.
This research also identified separate dolphin communities in Port Stephens, which Jo examined more closely. She found that each group had a preference for particular habitats influenced by either marine or estuarine waters.
Female dolphins were also shown to form strong bonds with male and female relatives, while the male dolphins formed strong bonds with other males based on competitive ability, which was later linked to reproduction success.
“We knew that social relationships existed with the dolphins, so we were looking more at the long-term changes and the stability of those relationships,” says Jo. “Dolphins are well-studied, so we wanted to move to sharks, as there has been only limited research in this field.”
Preliminary results in the Port Jackson study already hint that the sharks do exhibit complex social behaviour and that individuals form stable social bonds.
During the breeding season they have a limited home range and tend to organise themselves by size, but not sex.
Female sharks also tend to interact with each other and avoid the males, while the males tend to direct their interaction towards the females. Nathan reckons
these results suggest that the males are looking to reproduce, while the females are trying to avoid the harassment.
“A key potential of using this technology is to determine the connectivity between social structure, segregation and habitat usage, which can ultimately contribute to their management,” says Nathan.
Commercial and recreational fisheries don’t target Port Jackson sharks, but they are commonly caught as by-catch. It’s important to manage these aggregations, as their life-history characteristics make them, along with other shark species, highly susceptible to over-exploitation.
Understanding the social behaviour of a single shark species won’t uncover the secrets of global shark conservation.
It is, however, a significant first step towards setting a baseline of behavioural assumptions that can be tested with other more threatened shark species.
“By understanding the formation of shark aggregations and shark society, we’ll learn how to better manage shark populations and maintain healthy marine eco-systems,” says Nathan.
If you would like to get involved with this study, you can email him at: nathan.bass@students.mq.edu.au