Updating knowledge of Australian white sharks

Previous research funded by the National Environmental Science Program (NESP) provided updated estimates of white shark breeding population size and trend. These were based on modest datasets, however, and were limited by poor knowledge of pupping and juvenile nursery areas, and uncertainty about how populations are connected between eastern and south-western Australia.

This project will provide an update and reduce uncertainty regarding the status and population structure of white sharks in Australian waters. Three project sub-components will involve:

• investigating the feasibility of filling knowledge gaps about juvenile and pupping areas and adult movements;
• investigating population structure to resolve mixing/connectivity questions; and
• updating population estimates based on significant new data.

Approach

A pilot study will assess the effectiveness of tagging adult females (>4.5 metres) and young sharks >2 m in length throughout the southern-western white shark range. Genetic samples will be gathered from around Australia and sought from South Africa and New Zealand to conduct a comprehensive update of white shark stock structure.

An expanded tissue sample set from New South Wales (~1000 samples) will be used to update and refine estimates of adult population size and population trend for the eastern white shark population. Data from the New South Wales shark management program will be used to estimate juvenile numbers. Additional samples from South Australia and Western Australia will be combined with previous samples in the southern-western population to refine estimates of population size.

The population estimates will be determined using close-kin mark-recapture, a technique that combines advanced genetics and statistical modelling to infer population demographics by identifying close-kin-pairs (parent-offspring or half-siblings) among a collection of sampled animals. The updated estimates of population size and growth will be used to determine an appropriate and cost-effective assessment cycle for ongoing monitoring and assessment.

Key project outputs will include:

• estimates of adult abundance and trend;
• a comprehensive update of white shark Southern Hemisphere stock structure using samples from around Australia and overseas;
• an improved understanding of the movement and habitat usage of large adults in both the eastern and southern-western populations;
• a review of information, including Traditional Ecological Knowledge, related to the identification of critical white shark habitat for the south-western population; and
• development of a recommended research program to assist in the identification of additional critical habitat for the south-western white shark population.

Expected outcomes

Reduced uncertainty regarding the status and population structure of white sharks in Australian waters is directly relevant to managing the conservation listing and recovery of this species in commonwealth and state waters. Guidance on the required frequency of white shark assessments will ensure that significant changes in the population are tracked in a cost-effective manner.

Project location