Our research is providing insight into white shark movement patterns and behaviour, juvenile nursery areas, and adult population estimates for the eastern and southern-western Australasian populations.
Movement of white sharks
White sharks occur in coastal, shelf, and continental slope waters around Australia from the Montebello Islands in north-western Western Australia, south around the coast to central Queensland including Tasmanian waters.
The sharks' movements indicate a pattern of temporary residency at favoured sites intermixed with periods of long-distance travel that may include common corridors.
They are not permanent residents at any one site.
Areas close to favoured sites and common corridors of travel are likely to experience higher encounter frequencies with white sharks.
There is no scientific evidence showing tagged sharks being involved in human encounters.
Why are white sharks vulnerable?
White sharks are a long-lived and slow growing species. Females do not reproduce in Australian waters until approximately five metres in length and about 16 years of age. Males are sexually mature at a smaller size and slightly younger age.
The gestation period for adult females is 18 months and they produce few young, called 'pups' (up to 10 per reproductive event), and do not reproduce each year.
These characteristics mean white shark populations are vulnerable to low levels of exploitation (including incidental bycatch) and are slow to recover once they are depleted.
Two Australian populations
Genetic and tracking evidence reveal there are two white shark populations in Australia, an eastern population and a southern-western population.
The eastern Australasian population ranges along the entire eastern seaboard from the cold waters as far south as Macquarie Island into tropical waters of Papua New Guinea, and extends eastwards to include New Zealand and tropical islands such as New Caledonia. The southern-western population ranges from western Victoria to northwest Western Australia.
This population structuring east and west of Bass Strait is consistent with a number of other species of sharks, finfish and invertebrate species in Australian waters.
Short-term local increases and decreases in sightings frequency, encounters and shark attacks are, by themselves, poor predictors of shark population status.
White sharks can have highly localised and geographically discrete inshore nursery areas which include surf zone habitats. Sharks in these nursery areas are typically 1.7–3 metres in length.
At nursery areas close to human population centres, the frequency of encounters between people and sharks can be high, although the frequency of attacks in such areas is very low.
White sharks move between eastern Australia and south Pacific waters (including New Zealand) and between South Africa and Western Australia.
The population implications of these movements are unknown.
White sharks in Western Australia are part of a combined South Australia/Western Australia population and travel between western Victorian and northwestern Australian waters with possible links to South Africa.
Shifts in abundance
The local abundance of white sharks in shelf and coastal waters varies seasonally and between years as a result of variations in their distribution and movement patterns.
The drivers for these variations are poorly understood but are likely to include factors influencing prey distribution and variations in the physical ocean environment. We are working with the NSW Department of Primary Industries to carry out further data analysis to determine other potential contributing factors.
Short-term (seasonal/annual) local increases and decreases in sightings frequency, encounters and shark attacks are thus, by themselves, poor predictors of shark population status.
Electronic tagging studies have located two nursery areas for juvenile white sharks in eastern Australia: the Port Stephens region of New South Wales and 90 Mile Beach-Corner Inlet region of eastern Victoria.
The more accessible of these regions is a 50–60 kilometre stretch of coastline centred on the Port Stephens area where sharks occupy habitat from the shore to approximately 120 metres depth.
They also spend a significant amount of time in the surf zone in water depths of one to five metres where they are more frequently seen by the public.
Juvenile white sharks aggregate in the Port Stephens region from early spring to mid-summer. The sharks are usually 1.8 to 2.6 metres in length and approximately one to five years old.
They stay for weeks or months in local areas of the coast, specifically along northern Stockton Beach, Bennett's Beach and Mungo Brush.
Contributing to population estimates
The tagging program aims to establish the patterns of residency and habitat use by juvenile white sharks and to contribute information on the overall movement and population dynamics of juvenile white sharks on the east coast of Australia. By using DNA sampling from juvenile sharks, we can also estimate adult white shark numbers.
This information, combined with estimates of adult numbers from the genetic data, have contributed to Australia's first white shark population estimates and models that use measured data to asses population status, rather than information that is assumed or best-guessed.
Our research provides key information on populations of adult eastern and southern-western white sharks, as well as helping to determine the survival rate of adults and juveniles.
As more juveniles are sampled over time, the parental marks we detect can reveal patterns of adult survival, which we determined to be greater than 90 per cent.
Estimating the trend in total population size for both populations requires sampling and analyses, developing methods and continued collaboration with our partners. This will help to inform policy and conservation efforts for white sharks in Australia.
Find out more about the national assessment of the status of white sharks.