Our research has revealed where white sharks go and how they behave, identified nursery areas and eastern and western populations, and developed techniques for measuring their abundance.
Breeding, mixing, growing and moving
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.
Why are white sharks vulnerable?
White sharks are long-lived, slow growing species that do not reproduce in Australian waters until approximately five metres in length and 18-20 years of age.
Adult females produce few young called ‘pups’ (up to 10 per reproductive event) and they do not reproduce each year.
These characteristics mean white shark populations are vulnerable to low levels of exploitation (including incidental bycatch) and slow to recover once they are depleted.
Two Australian populations
Genetic evidence suggests there are two white shark populations in Australia, an eastern population (ranging along the east coast from Tasmania to central Queensland) and a western population ranging 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 1.7–3 m 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 SA/WA 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 known but are likely to include factors influencing prey distribution and variations in the physical ocean environment.
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 between 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 easily seen and frequently encountered by the public.
Juvenile white sharks aggregate in the Port Stephens region from early spring to midsummer. The sharks are usually 1.8 to 2.6 m 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.
Specific goals are to determine the survival rate of adults and juveniles, and, in conjunction with aerial surveys, provide estimates of juvenile abundance.
This information when combined with estimates of adult numbers from the genetic data, will contribute to Australia’s first white shark population estimates and develop models that use measured data to asses population status, rather than information that is assumed or best-guessed.
A lack of information on population status is one of the key issues limiting the assessment of conservation efforts for white sharks in Australia.
Aerial surveys have shown there is a seasonal pattern to the presence of juvenile white sharks in the Port Stephens nursery area, but that low numbers of sharks may occur in the area at any time of year.
In the 2012-2013 season, about 250 juvenile white sharks may have been present in the nursery area on survey days with peak abundance in October-November, as previously observed for the region.