Are great white shark numbers rising?
DESPITE claims following a spate of attacks on surfers in northern NSW that white shark numbers are on the increase, that may ultimately not prove to be the case.
Scientists have found a new and more accurate way to estimate white shark populations, a methodology that may eventually allow bull shark numbers to also be better understood.
The research, conducted by the CSIRO, has used genetic material to link family groupings.
It estimates the size of the east Australian and New Zealand adult white shark population at between 280 and 650 individuals.
Combined with juveniles, the total white shark number is estimated at 2500 to 6750 with juvenile survival rates of around 70-75 per cent.
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Griffith University lecturer Dr Jonathan Werry, who previously ran Ocean and Coast Research which focused on tagging and tracking bull sharks between Sunshine Coast waterways and the Gold Coast, contributed to the CSIRO study.
He said what was really exciting about the new shark-counting technique was the way genetic samples taken from juveniles were used to work out relationships, whether they shared parents or siblings.
Dr Werry said hopefully the methodology could be used to develop a coherent idea about east coast bull shark numbers.
He said a lot of factors came into play, including birth rates, mortality and life span.
However a lot of tracking had already been done of east coast bull sharks that included tissue collection.
Dr Werry said ultimately the research may answer questions about whether shark numbers were growing.
Commercial line fishers have raised real concerns that numbers are on the increase, saying they could struggle to get two of 10 fish caught to the surface.
Fisher Michael Thompson said the reduction in beach netting licences had led to a reduced number of juvenile bull sharks being taken for flake in fish and chip shops.
Commercial operators were finding it increasingly difficult to get fish into their boats.
Dr Werry said it may be the case that netting bans have increased numbers.
He said more research was needed, however, to reach that conclusion.
Scientists hope that the methodology and results offered a realistic and achievable route for underpinning evidence-based conservation and risk-management decisions for a range of species across the globe.