RESEARCH led by the CSIRO has found there is likely more than 1000 adult great white sharks in waters of South Australia and Western Australia.
Looking for brothers and sisters among juvenile white sharks provided the final pieces of information needed to estimate the size of populations in Australian waters.
The research found Australia has two white shark populations, an eastern population ranging east of Wilson’s Promontory in Victoria, to central Queensland and across to New Zealand, and a southern-western population ranging west of Wilson’s Promontory to north-western Western Australia.
Using tell-tale markers in the DNA collected from juvenile white sharks scientists were able to estimate a population of about 750 adults sharks in the eastern population and double that number in the southern-western population.
Lead researcher doctor Richard Hillary said the chances of any two juveniles in a population sharing sharing a parent depended on how many adults shared reproduction.
“In a small population, more juvenile share a parent than in large population and vice-versa,” Dr Hillary said.
“As more juveniles are sampled over time, the parental marks we detect also reveal patterns of adult survival.”
Rodney Fox Shark Expeditions researcher Andrew Fox and his team contributed to the research, collecting biopsies and DNA.
He said for the first time ever scientists and researchers now had a good estimate of the baseline shark population.
“For years we have been living and breathing this, it’s been frustrating because everyone wants to know how many sharks are out there so it is so relieving to get this baseline data,” Mr Fox said.
“Using this we will be able to see how the population is travelling and make properly informed management and conservation decisions.”
In the southern-western population, DNA samples were collected from 175 sub-adult and young adult males from WA to western Victoria and of those 27 were half-sibling pairs.
A total population estimate for the southern-western region was not compiled as direct estimates of juvenile survival rates – obtained by tagging a high number of juvenile sharks – were not available.