Many shark species are declining worldwide, and, as a top-order predator, their conservation is becoming a major focus for marine scientists.
While information on the movement and behaviour of sharks is limited due to the difficulties of studying these animals in the wild, recent advancements in monitoring devices (e.g. acoustic tags and receivers, and accelerometers) are widening the scope of investigations into shark behaviour.
Researchers from Taronga and Macquarie University have been studying Port Jackson sharks (Heterodontus portusjacksoni) since 2012, tagging and tracking them in the wild to better understand their ecology and life history. As a result of this research, we now know that many of these sharks migrate up to 2000km per year from breeding sites in Jervis Bay to the Bass Strait.
As part of this study, in 2015 and 2016 a group of wild Port Jackson sharks from Sydney Harbour were temporarily transferred to Taronga to allow scientists to better understand their behaviour.
The work is continuing this year with a new cohort of sharks, which can be seen in Taronga’s seal pool for the next month, before they are released back into the sea.
The wild sharks are collected from Sydney Harbour by scuba divers. “Once caught, we bring the sharks to the surface and swim them to the boat where they’re lifted up and put in a big tank of sea water,” says Taronga Zoo researcher Dr Jo Day. Once the boat returns to shore, the sharks are transported to Taronga in a tank by the Marine Mammal Team.
During their stay at Taronga, the sharks will be in breeding mode, and will be fitted with accelerometers that measures the animals’ movements and orientation during different behaviours – for example, while feeding, mating and egg-laying). The sharks are also placed under daily video surveillance.
“This technology is allowing us to study sharks like we never have before,” says Day. Already, Taronga researchers have observed that the sharks are nocturnal, and males have shown an increase in activity late in the season, which corresponded to the timing of the southerly migration of Port Jackson Sharks.
Day and her team hope to use the behavioural information recorded at Taronga as a kind of yardstick, by which to interpret the data from accelerometers placed on wild Port Jackson sharks in the future.
“This will allow us to correctly identify the behaviours of sharks at sea, and better understand their energetic requirements and minimum food requirements,” says Day.
The results from this study, in combination with information on the sharks movement and migration patterns (currently being investigated using acoustic tagging), could also impact how shark populations are managed.
“An understanding of the factors driving aggregative behaviour in sharks is urgently required to better manage these species and obtain a clearer insight into the role of these top marine predators in the marine ecosystem, so that effective fisheries and conservation management plans can be implemented,” says Day.